Patent Publication Number: US-11650416-B2

Title: See-through computer display systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to and is a continuation of U.S. non-provisional application Ser. No. 16/684,506, filed Nov. 14, 2019, which is a continuation of U.S. non-provisional application Ser. No. 15/988,313, filed on May 24, 2018, which claims the benefit of priority and is a continuation of U.S. non-provisional application Ser. No. 14/562,105, filed Dec. 5, 2014. 
     U.S. non-provisional application Ser. No. 14/562,105 claims the benefit of priority to and is a continuation of U.S. non-provisional application Ser. No. 14/561,146, filed Dec. 4, 2014. 
     U.S. non-provisional application Ser. No. 14/561,146 claims the benefit of priority to and is a continuation-in-part of the following U.S. patent applications, each of which is hereby incorporated by reference in its entirety: 
     U.S. non-provisional application Ser. No. 14/160,377, filed Jan. 21, 2014; 
     U.S. non-provisional application Ser. No. 14/172,901, filed Feb. 4, 2014 which is a continuation-in-part of U.S. non-provisional application Ser. No. 14/160,377, filed Jan. 21, 2014 and U.S. non-provisional application Ser. No. 14/163,646, filed Jan. 24, 2014. 
     U.S. non-provisional application Ser. No. 14/181,459, filed Feb. 14, 2014 which is a continuation-in-part of the following four U.S. patent applications, each of which is hereby incorporated by reference in its entirety: 
     U.S. non-provisional application Ser. No. 14/172,901, filed Feb. 4, 2014, which is a continuation-in-part of (i) U.S. non-provisional application Ser. No. 14/160,377, filed Jan. 21, 2014 and (ii) U.S. non-provisional application Ser. No. 14/163,646, filed Jan. 24, 2014; and U.S. non-provisional application Ser. No. 14/178,047, filed Feb. 11, 2014. 
     U.S. non-provisional application Ser. No. 14/296,699, filed Jun. 5, 2014. 
     U.S. non-provisional application Ser. No. 14/325,991, filed Jul. 8, 2014. 
     U.S. non-provisional application Ser. No. 14/489,706, filed Sep. 18, 2014. 
     U.S. non-provisional application Ser. No. 14/498,765, filed Sep. 26, 2014. 
     U.S. non-provisional application Ser. No. 14/504,723, filed Oct. 2, 2014 which is a continuation-in-part of U.S. non-provisional application Ser. No. 14/498,765, filed Sep. 26, 2014. 
     U.S. non-provisional application Ser. No. 14/216,175, filed Mar. 17, 2014. 
     U.S. non-provisional application Ser. No. 14/254,253, filed Apr. 16, 2014. 
    
    
     BACKGROUND 
     Field of the Invention 
     This invention relates to see-through computer display systems. 
     Description of Related Art 
     Head mounted displays (HMD) and particularly HMDs that provide a see-through view of the environment are sensitive to the effects of stray light. Where, stray light includes light that is not intended to be included in the displayed image, including light that is scattered or inadvertently reflected from surfaces within the optics of the HMD. This stray light reduces the sharpness and contrast of the displayed image in the HMD. In addition, the stray light causes the black areas of the displayed image to be gray and this effect adversely affects the see-through view of the environment because the see-through view is produced by the combination of the light from the environment and the light from the displayed image, which is in the best case the black portions of displayed image. As a result, it is important to reduce stray light within the optics so that very dark black areas and high contrast can be provided in the images displayed by the HMDs. 
     SUMMARY 
     Aspects of the present invention relate to methods and systems for the see-through computer display systems. 
     These and other systems, methods, objects, features, and advantages of the present invention will be apparent to those skilled in the art from the following detailed description of the preferred embodiment and the drawings. All documents mentioned herein are hereby incorporated in their entirety by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments are described with reference to the following Figures. The same numbers may be used throughout to reference like features and components that are shown in the Figures: 
         FIG.  1    illustrates a head worn computing system in accordance with the principles of the present invention. 
         FIG.  2    illustrates a head worn computing system with optical system in accordance with the principles of the present invention. 
         FIG.  3   a    illustrates a large prior art optical arrangement. 
         FIG.  3   b    illustrates an upper optical module in accordance with the principles of the present invention. 
         FIG.  4    illustrates an upper optical module in accordance with the principles of the present invention. 
         FIG.  4   a    illustrates an upper optical module in accordance with the principles of the present invention. 
         FIG.  4   b    illustrates an upper optical module in accordance with the principles of the present invention. 
         FIG.  5    illustrates an upper optical module in accordance with the principles of the present invention. 
         FIG.  5   a    illustrates an upper optical module in accordance with the principles of the present invention. 
         FIG.  5   b    illustrates an upper optical module and dark light trap according to the principles of the present invention. 
         FIG.  5   c    illustrates an upper optical module and dark light trap according to the principles of the present invention. 
         FIG.  5   d    illustrates an upper optical module and dark light trap according to the principles of the present invention. 
         FIG.  5   e    illustrates an upper optical module and dark light trap according to the principles of the present invention. 
         FIG.  6    illustrates upper and lower optical modules in accordance with the principles of the present invention. 
         FIG.  7    illustrates angles of combiner elements in accordance with the principles of the present invention. 
         FIG.  8    illustrates upper and lower optical modules in accordance with the principles of the present invention. 
         FIG.  8   a    illustrates upper and lower optical modules in accordance with the principles of the present invention. 
         FIG.  8   b    illustrates upper and lower optical modules in accordance with the principles of the present invention. 
         FIG.  8   c    illustrates upper and lower optical modules in accordance with the principles of the present invention. 
         FIG.  9    illustrates an eye imaging system in accordance with the principles of the present invention. 
         FIG.  10    illustrates a light source in accordance with the principles of the present invention. 
         FIG.  10   a    illustrates a back lighting system in accordance with the principles of the present invention. 
         FIG.  10   b    illustrates a back lighting system in accordance with the principles of the present invention. 
         FIGS.  11   a  to  11   d    illustrate light source and filters in accordance with the principles of the present invention. 
         FIGS.  12   a  to  12   c    illustrate light source and quantum dot systems in accordance with the principles of the present invention. 
         FIGS.  13   a  to  13   c    illustrate peripheral lighting systems in accordance with the principles of the present invention. 
         FIGS.  14   a  to  14   c    illustrate a light suppression systems in accordance with the principles of the present invention. 
         FIG.  15    illustrates an external user interface in accordance with the principles of the present invention. 
         FIGS.  16   a  to  16   c    illustrate distance control systems in accordance with the principles of the present invention. 
         FIGS.  17   a  to  17   c    illustrate force interpretation systems in accordance with the principles of the present invention. 
         FIGS.  18   a  to  18   c    illustrate user interface mode selection systems in accordance with the principles of the present invention. 
         FIG.  19    illustrates interaction systems in accordance with the principles of the present invention. 
         FIG.  20    illustrates external user interfaces in accordance with the principles of the present invention. 
         FIG.  21    illustrates mD trace representations presented in accordance with the principles of the present invention. 
         FIG.  22    illustrates mD trace representations presented in accordance with the principles of the present invention. 
         FIG.  23    illustrates an mD scanned environment in accordance with the principles of the present invention. 
         FIG.  23   a    illustrates mD trace representations presented in accordance with the principles of the present invention. 
         FIG.  24    illustrates a stray light suppression technology in accordance with the principles of the present invention. 
         FIG.  25    illustrates a stray light suppression technology in accordance with the principles of the present invention. 
         FIG.  26    illustrates a stray light suppression technology in accordance with the principles of the present invention. 
         FIG.  27    illustrates a stray light suppression technology in accordance with the principles of the present invention. 
         FIGS.  28   a  to  28   c    illustrate DLP mirror angles. 
         FIGS.  29  to  33    illustrate eye imaging systems according to the principles of the present invention. 
         FIGS.  34  and  34     a  illustrate structured eye lighting systems according to the principles of the present invention. 
         FIG.  35    illustrates eye glint in the prediction of eye direction analysis in accordance with the principles of the present invention. 
         FIG.  36   a    illustrates eye characteristics that may be used in personal identification through analysis of a system according to the principles of the present invention. 
         FIG.  36   b    illustrates a digital content presentation reflection off of the wearer&#39;s eye that may be analyzed in accordance with the principles of the present invention. 
         FIG.  37    illustrates eye imaging along various virtual target lines and various focal planes in accordance with the principles of the present invention. 
         FIG.  38    illustrates content control with respect to eye movement based on eye imaging in accordance with the principles of the present invention. 
         FIG.  39    illustrates eye imaging and eye convergence in accordance with the principles of the present invention. 
         FIG.  40    illustrates content position dependent on sensor feedback in accordance with the principles of the present invention. 
         FIG.  41    illustrates content position dependent on sensor feedback in accordance with the principles of the present invention. 
         FIG.  42    illustrates content position dependent on sensor feedback in accordance with the principles of the present invention. 
         FIG.  43    illustrates content position dependent on sensor feedback in accordance with the principles of the present invention. 
         FIG.  44    illustrates content position dependent on sensor feedback in accordance with the principles of the present invention. 
         FIG.  45    illustrates various headings over time in an example. 
         FIG.  46    illustrates content position dependent on sensor feedback in accordance with the principles of the present invention. 
         FIG.  47    illustrates content position dependent on sensor feedback in accordance with the principles of the present invention. 
         FIG.  48    illustrates content position dependent on sensor feedback in accordance with the principles of the present invention. 
         FIG.  49    illustrates content position dependent on sensor feedback in accordance with the principles of the present invention. 
         FIG.  50    illustrates light impinging an eye in accordance with the principles of the present invention. 
         FIG.  51    illustrates a view of an eye in accordance with the principles of the present invention. 
         FIGS.  52   a  and  52   b    illustrate views of an eye with a structured light pattern in accordance with the principles of the present invention. 
         FIG.  53    illustrates an optics module in accordance with the principles of the present invention. 
         FIG.  54    illustrates an optics module in accordance with the principles of the present invention. 
         FIG.  55    shows a series of example spectrum for a variety of controlled substances as measured using a form of infrared spectroscopy. 
         FIG.  56    shows an infrared absorbance spectrum for glucose. 
         FIG.  57    illustrates a scene where a person is walking with a HWC mounted on his head. 
         FIG.  58    illustrates a system for receiving, developing and using movement heading, sight heading, eye heading and/or persistence information from HWC(s). 
         FIG.  59    illustrates a presentation technology in accordance with the principles of the present invention. 
         FIG.  60    illustrates a presentation technology in accordance with the principles of the present invention. 
         FIG.  61    illustrates a presentation technology in accordance with the principles of the present invention. 
         FIG.  62    illustrates a presentation technology in accordance with the principles of the present invention. 
         FIG.  63    illustrates a presentation technology in accordance with the principles of the present invention. 
         FIG.  64    illustrates a presentation technology in accordance with the principles of the present invention. 
         FIG.  65    illustrates a presentation technology in accordance with the principles of the present invention. 
         FIG.  66    illustrates a presentation technology in accordance with the principles of the present invention. 
         FIG.  67    illustrates an optical configuration in accordance with the principles of the present invention. 
         FIG.  68    illustrates an optical configuration in accordance with the principles of the present invention. 
         FIG.  69    illustrates an optical configuration in accordance with the principles of the present invention. 
         FIG.  70    illustrates an optical configuration in accordance with the principles of the present invention. 
         FIG.  71    illustrates an optical configuration in accordance with the principles of the present invention. 
         FIG.  72    illustrates an optical element in accordance with the principles of the present invention. 
         FIG.  73    illustrates an optical element in accordance with the principles of the present invention. 
         FIG.  74    illustrates an optical element in accordance with the principles of the present invention. 
         FIG.  75    illustrates an optical element in accordance with the principles of the present invention. 
         FIG.  76    illustrates an optical element in a see-through computer display in accordance with the principles of the present invention. 
         FIG.  77    illustrates an optical element in accordance with the principles of the present invention. 
         FIG.  78    illustrates an optical element in accordance with the principles of the present invention. 
         FIG.  79   a    illustrates a schematic of an upper optic in accordance with the principles of the present invention. 
         FIG.  79    illustrates a schematic of an upper optic in accordance with the principles of the present invention. 
         FIG.  80    illustrates a stray light control technology in accordance with the principles of the present invention. 
         FIGS.  81   a  and  81   b    illustrate a display with a gap and masked technologies in accordance with the principles of the present invention. 
         FIG.  82    illustrates an upper module with a trim polarizer in accordance with the principles of the present invention. 
         FIG.  83    illustrates an optical system with a laminated multiple polarizer film in accordance with the principles of the present invention. 
         FIGS.  84   a  and  84   b    illustrate partially reflective layers in accordance with the principles of the present invention. 
         FIG.  84   c    illustrates a laminated multiple polarizer with a complex curve in accordance with the principles of the present invention. 
         FIG.  84   d    illustrates a laminated multiple polarizer with a curve in accordance with the principles of the present invention. 
         FIG.  85    illustrates an optical system adapted for a head-mounted display in accordance with the principles of the present invention. 
         FIG.  86    illustrates an optical system adapted for a head-mounted display in accordance with the principles of the present invention. 
         FIG.  87    illustrates an optical system adapted for a head-mounted display in 
         FIG.  88    illustrates an optical system adapted for a head-mounted display in accordance with the principles of the present invention. 
         FIG.  89    illustrates an optical system adapted for a head-mounted display in accordance with the principles of the present invention. 
         FIG.  90    illustrates an optical system adapted for a head-mounted display in accordance with the principles of the present invention. 
         FIG.  91    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  92    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  93    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  94    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  95    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  96    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  97    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  98    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  99    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  100    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  101    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  102    illustrates an optical system in accordance with the principles of the present invention. 
         FIGS.  103 ,  103     a  and  103   b  illustrate optical systems in accordance with the principles of the present invention. 
         FIG.  104    illustrates an optical system in accordance with the principles of the present invention. 
         FIG.  105    illustrates a blocking optic in accordance with the principles of the present invention. 
         FIGS.  106   a ,  106   b , and  106   c    illustrate a blocking optic system in accordance with the principles of the present invention. 
     
    
    
     While the invention has been described in connection with certain preferred embodiments, other embodiments would be understood by one of ordinary skill in the art and are encompassed herein. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Aspects of the present invention relate to head-worn computing (“HWC”) systems. HWC involves, in some instances, a system that mimics the appearance of head-worn glasses or sunglasses. The glasses may be a fully developed computing platform, such as including computer displays presented in each of the lenses of the glasses to the eyes of the user. In embodiments, the lenses and displays may be configured to allow a person wearing the glasses to see the environment through the lenses while also seeing, simultaneously, digital imagery, which forms an overlaid image that is perceived by the person as a digitally augmented image of the environment, or augmented reality (“AR”). 
     HWC involves more than just placing a computing system on a person&#39;s head. The system may need to be designed as a lightweight, compact and fully functional computer display, such as wherein the computer display includes a high resolution digital display that provides a high level of emersion comprised of the displayed digital content and the see-through view of the environmental surroundings. User interfaces and control systems suited to the HWC device may be required that are unlike those used for a more conventional computer such as a laptop. For the HWC and associated systems to be most effective, the glasses may be equipped with sensors to determine environmental conditions, geographic location, relative positioning to other points of interest, objects identified by imaging and movement by the user or other users in a connected group, and the like. The HWC may then change the mode of operation to match the conditions, location, positioning, movements, and the like, in a method generally referred to as a contextually aware HWC. The glasses also may need to be connected, wirelessly or otherwise, to other systems either locally or through a network. Controlling the glasses may be achieved through the use of an external device, automatically through contextually gathered information, through user gestures captured by the glasses sensors, and the like. Each technique may be further refined depending on the software application being used in the glasses. The glasses may further be used to control or coordinate with external devices that are associated with the glasses. 
     Referring to  FIG.  1   , an overview of the HWC system  100  is presented. As shown, the HWC system  100  comprises a HWC  102 , which in this instance is configured as glasses to be worn on the head with sensors such that the HWC  102  is aware of the objects and conditions in the environment  114 . In this instance, the HWC  102  also receives and interprets control inputs such as gestures and movements  116 . The HWC  102  may communicate with external user interfaces  104 . The external user interfaces  104  may provide a physical user interface to take control instructions from a user of the HWC  102  and the external user interfaces  104  and the HWC  102  may communicate bi-directionally to affect the user&#39;s command and provide feedback to the external device  108 . The HWC  102  may also communicate bi-directionally with externally controlled or coordinated local devices  108 . For example, an external user interface  104  may be used in connection with the HWC  102  to control an externally controlled or coordinated local device  108 . The externally controlled or coordinated local device  108  may provide feedback to the HWC  102  and a customized GUI may be presented in the HWC  102  based on the type of device or specifically identified device  108 . The HWC  102  may also interact with remote devices and information sources  112  through a network connection  110 . Again, the external user interface  104  may be used in connection with the HWC  102  to control or otherwise interact with any of the remote devices  108  and information sources  112  in a similar way as when the external user interfaces  104  are used to control or otherwise interact with the externally controlled or coordinated local devices  108 . Similarly, HWC  102  may interpret gestures  116  (e.g. captured from forward, downward, upward, rearward facing sensors such as camera(s), range finders, IR sensors, etc.) or environmental conditions sensed in the environment  114  to control either local or remote devices  108  or  112 . 
     We will now describe each of the main elements depicted on  FIG.  1    in more detail; however, these descriptions are intended to provide general guidance and should not be construed as limiting. Additional description of each element may also be further described herein. 
     The HWC  102  is a computing platform intended to be worn on a person&#39;s head. The HWC  102  may take many different forms to fit many different functional requirements. In some situations, the HWC  102  will be designed in the form of conventional glasses. The glasses may or may not have active computer graphics displays. In situations where the HWC  102  has integrated computer displays the displays may be configured as see-through displays such that the digital imagery can be overlaid with respect to the user&#39;s view of the environment  114 . There are a number of see-through optical designs that may be used, including ones that have a reflective display (e.g. LCoS, DLP), emissive displays (e.g. OLED, LED), hologram, TIR waveguides, and the like. In embodiments, lighting systems used in connection with the display optics may be solid state lighting systems, such as LED, OLED, quantum dot, quantum dot LED, etc. In addition, the optical configuration may be monocular or binocular. It may also include vision corrective optical components. In embodiments, the optics may be packaged as contact lenses. In other embodiments, the HWC  102  may be in the form of a helmet with a see-through shield, sunglasses, safety glasses, goggles, a mask, fire helmet with see-through shield, police helmet with see through shield, military helmet with see-through shield, utility form customized to a certain work task (e.g. inventory control, logistics, repair, maintenance, etc.), and the like. 
     The HWC  102  may also have a number of integrated computing facilities, such as an integrated processor, integrated power management, communication structures (e.g. cell net, WiFi, Bluetooth, local area connections, mesh connections, remote connections (e.g. client server, etc.)), and the like. The HWC  102  may also have a number of positional awareness sensors, such as GPS, electronic compass, altimeter, tilt sensor, IMU, and the like. It may also have other sensors such as a camera, rangefinder, hyper-spectral camera, Geiger counter, microphone, spectral illumination detector, temperature sensor, chemical sensor, biologic sensor, moisture sensor, ultrasonic sensor, and the like. 
     The HWC  102  may also have integrated control technologies. The integrated control technologies may be contextual based control, passive control, active control, user control, and the like. For example, the HWC  102  may have an integrated sensor (e.g. camera) that captures user hand or body gestures  116  such that the integrated processing system can interpret the gestures and generate control commands for the HWC  102 . In another example, the HWC  102  may have sensors that detect movement (e.g. a nod, head shake, and the like) including accelerometers, gyros and other inertial measurements, where the integrated processor may interpret the movement and generate a control command in response. The HWC  102  may also automatically control itself based on measured or perceived environmental conditions. For example, if it is bright in the environment the HWC  102  may increase the brightness or contrast of the displayed image. In embodiments, the integrated control technologies may be mounted on the HWC  102  such that a user can interact with it directly. For example, the HWC  102  may have a button(s), touch capacitive interface, and the like. 
     As described herein, the HWC  102  may be in communication with external user interfaces  104 . The external user interfaces may come in many different forms. For example, a cell phone screen may be adapted to take user input for control of an aspect of the HWC  102 . The external user interface may be a dedicated UI, such as a keyboard, touch surface, button(s), joy stick, and the like. In embodiments, the external controller may be integrated into another device such as a ring, watch, bike, car, and the like. In each case, the external user interface  104  may include sensors (e.g. IMU, accelerometers, compass, altimeter, and the like) to provide additional input for controlling the HWD  104 . 
     As described herein, the HWC  102  may control or coordinate with other local devices  108 . The external devices  108  may be an audio device, visual device, vehicle, cell phone, computer, and the like. For instance, the local external device  108  may be another HWC  102 , where information may then be exchanged between the separate HWCs  108 . 
     Similar to the way the HWC  102  may control or coordinate with local devices  106 , the HWC  102  may control or coordinate with remote devices  112 , such as the HWC  102  communicating with the remote devices  112  through a network  110 . Again, the form of the remote device  112  may have many forms. Included in these forms is another HWC  102 . For example, each HWC  102  may communicate its GPS position such that all the HWCs  102  know where all of HWC  102  are located. 
       FIG.  2    illustrates a HWC  102  with an optical system that includes an upper optical module  202  and a lower optical module  204 . While the upper and lower optical modules  202  and  204  will generally be described as separate modules, it should be understood that this is illustrative only and the present invention includes other physical configurations, such as that when the two modules are combined into a single module or where the elements making up the two modules are configured into more than two modules. In embodiments, the upper module  202  includes a computer controlled display (e.g. LCoS, DLP, OLED, etc.) and image light delivery optics. In embodiments, the lower module includes eye delivery optics that are configured to receive the upper module&#39;s image light and deliver the image light to the eye of a wearer of the HWC. In  FIG.  2   , it should be noted that while the upper and lower optical modules  202  and  204  are illustrated in one side of the HWC such that image light can be delivered to one eye of the wearer, that it is envisioned by the present invention that embodiments will contain two image light delivery systems, one for each eye. 
       FIG.  3   b    illustrates an upper optical module  202  in accordance with the principles of the present invention. In this embodiment, the upper optical module  202  includes a DLP (also known as DMD or digital micromirror device) computer operated display  304  which includes pixels comprised of rotatable mirrors (such as, for example, the DLP3000 available from Texas Instruments), polarized light source  302 , ¼ wave retarder film  308 , reflective polarizer  310  and a field lens  312 . The polarized light source  302  provides substantially uniform polarized light that is generally directed towards the reflective polarizer  310 . The reflective polarizer reflects light of one polarization state (e.g. S polarized light) and transmits light of the other polarization state (e.g. P polarized light). The polarized light source  302  and the reflective polarizer  310  are oriented so that the polarized light from the polarized light source  302  is reflected generally towards the DLP  304 . The light then passes through the ¼ wave film  308  once before illuminating the pixels of the DLP  304  and then again after being reflected by the pixels of the DLP  304 . In passing through the ¼ wave film  308  twice, the light is converted from one polarization state to the other polarization state (e.g. the light is converted from S to P polarized light). The light then passes through the reflective polarizer  310 . In the event that the DLP pixel(s) are in the “on” state (i.e. the mirrors are positioned to reflect light towards the field lens  312 , the “on” pixels reflect the light generally along the optical axis and into the field lens  312 . This light that is reflected by “on” pixels and which is directed generally along the optical axis of the field lens  312  will be referred to as image light  316 . The image light  316  then passes through the field lens to be used by a lower optical module  204 . 
     The light that is provided by the polarized light source  302 , which is subsequently reflected by the reflective polarizer  310  before it reflects from the DLP  304 , will generally be referred to as illumination light. The light that is reflected by the “off” pixels of the DLP  304  is reflected at a different angle than the light reflected by the “on” pixels, so that the light from the “off” pixels is generally directed away from the optical axis of the field lens  312  and toward the side of the upper optical module  202  as shown in  FIG.  3   . The light that is reflected by the “off” pixels of the DLP  304  will be referred to as dark state light  314 . 
     The DLP  304  operates as a computer controlled display and is generally thought of as a MEMs device. The DLP pixels are comprised of small mirrors that can be directed. The mirrors generally flip from one angle to another angle. The two angles are generally referred to as states. When light is used to illuminate the DLP the mirrors will reflect the light in a direction depending on the state. In embodiments herein, we generally refer to the two states as “on” and “off,” which is intended to depict the condition of a display pixel. “On” pixels will be seen by a viewer of the display as emitting light because the light is directed along the optical axis and into the field lens and the associated remainder of the display system. “Off” pixels will be seen by a viewer of the display as not emitting light because the light from these pixels is directed to the side of the optical housing and into a light trap or light dump where the light is absorbed. The pattern of “on” and “off” pixels produces image light that is perceived by a viewer of the display as a computer generated image. Full color images can be presented to a user by sequentially providing illumination light with complimentary colors such as red, green and blue. Where the sequence is presented in a recurring cycle that is faster than the user can perceive as separate images and as a result the user perceives a full color image comprised of the sum of the sequential images. Bright pixels in the image are provided by pixels that remain in the “on” state for the entire time of the cycle, while dimmer pixels in the image are provided by pixels that switch between the “on” state and “off” state within the time of the cycle, or frame time when in a video sequence of images. 
       FIG.  3   a    shows an illustration of a system for a DLP  304  in which the unpolarized light source  350  is pointed directly at the DLP  304 . In this case, the angle required for the illumination light is such that the field lens  352  must be positioned substantially distant from the DLP  304  to avoid the illumination light from being clipped by the field lens  352 . The large distance between the field lens  352  and the DLP  304  along with the straight path of the dark state light  354 , means that the light trap for the dark state light  354  is also located at a substantial distance from the DLP. For these reasons, this configuration is larger in size compared to the upper optics module  202  of the preferred embodiments. 
     The configuration illustrated in  FIG.  3   b    can be lightweight and compact such that it fits into a small portion of a HWC. For example, the upper modules  202  illustrated herein can be physically adapted to mount in an upper frame of a HWC such that the image light can be directed into a lower optical module  204  for presentation of digital content to a wearer&#39;s eye. The package of components that combine to generate the image light (i.e. the polarized light source  302 , DLP  304 , reflective polarizer  310  and ¼ wave film  308 ) is very light and is compact. The height of the system, excluding the field lens, may be less than 8 mm. The width (i.e. from front to back) may be less than 8 mm. The weight may be less than 2 grams. The compactness of this upper optical module  202  allows for a compact mechanical design of the HWC and the light weight nature of these embodiments help make the HWC lightweight to provide for a HWC that is comfortable for a wearer of the HWC. 
     The configuration illustrated in  FIG.  3   b    can produce sharp contrast, high brightness and deep blacks, especially when compared to LCD or LCoS displays used in HWC. The “on” and “off” states of the DLP provide for a strong differentiator in the light reflection path representing an “on” pixel and an “off pixel. As will be discussed in more detail below, the dark state light from the “off” pixel reflections can be managed to reduce stray light in the display system to produce images with high contrast. 
       FIG.  4    illustrates another embodiment of an upper optical module  202  in accordance with the principles of the present invention. This embodiment includes a light source  404 , but in this case, the light source can provide unpolarized illumination light. The illumination light from the light source  404  is directed into a TIR wedge  418  such that the illumination light is incident on an internal surface of the TIR wedge  418  (shown as the angled lower surface of the TRI wedge  418  in  FIG.  4   ) at an angle that is beyond the critical angle as defined by Eqn 1.
 
Critical angle=arc-sin(1/ n )  Eqn 1
 
     Where the critical angle is the angle beyond which the illumination light is reflected from the internal surface when the internal surface comprises an interface from a solid with a higher refractive index (n) to air with a refractive index of 1 (e.g. for an interface of acrylic, with a refractive index of n=1.5, to air, the critical angle is 41.8 degrees; for an interface of polycarbonate, with a refractive index of n=1.59, to air the critical angle is 38.9 degrees). Consequently, the TIR wedge  418  is associated with a thin air gap  408  along the internal surface to create an interface between a solid with a higher refractive index and air. By choosing the angle of the light source  404  relative to the DLP  402  in correspondence to the angle of the internal surface of the TIR wedge  418 , illumination light is turned toward the DLP  402  at an angle suitable for providing image light  414  as reflected from “on” pixels. Wherein, the illumination light is provided to the DLP  402  at approximately twice the angle of the pixel mirrors in the DLP  402  that are in the “on” state, such that after reflecting from the pixel mirrors, the image light  414  is directed generally along the optical axis of the field lens. Depending on the state of the DLP pixels, the illumination light from “on” pixels may be reflected as image light  414  which is directed towards a field lens and a lower optical module  204 , while illumination light reflected from “off” pixels (generally referred to herein as “dark” state light, “off” pixel light or “off” state light)  410  is directed in a separate direction, which may be trapped and not used for the image that is ultimately presented to the wearer&#39;s eye. 
     The light trap for the dark state light  410  may be located along the optical axis defined by the direction of the dark state light  410  and in the side of the housing, with the function of absorbing the dark state light. To this end, the light trap may be comprised of an area outside of the cone of image light  414  from the “on” pixels. The light trap is typically made up of materials that absorb light including coatings of black paints or other light absorbing materials to prevent light scattering from the dark state light degrading the image perceived by the user. In addition, the light trap may be recessed into the wall of the housing or include masks or guards to block scattered light and prevent the light trap from being viewed adjacent to the displayed image. 
     The embodiment of  FIG.  4    also includes a corrective wedge  420  to correct the effect of refraction of the image light  414  as it exits the TIR wedge  418 . By including the corrective wedge  420  and providing a thin air gap  408  (e.g. 25 micron), the image light from the “on” pixels can be maintained generally in a direction along the optical axis of the field lens (i.e. the same direction as that defined by the image light  414 ) so it passes into the field lens and the lower optical module  204 . As shown in  FIG.  4   , the image light  414  from the “on” pixels exits the corrective wedge  420  generally perpendicular to the surface of the corrective wedge  420  while the dark state light exits at an oblique angle. As a result, the direction of the image light  414  from the “on” pixels is largely unaffected by refraction as it exits from the surface of the corrective wedge  420 . In contrast, the dark state light  410  is substantially changed in direction by refraction when the dark state light  410  exits the corrective wedge  420 . 
     The embodiment illustrated in  FIG.  4    has the similar advantages of those discussed in connection with the embodiment of  FIG.  3   b   . The dimensions and weight of the upper module  202  depicted in  FIG.  4    may be approximately 8×8 mm with a weight of less than 3 grams. A difference in overall performance between the configuration illustrated in  FIGS.  3   b    and the configuration illustrated in  FIG.  4    is that the embodiment of  FIG.  4    doesn&#39;t require the use of polarized light as supplied by the light source  404 . This can be an advantage in some situations as will be discussed in more detail below (e.g. increased see-through transparency of the HWC optics from the user&#39;s perspective). Polarized light may be used in connection with the embodiment depicted in  FIG.  4   , in embodiments. An additional advantage of the embodiment of  FIG.  4    compared to the embodiment shown in  FIG.  3   b    is that the dark state light (shown as DLP off light  410 ) is directed at a steeper angle away from the optical axis of the image light  414  due to the added refraction encountered when the dark state light  410  exits the corrective wedge  420 . This steeper angle of the dark state light  410  allows for the light trap to be positioned closer to the DLP  402  so that the overall size of the upper module  202  can be reduced. The light trap can also be made larger since the light trap doesn&#39;t interfere with the field lens, thereby the efficiency of the light trap can be increased and as a result, stray light can be reduced and the contrast of the image perceived by the user can be increased.  FIG.  4   a    illustrates the embodiment described in connection with  FIG.  4    with an example set of corresponding angles at the various surfaces with the reflected angles of a ray of light passing through the upper optical module  202 . In this example, the DLP mirrors are provided at 17 degrees to the surface of the DLP device. The angles of the TIR wedge are selected in correspondence to one another to provide TIR reflected illumination light at the correct angle for the DLP mirrors while allowing the image light and dark state light to pass through the thin air gap, various combinations of angles are possible to achieve this. 
       FIG.  5    illustrates yet another embodiment of an upper optical module  202  in accordance with the principles of the present invention. As with the embodiment shown in  FIG.  4   , the embodiment shown in  FIG.  5    does not require the use of polarized light. Polarized light may be used in connection with this embodiment, but it is not required. The optical module  202  depicted in  FIG.  5    is similar to that presented in connection with  FIG.  4   ; however, the embodiment of  FIG.  5    includes an off light redirection wedge  502 . As can be seen from the illustration, the off light redirection wedge  502  allows the image light  414  to continue generally along the optical axis toward the field lens and into the lower optical module  204  (as illustrated). However, the off light  504  is redirected substantially toward the side of the corrective wedge  420  where it passes into the light trap. This configuration may allow further height compactness in the HWC because the light trap (not illustrated) that is intended to absorb the off light  504  can be positioned laterally adjacent the upper optical module  202  as opposed to below it. In the embodiment depicted in  FIG.  5    there is a thin air gap between the TIR wedge  418  and the corrective wedge  420  (similar to the embodiment of  FIG.  4   ). There is also a thin air gap between the corrective wedge  420  and the off light redirection wedge  502 . There may be HWC mechanical configurations that warrant the positioning of a light trap for the dark state light elsewhere and the illustration depicted in  FIG.  5    should be considered illustrative of the concept that the off light can be redirected to create compactness of the overall HWC.  FIG.  5   a    illustrates an example of the embodiment described in connection with  FIG.  5    with the addition of more details on the relative angles at the various surfaces and a light ray trace for image light and a light ray trace for dark light are shown as it passes through the upper optical module  202 . Again, various combinations of angles are possible. 
       FIG.  4   b    shows an illustration of a further embodiment in which a solid transparent matched set of wedges  456  is provided with a reflective polarizer  450  at the interface between the wedges. Wherein the interface between the wedges in the wedge set  456  is provided at an angle so that illumination light  452  from the polarized light source  458  is reflected at the proper angle (e.g. 34 degrees for a 17 degree DLP mirror) for the DLP mirror “on” state so that the reflected image light  414  is provided along the optical axis of the field lens. The general geometry of the wedges in the wedge set  456  is similar to that shown in  FIGS.  4  and  4     a . A quarter wave film  454  is provided on the DLP  402  surface so that the illumination light  452  is one polarization state (e.g. S polarization state) while in passing through the quarter wave film  454 , reflecting from the DLP mirror and passing back through the quarter wave film  454 , the image light  414  is converted to the other polarization state (e.g. P polarization state). The reflective polarizer is oriented such that the illumination light  452  with its polarization state is reflected and the image light  414  with its other polarization state is transmitted. Since the dark state light from the “off pixels  410  also passes through the quarter wave film  454  twice, it is also the other polarization state (e.g. P polarization state) so that it is transmitted by the reflective polarizer  450 . 
     The angles of the faces of the wedge set  450  correspond to the needed angles to provide illumination light  452  at the angle needed by the DLP mirrors when in the “on” state so that the reflected image light  414  is reflected from the DLP along the optical axis of the field lens. The wedge set  456  provides an interior interface where a reflective polarizer film can be located to redirect the illumination light  452  toward the mirrors of the DLP  402 . The wedge set also provides a matched wedge on the opposite side of the reflective polarizer  450  so that the image light  414  from the “on” pixels exits the wedge set  450  substantially perpendicular to the exit surface, while the dark state light from the ‘off’ pixels  410  exits at an oblique angle to the exit surface. As a result, the image light  414  is substantially unrefracted upon exiting the wedge set  456 , while the dark state light from the “off” pixels  410  is substantially refracted upon exiting the wedge set  456  as shown in  FIG.  4     b.    
     By providing a solid transparent matched wedge set, the flatness of the interface is reduced, because variations in the flatness have a negligible effect as long as they are within the cone angle of the illuminating light  452 . Which can be f #2.2 with a 26 degree cone angle. In a preferred embodiment, the reflective polarizer is bonded between the matched internal surfaces of the wedge set  456  using an optical adhesive so that Fresnel reflections at the interfaces on either side of the reflective polarizer  450  are reduced. The optical adhesive can be matched in refractive index to the material of the wedge set  456  and the pieces of the wedge set  456  can be all made from the same material such as BK 7  glass or cast acrylic. Wherein the wedge material can be selected to have low birefringence as well to reduce non-uniformities in brightness. The wedge set  456  and the quarter wave film  454  can also be bonded to the DLP  402  to further reduce Fresnel reflections at the DLP interface losses. In addition, since the image light  414  is substantially normal to the exit surface of the wedge set  456 , the flatness of the surface is not critical to maintain the wavefront of the image light  414  so that high image quality can be obtained in the displayed image without requiring very tightly toleranced flatness on the exit surface. 
     A yet further embodiment of the invention that is not illustrated, combines the embodiments illustrated in  FIG.  4   b    and  FIG.  5   . In this embodiment, the wedge set  456  is comprised of three wedges with the general geometry of the wedges in the wedge set corresponding to that shown in  FIGS.  5  and  5     a . A reflective polarizer is bonded between the first and second wedges similar to that shown in  FIG.  4   b   , however, a third wedge is provided similar to the embodiment of  FIG.  5   . Wherein there is an angled thin air gap between the second and third wedges so that the dark state light is reflected by TIR toward the side of the second wedge where it is absorbed in a light trap. This embodiment, like the embodiment shown in  FIG.  4   b   , uses a polarized light source as has been previously described. The difference in this embodiment is that the image light is transmitted through the reflective polarizer and is transmitted through the angled thin air gap so that it exits normal to the exit surface of the third wedge. 
       FIG.  5   b    illustrates an upper optical module  202  with a dark light trap  514   a . As described in connection with  FIGS.  4  and  4     a , image light can be generated from a DLP when using a TIR and corrective lens configuration. The upper module may be mounted in a HWC housing  510  and the housing  510  may include a dark light trap  514   a . The dark light trap  514   a  is generally positioned/constructed/formed in a position that is optically aligned with the dark light optical axis  512 . As illustrated, the dark light trap may have depth such that the trap internally reflects dark light in an attempt to further absorb the light and prevent the dark light from combining with the image light that passes through the field lens. The dark light trap may be of a shape and depth such that it absorbs the dark light. In addition, the dark light trap  514   b , in embodiments, may be made of light absorbing materials or coated with light absorbing materials. In embodiments, the recessed light trap  514   a  may include baffles to block a view of the dark state light. This may be combined with black surfaces and textured or fibrous surfaces to help absorb the light. The baffles can be part of the light trap, associated with the housing, or field lens, etc. 
       FIG.  5   c    illustrates another embodiment with a light trap  514   b . As can be seen in the illustration, the shape of the trap is configured to enhance internal reflections within the light trap  514   b  to increase the absorption of the dark light  512 .  FIG.  5   d    illustrates another embodiment with a light trap  514   c . As can be seen in the illustration, the shape of the trap  514   c  is configured to enhance internal reflections to increase the absorption of the dark light  512 . 
       FIG.  5   e    illustrates another embodiment of an upper optical module  202  with a dark light trap  514   d . This embodiment of upper module  202  includes an off light reflection wedge  502 , as illustrated and described in connection with the embodiment of  FIGS.  5  and  5     a . As can be seen in  FIG.  5   e   , the light trap  514   d  is positioned along the optical path of the dark light  512 . The dark light trap  514   d  may be configured as described in other embodiments herein. The embodiment of the light trap  514   d  illustrated in  FIG.  5   e    includes a black area on the side wall of the wedge, wherein the side wall is located substantially away from the optical axis of the image light  414 . In addition, baffles  5252  may be added to one or more edges of the field lens  312  to block the view of the light trap  514   d  adjacent to the displayed image seen by the user. 
       FIG.  6    illustrates a combination of an upper optical module  202  with a lower optical module  204 . In this embodiment, the image light projected from the upper optical module  202  may or may not be polarized. The image light is reflected off a flat combiner element  602  such that it is directed towards the user&#39;s eye. Wherein, the combiner element  602  is a partial mirror that reflects image light while transmitting a substantial portion of light from the environment so the user can look through the combiner element and see the environment surrounding the HWC. 
     The combiner  602  may include a holographic pattern, to form a holographic mirror. If a monochrome image is desired, there may be a single wavelength reflection design for the holographic pattern on the surface of the combiner  602 . If the intention is to have multiple colors reflected from the surface of the combiner  602 , a multiple wavelength holographic mirror may be included on the combiner surface. For example, in a three-color embodiment, where red, green and blue pixels are generated in the image light, the holographic mirror may be reflective to wavelengths substantially matching the wavelengths of the red, green and blue light provided by the light source. This configuration can be used as a wavelength specific mirror where pre-determined wavelengths of light from the image light are reflected to the user&#39;s eye. This configuration may also be made such that substantially all other wavelengths in the visible pass through the combiner element  602  so the user has a substantially clear view of the surroundings when looking through the combiner element  602 . The transparency between the user&#39;s eye and the surrounding may be approximately 80% when using a combiner that is a holographic mirror. Wherein holographic mirrors can be made using lasers to produce interference patterns in the holographic material of the combiner where the wavelengths of the lasers correspond to the wavelengths of light that are subsequently reflected by the holographic mirror. 
     In another embodiment, the combiner element  602  may include a notch mirror comprised of a multilayer coated substrate wherein the coating is designed to substantially reflect the wavelengths of light provided by the light source and substantially transmit the remaining wavelengths in the visible spectrum. For example, in the case where red, green and blue light is provided by the light source to enable full color images to be provided to the user, the notch mirror is a tristimulus notch mirror wherein the multilayer coating is designed to reflect narrow bands of red, green and blue light that are matched to the what is provided by the light source and the remaining visible wavelengths are transmitted through the coating to enable a view of the environment through the combiner. In another example where monochrome images are provided to the user, the notch mirror is designed to reflect a single narrow band of light that is matched to the wavelength range of the light provided by the light source while transmitting the remaining visible wavelengths to enable a see-thru view of the environment. The combiner  602  with the notch mirror would operate, from the user&#39;s perspective, in a manner similar to the combiner that includes a holographic pattern on the combiner element  602 . The combiner, with the tristimulus notch mirror, would reflect the “on” pixels to the eye because of the match between the reflective wavelengths of the notch mirror and the color of the image light, and the wearer would be able to see with high clarity the surroundings. The transparency between the user&#39;s eye and the surrounding may be approximately 80% when using the tristimulus notch mirror. In addition, the image provided by the upper optical module  202  with the notch mirror combiner can provide higher contrast images than the holographic mirror combiner due to less scattering of the imaging light by the combiner. 
     Light can escape through the combiner  602  and may produce face glow as the light is generally directed downward onto the cheek of the user. When using a holographic mirror combiner or a tristimulus notch mirror combiner, the escaping light can be trapped to avoid face glow. In embodiments, if the image light is polarized before the combiner, a linear polarizer can be laminated, or otherwise associated, to the combiner, with the transmission axis of the polarizer oriented relative to the polarized image light so that any escaping image light is absorbed by the polarizer. In embodiments, the image light would be polarized to provide S polarized light to the combiner for better reflection. As a result, the linear polarizer on the combiner would be oriented to absorb S polarized light and pass P polarized light. This provides the preferred orientation of polarized sunglasses as well. 
     If the image light is unpolarized, a microlouvered film such as a privacy filter can be used to absorb the escaping image light while providing the user with a see-thru view of the environment. In this case, the absorbance or transmittance of the microlouvered film is dependent on the angle of the light. Where steep angle light is absorbed and light at less of an angle is transmitted. For this reason, in an embodiment, the combiner with the microlouver film is angled at greater than 45 degrees to the optical axis of the image light (e.g. the combiner can be oriented at 50 degrees so the image light from the file lens is incident on the combiner at an oblique angle. 
       FIG.  7    illustrates an embodiment of a combiner element  602  at various angles when the combiner element  602  includes a holographic mirror. Normally, a mirrored surface reflects light at an angle equal to the angle that the light is incident to the mirrored surface. Typically, this necessitates that the combiner element be at 45 degrees,  602   a , if the light is presented vertically to the combiner so the light can be reflected horizontally towards the wearer&#39;s eye. In embodiments, the incident light can be presented at angles other than vertical to enable the mirror surface to be oriented at other than 45 degrees, but in all cases wherein a mirrored surface is employed (including the tristimulus notch mirror described previously), the incident angle equals the reflected angle. As a result, increasing the angle of the combiner  602   a  requires that the incident image light be presented to the combiner  602   a  at a different angle which positions the upper optical module  202  to the left of the combiner as shown in  FIG.  7   . In contrast, a holographic mirror combiner, included in embodiments, can be made such that light is reflected at a different angle from the angle that the light is incident onto the holographic mirrored surface. This allows freedom to select the angle of the combiner element  602   b  independent of the angle of the incident image light and the angle of the light reflected into the wearer&#39;s eye. In embodiments, the angle of the combiner element  602   b  is greater than 45 degrees (shown in  FIG.  7   ) as this allows a more laterally compact HWC design. The increased angle of the combiner element  602   b  decreases the front to back width of the lower optical module  204  and may allow for a thinner HWC display (i.e. the furthest element from the wearer&#39;s eye can be closer to the wearer&#39;s face). 
       FIG.  8    illustrates another embodiment of a lower optical module  204 . In this embodiment, polarized image light provided by the upper optical module  202 , is directed into the lower optical module  204 . The image light reflects off a polarized mirror  804  and is directed to a focusing partially reflective mirror  802 , which is adapted to reflect the polarized light. An optical element such as a ¼ wave film located between the polarized mirror  804  and the partially reflective mirror  802 , is used to change the polarization state of the image light such that the light reflected by the partially reflective mirror  802  is transmitted by the polarized mirror  804  to present image light to the eye of the wearer. The user can also see through the polarized mirror  804  and the partially reflective mirror  802  to see the surrounding environment. As a result, the user perceives a combined image comprised of the displayed image light overlaid onto the see-thru view of the environment. 
     While many of the embodiments of the present invention have been referred to as upper and lower modules containing certain optical components, it should be understood that the image light and dark light production and management functions described in connection with the upper module may be arranged to direct light in other directions (e.g. upward, sideward, etc.). In embodiments, it may be preferred to mount the upper module  202  above the wearer&#39;s eye, in which case the image light would be directed downward. In other embodiments it may be preferred to produce light from the side of the wearer&#39;s eye, or from below the wearer&#39;s eye. In addition, the lower optical module is generally configured to deliver the image light to the wearer&#39;s eye and allow the wearer to see through the lower optical module, which may be accomplished through a variety of optical components. 
       FIG.  8   a    illustrates an embodiment of the present invention where the upper optical module  202  is arranged to direct image light into a TIR waveguide  810 . In this embodiment, the upper optical module  202  is positioned above the wearer&#39;s eye  812  and the light is directed horizontally into the TIR waveguide  810 . The TIR waveguide is designed to internally reflect the image light in a series of downward TIR reflections until it reaches the portion in front of the wearer&#39;s eye, where the light passes out of the TIR waveguide  812  into the wearer&#39;s eye. In this embodiment, an outer shield  814  is positioned in front of the TIR waveguide  810 . 
       FIG.  8   b    illustrates an embodiment of the present invention where the upper optical module  202  is arranged to direct image light into a TIR waveguide  818 . In this embodiment, the upper optical module  202  is arranged on the side of the TIR waveguide  818 . For example, the upper optical module may be positioned in the arm or near the arm of the HWC when configured as a pair of head worn glasses. The TIR waveguide  818  is designed to internally reflect the image light in a series of TIR reflections until it reaches the portion in front of the wearer&#39;s eye, where the light passes out of the TIR waveguide  812  into the wearer&#39;s eye. 
       FIG.  8   c    illustrates yet further embodiments of the present invention where an upper optical module  202  is directing polarized image light into an optical guide  828  where the image light passes through a polarized reflector  824 , changes polarization state upon reflection of the optical element  822  which includes a ¼ wave film for example and then is reflected by the polarized reflector  824  towards the wearer&#39;s eye, due to the change in polarization of the image light. The upper optical module  202  may be positioned to direct light to a mirror  820 , to position the upper optical module  202  laterally, in other embodiments, the upper optical module  202  may direct the image light directly towards the polarized reflector  824 . It should be understood that the present invention comprises other optical arrangements intended to direct image light into the wearer&#39;s eye. 
     Another aspect of the present invention relates to eye imaging. In embodiments, a camera is used in connection with an upper optical module  202  such that the wearer&#39;s eye can be imaged using pixels in the “off” state on the DLP.  FIG.  9    illustrates a system where the eye imaging camera  802  is mounted and angled such that the field of view of the eye imaging camera  802  is redirected toward the wearer&#39;s eye by the mirror pixels of the DLP  402  that are in the “off” state. In this way, the eye imaging camera  802  can be used to image the wearer&#39;s eye along the same optical axis as the displayed image that is presented to the wearer. Wherein, image light that is presented to the wearer&#39;s eye illuminates the wearer&#39;s eye so that the eye can be imaged by the eye imaging camera  802 . In the process, the light reflected by the eye passes back though the optical train of the lower optical module  204  and a portion of the upper optical module to where the light is reflected by the “off” pixels of the DLP  402  toward the eye imaging camera  802 . 
     In embodiments, the eye imaging camera may image the wearer&#39;s eye at a moment in time where there are enough “off” pixels to achieve the required eye image resolution. In another embodiment, the eye imaging camera collects eye image information from “off” pixels over time and forms a time lapsed image. In another embodiment, a modified image is presented to the user wherein enough “off” state pixels are included that the camera can obtain the desired resolution and brightness for imaging the wearer&#39;s eye and the eye image capture is synchronized with the presentation of the modified image. 
     The eye imaging system may be used for security systems. The HWC may not allow access to the HWC or other system if the eye is not recognized (e.g. through eye characteristics including retina or iris characteristics, etc.). The HWC may be used to provide constant security access in some embodiments. For example, the eye security confirmation may be a continuous, near-continuous, real-time, quasi real-time, periodic, etc. process so the wearer is effectively constantly being verified as known. In embodiments, the HWC may be worn and eye security tracked for access to other computer systems. 
     The eye imaging system may be used for control of the HWC. For example, a blink, wink, or particular eye movement may be used as a control mechanism for a software application operating on the HWC or associated device. 
     The eye imaging system may be used in a process that determines how or when the HWC  102  delivers digitally displayed content to the wearer. For example, the eye imaging system may determine that the user is looking in a direction and then HWC may change the resolution in an area of the display or provide some content that is associated with something in the environment that the user may be looking at. Alternatively, the eye imaging system may identify different user&#39;s and change the displayed content or enabled features provided to the user. User&#39;s may be identified from a database of users eye characteristics either located on the HWC  102  or remotely located on the network  110  or on a server  112 . In addition, the HWC may identify a primary user or a group of primary users from eye characteristics wherein the primary user(s) are provided with an enhanced set of features and all other users are provided with a different set of features. Thus in this use case, the HWC  102  uses identified eye characteristics to either enable features or not and eye characteristics need only be analyzed in comparison to a relatively small database of individual eye characteristics. 
       FIG.  10    illustrates a light source that may be used in association with the upper optics module  202  (e.g. polarized light source if the light from the solid state light source is polarized such as polarized light source  302  and  458 ), and light source  404 . In embodiments, to provide a uniform surface of light  1008  to be directed into the upper optical module  202  and towards the DLP of the upper optical module, either directly or indirectly, the solid state light source  1002  may be projected into a backlighting optical system  1004 . The solid state light source  1002  may be one or more LEDs, laser diodes, OLEDs. In embodiments, the backlighting optical system  1004  includes an extended section with a length/distance ratio of greater than 3, wherein the light undergoes multiple reflections from the sidewalls to mix of homogenize the light as supplied by the solid state light source  1002 . The backlighting optical system  1004  can also include structures on the surface opposite (on the left side as shown in  FIG.  10   ) to where the uniform light  1008  exits the backlight  1004  to change the direction of the light toward the DLP  302  and the reflective polarizer  310  or the DLP  402  and the TIR wedge  418 . The backlighting optical system  1004  may also include structures to collimate the uniform light  1008  to provide light to the DLP with a smaller angular distribution or narrower cone angle. Diffusers or polarizers can be used on the entrance or exit surface of the backlighting optical system. Diffusers can be used to spread or uniformize the exiting light from the backlight to improve the uniformity or increase the angular spread of the uniform light  1008 . Elliptical diffusers that diffuse the light more in some directions and less in others can be used to improve the uniformity or spread of the uniform light  1008  in directions orthogonal to the optical axis of the uniform light  1008 . Linear polarizers can be used to convert unpolarized light as supplied by the solid state light source  1002  to polarized light so the uniform light  1008  is polarized with a desired polarization state. A reflective polarizer can be used on the exit surface of the backlight  1004  to polarize the uniform light  1008  to the desired polarization state, while reflecting the other polarization state back into the backlight where it is recycled by multiple reflections within the backlight  1004  and at the solid state light source  1002 . Therefore by including a reflective polarizer at the exit surface of the backlight  1004 , the efficiency of the polarized light source is improved. 
       FIGS.  10   a  and  10   b    show illustrations of structures in backlight optical systems  1004  that can be used to change the direction of the light provided to the entrance face  1045  by the light source and then collimates the light in a direction lateral to the optical axis of the exiting uniform light  1008 . Structure  1060  includes an angled sawtooth pattern in a transparent waveguide wherein the left edge of each sawtooth clips the steep angle rays of light thereby limiting the angle of the light being redirected. The steep surface at the right (as shown) of each sawtooth then redirects the light so that it reflects off the left angled surface of each sawtooth and is directed toward the exit surface  1040 . The sawtooth surfaces shown on the lower surface in  FIGS.  10   a  and  10   b   , can be smooth and coated (e.g. with an aluminum coating or a dielectric mirror coating) to provide a high level of reflectivity without scattering. Structure  1050  includes a curved face on the left side (as shown) to focus the rays after they pass through the exit surface  1040 , thereby providing a mechanism for collimating the uniform light  1008 . In a further embodiment, a diffuser can be provided between the solid state light source  1002  and the entrance face  1045  to homogenize the light provided by the solid state light source  1002 . In yet a further embodiment, a polarizer can be used between the diffuser and the entrance face  1045  of the backlight  1004  to provide a polarized light source. Because the sawtooth pattern provides smooth reflective surfaces, the polarization state of the light can be preserved from the entrance face  1045  to the exit face  1040 . In this embodiment, the light entering the backlight from the solid state light source  1002  passes through the polarizer so that it is polarized with the desired polarization state. If the polarizer is an absorptive linear polarizer, the light of the desired polarization state is transmitted while the light of the other polarization state is absorbed. If the polarizer is a reflective polarizer, the light of the desired polarization state is transmitted into the backlight  1004  while the light of the other polarization state is reflected back into the solid state light source  1002  where it can be recycled as previously described, to increase the efficiency of the polarized light source. 
       FIG.  11   a    illustrates a light source  1100  that may be used in association with the upper optics module  202 . In embodiments, the light source  1100  may provide light to a backlighting optical system  1004  as described above in connection with  FIG.  10   . In embodiments, the light source  1100  includes a tristimulus notch filter  1102 . The tristimulus notch filter  1102  has narrow band pass filters for three wavelengths, as indicated in  FIG.  11   c    in a transmission graph  1108 . The graph shown in  FIG.  11   b   , as  1104  illustrates an output of three different colored LEDs. One can see that the bandwidths of emission are narrow, but they have long tails. The tristimulus notch filter  1102  can be used in connection with such LEDs to provide a light source  1100  that emits narrow filtered wavelengths of light as shown in  FIG.  11   d    as the transmission graph  1110 . Wherein the clipping effects of the tristimulus notch filter  1102  can be seen to have cut the tails from the LED emission graph  1104  to provide narrower wavelength bands of light to the upper optical module  202 . The light source  1100  can be used in connection with a combiner  602  with a holographic mirror or tristimulus notch mirror to provide narrow bands of light that are reflected toward the wearer&#39;s eye with less waste light that does not get reflected by the combiner, thereby improving efficiency and reducing escaping light that can cause faceglow. 
       FIG.  12   a    illustrates another light source  1200  that may be used in association with the upper optics module  202 . In embodiments, the light source  1200  may provide light to a backlighting optical system  1004  as described above in connection with  FIG.  10   . In embodiments, the light source  1200  includes a quantum dot cover glass  1202 . Where the quantum dots absorb light of a shorter wavelength and emit light of a longer wavelength ( FIG.  12   b    shows an example wherein a UV spectrum  1202  applied to a quantum dot results in the quantum dot emitting a narrow band shown as a PL spectrum  1204 ) that is dependent on the material makeup and size of the quantum dot. As a result, quantum dots in the quantum dot cover glass  1202  can be tailored to provide one or more bands of narrow bandwidth light (e.g. red, green and blue emissions dependent on the different quantum dots included as illustrated in the graph shown in  FIG.  12   c    where three different quantum dots are used. In embodiments, the LED driver light emits UV light, deep blue or blue light. For sequential illumination of different colors, multiple light sources  1200  would be used where each light source  1200  would include a quantum dot cover glass  1202  with a quantum dot selected to emit at one of the desired colors. The light source  1100  can be used in connection with a combiner  602  with a holographic mirror or tristimulus notch mirror to provide narrow transmission bands of light that are reflected toward the wearer&#39;s eye with less waste light that does not get reflected. 
     Another aspect of the present invention relates to the generation of peripheral image lighting effects for a person wearing a HWC. In embodiments, a solid state lighting system (e.g. LED, OLED, etc), or other lighting system, may be included inside the optical elements of an lower optical module  204 . The solid state lighting system may be arranged such that lighting effects outside of a field of view (FOV) of the presented digital content is presented to create an immersive effect for the person wearing the HWC. To this end, the lighting effects may be presented to any portion of the HWC that is visible to the wearer. The solid state lighting system may be digitally controlled by an integrated processor on the HWC. In embodiments, the integrated processor will control the lighting effects in coordination with digital content that is presented within the FOV of the HWC. For example, a movie, picture, game, or other content, may be displayed or playing within the FOV of the HWC. The content may show a bomb blast on the right side of the FOV and at the same moment, the solid state lighting system inside of the upper module optics may flash quickly in concert with the FOV image effect. The effect may not be fast, it may be more persistent to indicate, for example, a general glow or color on one side of the user. The solid state lighting system may be color controlled, with red, green and blue LEDs, for example, such that color control can be coordinated with the digitally presented content within the field of view. 
       FIG.  13   a    illustrates optical components of a lower optical module  204  together with an outer lens  1302 .  FIG.  13   a    also shows an embodiment including effects LED&#39;s  1308   a  and  1308   b .  FIG.  13   a    illustrates image light  1312 , as described herein elsewhere, directed into the upper optical module where it will reflect off of the combiner element  1304 , as described herein elsewhere. The combiner element  1304  in this embodiment is angled towards the wearer&#39;s eye at the top of the module and away from the wearer&#39;s eye at the bottom of the module, as also illustrated and described in connection with  FIG.  8    (e.g. at a 45 degree angle). The image light  1312  provided by an upper optical module  202  (not shown in  FIG.  13   a   ) reflects off of the combiner element  1304  towards the collimating mirror  1310 , away from the wearer&#39;s eye, as described herein elsewhere. The image light  1312  then reflects and focuses off of the collimating mirror  1304 , passes back through the combiner element  1304 , and is directed into the wearer&#39;s eye. The wearer can also view the surrounding environment through the transparency of the combiner element  1304 , collimating mirror  1310 , and outer lens  1302  (if it is included). As described herein elsewhere, various surfaces are polarized to create the optical path for the image light and to provide transparency of the elements such that the wearer can view the surrounding environment. The wearer will generally perceive that the image light forms an image in the FOV  1305 . In embodiments, the outer lens  1302  may be included. The outer lens  1302  is an outer lens that may or may not be corrective and it may be designed to conceal the lower optical module components in an effort to make the HWC appear to be in a form similar to standard glasses or sunglasses. 
     In the embodiment illustrated in  FIG.  13   a   , the effects LEDs  1308   a  and  1308   b  are positioned at the sides of the combiner element  1304  and the outer lens  1302  and/or the collimating mirror  1310 . In embodiments, the effects LEDs  1308   a  are positioned within the confines defined by the combiner element  1304  and the outer lens  1302  and/or the collimating mirror. The effects LEDs  1308   a  and  1308   b  are also positioned outside of the FOV  1305 . In this arrangement, the effects LEDs  1308   a  and  1308   b  can provide lighting effects within the lower optical module outside of the FOV  1305 . In embodiments the light emitted from the effects LEDs  1308   a  and  1308   b  may be polarized such that the light passes through the combiner element  1304  toward the wearer&#39;s eye and does not pass through the outer lens  1302  and/or the collimating mirror  1310 . This arrangement provides peripheral lighting effects to the wearer in a more private setting by not transmitting the lighting effects through the front of the HWC into the surrounding environment. However, in other embodiments, the effects LEDs  1308   a  and  1308   b  may be unpolarized so the lighting effects provided are made to be purposefully viewable by others in the environment for entertainment such as giving the effect of the wearer&#39;s eye glowing in correspondence to the image content being viewed by the wearer. 
       FIG.  13   b    illustrates a cross section of the embodiment described in connection with  FIG.  13   a   . As illustrated, the effects LED  1308   a  is located in the upper-front area inside of the optical components of the lower optical module. It should be understood that the effects LED  1308   a  position in the described embodiments is only illustrative and alternate placements are encompassed by the present invention. Additionally, in embodiments, there may be one or more effects LEDs  1308   a  in each of the two sides of HWC to provide peripheral lighting effects near one or both eyes of the wearer. 
       FIG.  13   c    illustrates an embodiment where the combiner element  1304  is angled away from the eye at the top and towards the eye at the bottom (e.g. in accordance with the holographic or notch filter embodiments described herein). In this embodiment, the effects LED  1308   a  is located on the outer lens  1302  side of the combiner element  1304  to provide a concealed appearance of the lighting effects. As with other embodiments, the effects LED  1308   a  of  FIG.  13   c    may include a polarizer such that the emitted light can pass through a polarized element associated with the combiner element  1304  and be blocked by a polarized element associated with the outer lens  1302 . 
     Another aspect of the present invention relates to the mitigation of light escaping from the space between the wearer&#39;s face and the HWC itself. Another aspect of the present invention relates to maintaining a controlled lighting environment in proximity to the wearer&#39;s eyes. In embodiments, both the maintenance of the lighting environment and the mitigation of light escape are accomplished by including a removable and replaceable flexible shield for the HWC. Wherein the removable and replaceable shield can be provided for one eye or both eyes in correspondence to the use of the displays for each eye. For example, in a night vision application, the display to only one eye could be used for night vision while the display to the other eye is turned off to provide good see-thru when moving between areas where visible light is available and dark areas where night vision enhancement is needed. 
       FIG.  14   a    illustrates a removable and replaceable flexible eye cover  1402  with an opening  1408  that can be attached and removed quickly from the HWC  102  through the use of magnets. Other attachment methods may be used, but for illustration of the present invention we will focus on a magnet implementation. In embodiments, magnets may be included in the eye cover  1402  and magnets of an opposite polarity may be included (e.g. embedded) in the frame of the HWC  102 . The magnets of the two elements would attract quite strongly with the opposite polarity configuration. In another embodiment, one of the elements may have a magnet and the other side may have metal for the attraction. In embodiments, the eye cover  1402  is a flexible elastomeric shield. In embodiments, the eye cover  1402  may be an elastomeric bellows design to accommodate flexibility and more closely align with the wearer&#39;s face.  FIG.  14   b    illustrates a removable and replaceable flexible eye cover  1404  that is adapted as a single eye cover. In embodiments, a single eye cover may be used for each side of the HWC to cover both eyes of the wearer. In embodiments, the single eye cover may be used in connection with a HWC that includes only one computer display for one eye. These configurations prevent light that is generated and directed generally towards the wearer&#39;s face by covering the space between the wearer&#39;s face and the HWC. The opening  1408  allows the wearer to look through the opening  1408  to view the displayed content and the surrounding environment through the front of the HWC. The image light in the lower optical module  204  can be prevented from emitting from the front of the HWC through internal optics polarization schemes, as described herein, for example. 
       FIG.  14   c    illustrates another embodiment of a light suppression system. In this embodiment, the eye cover  1410  may be similar to the eye cover  1402 , but eye cover  1410  includes a front light shield  1412 . The front light shield  1412  may be opaque to prevent light from escaping the front lens of the HWC. In other embodiments, the front light shield  1412  is polarized to prevent light from escaping the front lens. In a polarized arrangement, in embodiments, the internal optical elements of the HWC (e.g. of the lower optical module  204 ) may polarize light transmitted towards the front of the HWC and the front light shield  1412  may be polarized to prevent the light from transmitting through the front light shield  1412 . 
     In embodiments, an opaque front light shield  1412  may be included and the digital content may include images of the surrounding environment such that the wearer can visualize the surrounding environment. One eye may be presented with night vision environmental imagery and this eye&#39;s surrounding environment optical path may be covered using an opaque front light shield  1412 . In other embodiments, this arrangement may be associated with both eyes. 
     Another aspect of the present invention relates to automatically configuring the lighting system(s) used in the HWC  102 . In embodiments, the display lighting and/or effects lighting, as described herein, may be controlled in a manner suitable for when an eye cover  1408  is attached or removed from the HWC  102 . For example, at night, when the light in the environment is low, the lighting system(s) in the HWC may go into a low light mode to further control any amounts of stray light escaping from the HWC and the areas around the HWC. Covert operations at night, while using night vision or standard vision, may require a solution which prevents as much escaping light as possible so a user may clip on the eye cover(s)  1408  and then the HWC may go into a low light mode. The low light mode may, in some embodiments, only go into a low light mode when the eye cover  1408  is attached if the HWC identifies that the environment is in low light conditions (e.g. through environment light level sensor detection). In embodiments, the low light level may be determined to be at an intermediate point between full and low light dependent on environmental conditions. 
     Another aspect of the present invention relates to automatically controlling the type of content displayed in the HWC when eye covers  1408  are attached or removed from the HWC. In embodiments, when the eye cover(s)  1408  is attached to the HWC, the displayed content may be restricted in amount or in color amounts. For example, the display(s) may go into a simple content delivery mode to restrict the amount of information displayed. This may be done to reduce the amount of light produced by the display(s). In an embodiment, the display(s) may change from color displays to monochrome displays to reduce the amount of light produced. In an embodiment, the monochrome lighting may be red to limit the impact on the wearer&#39;s eyes to maintain an ability to see better in the dark. 
     Referring to  FIG.  15   , we now turn to describe a particular external user interface  104 , referred to generally as a pen  1500 . The pen  1500  is a specially designed external user interface  104  and can operate as a user interface, such as to many different styles of HWC  102 . The pen  1500  generally follows the form of a conventional pen, which is a familiar user handled device and creates an intuitive physical interface for many of the operations to be carried out in the HWC system  100 . The pen  1500  may be one of several user interfaces  104  used in connection with controlling operations within the HWC system  100 . For example, the HWC  102  may watch for and interpret hand gestures  116  as control signals, where the pen  1500  may also be used as a user interface with the same HWC  102 . Similarly, a remote keyboard may be used as an external user interface  104  in concert with the pen  1500 . The combination of user interfaces or the use of just one control system generally depends on the operation(s) being executed in the HWC&#39;s system  100 . 
     While the pen  1500  may follow the general form of a conventional pen, it contains numerous technologies that enable it to function as an external user interface  104 .  FIG.  15    illustrates technologies comprised in the pen  1500 . As can be seen, the pen  1500  may include a camera  1508 , which is arranged to view through lens  1502 . The camera may then be focused, such as through lens  1502 , to image a surface upon which a user is writing or making other movements to interact with the HWC  102 . There are situations where the pen  1500  will also have an ink, graphite, or other system such that what is being written can be seen on the writing surface. There are other situations where the pen  1500  does not have such a physical writing system so there is no deposit on the writing surface, where the pen would only be communicating data or commands to the HWC  102 . The lens configuration is described in greater detail herein. The function of the camera is to capture information from an unstructured writing surface such that pen strokes can be interpreted as intended by the user. To assist in the predication of the intended stroke path, the pen  1500  may include a sensor, such as an IMU  1512 . Of course, the IMU could be included in the pen  1500  in its separate parts (e.g. gyro, accelerometer, etc.) or an IMU could be included as a single unit. In this instance, the IMU  1512  is used to measure and predict the motion of the pen  1500 . In turn, the integrated microprocessor  1510  would take the IMU information and camera information as inputs and process the information to form a prediction of the pen tip movement. 
     The pen  1500  may also include a pressure monitoring system  1504 , such as to measure the pressure exerted on the lens  1502 . As will be described in greater detail herein, the pressure measurement can be used to predict the user&#39;s intention for changing the weight of a line, type of a line, type of brush, click, double click, and the like. In embodiments, the pressure sensor may be constructed using any force or pressure measurement sensor located behind the lens  1502 , including for example, a resistive sensor, a current sensor, a capacitive sensor, a voltage sensor such as a piezoelectric sensor, and the like. 
     The pen  1500  may also include a communications module  1518 , such as for bi-directional communication with the HWC  102 . In embodiments, the communications module  1518  may be a short distance communication module (e.g. Bluetooth). The communications module  1518  may be security matched to the HWC  102 . The communications module  1518  may be arranged to communicate data and commands to and from the microprocessor  1510  of the pen  1500 . The microprocessor  1510  may be programmed to interpret data generated from the camera  1508 , IMU  1512 , and pressure sensor  1504 , and the like, and then pass a command onto the HWC  102  through the communications module  1518 , for example. In another embodiment, the data collected from any of the input sources (e.g. camera  1508 , IMU  1512 , pressure sensor  1504 ) by the microprocessor may be communicated by the communication module  1518  to the HWC  102 , and the HWC  102  may perform data processing and prediction of the user&#39;s intention when using the pen  1500 . In yet another embodiment, the data may be further passed on through a network  110  to a remote device  112 , such as a server, for the data processing and prediction. The commands may then be communicated back to the HWC  102  for execution (e.g. display writing in the glasses display, make a selection within the UI of the glasses display, control a remote external device  112 , control a local external device  108 ), and the like. The pen may also include memory  1514  for long or short term uses. 
     The pen  1500  may also include a number of physical user interfaces, such as quick launch buttons  1522 , a touch sensor  1520 , and the like. The quick launch buttons  1522  may be adapted to provide the user with a fast way of jumping to a software application in the HWC system  100 . For example, the user may be a frequent user of communication software packages (e.g. email, text, Twitter, Instagram, Facebook, Google+, and the like), and the user may program a quick launch button  1522  to command the HWC  102  to launch an application. The pen  1500  may be provided with several quick launch buttons  1522 , which may be user programmable or factory programmable. The quick launch button  1522  may be programmed to perform an operation. For example, one of the buttons may be programmed to clear the digital display of the HWC  102 . This would create a fast way for the user to clear the screens on the HWC  102  for any reason, such as for example to better view the environment. The quick launch button functionality will be discussed in further detail below. The touch sensor  1520  may be used to take gesture style input from the user. For example, the user may be able to take a single finger and run it across the touch sensor  1520  to affect a page scroll. 
     The pen  1500  may also include a laser pointer  1524 . The laser pointer  1524  may be coordinated with the IMU  1512  to coordinate gestures and laser pointing. For example, a user may use the laser  1524  in a presentation to help with guiding the audience with the interpretation of graphics and the IMU  1512  may, either simultaneously or when the laser  1524  is off, interpret the user&#39;s gestures as commands or data input. 
       FIGS.  16 A-C  illustrate several embodiments of lens and camera arrangements  1600  for the pen  1500 . One aspect relates to maintaining a constant distance between the camera and the writing surface to enable the writing surface to be kept in focus for better tracking of movements of the pen  1500  over the writing surface. Another aspect relates to maintaining an angled surface following the circumference of the writing tip of the pen  1500  such that the pen  1500  can be rolled or partially rolled in the user&#39;s hand to create the feel and freedom of a conventional writing instrument. 
       FIG.  16 A  illustrates an embodiment of the writing lens end of the pen  1500 . The configuration includes a ball lens  1604 , a camera or image capture surface  1602 , and a domed cover lens  1608 . In this arrangement, the camera views the writing surface through the ball lens  1604  and dome cover lens  1608 . The ball lens  1604  causes the camera to focus such that the camera views the writing surface when the pen  1500  is held in the hand in a natural writing position, such as with the pen  1500  in contact with a writing surface. In embodiments, the ball lens  1604  should be separated from the writing surface to obtain the highest resolution of the writing surface at the camera  1602 . In embodiments, the ball lens  1604  is separated by approximately 1 to 3 mm. In this configuration, the domed cover lens  1608  provides a surface that can keep the ball lens  1604  separated from the writing surface at a constant distance, such as substantially independent of the angle used to write on the writing surface. For instance, in embodiments the field of view of the camera in this arrangement would be approximately 60 degrees. 
     The domed cover lens, or other lens  1608  used to physically interact with the writing surface, will be transparent or transmissive within the active bandwidth of the camera  1602 . In embodiments, the domed cover lens  1608  may be spherical or other shape and comprised of glass, plastic, sapphire, diamond, and the like. In other embodiments where low resolution imaging of the surface is acceptable. The pen  1500  can omit the domed cover lens  1608  and the ball lens  1604  can be in direct contact with the surface. 
       FIG.  16 B  illustrates another structure where the construction is somewhat similar to that described in connection with  FIG.  16 A ; however this embodiment does not use a dome cover lens  1608 , but instead uses a spacer  1610  to maintain a predictable distance between the ball lens  1604  and the writing surface, wherein the spacer may be spherical, cylindrical, tubular or other shape that provides spacing while allowing for an image to be obtained by the camera  1602  through the lens  1604 . In a preferred embodiment, the spacer  1610  is transparent. In addition, while the spacer  1610  is shown as spherical, other shapes such as an oval, doughnut shape, half sphere, cone, cylinder or other form may be used. 
       FIG.  16 C  illustrates yet another embodiment, where the structure includes a post  1614 , such as running through the center of the lensed end of the pen  1500 . The post  1614  may be an ink deposition system (e.g. ink cartridge), graphite deposition system (e.g. graphite holder), or a dummy post whose purpose is mainly only that of alignment. The selection of the post type is dependent on the pen&#39;s use. For instance, in the event the user wants to use the pen  1500  as a conventional ink depositing pen as well as a fully functional external user interface  104 , the ink system post would be the best selection. If there is no need for the ‘writing’ to be visible on the writing surface, the selection would be the dummy post. The embodiment of  FIG.  16 C  includes camera(s)  1602  and an associated lens  1612 , where the camera  1602  and lens  1612  are positioned to capture the writing surface without substantial interference from the post  1614 . In embodiments, the pen  1500  may include multiple cameras  1602  and lenses  1612  such that more or all of the circumference of the tip  1614  can be used as an input system. In an embodiment, the pen  1500  includes a contoured grip that keeps the pen aligned in the user&#39;s hand so that the camera  1602  and lens  1612  remains pointed at the surface. 
     Another aspect of the pen  1500  relates to sensing the force applied by the user to the writing surface with the pen  1500 . The force measurement may be used in a number of ways. For example, the force measurement may be used as a discrete value, or discontinuous event tracking, and compared against a threshold in a process to determine a user&#39;s intent. The user may want the force interpreted as a ‘click’ in the selection of an object, for instance. The user may intend multiple force exertions interpreted as multiple clicks. There may be times when the user holds the pen  1500  in a certain position or holds a certain portion of the pen  1500  (e.g. a button or touch pad) while clicking to affect a certain operation (e.g. a ‘right click’). In embodiments, the force measurement may be used to track force and force trends. The force trends may be tracked and compared to threshold limits, for example. There may be one such threshold limit, multiple limits, groups of related limits, and the like. For example, when the force measurement indicates a fairly constant force that generally falls within a range of related threshold values, the microprocessor  1510  may interpret the force trend as an indication that the user desires to maintain the current writing style, writing tip type, line weight, brush type, and the like. In the event that the force trend appears to have gone outside of a set of threshold values intentionally, the microprocessor may interpret the action as an indication that the user wants to change the current writing style, writing tip type, line weight, brush type, and the like. Once the microprocessor has made a determination of the user&#39;s intent, a change in the current writing style, writing tip type, line weight, brush type, and the like may be executed. In embodiments, the change may be noted to the user (e.g. in a display of the HWC  102 ), and the user may be presented with an opportunity to accept the change. 
       FIG.  17 A  illustrates an embodiment of a force sensing surface tip  1700  of a pen  1500 . The force sensing surface tip  1700  comprises a surface connection tip  1702  (e.g. a lens as described herein elsewhere) in connection with a force or pressure monitoring system  1504 . As a user uses the pen  1500  to write on a surface or simulate writing on a surface the force monitoring system  1504  measures the force or pressure the user applies to the writing surface and the force monitoring system communicates data to the microprocessor  1510  for processing. In this configuration, the microprocessor  1510  receives force data from the force monitoring system  1504  and processes the data to make predictions of the user&#39;s intent in applying the particular force that is currently being applied. In embodiments, the processing may be provided at a location other than on the pen (e.g. at a server in the HWC system  100 , on the HWC  102 ). For clarity, when reference is made herein to processing information on the microprocessor  1510 , the processing of information contemplates processing the information at a location other than on the pen. The microprocessor  1510  may be programmed with force threshold(s), force signature(s), force signature library and/or other characteristics intended to guide an inference program in determining the user&#39;s intentions based on the measured force or pressure. The microprocessor  1510  may be further programmed to make inferences from the force measurements as to whether the user has attempted to initiate a discrete action (e.g. a user interface selection ‘click’) or is performing a constant action (e.g. writing within a particular writing style). The inferencing process is important as it causes the pen  1500  to act as an intuitive external user interface  104 . 
       FIG.  17 B  illustrates a force  1708  versus time  1710  trend chart with a single threshold  1718 . The threshold  1718  may be set at a level that indicates a discrete force exertion indicative of a user&#39;s desire to cause an action (e.g. select an object in a GUI). Event  1712 , for example, may be interpreted as a click or selection command because the force quickly increased from below the threshold  1718  to above the threshold  1718 . The event  1714  may be interpreted as a double click because the force quickly increased above the threshold  1718 , decreased below the threshold  1718  and then essentially repeated quickly. The user may also cause the force to go above the threshold  1718  and hold for a period indicating that the user is intending to select an object in the GUI (e.g. a GUI presented in the display of the HWC  102 ) and ‘hold’ for a further operation (e.g. moving the object). 
     While a threshold value may be used to assist in the interpretation of the user&#39;s intention, a signature force event trend may also be used. The threshold and signature may be used in combination or either method may be used alone. For example, a single-click signature may be represented by a certain force trend signature or set of signatures. The single-click signature(s) may require that the trend meet a criteria of a rise time between x any y values, a hold time of between a and b values and a fall time of between c and d values, for example. Signatures may be stored for a variety of functions such as click, double click, right click, hold, move, etc. The microprocessor  1510  may compare the real-time force or pressure tracking against the signatures from a signature library to make a decision and issue a command to the software application executing in the GUI. 
       FIG.  17 C  illustrates a force  1708  versus time  1710  trend chart with multiple thresholds  1718 . By way of example, the force trend is plotted on the chart with several pen force or pressure events. As noted, there are both presumably intentional events  1720  and presumably non-intentional events  1722 . The two thresholds  1718  of  FIG.  4 C  create three zones of force: a lower, middle and higher range. The beginning of the trend indicates that the user is placing a lower zone amount of force. This may mean that the user is writing with a given line weight and does not intend to change the weight, the user is writing. Then the trend shows a significant increase  1720  in force into the middle force range. This force change appears, from the trend to have been sudden and thereafter it is sustained. The microprocessor  1510  may interpret this as an intentional change and as a result change the operation in accordance with preset rules (e.g. change line width, increase line weight, etc.). The trend then continues with a second apparently intentional event  1720  into the higher-force range. During the performance in the higher-force range, the force dips below the upper threshold  1718 . This may indicate an unintentional force change and the microprocessor may detect the change in range however not affect a change in the operations being coordinated by the pen  1500 . As indicated above, the trend analysis may be done with thresholds and/or signatures. 
     Generally, in the present disclosure, instrument stroke parameter changes may be referred to as a change in line type, line weight, tip type, brush type, brush width, brush pressure, color, and other forms of writing, coloring, painting, and the like. 
     Another aspect of the pen  1500  relates to selecting an operating mode for the pen  1500  dependent on contextual information and/or selection interface(s). The pen  1500  may have several operating modes. For instance, the pen  1500  may have a writing mode where the user interface(s) of the pen  1500  (e.g. the writing surface end, quick launch buttons  1522 , touch sensor  1520 , motion based gesture, and the like) is optimized or selected for tasks associated with writing. As another example, the pen  1500  may have a wand mode where the user interface(s) of the pen is optimized or selected for tasks associated with software or device control (e.g. the HWC  102 , external local device, remote device  112 , and the like). The pen  1500 , by way of another example, may have a presentation mode where the user interface(s) is optimized or selected to assist a user with giving a presentation (e.g. pointing with the laser pointer  1524  while using the button(s)  1522  and/or gestures to control the presentation or applications relating to the presentation). The pen may, for example, have a mode that is optimized or selected for a particular device that a user is attempting to control. The pen  1500  may have a number of other modes and an aspect of the present invention relates to selecting such modes. 
       FIG.  18 A  illustrates an automatic user interface(s) mode selection based on contextual information. The microprocessor  1510  may be programmed with IMU thresholds  1814  and  1812 . The thresholds  1814  and  1812  may be used as indications of upper and lower bounds of an angle  1804  and  1802  of the pen  1500  for certain expected positions during certain predicted modes. When the microprocessor  1510  determines that the pen  1500  is being held or otherwise positioned within angles  1802  corresponding to writing thresholds  1814 , for example, the microprocessor  1510  may then institute a writing mode for the pen&#39;s user interfaces. Similarly, if the microprocessor  1510  determines (e.g. through the IMU  1512 ) that the pen is being held at an angle  1804  that falls between the predetermined wand thresholds  1812 , the microprocessor may institute a wand mode for the pen&#39;s user interface. Both of these examples may be referred to as context based user interface mode selection as the mode selection is based on contextual information (e.g. position) collected automatically and then used through an automatic evaluation process to automatically select the pen&#39;s user interface(s) mode. 
     As with other examples presented herein, the microprocessor  1510  may monitor the contextual trend (e.g. the angle of the pen over time) in an effort to decide whether to stay in a mode or change modes. For example, through signatures, thresholds, trend analysis, and the like, the microprocessor may determine that a change is an unintentional change and therefore no user interface mode change is desired. 
       FIG.  18 B  illustrates an automatic user interface(s) mode selection based on contextual information. In this example, the pen  1500  is monitoring (e.g. through its microprocessor) whether or not the camera at the writing surface end  1508  is imaging a writing surface in close proximity to the writing surface end of the pen  1500 . If the pen  1500  determines that a writing surface is within a predetermined relatively short distance, the pen  1500  may decide that a writing surface is present  1820  and the pen may go into a writing mode user interface(s) mode. In the event that the pen  1500  does not detect a relatively close writing surface  1822 , the pen may predict that the pen is not currently being used to as a writing instrument and the pen may go into a non-writing user interface(s) mode. 
       FIG.  18 C  illustrates a manual user interface(s) mode selection. The user interface(s) mode may be selected based on a twist of a section  1824  of the pen  1500  housing, clicking an end button  1828 , pressing a quick launch button  1522 , interacting with touch sensor  1520 , detecting a predetermined action at the pressure monitoring system (e.g. a click), detecting a gesture (e.g. detected by the IMU), etc. The manual mode selection may involve selecting an item in a GUI associated with the pen  1500  (e.g. an image presented in the display of HWC  102 ). 
     In embodiments, a confirmation selection may be presented to the user in the event a mode is going to change. The presentation may be physical (e.g. a vibration in the pen  1500 ), through a GUI, through a light indicator, etc. 
       FIG.  19    illustrates a couple pen use-scenarios  1900  and  1901 . There are many use scenarios and we have presented a couple in connection with  FIG.  19    as a way of illustrating use scenarios to further the understanding of the reader. As such, the use-scenarios should be considered illustrative and non-limiting. 
     Use scenario  1900  is a writing scenario where the pen  1500  is used as a writing instrument. In this example, quick launch button  122 A is pressed to launch a note application  1910  in the GUI  1908  of the HWC  102  display  1904 . Once the quick launch button  122 A is pressed, the HWC  102  launches the note program  1910  and puts the pen into a writing mode. The user uses the pen  1500  to scribe symbols  1902  on a writing surface, the pen records the scribing and transmits the scribing to the HWC  102  where symbols representing the scribing are displayed  1912  within the note application  1910 . 
     Use scenario  1901  is a gesture scenario where the pen  1500  is used as a gesture capture and command device. In this example, the quick launch button  122 B is activated and the pen  1500  activates a wand mode such that an application launched on the HWC  102  can be controlled. Here, the user sees an application chooser  1918  in the display(s) of the HWC  102  where different software applications can be chosen by the user. The user gestures (e.g. swipes, spins, turns, etc.) with the pen to cause the application chooser  1918  to move from application to application. Once the correct application is identified (e.g. highlighted) in the chooser  1918 , the user may gesture or click or otherwise interact with the pen  1500  such that the identified application is selected and launched. Once an application is launched, the wand mode may be used to scroll, rotate, change applications, select items, initiate processes, and the like, for example. 
     In an embodiment, the quick launch button  122 A may be activated and the HWC  102  may launch an application chooser presenting to the user a set of applications. For example, the quick launch button may launch a chooser to show all communication programs (e.g. SMS, Twitter, Instagram, Facebook, email, etc.) available for selection such that the user can select the program the user wants and then go into a writing mode. By way of further example, the launcher may bring up selections for various other groups that are related or categorized as generally being selected at a given time (e.g. Microsoft Office products, communication products, productivity products, note products, organizational products, and the like) 
       FIG.  20    illustrates yet another embodiment of the present invention.  FIG.  2000    illustrates a watchband clip on controller  2000 . The watchband clip on controller may be a controller used to control the HWC  102  or devices in the HWC system  100 . The watchband clip on controller  2000  has a fastener  2018  (e.g. rotatable clip) that is mechanically adapted to attach to a watchband, as illustrated at  2004 . 
     The watchband controller  2000  may have quick launch interfaces  2008  (e.g. to launch applications and choosers as described herein), a touch pad  2014  (e.g. to be used as a touch style mouse for GUI control in a HWC  102  display) and a display  2012 . The clip  2018  may be adapted to fit a wide range of watchbands so it can be used in connection with a watch that is independently selected for its function. The clip, in embodiments, is rotatable such that a user can position it in a desirable manner. In embodiments the clip may be a flexible strap. In embodiments, the flexible strap may be adapted to be stretched to attach to a hand, wrist, finger, device, weapon, and the like. 
     In embodiments, the watchband controller may be configured as a removable and replaceable watchband. For example, the controller may be incorporated into a band with a certain width, segment spacing&#39;s, etc. such that the watchband, with its incorporated controller, can be attached to a watch body. The attachment, in embodiments, may be mechanically adapted to attach with a pin upon which the watchband rotates. In embodiments, the watchband controller may be electrically connected to the watch and/or watch body such that the watch, watch body and/or the watchband controller can communicate data between them. 
     The watchband controller may have 3-axis motion monitoring (e.g. through an IMU, accelerometers, magnetometers, gyroscopes, etc.) to capture user motion. The user motion may then be interpreted for gesture control. 
     In embodiments, the watchband controller may comprise fitness sensors and a fitness computer. The sensors may track heart rate, calories burned, strides, distance covered, and the like. The data may then be compared against performance goals and/or standards for user feedback. 
     Another aspect of the present invention relates to visual display techniques relating to micro Doppler (“mD”) target tracking signatures (“mD signatures”). mD is a radar technique that uses a series of angle dependent electromagnetic pulses that are broadcast into an environment and return pulses are captured. Changes between the broadcast pulse and return pulse are indicative of changes in the shape, distance and angular location of objects or targets in the environment. These changes provide signals that can be used to track a target and identify the target through the mD signature. Each target or target type has a unique mD signature. Shifts in the radar pattern can be analyzed in the time domain and frequency domain based on mD techniques to derive information about the types of targets present (e.g. whether people are present), the motion of the targets and the relative angular location of the targets and the distance to the targets. By selecting a frequency used for the mD pulse relative to known objects in the environment, the pulse can penetrate the known objects to enable information about targets to be gathered even when the targets are visually blocked by the known objects. For example, pulse frequencies can be used that will penetrate concrete buildings to enable people to be identified inside the building. Multiple pulse frequencies can be used as well in the mD radar to enable different types of information to be gathered about the objects in the environment. In addition, the mD radar information can be combined with other information such as distance measurements or images captured of the environment that are analyzed jointly to provide improved object identification and improved target identification and tracking. In embodiments, the analysis can be performed on the HWC or the information can be transmitted to a remote network for analysis and results transmitted back to the HWC. Distance measurements can be provided by laser range finding, structured lighting, stereoscopic depth maps or sonar measurements. Images of the environment can be captured using one or more cameras capable of capturing images from visible, ultraviolet or infrared light. The mD radar can be attached to the HWC, located adjacently (e.g. in a vehicle) and associated wirelessly with the HWC or located remotely. Maps or other previously determined information about the environment can also be used in the analysis of the mD radar information. Embodiments of the present invention relate to visualizing the mD signatures in useful ways. 
       FIG.  21    illustrates a FOV  2102  of a HWC  102  from a wearer&#39;s perspective. The wearer, as described herein elsewhere, has a see-through FOV  2102  wherein the wearer views adjacent surroundings, such as the buildings illustrated in  FIG.  21   . The wearer, as described herein elsewhere, can also see displayed digital content presented within a portion of the FOV  2102 . The embodiment illustrated in  FIG.  21    is indicating that the wearer can see the buildings and other surrounding elements in the environment and digital content representing traces, or travel paths, of bullets being fired by different people in the area. The surroundings are viewed through the transparency of the FOV  2102 . The traces are presented via the digital computer display, as described herein elsewhere. In embodiments, the trace presented is based on a mD signature that is collected and communicated to the HWC in real time. The mD radar itself may be on or near the wearer of the HWC  102  or it may be located remote from the wearer. In embodiments, the mD radar scans the area, tracks and identifies targets, such as bullets, and communicates traces, based on locations, to the HWC  102 . 
     There are several traces  2108  and  2104  presented to the wearer in the embodiment illustrated in  FIG.  21   . The traces communicated from the mD radar may be associated with GPS locations and the GPS locations may be associated with objects in the environment, such as people, buildings, vehicles, etc, both in latitude and longitude perspective and an elevation perspective. The locations may be used as markers for the HWC such that the traces, as presented in the FOV, can be associated, or fixed in space relative to the markers. For example, if the friendly fire trace  2108  is determined, by the mD radar, to have originated from the upper right window of the building on the left, as illustrated in  FIG.  21   , then a virtual marker may be set on or near the window. When the HWC views, through its camera or other sensor, for example, the building&#39;s window, the trace may then virtually anchor with the virtual marker on the window. Similarly, a marker may be set near the termination position or other flight position of the friendly fire trace  2108 , such as the upper left window of the center building on the right, as illustrated in  FIG.  21   . This technique fixes in space the trace such that the trace appears fixed to the environmental positions independent of where the wearer is looking. So, for example, as the wearer&#39;s head turns, the trace appears fixed to the marked locations. 
     In embodiments, certain user positions may be known and thus identified in the FOV. For example, the shooter of the friendly fire trace  2108  may be from a known friendly combatant and as such his location may be known. The position may be known based on his GPS location based on a mobile communication system on him, such as another HWC  102 . In other embodiments, the friendly combatant may be marked by another friendly. For example, if the friendly position in the environment is known through visual contact or communicated information, a wearer of the HWC  102  may use a gesture or external user interface  104  to mark the location. If a friendly combatant location is known the originating position of the friendly fire trace  2108  may be color coded or otherwise distinguished from unidentified traces on the displayed digital content. Similarly, enemy fire traces  2104  may be color coded or otherwise distinguished on the displayed digital content. In embodiments, there may be an additional distinguished appearance on the displayed digital content for unknown traces. 
     In addition to situationally associated trace appearance, the trace colors or appearance may be different from the originating position to the terminating position. This path appearance change may be based on the mD signature. The mD signature may indicate that the bullet, for example, is slowing as it propagates and this slowing pattern may be reflected in the FOV  2102  as a color or pattern change. This can create an intuitive understanding of wear the shooter is located. For example, the originating color may be red, indicative of high speed, and it may change over the course of the trace to yellow, indicative of a slowing trace. This pattern changing may also be different for a friendly, enemy and unknown combatant. The enemy may go blue to green for a friendly trace, for example. 
       FIG.  21    illustrates an embodiment where the user sees the environment through the FOV and may also see color coded traces, which are dependent on bullet speed and combatant type, where the traces are fixed in environmental positions independent on the wearer&#39;s perspective. Other information, such as distance, range, range rings, time of day, date, engagement type (e.g. hold, stop firing, back away, etc.) may also be displayed in the FOV. 
     Another aspect of the present invention relates to mD radar techniques that trace and identify targets through other objects, such as walls (referred to generally as through wall mD), and visualization techniques related therewith.  FIG.  22    illustrates a through wall mD visualization technique according to the principles of the present invention. As described herein elsewhere, the mD radar scanning the environment may be local or remote from the wearer of a HWC  102 . The mD radar may identify a target (e.g. a person) that is visible  2204  and then track the target as he goes behind a wall  2208 . The tracking may then be presented to the wearer of a HWC  102  such that digital content reflective of the target and the target&#39;s movement, even behind the wall, is presented in the FOV  2202  of the HWC  102 . In embodiments, the target, when out of visible sight, may be represented by an avatar in the FOV to provide the wearer with imagery representing the target. 
     mD target recognition methods can identify the identity of a target based on the vibrations and other small movements of the target. This can provide a personal signature for the target. In the case of humans, this may result in a personal identification of a target that has been previously characterized. The cardio, heartbeat, lung expansion and other small movements within the body may be unique to a person and if those attributes are pre-identified they may be matched in real time to provide a personal identification of a person in the FOV  2202 . The person&#39;s mD signatures may be determined based on the position of the person. For example, the database of personal mD signature attributes may include mD signatures for a person standing, sitting, laying down, running, walking, jumping, etc. This may improve the accuracy of the personal data match when a target is tracked through mD signature techniques in the field. In the event a person is personally identified, a specific indication of the person&#39;s identity may be presented in the FOV  2202 . The indication may be a color, shape, shade, name, indication of the type of person (e.g. enemy, friendly, etc.), etc. to provide the wearer with intuitive real time information about the person being tracked. This may be very useful in a situation where there is more than one person in an area of the person being tracked. If just one person in the area is personally identified, that person or the avatar of that person can be presented differently than other people in the area. 
       FIG.  23    illustrates an mD scanned environment  2300 . An mD radar may scan an environment in an attempt to identify objects in the environment. In this embodiment, the mD scanned environment reveals two vehicles  2302   a  and  2302   b , an enemy combatant  2309 , two friendly combatants  2308   a  and  2308   b  and a shot trace  2318 . Each of these objects may be personally identified or type identified. For example, the vehicles  2302   a  and  2302   b  may be identified through the mD signatures as a tank and heavy truck. The enemy combatant  2309  may be identified as a type (e.g. enemy combatant) or more personally (e.g. by name). The friendly combatants may be identified as a type (e.g. friendly combatant) or more personally (e.g. by name). The shot trace  2318  may be characterized by type of projectile or weapon type for the projectile, for example. 
       FIG.  23   a    illustrates two separate HWC  102  FOV display techniques according to the principles of the present invention. FOV  2312  illustrates a map view  2310  where the mD scanned environment is presented. Here, the wearer has a perspective on the mapped area so he can understand all tracked targets in the area. This allows the wearer to traverse the area with knowledge of the targets. FOV  2312  illustrates a heads-up view to provide the wearer with an augmented reality style view of the environment that is in proximity of the wearer. 
     An aspect of the present invention relates to suppression of extraneous or stray light. As discussed herein elsewhere, eyeglow and faceglow are two such artifacts that develop from such light. Eyeglow and faceglow can be caused by image light escaping from the optics module. The escaping light is then visible, particularly in dark environments when the user is viewing bright displayed images with the HWC. Light that escapes through the front of the HWC is visible as eyeglow as it that light that is visible in the region of the user&#39;s eyes. Eyeglow can appear in the form of a small version of the displayed image that the user is viewing. Light that escapes from the bottom of the HWC shines onto the user&#39;s face, cheek or chest so that these portions of the user appear to glow. Eyeglow and faceglow can both increase the visibility of the user and highlight the use of the HWC, which may be viewed negatively by the user. As such, reducing eyeglow and faceglow is advantageous. In combat situations (e.g. the mD trace presentation scenarios described herein) and certain gaming situations, the suppression of extraneous or stray light is very important. 
     The disclosure relating to  FIG.  6    shows an example where a portion of the image light passes through the combiner  602  such that the light shines onto the user&#39;s face, thereby illuminating a portion of the user&#39;s face in what is generally referred to herein as faceglow. Faceglow be caused by any portion of light from the HWC that illuminates the user&#39;s face. 
     An example of the source for the faceglow light can come from wide cone angle light associated with the image light incident onto the combiner  602 . Where the combiner can include a holographic mirror or a notch mirror in which the narrow bands of high reflectivity are matched to wavelengths of light by the light source. The wide cone angle associated with the image light corresponds with the field of view provided by the HWC. Typically the reflectivity of holographic mirrors and notch mirrors is reduced as the cone angle of the incident light is increased above 8 degrees. As a result, for a field of view of 30 degrees, substantial image light can pass through the combiner and cause faceglow. 
       FIG.  24    shows an illustration of a light trap  2410  for the faceglow light. In this embodiment, an extension of the outer shield lens of the HWC is coated with a light absorbing material in the region where the converging light responsible for faceglow is absorbed in a light trap  2410 . The light absorbing material can be black or it can be a filter designed to absorb only the specific wavelengths of light provided by the light source(s) in the HWC. In addition, the surface of the light trap  2410  may be textured or fibrous to further improve the absorption. 
       FIG.  25    illustrates an optical system for a HWC that includes an outer absorptive polarizer  2520  to block the faceglow light. In this embodiment, the image light is polarized and as a result the light responsible for faceglow is similarly polarized. The absorptive polarizer is oriented with a transmission axis such that the faceglow light is absorbed and not transmitted. In this case, the rest of the imaging system in the HWC may not require polarized image light and the image light may be polarized at any point before the combiner. In embodiments, the transmission axis of the absorptive polarizer  2520  is oriented vertically so that external glare from water (S polarized light) is absorbed and correspondingly, the polarization of the image light is selected to be horizontal (S polarization). Consequently, image light that passes through the combiner  602  and is then incident onto the absorptive polarizer  2520 , is absorbed. In  FIG.  25    the absorptive polarizer  2520  is shown outside the shield lens, alternatively the absorptive polarizer  2520  can be located inside the shield lens. 
       FIG.  26    illustrates an optical system for a HWC that includes a film with an absorptive notch filter  2620 . In this case, the absorptive notch filter absorbs narrow bands of light that are selected to match the light provided by the optical system&#39;s light source. As a result, the absorptive notch filter is opaque with respect to the faceglow light and is transparent to the remainder of the wavelengths included in the visible spectrum so that the user has a clear view of the surrounding environment. A triple notch filter suitable for this approach is available from Iridian Spectral Technologies, Ottawa, ON: http://www.ilphotonics.com/cdv2/Iridian-Interference %20Filters/New %20filters/Triple %20Notch %20Filter.pdf 
     In embodiments, the combiner  602  may include a notch mirror coating to reflect the wavelengths of light in the image light and a notch filter  2620  can be selected in correspondence to the wavelengths of light provided by the light source and the narrow bands of high reflectivity provided by the notch mirror. In this way, image light that is not reflected by the notch mirror is absorbed by the notch filter  2620 . In embodiments of the invention the light source can provide one narrow band of light for a monochrome imaging or three narrow bands of light for full color imaging. The notch mirror and associated notch filter would then each provide one narrow band or three narrow bands of high reflectivity and absorption respectively. 
       FIG.  27    includes a microlouver film  2750  to block the faceglow light. Microlouver film is sold by 3M as ALCF-P, for example and is typically used as a privacy filter for computer. See http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSuH8gc7nZxtUoY_x1Y_eevUqe 17zHvTSevTSeSSSSSS--&amp;fn=ALCF-P_ABR2_Control_Film_DS.pdf The microlouver film transmits light within a somewhat narrow angle (e.g. 30 degrees of normal and absorbs light beyond 30 degrees of normal). In  FIG.  27   , the microlouver film  2750  is positioned such that the faceglow light  2758  is incident beyond 30 degrees from normal while the see-through light  2755  is incident within 30 degrees of normal to the microlouver film  2750 . As such, the faceglow light  2758  is absorbed by the microlouver film and the see-through light  2755  is transmitted so that the user has a bright see-thru view of the surrounding environment. 
     We now turn back to a description of eye imaging technologies. Aspects of the present invention relate to various methods of imaging the eye of a person wearing the HWC  102 . In embodiments, technologies for imaging the eye using an optical path involving the “off” state and “no power” state, which is described in detail below, are described. In embodiments, technologies for imaging the eye with optical configurations that do not involve reflecting the eye image off of DLP mirrors is described. In embodiments, unstructured light, structured light, or controlled lighting conditions, are used to predict the eye&#39;s position based on the light reflected off of the front of the wearer&#39;s eye. In embodiments, a reflection of a presented digital content image is captured as it reflects off of the wearer&#39;s eye and the reflected image may be processed to determine the quality (e.g. sharpness) of the image presented. In embodiments, the image may then be adjusted (e.g. focused differently) to increase the quality of the image presented based on the image reflection. 
       FIGS.  28   a ,  28   b  and  28   c    show illustrations of the various positions of the DLP mirrors.  FIG.  28   a    shows the DLP mirrors in the “on” state  2815 . With the mirror in the “on” state  2815 , illumination light  2810  is reflected along an optical axis  2820  that extends into the lower optical module  204 .  FIG.  28   b    shows the DLP mirrors in the “off” state  2825 . With the mirror in the “off” state  2825 , illumination light  2810  is reflected along an optical axis  2830  that is substantially to the side of optical axis  2820  so that the “off” state light is directed toward a dark light trap as has been described herein elsewhere.  FIG.  28   c    shows the DLP mirrors in a third position, which occurs when no power is applied to the DLP. This “no power” state differs from the “on” and “off” states in that the mirror edges are not in contact with the substrate and as such are less accurately positioned.  FIG.  28   c    shows all of the DLP mirrors in the “no power” state  2835 . The “no power” state is achieved by simultaneously setting the voltage to zero for the “on” contact and “off” contact for a DLP mirror, as a result, the mirror returns to a no stress position where the DLP mirror is in the plane of the DLP platform as shown in  FIG.  28   c   . Although not normally done, it is also possible to apply the “no power” state to individual DLP mirrors. When the DLP mirrors are in the “no power” state they do not contribute image content. Instead, as shown in  FIG.  28   c   , when the DLP mirrors are in the “no power” state, the illumination light  2810  is reflected along an optical axis  2840  that is between the optical axes  2820  and  2830  that are respectively associated with the “on” and “off” states and as such this light doesn&#39;t contribute to the displayed image as a bright or dark pixel. This light can however contribute scattered light into the lower optical module  204  and as a result the displayed image contrast can be reduced or artifacts can be created in the image that detract from the image content. Consequently, it is generally desirable, in embodiments, to limit the time associated with the “no power” state to times when images are not displayed or to reduce the time associated with having DLP mirrors in the “no power” state so that the effect of the scattered light is reduced. 
       FIG.  29    shows an embodiment of the invention that can be used for displaying digital content images to a wearer of the HWC  102  and capturing images of the wearer&#39;s eye. In this embodiment, light from the eye  2971  passes back through the optics in the lower module  204 , the solid corrective wedge  2966 , at least a portion of the light passes through the partially reflective layer  2960 , the solid illumination wedge  2964  and is reflected by a plurality of DLP mirrors on the DLP  2955  that are in the “no power” state. The reflected light then passes back through the illumination wedge  2964  and at least a portion of the light is reflected by the partially reflective layer  2960  and the light is captured by the camera  2980 . 
     For comparison, illuminating light rays  2973  from the light source  2958  are also shown being reflected by the partially reflective layer  2960 . Where the angle of the illuminating light  2973  is such that the DLP mirrors, when in the “on” state, reflect the illuminating light  2973  to form image light  2969  that substantially shares the same optical axis as the light from the wearer&#39;s eye  2971 . In this way, images of the wearer&#39;s eye are captured in a field of view that overlaps the field of view for the displayed image content. In contrast, light reflected by DLP mirrors in the “off” state form dark light  2975  which is directed substantially to the side of the image light  2969  and the light from eye  2971 . Dark light  2975  is directed toward a light trap  2962  that absorbs the dark light to improve the contrast of the displayed image as has been described above in this specification. 
     In an embodiment, partially reflective layer  2960  is a reflective polarizer. The light that is reflected from the eye  2971  can then be polarized prior to entering the corrective wedge  2966  (e.g. with an absorptive polarizer between the upper module  202  and the lower module  204 ), with a polarization orientation relative to the reflective polarizer that enables the light reflected from the eye  2971  to substantially be transmitted by the reflective polarizer. A quarter wave retarder layer  2957  is then included adjacent to the DLP  2955  (as previously disclosed in  FIG.  3   b   ) so that the light reflected from the eye  2971  passes through the quarter wave retarder layer  2957  once before being reflected by the plurality of DLP mirrors in the “no power” state and then passes through a second time after being reflected. By passing through the quarter wave retarder layer  2957  twice, the polarization state of the light from the eye  2971  is reversed, such that when it is incident upon the reflective polarizer, the light from the eye  2971  is then substantially reflected toward the camera  2980 . By using a partially reflective layer  2960  that is a reflective polarizer and polarizing the light from the eye  2971  prior to entering the corrective wedge  2964 , losses attributed to the partially reflective layer  2960  are reduced. 
       FIG.  28   c    shows the case wherein the DLP mirrors are simultaneously in the “no power” state, this mode of operation can be particularly useful when the HWC  102  is first put onto the head of the wearer. When the HWC  102  is first put onto the head of the wearer, it is not necessary to display an image yet. As a result, the DLP can be in a “no power” state for all the DLP mirrors and an image of the wearer&#39;s eyes can be captured. The captured image of the wearer&#39;s eye can then be compared to a database, using iris identification techniques, or other eye pattern identification techniques to determine, for example, the identity of the wearer. 
     In a further embodiment illustrated by  FIG.  29    all of the DLP mirrors are put into the “no power” state for a portion of a frame time (e.g. 50% of a frame time for the displayed digital content image) and the capture of the eye image is synchronized to occur at the same time and for the same duration. By reducing the time that the DLP mirrors are in the “no power” state, the time where light is scattered by the DLP mirrors being in the “no power” state is reduced such that the wearer doesn&#39;t perceive a change in the displayed image quality. This is possible because the DLP mirrors have a response time on the order of microseconds while typical frame times for a displayed image are on the order of 0.016 seconds. This method of capturing images of the wearer&#39;s eye can be used periodically to capture repetitive images of the wearer&#39;s eye. For example, eye images could be captured for 50% of the frame time of every 10th frame displayed to the wearer. In another example, eye images could be captured for 10% of the frame time of every frame displayed to the wearer. 
     Alternately, the “no power” state can be applied to a subset of the DLP mirrors (e.g. 10% of the DLP mirrors) within while another subset is in busy generating image light for content to be displayed. This enables the capture of an eye image(s) during the display of digital content to the wearer. The DLP mirrors used for eye imaging can, for example, be distributed randomly across the area of the DLP to minimize the impact on the quality of the digital content being displayed to the wearer. To improve the displayed image perceived by the wearer, the individual DLP mirrors put into the “no power” state for capturing each eye image, can be varied over time such as in a random pattern, for example. In yet a further embodiment, the DLP mirrors put into the “no power” state for eye imaging may be coordinated with the digital content in such a way that the “no power” mirrors are taken from a portion of the image that requires less resolution. 
     In the embodiments of the invention as illustrated in  FIGS.  9  and  29   , in both cases the reflective surfaces provided by the DLP mirrors do not preserve the wavefront of the light from the wearer&#39;s eye so that the image quality of captured image of the eye is somewhat limited. It may still be useful in certain embodiments, but it is somewhat limited. This is due to the DLP mirrors not being constrained to be on the same plane. In the embodiment illustrated in  FIG.  9   , the DLP mirrors are tilted so that they form rows of DLP mirrors that share common planes. In the embodiment illustrated in  FIG.  29   , the individual DLP mirrors are not accurately positioned to be in the same plane since they are not in contact with the substrate. Examples of advantages of the embodiments associated with  FIG.  29    are: first, the camera  2980  can be located between the DLP  2955  and the illumination light source  2958  to provide a more compact upper module  202 . Second, the polarization state of the light reflected from the eye  2971  can be the same as that of the image light  2969  so that the optical path of the light reflected from the eye and the image light can be the same in the lower module  204 . 
       FIG.  30    shows an illustration of an embodiment for displaying images to the wearer and simultaneously capturing images of the wearer&#39;s eye, wherein light from the eye  2971  is reflected towards a camera  3080  by the partially reflective layer  2960 . The partially reflective layer  2960  can be an optically flat layer such that the wavefront of the light from the eye  2971  is preserved and as a result, higher quality images of the wearer&#39;s eye can be captured. In addition, since the DLP  2955  is not included in the optical path for the light from the eye  2971 , and the eye imaging process shown in  FIG.  30    does not interfere with the displayed image, images of the wearer&#39;s eye can be captured independently (e.g. with independent of timing, impact on resolution, or pixel count used in the image light) from the displayed images. 
     In the embodiment illustrated in  FIG.  30   , the partially reflective layer  2960  is a reflective polarizer, the illuminating light  2973  is polarized, the light from the eye  2971  is polarized and the camera  3080  is located behind a polarizer  3085 . The polarization axis of the illuminating light  2973  and the polarization axis of the light from the eye are oriented perpendicular to the transmission axis of the reflective polarizer so that they are both substantially reflected by the reflective polarizer. The illumination light  2973  passes through a quarter wave layer  2957  before being reflected by the DLP mirrors in the DLP  2955 . The reflected light passes back through the quarter wave layer  2957  so that the polarization states of the image light  2969  and dark light  2975  are reversed in comparison to the illumination light  2973 . As such, the image light  2969  and dark light  2975  are substantially transmitted by the reflective polarizer. Where the DLP mirrors in the “on” state provide the image light  2969  along an optical axis that extends into the lower optical module  204  to display an image to the wearer. At the same time, DLP mirrors in the “off” state provide the dark light  2975  along an optical axis that extends to the side of the upper optics module  202 . In the region of the corrective wedge  2966  where the dark light  2975  is incident on the side of the upper optics module  202 , an absorptive polarizer  3085  is positioned with its transmission axis perpendicular to the polarization axis of the dark light and parallel to the polarization axis of the light from the eye so that the dark light  2975  is absorbed and the light from the eye  2971  is transmitted to the camera  3080 . 
       FIG.  31    shows an illustration of another embodiment of a system for displaying images and simultaneously capturing image of the wearer&#39;s eye that is similar to the one shown in  FIG.  30   . The difference in the system shown in  FIG.  31    is that the light from the eye  2971  is subjected to multiple reflections before being captured by the camera  3180 . To enable the multiple reflections, a mirror  3187  is provided behind the absorptive polarizer  3185 . Therefore, the light from the eye  2971  is polarized prior to entering the corrective wedge  2966  with a polarization axis that is perpendicular to the transmission axis of the reflective polarizer that comprises the partially reflective layer  2960 . In this way, the light from the eye  2971  is reflected first by the reflective polarizer, reflected second by the mirror  3187  and reflected third by the reflective polarizer before being captured by the camera  3180 . While the light from the eye  2971  passes through the absorptive polarizer  3185  twice, since the polarization axis of the light from the eye  2971  is oriented parallel to the polarization axis of the light from the eye  2971 , it is substantially transmitted by the absorptive polarizer  3185 . As with the system described in connection with  FIG.  30   , the system shown in  FIG.  31    includes an optically flat partially reflective layer  2960  that preserves the wavefront of the light from the eye  2971  so that higher quality images of the wearer&#39;s eye can be captured. Also, since the DLP  2955  is not included in the optical path for the light reflected from the eye  2971  and the eye imaging process shown in  FIG.  31    does not interfere with the displayed image, images of the wearer&#39;s eye can be captured independently from the displayed images. 
       FIG.  32    shows an illustration of a system for displaying images and simultaneously capturing images of the wearer&#39;s eye that includes a beam splitter plate  3212  comprised of a reflective polarizer, which is held in air between the light source  2958 , the DLP  2955  and the camera  3280 . The illumination light  2973  and the light from the eye  2971  are both polarized with polarization axes that are perpendicular to the transmission axis of the reflective polarizer. As a result, both the illumination light  2973  and the light from the eye  2971  are substantially reflected by the reflective polarizer. The illumination light  2873  is reflected toward the DLP  2955  by the reflective polarizer and split into image light  2969  and dark light  3275  depending on whether the individual DLP mirrors are respectively in the “on” state or the “off” state. By passing through the quarter wave layer  2957  twice, the polarization state of the illumination light  2973  is reversed in comparison to the polarization state of the image light  2969  and the dark light  3275 . As a result, the image light  2969  and the dark light  3275  are then substantially transmitted by the reflective polarizer. The absorptive polarizer  3285  at the side of the beam splitter plate  3212  has a transmission axis that is perpendicular to the polarization axis of the dark light  3275  and parallel to the polarization axis of the light from the eye  2971  so that the dark light  3275  is absorbed and the light from the eye  2971  is transmitted to the camera  3280 . As in the system shown in  FIG.  30   , the system shown in  FIG.  31    includes an optically flat beam splitter plate  3212  that preserves the wavefront of the light from the eye  2971  so that higher quality images of the wearer&#39;s eye can be captured. Also, since the DLP  2955  is not included in the optical path for the light from the eye  2971  and the eye imaging process shown in  FIG.  31    does not interfere with the displayed image, images of the wearer&#39;s eye can be captured independently from the displayed images. 
     Eye imaging systems where the polarization state of the light from the eye  2971  needs to be opposite to that of the image light  2969  (as shown in  FIGS.  30 ,  31  and  32   ), need to be used with lower modules  204  that include combiners that will reflect both polarization states. As such, these upper modules  202  are best suited for use with the lower modules  204  that include combiners that are reflective regardless of polarization state, examples of these lower modules are shown in  FIGS.  6 ,  8     a ,  8   b ,  8   c  and  24 - 27 . 
     In a further embodiment shown in  FIG.  33   , the partially reflective layer  3360  is comprised of a reflective polarizer on the side facing the illumination light  2973  and a short pass dichroic mirror on the side facing the light from the eye  3371  and the camera  3080 . Where the short pass dichroic mirror is a dielectric mirror coating that transmits visible light and reflects infrared light. The partially reflective layer  3360  can be comprised of a reflective polarizer bonded to the inner surface of the illumination wedge  2964  and a short pass dielectric mirror coating on the opposing inner surface of the corrective wedge  2966 , wherein the illumination wedge  2964  and the corrective wedge  2966  are then optically bonded together. Alternatively, the partially reflective layer  3360  can be comprised of a thin substrate that has a reflective polarizer bonded to one side and a short pass dichroic mirror coating on the other side, where the partially reflective layer  3360  is then bonded between the illumination wedge  2964  and the corrective wedge  2966 . In this embodiment, an infrared light is included to illuminate the eye so that the light from the eye and the images captured of the eye are substantially comprised of infrared light. The wavelength of the infrared light is then matched to the reflecting wavelength of the shortpass dichroic mirror and the wavelength that the camera can capture images, for example an 800 nm wavelength can be used. In this way, the short pass dichroic mirror transmits the image light and reflects the light from the eye. The camera  3080  is then positioned at the side of the corrective wedge  2966  in the area of the absorbing light trap  3382 , which is provided to absorb the dark light  2975 . By positioning the camera  3080  in a depression in the absorbing light trap  3382 , scattering of the dark light  2975  by the camera  3080  can be reduced so that higher contrast images can be displayed to the wearer. An advantage of this embodiment is that the light from the eye need not be polarized, which can simplify the optical system and increase efficiency for the eye imaging system. 
     In yet another embodiment shown in  FIG.  32   a    a beam splitter plate  3222  is comprised of a reflective polarizer on the side facing the illumination light  2973  and a short pass dichroic mirror on the side facing the light from the eye  3271  and the camera  3280 . An absorbing surface  3295  is provided to trap the dark light  3275  and the camera  3280  is positioned in an opening in the absorbing surface  3295 . In this way the system of  FIG.  32    can be made to function with unpolarized light from the eye  3271 . 
     In embodiments directed to capturing images of the wearer&#39;s eye, light to illuminate the wearer&#39;s eye can be provided by several different sources including: light from the displayed image (i.e. image light); light from the environment that passes through the combiner or other optics; light provided by a dedicated eye light, etc.  FIGS.  34  and  34     a  show illustrations of dedicated eye illumination lights  3420 .  FIG.  34    shows an illustration from a side view in which the dedicated illumination eye light  3420  is positioned at a corner of the combiner  3410  so that it doesn&#39;t interfere with the image light  3415 . The dedicated eye illumination light  3420  is pointed so that the eye illumination light  3425  illuminates the eyebox  3427  where the eye  3430  is located when the wearer is viewing displayed images provided by the image light  3415 .  FIG.  34   a    shows an illustration from the perspective of the eye of the wearer to show how the dedicated eye illumination light  3420  is positioned at the corner of the combiner  3410 . While the dedicated eye illumination light  3420  is shown at the upper left corner of the combiner  3410 , other positions along one of the edges of the combiner  3410 , or other optical or mechanical components, are possible as well. In other embodiments, more than one dedicated eye light  3420  with different positions can be used. In an embodiment, the dedicated eye light  3420  is an infrared light that is not visible by the wearer (e.g. 800 nm) so that the eye illumination light  3425  doesn&#39;t interfere with the displayed image perceived by the wearer. 
       FIG.  35    shows a series of illustrations of captured eye images that show the eye glint (i.e. light that reflects off the front of the eye) produced by a dedicated eye light. In this embodiment of the invention, captured images of the wearer&#39;s eye are analyzed to determine the relative positions of the iris  3550 , pupil, or other portion of the eye, and the eye glint  3560 . The eye glint is a reflected image of the dedicated eye light  3420  when the dedicated light is used.  FIG.  35    illustrates the relative positions of the iris  3550  and the eye glint  3560  for a variety of eye positions. By providing a dedicated eye light  3420  in a fixed position, combined with the fact that the human eye is essentially spherical, or at least a reliably repeatable shape, the eye glint provides a fixed reference point against which the determined position of the iris can be compared to determine where the wearer is looking, either within the displayed image or within the see-through view of the surrounding environment. By positioning the dedicated eye light  3420  at a corner of the combiner  3410 , the eye glint  3560  is formed away from the iris  3550  in the captured images. As a result, the positions of the iris and the eye glint can be determined more easily and more accurately during the analysis of the captured images, since they do not interfere with one another. In a further embodiment, the combiner includes an associated cut filter that prevents infrared light from the environment from entering the HWC and the camera is an infrared camera, so that the eye glint is only provided by light from the dedicated eye light. For example, the combiner can include a low pass filter that passes visible light while absorbing infrared light and the camera can include a high pass filter that absorbs visible light while passing infrared light. 
     In an embodiment of the eye imaging system, the lens for the camera is designed to take into account the optics associated with the upper module  202  and the lower module  204 . This is accomplished by designing the camera to include the optics in the upper module  202  and optics in the lower module  204 , so that a high MTF image is produced, at the image sensor in the camera, of the wearer&#39;s eye. In yet a further embodiment, the camera lens is provided with a large depth of field to eliminate the need for focusing the camera to enable sharp image of the eye to be captured. Where a large depth of field is typically provided by a high f/# lens (e.g. f/#&gt;5). In this case, the reduced light gathering associated with high f/# lenses is compensated by the inclusion of a dedicated eye light to enable a bright image of the eye to be captured. Further, the brightness of the dedicated eye light can be modulated and synchronized with the capture of eye images so that the dedicated eye light has a reduced duty cycle and the brightness of infrared light on the wearer&#39;s eye is reduced. 
     In a further embodiment,  FIG.  36   a    shows an illustration of an eye image that is used to identify the wearer of the HWC. In this case, an image of the wearer&#39;s eye  3611  is captured and analyzed for patterns of identifiable features  3612 . The patterns are then compared to a database of eye images to determine the identity of the wearer. After the identity of the wearer has been verified, the operating mode of the HWC and the types of images, applications, and information to be displayed can be adjusted and controlled in correspondence to the determined identity of the wearer. Examples of adjustments to the operating mode depending on who the wearer is determined to be or not be include: making different operating modes or feature sets available, shutting down or sending a message to an external network, allowing guest features and applications to run, etc. 
       FIG.  36   b    is an illustration of another embodiment using eye imaging, in which the sharpness of the displayed image is determined based on the eye glint produced by the reflection of the displayed image from the wearer&#39;s eye surface. By capturing images of the wearer&#39;s eye  3611 , an eye glint  3622 , which is a small version of the displayed image can be captured and analyzed for sharpness. If the displayed image is determined to not be sharp, then an automated adjustment to the focus of the HWC optics can be performed to improve the sharpness. This ability to perform a measurement of the sharpness of a displayed image at the surface of the wearer&#39;s eye can provide a very accurate measurement of image quality. Having the ability to measure and automatically adjust the focus of displayed images can be very useful in augmented reality imaging where the focus distance of the displayed image can be varied in response to changes in the environment or changes in the method of use by the wearer. 
     An aspect of the present invention relates to controlling the HWC  102  through interpretations of eye imagery. In embodiments, eye-imaging technologies, such as those described herein, are used to capture an eye image or series of eye images for processing. The image(s) may be process to determine a user intended action, an HWC predetermined reaction, or other action. For example, the imagery may be interpreted as an affirmative user control action for an application on the HWC  102 . Or, the imagery may cause, for example, the HWC  102  to react in a pre-determined way such that the HWC  102  is operating safely, intuitively, etc. 
       FIG.  37    illustrates a eye imagery process that involves imaging the HWC  102  wearer&#39;s eye(s) and processing the images (e.g. through eye imaging technologies described herein) to determine in what position  3702  the eye is relative to its neutral or forward looking position and/or the FOV  3708 . The process may involve a calibration step where the user is instructed, through guidance provided in the FOV of the HWC  102 , to look in certain directions such that a more accurate prediction of the eye position relative to areas of the FOV can be made. In the event the wearer&#39;s eye is determined to be looking towards the right side of the FOV  3708  (as illustrated in  FIG.  37   , the eye is looking out of the page) a virtual target line may be established to project what in the environment the wearer may be looking towards or at. The virtual target line may be used in connection with an image captured by camera on the HWC  102  that images the surrounding environment in front of the wearer. In embodiments, the field of view of the camera capturing the surrounding environment matches, or can be matched (e.g. digitally), to the FOV  3708  such that making the comparison is made more clear. For example, with the camera capturing the image of the surroundings in an angle that matches the FOV  3708  the virtual line can be processed (e.g. in 2d or 3d, depending on the camera images capabilities and/or the processing of the images) by projecting what surrounding environment objects align with the virtual target line. In the event there are multiple objects along the virtual target line, focal planes may be established corresponding to each of the objects such that digital content may be placed in an area in the FOV  3708  that aligns with the virtual target line and falls at a focal plane of an intersecting object. The user then may see the digital content when he focuses on the object in the environment, which is at the same focal plane. In embodiments, objects in line with the virtual target line may be established by comparison to mapped information of the surroundings. 
     In embodiments, the digital content that is in line with the virtual target line may not be displayed in the FOV until the eye position is in the right position. This may be a predetermined process. For example, the system may be set up such that a particular piece of digital content (e.g. an advertisement, guidance information, object information, etc.) will appear in the event that the wearer looks at a certain object(s) in the environment. A virtual target line(s) may be developed that virtually connects the wearer&#39;s eye with an object(s) in the environment (e.g. a building, portion of a building, mark on a building, gps location, etc.) and the virtual target line may be continually updated depending on the position and viewing direction of the wearer (e.g. as determined through GPS, e-compass, IMU, etc.) and the position of the object. When the virtual target line suggests that the wearer&#39;s pupil is substantially aligned with the virtual target line or about to be aligned with the virtual target line, the digital content may be displayed in the FOV  3704 . 
     In embodiments, the time spent looking along the virtual target line and/or a particular portion of the FOV  3708  may indicate that the wearer is interested in an object in the environment and/or digital content being displayed. In the event there is no digital content being displayed at the time a predetermined period of time is spent looking at a direction, digital content may be presented in the area of the FOV  3708 . The time spent looking at an object may be interpreted as a command to display information about the object, for example. In other embodiments, the content may not relate to the object and may be presented because of the indication that the person is relatively inactive. In embodiments, the digital content may be positioned in proximity to the virtual target line, but not in-line with it such that the wearer&#39;s view of the surroundings are not obstructed but information can augment the wearer&#39;s view of the surroundings. In embodiments, the time spent looking along a target line in the direction of displayed digital content may be an indication of interest in the digital content. This may be used as a conversion event in advertising. For example, an advertiser may pay more for an add placement if the wearer of the HWC  102  looks at a displayed advertisement for a certain period of time. As such, in embodiments, the time spent looking at the advertisement, as assessed by comparing eye position with the content placement, target line or other appropriate position may be used to determine a rate of conversion or other compensation amount due for the presentation. 
     An aspect of the invention relates to removing content from the FOV of the HWC  102  when the wearer of the HWC  102  apparently wants to view the surrounding environments clearly.  FIG.  38    illustrates a situation where eye imagery suggests that the eye has or is moving quickly so the digital content  3804  in the FOV  3808  is removed from the FOV  3808 . In this example, the wearer may be looking quickly to the side indicating that there is something on the side in the environment that has grabbed the wearer&#39;s attention. This eye movement  3802  may be captured through eye imaging techniques (e.g. as described herein) and if the movement matches a predetermined movement (e.g. speed, rate, pattern, etc.) the content may be removed from view. In embodiments, the eye movement is used as one input and HWC movements indicated by other sensors (e.g. IMU in the HWC) may be used as another indication. These various sensor movements may be used together to project an event that should cause a change in the content being displayed in the FOV. 
     Another aspect of the present invention relates to determining a focal plane based on the wearer&#39;s eye convergence. Eyes are generally converged slightly and converge more when the person focuses on something very close. This is generally referred to as convergence. In embodiments, convergence is calibrated for the wearer. That is, the wearer may be guided through certain focal plane exercises to determine how much the wearer&#39;s eyes converge at various focal planes and at various viewing angles. The convergence information may then be stored in a database for later reference. In embodiments, a general table may be used in the event there is no calibration step or the person skips the calibration step. The two eyes may then be imaged periodically to determine the convergence in an attempt to understand what focal plane the wearer is focused on. In embodiments, the eyes may be imaged to determine a virtual target line and then the eye&#39;s convergence may be determined to establish the wearer&#39;s focus, and the digital content may be displayed or altered based thereon. 
       FIG.  39    illustrates a situation where digital content is moved  3902  within one or both of the FOVs  3908  and  3910  to align with the convergence of the eyes as determined by the pupil movement  3904 . By moving the digital content to maintain alignment, in embodiments, the overlapping nature of the content is maintained so the object appears properly to the wearer. This can be important in situations where 3D content is displayed. 
     An aspect of the present invention relates to controlling the HWC  102  based on events detected through eye imaging. A wearer winking, blinking, moving his eyes in a certain pattern, etc. may, for example, control an application of the HWC  102 . Eye imaging (e.g. as described herein) may be used to monitor the eye(s) of the wearer and once a pre-determined pattern is detected an application control command may be initiated. 
     An aspect of the invention relates to monitoring the health of a person wearing a HWC  102  by monitoring the wearer&#39;s eye(s). Calibrations may be made such that the normal performance, under various conditions (e.g. lighting conditions, image light conditions, etc.) of a wearer&#39;s eyes may be documented. The wearer&#39;s eyes may then be monitored through eye imaging (e.g. as described herein) for changes in their performance. Changes in performance may be indicative of a health concern (e.g. concussion, brain injury, stroke, loss of blood, etc.). If detected the data indicative of the change or event may be communicated from the HWC  102 . 
     Aspects of the present invention relate to security and access of computer assets (e.g. the HWC itself and related computer systems) as determined through eye image verification. As discussed herein elsewhere, eye imagery may be compared to known person eye imagery to confirm a person&#39;s identity. Eye imagery may also be used to confirm the identity of people wearing the HWCs  102  before allowing them to link together or share files, streams, information, etc. 
     A variety of use cases for eye imaging are possible based on technologies described herein. An aspect of the present invention relates to the timing of eye image capture. The timing of the capture of the eye image and the frequency of the capture of multiple images of the eye can vary dependent on the use case for the information gathered from the eye image. For example, capturing an eye image to identify the user of the HWC may be required only when the HWC has been turned ON or when the HWC determines that the HWC has been put onto a wearer&#39;s head to control the security of the HWC and the associated information that is displayed to the user. Wherein, the orientation, movement pattern, stress or position of the earhorns (or other portions of the HWC) of the HWC can be used to determine that a person has put the HWC onto their head with the intention to use the HWC. Those same parameters may be monitored in an effort to understand when the HWC is dismounted from the user&#39;s head. This may enable a situation where the capture of an eye image for identifying the wearer may be completed only when a change in the wearing status is identified. In a contrasting example, capturing eye images to monitor the health of the wearer may require images to be captured periodically (e.g. every few seconds, minutes, hours, days, etc.). For example, the eye images may be taken in minute intervals when the images are being used to monitor the health of the wearer when detected movements indicate that the wearer is exercising. In a further contrasting example, capturing eye images to monitor the health of the wearer for long-term effects may only require that eye images be captured monthly. Embodiments of the invention relate to selection of the timing and rate of capture of eye images to be in correspondence with the selected use scenario associated with the eye images. These selections may be done automatically, as with the exercise example above where movements indicate exercise, or these selections may be set manually. In a further embodiment, the selection of the timing and rate of eye image capture is adjusted automatically depending on the mode of operation of the HWC. The selection of the timing and rate of eye image capture can further be selected in correspondence with input characteristics associated with the wearer including age and health status, or sensed physical conditions of the wearer including heart rate, chemical makeup of the blood and eye blink rate. 
       FIG.  40    illustrates an embodiment in which digital content presented in a see-through FOV is positioned based on the speed in which the wearer is moving. When the person is not moving, as measured by sensor(s) in the HWC  102  (e.g. IMU, GPS based tracking, etc.), digital content may be presented at the stationary person content position  4004 . The content position  4004  is indicated as being in the middle of the see-through FOV  4002 ; however, this is meant to illustrate that the digital content is positioned within the see-through FOV at a place that is generally desirable knowing that the wearer is not moving and as such the wearer&#39;s surrounding see through view can be somewhat obstructed. So, the stationary person content position, or neutral position, may not be centered in the see-through FOV; it may be positioned somewhere in the see-through FOV deemed desirable and the sensor feedback may shift the digital content from the neutral position. The movement of the digital content for a quickly moving person is also shown in  FIG.  40    wherein as the person turns their head to the side, the digital content moves out of the see-through FOV to content position  4008  and then moves back as the person turns their head back. For a slowly moving person, the head movement can be more complex and as such the movement of the digital content in an out of the see-through FOV can follow a path such as that shown by content position  4010 . 
     In embodiments, the sensor that assesses the wearer&#39;s movements may be a GPS sensor, IMU, accelerometer, etc. The content position may be shifted from a neutral position to a position towards a side edge of the field of view as the forward motion increases. The content position may be shifted from a neutral position to a position towards a top or bottom edge of the field of view as the forward motion increases. The content position may shift based on a threshold speed of the assessed motion. The content position may shift linearly based on the speed of the forward motion. The content position may shift non-linearly based on the speed of the forward motion. The content position may shift outside of the field of view. In embodiments, the content is no longer displayed if the speed of movement exceeds a predetermined threshold and will be displayed again once the forward motion slows. 
     In embodiments, the content position may generally be referred to as shifting; it should be understood that the term shifting encompasses a process where the movement from one position to another within the see-through FOV or out of the FOV is visible to the wearer (e.g. the content appears to slowly or quickly move and the user perceives the movement itself) or the movement from one position to another may not be visible to the wearer (e.g. the content appears to jump in a discontinuous fashion or the content disappears and then reappears in the new position). 
     Another aspect of the present invention relates to removing the content from the field of view or shifting it to a position within the field of view that increases the wearer&#39;s view of the surrounding environment when a sensor causes an alert command to be issued. In embodiments, the alert may be due to a sensor or combination of sensors that sense a condition above a threshold value. For example, if an audio sensor detects a loud sound of a certain pitch, content in the field of view may be removed or shifted to provide a clear view of the surrounding environment for the wearer. In addition to the shifting of the content, in embodiments, an indication of why the content was shifted may be presented in the field of view or provided through audio feedback to the wearer. For instance, if a carbon monoxide sensor detects a high concentration in the area, content in the field of view may be shifted to the side of the field of view or removed from the field of view and an indication may be provided to the wearer that there is a high concentration of carbon monoxide in the area. This new information, when presented in the field of view, may similarly be shifted within or outside of the field of view depending on the movement speed of the wearer. 
       FIG.  41    illustrates how content may be shifted from a neutral position  4104  to an alert position  4108 . In this embodiment, the content is shifted outside of the see-through FOV  4102 . In other embodiments, the content may be shifted as described herein. 
     Another aspect of the present invention relates to identification of various vectors or headings related to the HWC  102 , along with sensor inputs, to determine how to position content in the field of view. In embodiments, the speed of movement of the wearer is detected and used as an input for position of the content and, depending on the speed, the content may be positioned with respect to a movement vector or heading (i.e. the direction of the movement), or a sight vector or heading (i.e. the direction of the wearer&#39;s sight direction). For example, if the wearer is moving very fast the content may be positioned within the field of view with respect to the movement vector because the wearer is only going to be looking towards the sides of himself periodically and for short periods of time. As another example, if the wearer is moving slowly, the content may be positioned with respect to the sight heading because the user may more freely be shifting his view from side to side. 
       FIG.  42    illustrates two examples where the movement vector may effect content positioning. Movement vector A  4202  is shorter than movement vector B  4210  indicating that the forward speed and/or acceleration of movement of the person associated with movement vector A  4202  is lower than the person associated with movement vector B  4210 . Each person is also indicated as having a sight vector or heading  4208  and  4212 . The sight vectors A  4208  and B  4210  are the same from a relative perspective. The white area inside of the black triangle in front of each person is indicative of how much time each person likely spends looking at a direction that is not in line with the movement vector. The time spent looking off angle A  4204  is indicated as being more than that of the time spent looking off angle B  4214 . This may be because the movement vector speed A is lower than movement vector speed B. The faster the person moves forward the more the person tends to look in the forward direction, typically. The FOVs A  4218  and B  4222  illustrate how content may be aligned depending on the movement vectors  4202  and  4210  and sight vectors  4208  and  4212 . FOV A  4218  is illustrated as presenting content in-line with the sight vector  4220 . This may be due to the lower speed of the movement vector A  4202 . This may also be due to the prediction of a larger amount of time spent looking off angle A  4204 . FOV B  4222  is illustrated as presenting content in line with the movement vector  4224 . This may be due to the higher speed of movement vector B  4210 . This may also be due to the prediction of a shorter amount of time spent looking off angle B  4214 . 
     Another aspect of the present invention relates to damping a rate of content position change within the field of view. As illustrated in  FIG.  43   , the sight vector may undergo a rapid change  4304 . This rapid change may be an isolated event or it may be made at or near a time when other sight vector changes are occurring. The wearer&#39;s head may be turning back and forth for some reason. In embodiments, the rapid successive changes in sight vector may cause a damped rate of content position change  4308  within the FOV  4302 . For example, the content may be positioned with respect to the sight vector, as described herein, and the rapid change in sight vector may normally cause a rapid content position change; however, since the sight vector is successively changing, the rate of position change with respect to the sight vector may be damped, slowed, or stopped. The position rate change may be altered based on the rate of change of the sight vector, average of the sight vector changes, or otherwise altered. 
     Another aspect of the present invention relates to simultaneously presenting more than one content in the field of view of a see-through optical system of a HWC  102  and positioning one content with the sight heading and one content with the movement heading.  FIG.  44    illustrates two FOV&#39;s A  4414  and B  4420 , which correspond respectively to the two identified sight vectors A  4402  and B  4404 .  FIG.  44    also illustrates an object in the environment  4408  at a position relative to the sight vectors A  4402  and B  4404 . When the person is looking along sight vector A  4402 , the environment object  4408  can be seen through the field of view A  4414  at position  4412 . As illustrated, sight heading aligned content is presented as TEXT in proximity with the environment object  4412 . At the same time, other content  4418  is presented in the field of view A  4414  at a position aligned in correspondence with the movement vector. As the movement speed increases, the content  4418  may shift as described herein. When the sight vector of the person is sight vector B  4404  the environmental object  4408  is not seen in the field of view B  4420 . As a result, the sight aligned content  4410  is not presented in field of view B  4420 ; however, the movement aligned content  4418  is presented and is still dependent on the speed of the motion. 
       FIG.  45    shows an example set of data for a person moving through an environment over a path that starts with a movement heading of 0 degrees and ends with a movement heading of 114 degrees during which time the speed of movement varies from 0 m/sec to 20 m/sec. The sight heading can be seen to vary on either side of the movement heading while moving as the person looks from side to side. Large changes in sight heading occur when the movement speed is 0 m/sec when the person is standing still, followed by step changes in movement heading. 
     Embodiments provide a process for determining the display heading that takes into account the way a user moves through an environment and provides a display heading that makes it easy for the user to find the displayed information while also providing unencumbered see-through views of the environment in response to different movements, speed of movement or different types of information being displayed. 
       FIG.  46    illustrates a see-through view as may be seen when using a HWC wherein information is overlaid onto a see-through view of the environment. The tree and the building are actually in the environment and the text is displayed in the see-through display such that it appears overlaid on the environment. In addition to text information such as, for example, instructions and weather information, some augmented reality information is shown that relates to nearby objects in the environment. 
     In an embodiment, the display heading is determined based on speed of movement. At low speeds, the display heading may be substantially the same as the sight heading while at high speed the display heading may be substantially the same as the movement heading. In embodiments, as long as the user remains stationary, the displayed information is presented directly in front of the user and HWC. However, as the movement speed increases (e.g. above a threshold or continually, etc.) the display heading becomes substantially the same as the movement heading regardless of the direction the user is looking, so that when the user looks in the direction of movement, the displayed information is directly in front of the user and HMD and when the user looks to the side the displayed information is not visible. 
     Rapid changes in sight heading can be followed by a slower change in the display heading to provide a damped response to head rotation. Alternatively, the display heading can be substantially the time averaged sight heading so that the displayed information is presented at a heading that is in the middle of a series of sight headings over a period of time. In this embodiment, if the user stops moving their head, the display heading gradually becomes the same as the sight heading and the displayed information moves into the display field of view in front of the user and HMD. In embodiments, when there is a high rate of sight heading change, the process delays the effect of the time averaged sight heading on the display heading. In this way, the effect of rapid head movements on display heading is reduced and the positioning of the displayed information within the display field of view is stabilized laterally. 
     In another embodiment, display heading is determined based on speed of movement where at high-speed, the display heading is substantially the same as the movement heading. At mid-speed the display heading is substantially the same as a time averaged sight heading so that rapid head rotations are damped out and the display heading is in the middle of back and forth head movements. 
     In yet another embodiment, the type of information being displayed is included in determining how the information should be displayed. Augmented reality information that is connected to objects in the environment is given a display heading that substantially matches the sight heading. In this way, as the user rotates their head, augmented reality information comes into view that is related to objects that are in the see-through view of the environment. At the same time, information that is not connected to objects in the environment is given a display heading that is determined based on the type of movements and speed of movements as previously described in this specification. 
     In yet a further embodiment, when the speed of movement is determined to be above a threshold, the information displayed is moved downward in the display field of view so that the upper portion of the display field of view has less information or no information displayed to provide the user with an unencumbered see-through view of the environment. 
       FIGS.  47  and  48    show illustrations of a see-through view including overlaid displayed information.  FIG.  47    shows the see-through view immediately after a rapid change in sight heading from the sight heading associated with the see-through view shown in  FIG.  46    wherein the change in sight heading comes from a head rotation. In this case, the display heading is delayed.  FIG.  48    shows how at a later time, the display heading catches up to the sight heading. The augmented reality information remains in positions within the display field of view where the association with objects in the environment can be readily made by the user. 
       FIG.  49    shows an illustration of a see-through view example including overlaid displayed information that has been shifted downward in the display field of view to provide an unencumbered see-through view in the upper portion of the see-through view. At the same time, augmented reality labels have been maintained in locations within the display field of view so they can be readily associated with objects in the environment. 
     In a further embodiment, in an operating mode such as when the user is moving in an environment, digital content is presented at the side of the user&#39;s see-through FOV so that the user can only view the digital content by turning their head. In this case, when the user is looking straight ahead, such as when the movement heading matches the sight heading, the see-through view FOV does not include digital content. The user then accesses the digital content by turning their head to the side whereupon the digital content moves laterally into the user&#39;s see-through FOV. In another embodiment, the digital content is ready for presentation and will be presented if an indication for its presentation is received. For example, the information may be ready for presentation and if the sight heading or predetermined position of the HWC  102  is achieved the content may then be presented. The wearer may look to the side and the content may be presented. In another embodiment, the user may cause the content to move into an area in the field of view by looking in a direction for a predetermined period of time, blinking, winking, or displaying some other pattern that can be captured through eye imaging technologies (e.g. as described herein elsewhere). 
     In yet another embodiment, an operating mode is provided wherein the user can define sight headings wherein the associated see-through FOV includes digital content or does not include digital content. In an example, this operating mode can be used in an office environment where when the user is looking at a wall digital content is provided within the FOV, whereas when the user is looking toward a hallway, the FOV is unencumbered by digital content. In another example, when the user is looking horizontally digital content is provided within the FOV, but when the user looks down (e.g. to look at a desktop or a cellphone) the digital content is removed from the FOV. 
     Another aspect of the present invention relates to collecting and using eye position and sight heading information. Head worn computing with motion heading, sight heading, and/or eye position prediction (sometimes referred to as “eye heading” herein) may be used to identify what a wearer of the HWC  102  is apparently interested in and the information may be captured and used. In embodiments, the information may be characterized as viewing information because the information apparently relates to what the wearer is looking at. The viewing information may be used to develop a personal profile for the wearer, which may indicate what the wearer tends to look at. The viewing information from several or many HWC&#39;s  102  may be captured such that group or crowd viewing trends may be established. For example, if the movement heading and sight heading are known, a prediction of what the wearer is looking at may be made and used to generate a personal profile or portion of a crowd profile. In another embodiment, if the eye heading and location, sight heading and/or movement heading are known, a prediction of what is being looked at may be predicted. The prediction may involve understanding what is in proximity of the wearer and this may be understood by establishing the position of the wearer (e.g. through GPS or other location technology) and establishing what mapped objects are known in the area. The prediction may involve interpreting images captured by the camera or other sensors associated with the HWC  102 . For example, if the camera captures an image of a sign and the camera is in-line with the sight heading, the prediction may involve assessing the likelihood that the wearer is viewing the sign. The prediction may involve capturing an image or other sensory information and then performing object recognition analysis to determine what is being viewed. For example, the wearer may be walking down a street and the camera that is in the HWC  102  may capture an image and a processor, either on-board or remote from the HWC  102 , may recognize a face, object, marker, image, etc. and it may be determined that the wearer may have been looking at it or towards it. 
       FIG.  50    illustrates a cross section of an eyeball of a wearer of an HWC with focus points that can be associated with the eye imaging system of the invention. The eyeball  5010  includes an iris  5012  and a retina  5014 . Because the eye imaging system of the invention provides coaxial eye imaging with a display system, images of the eye can be captured from a perspective directly in front of the eye and in line with where the wearer is looking. In embodiments of the invention, the eye imaging system can be focused at the iris  5012  and/or the retina  5014  of the wearer, to capture images of the external surface of the iris  5012  or the internal portions of the eye, which includes the retina  5014 .  FIG.  50    shows light rays  5020  and  5025  that are respectively associated with capturing images of the iris  5012  or the retina  5014  wherein the optics associated with the eye imaging system are respectively focused at the iris  5012  or the retina  5014 . Illuminating light can also be provided in the eye imaging system to illuminate the iris  5012  or the retina  5014 .  FIG.  51    shows an illustration of an eye including an iris  5130  and a sclera  5125 . In embodiments, the eye imaging system can be used to capture images that include the iris  5130  and portions the sclera  5125 . The images can then be analyzed to determine color, shapes and patterns that are associated with the user. In further embodiments, the focus of the eye imaging system is adjusted to enable images to be captured of the iris  5012  or the retina  5014 . Illuminating light can also be adjusted to illuminate the iris  5012  or to pass through the pupil of the eye to illuminate the retina  5014 . The illuminating light can be visible light to enable capture of colors of the iris  5012  or the retina  5014 , or the illuminating light can be ultraviolet (e.g. 340 nm), near infrared (e.g. 850 nm) or mid-wave infrared (e.g. 5000 nm) light to enable capture of hyperspectral characteristics of the eye. 
       FIG.  53    illustrates a display system that includes an eye imaging system. The display system includes a polarized light source  2958 , a DLP  2955 , a quarter wave film  2957  and a beam splitter plate  5345 . The eye imaging system includes a camera  3280 , illuminating lights  5355  and beam splitter plate  5345 . Where the beam splitter plate  5345  can be a reflective polarizer on the side facing the polarized light source  2958  and a hot mirror on the side facing the camera  3280 . Wherein the hot mirror reflects infrared light (e.g. wavelengths 700 to 2000 nm) and transmits visible light (e.g. wavelengths 400 to 670 nm). The beam splitter plate  5345  can be comprised of multiple laminated films, a substrate film with coatings or a rigid transparent substrate with films on either side. By providing a reflective polarizer on the one side, the light from the polarized light source  2958  is reflected toward the DLP  2955  where it passes through the quarter wave film  2957  once, is reflected by the DLP mirrors in correspondence with the image content being displayed by the DLP  2955  and then passes back through the quarter wave film  2957 . In so doing, the polarization state of the light from the polarized light source is changed, so that it is transmitted by the reflective polarizer on the beam splitter plate  5345  and the image light  2971  passes into the lower optics module  204  where the image is displayed to the user. At the same time, infrared light  5357  from the illuminating lights  5355  is reflected by the hot mirror so that it passes into the lower optics module  204  where it illuminates the user&#39;s eye. Portions of the infrared light  2969  are reflected by the user&#39;s eye and this light passes back through the lower optics module  204 , is reflected by the hot mirror on the beam splitter plate  5345  and is captured by the camera  3280 . In this embodiment, the image light  2971  is polarized while the infrared light  5357  and  2969  can be unpolarized. In an embodiment, the illuminating lights  5355  provide two different infrared wavelengths and eye images are captured in pairs, wherein the pairs of eye images are analyzed together to improve the accuracy of identification of the user based on iris analysis. 
       FIG.  54    shows an illustration of a further embodiment of a display system with an eye imaging system. In addition to the features of  FIG.  53   , this system includes a second camera  5460 . Wherein the second camera  5460  is provided to capture eye images in the visible wavelengths. Illumination of the eye can be provided by the displayed image or by see-through light from the environment. Portions of the displayed image can be modified to provide improved illumination of the user&#39;s eye when images of the eye are to be captured such as by increasing the brightness of the displayed image or increasing the white areas within the displayed image. Further, modified displayed images can be presented briefly for the purpose of capturing eye images and the display of the modified images can be synchronized with the capture of the eye images. As shown in  FIG.  54   , visible light  5467  is polarized when it is captured by the second camera  5460  since it passes through the beam splitter  5445  and the beam splitter  5445  is a reflective polarizer on the side facing the second camera  5460 . In this eye imaging system, visible eye images can be captured by the second camera  5460  at the same time that infrared eye images are captured by the camera  3280 . Wherein, the characteristics of the camera  3280  and the second camera  5460  and the associated respective images captured can be different in terms of resolution and capture rate. 
       FIGS.  52   a  and  52   b    illustrate captured images of eyes where the eyes are illuminated with structured light patterns. In  FIG.  52   a   , an eye  5220  is shown with a projected structured light pattern  5230 , where the light pattern is a grid of lines. A light pattern of such as  5230  can be provided by the light source  5355  show in  FIG.  53    by including a diffractive or a refractive device to modify the light  5357  as are known by those skilled in the art. A visible light source can also be included for the second camera  5460  shown in  FIG.  54    which can include a diffractive or refractive to modify the light  5467  to provide a light pattern.  FIG.  52   b    illustrates how the structured light pattern of  5230  becomes distorted to  5235  when the user&#39;s eye  5225  looks to the side. This distortion comes from the fact that the human eye is not spherical in shape, instead the iris sticks out slightly from the eyeball to form a bump in the area of the iris. As a result, the shape of the eye and the associated shape of the reflected structured light pattern is different depending on which direction the eye is pointed, when images of the eye are captured from a fixed position. Changes in the structured light pattern can subsequently be analyzed in captured eye images to determine the direction that the eye is looking. 
     The eye imaging system can also be used for the assessment of aspects of health of the user. In this case, information gained from analyzing captured images of the iris  5012  is different from information gained from analyzing captured images of the retina  5014 . Where images of the retina  5014  are captured using light  5357  that illuminates the inner portions of the eye including the retina  5014 . The light  5357  can be visible light, but in an embodiment, the light  5357  is infrared light (e.g. wavelength 1 to 5 microns) and the camera  3280  is an infrared light sensor (e.g. an InGaAs sensor) or a low resolution infrared image sensor that is used to determine the relative amount of light  5357  that is absorbed, reflected or scattered by the inner portions of the eye. Wherein the majority of the light that is absorbed, reflected or scattered can be attributed to materials in the inner portion of the eye including the retina where there are densely packed blood vessels with thin walls so that the absorption, reflection and scattering are caused by the material makeup of the blood. These measurements can be conducted automatically when the user is wearing the HWC, either at regular intervals, after identified events or when prompted by an external communication. In a preferred embodiment, the illuminating light is near infrared or mid infrared (e.g. 0.7 to 5 microns wavelength) to reduce the chance for thermal damage to the wearer&#39;s eye. In another embodiment, the polarizer  3285  is antireflection coated to reduce any reflections from this surface from the light  5357 , the light  2969  or the light  3275  and thereby increase the sensitivity of the camera  3280 . In a further embodiment, the light source  5355  and the camera  3280  together comprise a spectrometer wherein the relative intensity of the light reflected by the eye is analyzed over a series of narrow wavelengths within the range of wavelengths provided by the light source  5355  to determine a characteristic spectrum of the light that is absorbed, reflected or scattered by the eye. For example, the light source  5355  can provide a broad range of infrared light to illuminate the eye and the camera  3280  can include: a grating to laterally disperse the reflected light from the eye into a series of narrow wavelength bands that are captured by a linear photodetector so that the relative intensity by wavelength can be measured and a characteristic absorbance spectrum for the eye can be determined over the broad range of infrared. In a further example, the light source  5355  can provide a series of narrow wavelengths of light (ultraviolet, visible or infrared) to sequentially illuminate the eye and camera  3280  includes a photodetector that is selected to measure the relative intensity of the series of narrow wavelengths in a series of sequential measurements that together can be used to determine a characteristic spectrum of the eye. The determined characteristic spectrum is then compared to known characteristic spectra for different materials to determine the material makeup of the eye. In yet another embodiment, the illuminating light  5357  is focused on the retina  5014  and a characteristic spectrum of the retina  5014  is determined and the spectrum is compared to known spectra for materials that may be present in the user&#39;s blood. For example, in the visible wavelengths 540 nm is useful for detecting hemoglobin and 660 nm is useful for differentiating oxygenated hemoglobin. In a further example, in the infrared, a wide variety of materials can be identified as is known by those skilled in the art, including: glucose, urea, alcohol and controlled substances.  FIG.  55    shows a series of example spectrum for a variety of controlled substances as measured using a form of Infrared spectroscopy (ThermoScientific Application Note 51242, by C. Petty, B. Garland and the Mesa Police Department Forensic Laboratory, which is hereby incorporated by reference herein).  FIG.  56    shows an infrared absorbance spectrum for glucose (Hewlett Packard Company 1999, G. Hopkins, G. Mauze; “In-vivo NIR Diffuse-reflectance Tissue Spectroscopy of Human Subjects,” which is hereby incorporated by reference herein). U.S. Pat. No. 6,675,030, which is hereby incorporated by reference herein, provides a near infrared blood glucose monitoring system that includes infrared scans of a body part such as a foot. United States Patent publication 2006/0183986, which is hereby incorporated by reference herein, provides a blood glucose monitoring system including a light measurement of the retina. Embodiments of the present invention provide methods for automatic measurements of specific materials in the user&#39;s blood by illuminating at one or more narrow wavelengths into the iris of the wearer&#39;s eye and measuring the relative intensity of the light reflected by the eye to identify the relative absorbance spectrum and comparing the measured absorbance spectrum with known absorbance spectra for the specific material, such as illuminating at 540 and 660 nm to determine the level of hemoglobin present in the user&#39;s blood. 
     Another aspect of the present invention relates to collecting and using eye position and sight heading information. Head worn computing with motion heading, sight heading, and/or eye position prediction (sometimes referred to as “eye heading” herein) may be used to identify what a wearer of the HWC  102  is apparently interested in and the information may be captured and used. In embodiments, the information may be characterized as viewing information because the information apparently relates to what the wearer is looking at. The viewing information may be used to develop a personal profile for the wearer, which may indicate what the wearer tends to look at. The viewing information from several or many HWC&#39;s  102  may be captured such that group or crowd viewing trends may be established. For example, if the movement heading and sight heading are known, a prediction of what the wearer is looking at may be made and used to generate a personal profile or portion of a crowd profile. In another embodiment, if the eye heading and location, sight heading and/or movement heading are known, a prediction of what is being looked at may be predicted. The prediction may involve understanding what is in proximity of the wearer and this may be understood by establishing the position of the wearer (e.g. through GPS or other location technology) and establishing what mapped objects are known in the area. The prediction may involve interpreting images captured by the camera or other sensors associated with the HWC  102 . For example, if the camera captures an image of a sign and the camera is in-line with the sight heading, the prediction may involve assessing the likelihood that the wearer is viewing the sign. The prediction may involve capturing an image or other sensory information and then performing object recognition analysis to determine what is being viewed. For example, the wearer may be walking down a street and the camera that is in the HWC  102  may capture an image and a processor, either on-board or remote from the HWC  102 , may recognize a face, object, marker, image, etc. and it may be determined that the wearer may have been looking at it or towards it. 
       FIG.  57    illustrates a scene where a person is walking with a HWC  102  mounted on his head. In this scene, the person&#39;s geo-spatial location  5704  is known through a GPS sensor, which could be another location system, and his movement heading, sight heading  5714  and eye heading  5702  are known and can be recorded (e.g. through systems described herein). There are objects and a person in the scene. Person  5712  may be recognized by the wearer&#39;s HWC  102  system, the person may be mapped (e.g. the person&#39;s GPS location may be known or recognized), or otherwise known. The person may be wearing a garment or device that is recognizable. For example, the garment may be of a certain style and the HWC may recognize the style and record it&#39;s viewing. The scene also includes a mapped object  5718  and a recognized object  5720 . As the wearer moves through the scene, the sight and/or eye headings may be recorded and communicated from the HWC  102 . In embodiments, the time that the sight and/or eye heading maintains a particular position may be recorded. For example, if a person appears to look at an object or person for a predetermined period of time (e.g. 2 seconds or longer), the information may be communicated as gaze persistence information as an indication that the person may have been interested in the object. 
     In embodiments, sight headings may be used in conjunction with eye headings or eye and/or sight headings may be used alone. Sight headings can do a good job of predicting what direction a wearer is looking because many times the eyes are looking forward, in the same general direction as the sight heading. In other situations, eye headings may be a more desirable metric because the eye and sight headings are not always aligned. In embodiments herein examples may be provided with the term “eye/sight” heading, which indicates that either or both eye heading and sight heading may be used in the example. 
       FIG.  58    illustrates a system for receiving, developing and using movement heading, sight heading, eye heading and/or persistence information from HWC(s)  102 . The server  5804  may receive heading or gaze persistence information, which is noted as persistence information  5802 , for processing and/or use. The heading and/or gaze persistence information may be used to generate a personal profile  5808  and/or a group profile  5810 . The personal profile  5718  may reflect the wearer&#39;s general viewing tendencies and interests. The group profile  5810  may be an assemblage of different wearer&#39;s heading and persistence information to create impressions of general group viewing tendencies and interests. The group profile  5810  may be broken into different groups based on other information such as gender, likes, dislikes, biographical information, etc. such that certain groups can be distinguished from other groups. This may be useful in advertising because an advertiser may be interested in what a male adult sports goer is generally looking at as oppose to a younger female. The profiles  5808  and  5810  and raw heading and persistence information may be used by retailers  5814 , advertisers  5818 , trainers, etc. For example, an advertiser may have an advertisement posted in an environment and may be interested in knowing how many people look at the advertisement, how long they look at it and where they go after looking at it. This information may be used as conversion information to assess the value of the advertisement and thus the payment to be received for the advertisement. 
     In embodiments, the process involves collecting eye and/or sight heading information from a plurality of head-worn computers that come into proximity with an object in an environment. For example, a number of people may be walking through an area and each of the people may be wearing a head worn computer with the ability to track the position of the wearer&#39;s eye(s) as well as possibly the wearer&#39;s sight and movement headings. The various HWC wearing individuals may then walk, ride, or otherwise come into proximity with some object in the environment (e.g. a store, sign, person, vehicle, box, bag, etc.). When each person passes by or otherwise comes near the object, the eye imaging system may determine if the person is looking towards the object. All of the eye/sight heading information may be collected and used to form impressions of how the crowd reacted to the object. A store may be running a sale and so the store may put out a sign indicating such. The storeowners and managers may be very interested to know if anyone is looking at their sign. The sign may be set as the object of interest in the area and as people navigate near the sign, possibly determined by their GPS locations, the eye/sight heading determination system may record information relative to the environment and the sign. Once, or as, the eye/sight heading information is collected and associations between the eye headings and the sign are determined, feedback may be sent back to the storeowner, managers, advertiser, etc. as an indication of how well their sign is attracting people. In embodiments, the sign&#39;s effectiveness at attracting people&#39;s attention, as indicated through the eye/sight headings, may be considered a conversion metric and impact the economic value of the sign and/or the signs placement. 
     In embodiments, a map of the environment with the object may be generated by mapping the locations and movement paths of the people in the crowd as they navigate by the object (e.g. the sign). Layered on this map may be an indication of the various eye/sight headings. This may be useful in indicating wear people were in relation to the object when then viewed they object. The map may also have an indication of how long people looked at the object from the various positions in the environment and where they went after seeing the object. 
     In embodiments, the process involves collecting a plurality of eye/sight headings from a head-worn computer, wherein each of the plurality of eye/sight headings is associated with a different pre-determined object in an environment. This technology may be used to determine which of the different objects attracts more of the person&#39;s attention. For example, if there are three objects placed in an environment and a person enters the environment navigating his way through it, he may look at one or more of the objects and his eye/sight heading may persist on one or more objects longer than others. This may be used in making or refining the person&#39;s personal attention profile and/or it may be used in connection with other such people&#39;s data on the same or similar objects to determine an impression of how the population or crowd reacts to the objects. Testing advertisements in this way may provide good feedback of its effectiveness. 
     In embodiments, the process may involve capturing eye/sight headings once there is substantial alignment between the eye/sight heading and an object of interest. For example, the person with the HWC may be navigating through an environment and once the HWC detects substantial alignment or the projected occurrence of an upcoming substantial alignment between the eye/sight heading and the object of interest, the occurrence and/or persistence may be recorded for use. 
     In embodiments, the process may involve collecting eye/sight heading information from a head-worn computer and collecting a captured image from the head-worn computer that was taken at substantially the same time as the eye/sight heading information was captured. These two pieces of information may be used in conjunction to gain an understanding of what the wearer was looking at and possibly interested in. The process may further involve associating the eye/sight heading information with an object, person, or other thing found in the captured image. This may involve processing the captured image looking for objects or patterns. In embodiments, gaze time or persistence may be measured and used in conjunction with the image processing. The process may still involve object and/or pattern recognition, but it may also involve attempting to identify what the person gazed at for the period of time by more particularly identifying a portion of the image in conjunction with image processing. 
     In embodiments, the process may involve setting a pre-determined eye/sight heading from a pre-determined geospatial location and using them as triggers. In the event that a head worn computer enters the geospatial location and an eye/sight heading associated with the head worn computer aligns with the pre-determined eye/sight heading, the system may collect the fact that there was an apparent alignment and/or the system may record information identifying how long the eye/sight heading remains substantially aligned with the pre-determined eye/sight heading to form a persistence statistic. This may eliminate or reduce the need for image processing as the triggers can be used without having to image the area. In other embodiments, image capture and processing is performed in conjunction with the triggers. In embodiments, the triggers may be a series a geospatial locations with corresponding eye/sight headings such that many spots can be used as triggers that indicate when a person entered an area in proximity to an object of interest and/or when that person actually appeared to look at the object. 
     In embodiments, eye imaging may be used to capture images of both eyes of the wearer in order to determine the amount of convergence of the eyes (e.g. through technologies described herein elsewhere) to get an understanding of what focal plane is being concentrated on by the wearer. For example, if the convergence measurement suggests that the focal plane is within 15 feet of the wearer, than, even though the eye/sight headings may align with an object that is more than 15 feet away it may be determined that the wearer was not looking at the object. If the object were within the 15 foot suggested focal plane, the determination may be that the wearer was looking at the object.  FIG.  59    illustrates an environmentally position locked digital content  5912  that is indicative of a person&#39;s location  5902 . In this disclosure the term “BlueForce” is generally used to indicate team members or members for which geo-spatial locations are known and can be used. In embodiments, “BlueForce” is a term to indicate members of a tactical arms team (e.g. a police force, secret service force, security force, military force, national security force, intelligence force, etc.). In many embodiments herein one member may be referred to as the primary or first BlueForce member and it is this member, in many described embodiments, that is wearing the HWC. It should be understood that this terminology is to help the reader and make for clear presentations of the various situations and that other members of the Blueforce, or other people, may have HWC&#39;s  102  and have similar capabilities. In this embodiment, a first person is wearing a head-worn computer  102  that has a see through field of view (“FOV”)  5914 . The first person can see through the FOV to view the surrounding environment through the FOV and digital content can also be presented in the FOV such that the first person can view the actual surroundings, through the FOV, in a digitally augmented view. The other BlueForce person&#39;s location is known and is indicated at a position inside of a building at point  5902 . This location is known in three dimensions, longitude, latitude and altitude, which may have been determined by GPS along with an altimeter associated with the other Blueforce person. Similarly, the location of the first person wearing the HWC  102  is also known, as indicated in  FIG.  59    as point  5908 . In this embodiment, the compass heading  5910  of the first person is also known. With the compass heading  5910  known, the angle in which the first person is viewing the surroundings can be estimated. A virtual target line between the location of the first person  5908  and the other person&#39;s location  5902  can be established in three dimensional space and emanating from the HWC  102  proximate the FOV  5914 . The three dimensionally oriented virtual target line can then be used to present environmentally position locked digital content in the FOV  5914 , which is indicative of the other person&#39;s location  5902 . The environmentally position locked digital content  5902  can be positioned within the FOV  5914  such that the first person, who is wearing the HWC  102 , perceives the content  5902  as locked in position within the environment and marking the location of the other person  5902 . 
     The three dimensionally positioned virtual target line can be recalculated periodically (e.g. every millisecond, second, minute, etc.) to reposition the environmentally position locked content  5912  to remain in-line with the virtual target line. This can create the illusion that the content  5912  is staying positioned within the environment at a point that is associated with the other person&#39;s location  5902  independent of the location of the first person  5908  wearing the HWC  102  and independent of the compass heading of the HWC  102 . 
     In embodiments, the environmentally locked digital content  5912  may be positioned with an object  5904  that is between the first person&#39;s location  5908  and the other person&#39;s location  5902 . The virtual target line may intersect the object  5904  before intersecting with the other person&#39;s location  5902 . In embodiments, the environmentally locked digital content  5912  may be associated with the object intersection point  5904 . In embodiments, the intersecting object  5904  may be identified by comparing the two person&#39;s locations  5902  and  5908  with obstructions identified on a map. In embodiments the intersecting object  5904  may be identified by processing images captured from a camera, or other sensor, associated with the HWC  102 . In embodiments, the digital content  5912  has an appearance that is indicative of being at the location of the other person  5902 , at the location of the intersecting object  5904  to provide a more clear indication of the position of the other person&#39;s position  5902  in the FOV  5914 . 
       FIG.  60    illustrates how and where digital content may be positioned within the FOV  6008  based on a virtual target line between the location of the first person  5908 , who&#39;s wearing the HWC  102 , and the other person  5902 . In addition to positioning the content in a position within the FOV  6008  that is in-line with the virtual target line, the digital content may be presented such that it comes into focus by the first person when the first person focuses at a certain plane or distance in the environment. Presented object A  6018  is digitally generated content that is presented as an image at content position A  6012 . The position  6012  is based on the virtual target line. The presented object A  6018  is presented not only along the virtual target line but also at a focal plane B  6014  such that the content at position A  6012  in the FOV  6008  comes into focus by the first person when the first person&#39;s eye  6002  focuses at something in the surrounding environment at the focal plane B  6014  distance. Setting the focal plane of the presented content provides content that does not come into focus until the eye  6002  focuses at the set focal plane. In embodiments, this allows the content at position A to be presented without when the HWC&#39;s compass is indicative of the first person looking in the direction of the other person  5902  but it will only come into focus when the first person focuses on in the direction of the other person  5902  and at the focal plane of the other person  5902 . 
     Presented object B  6020  is aligned with a different virtual target line then presented object A  6018 . Presented object B  6020  is also presented at content position B  6004  at a different focal plane than the content position A  6012 . Presented content B  6020  is presented at a further focal plane, which is indicative that the other person  5902  is physically located at a further distance. If the focal planes are sufficiently different, the content at position A will come into focus at a different time than the content at position B because the two focal planes require different focus from the eye  6002 . 
       FIG.  61    illustrates several BlueForce members at locations with various points of view from the first person&#39;s perspective. In embodiments, the relative positions, distances and obstacles may cause the digital content indicative of the other person&#39;s location to be altered. For example, if the other person can be seen by the first person through the first person&#39;s FOV, the digital content may be locked at the location of the other person and the digital content may be of a type that indicates the other person&#39;s position is being actively marked and tracked. If the other person is in relatively close proximity, but cannot be seen by the first person, the digital content may be locked to an intersecting object or area and the digital content may indicate that the actual location of the other person cannot be seen but the mark is generally tracking the other persons general position. If the other person is not within a pre-determined proximity or is otherwise more significantly obscured from the first person&#39;s view, the digital content may generally indicate a direction or area where the other person is located and the digital content may indicate that the other person&#39;s location is not closely identified or tracked by the digital content, but that the other person is in the general area. 
     Continuing to refer to  FIG.  61   , several BlueForce members are presented at various positions within an area where the first person is located. The primary BlueForce member  6102  (also referred to generally as the first person, or the person wherein the HWC with the FOV for example purposes) can directly see the BlueForce member in the open field  6104 . In embodiments, the digital content provided in the FOV of the primary BlueForce member may be based on a virtual target line and virtually locked in an environment position that is indicative of the open field position of the BlueForce member  6104 . The digital content may also indicate that the location of the open field BlueForce member is marked and is being tracked. The digital content may change forms if the BlueForce member becomes obscured from the vision of the primary BlueForce member or otherwise becomes unavailable for direct viewing. 
     BlueForce member  6108  is obscured from the primary BlueForce member&#39;s  6102  view by an obstacle that is in close proximity to the obscured member  6108 . As depicted, the obscured member  6108  is in a building but close to one of the front walls. In this situation, the digital content provided in the FOV of the primary member  6102  may be indicative of the general position of the obscured member  6108  and the digital content may indicate that, while the other person&#39;s location is fairly well marked, it is obscured so it is not as precise as if the person was in direct view. In addition, the digital content may be virtually positionally locked to some feature on the outside of the building that the obscured member is in. This may make the environmental locking more stable and also provide an indication that the location of the person is somewhat unknown. 
     BlueForce member  6110  is obscured by multiple obstacles. The member  6110  is in a building and there is another building  6112  in between the primary member  6102  and the obscured member  6110 . In this situation, the digital content in the FOV of the primary member will be spatially quite short of the actual obscured member and as such the digital content may need to be presented in a way that indicates that the obscured member  6110  is in a general direction but that the digital marker is not a reliable source of information for the particular location of obscured member  6110 . 
       FIG.  62    illustrates yet another method for positioning digital content within the FOV of a HWC where the digital content is intended to indicate a position of another person. This embodiment is similar to the embodiment described in connection with  FIG.  62    herein. The main additional element in this embodiment is the additional step of verifying the distance between the first person  5908 , the one wearing the HWC with the FOV digital content presentation of location, and the other person at location  5902 . Here, the range finder may be included in the HWC and measure a distance at an angle that is represented by the virtual target line. In the event that the range finder finds an object obstructing the path of the virtual target line, the digital content presentation in the FOV may indicate such (e.g. as described herein elsewhere). In the event that the range finder confirms that there is a person or object at the end of the prescribed distance and angle defined by the virtual target line, the digital content may represent that the proper location has been marked, as described herein elsewhere. 
     Another aspect of the present invention relates to predicting the movement of BlueForce members to maintain proper virtual marking of the BlueForce member locations.  FIG.  63    illustrates a situation where the primary BlueForce member  6302  is tracking the locations of the other BlueForce members through an augmented environment using a HWC  102 , as described herein elsewhere (e.g. as described in connection with the above figures). The primary BlueForce member  6302  may have knowledge of the tactical movement plan  6308 . The tactical movement plan may be maintained locally (e.g. on the HWCs  102  with sharing of the plan between the BlueForce members) or remotely (e.g. on a server and communicated to the HWC&#39;s  102 , or communicated to a subset of HWC&#39;s  102  for HWC  102  sharing). In this case, the tactical plan involves the BlueForce group generally moving in the direction of the arrow  6308 . The tactical plan may influence the presentations of digital content in the FOV of the HWC  102  of the primary BlueForce member. For example, the tactical plan may assist in the prediction of the location of the other BlueForce member and the virtual target line may be adjusted accordingly. In embodiments, the area in the tactical movement plan may be shaded or colored or otherwise marked with digital content in the FOV such that the primary BlueForce member can manage his activities with respect to the tactical plan. For example, he may be made aware that one or more BlueForce members are moving towards the tactical path  6308 . He may also be made aware of movements in the tactical path that do not appear associated with BlueForce members. 
       FIG.  63    also illustrates that internal IMU sensors in the HWCs worn by the BlueForce members may provide guidance on the movement of the members  6304 . This may be helpful in identifying when a GPS location should be updated and hence updating the position of the virtual marker in the FOV. This may also be helpful in assessing the validity of the GPS location. For example, if the GPS location has not updated but there is significant IMU sensor activity, the system may call into question the accuracy of the identified location. The IMU information may also be useful to help track the position of a member in the event the GPS information is unavailable. For example, dead reckoning may be used if the GPS signal is lost and the virtual marker in the FOV may indicate both indicated movements of the team member and indicate that the location identification is not ideal. The current tactical plan  6308  may be updated periodically and the updated plans may further refine what is presented in the FOV of the HWC  102 . 
       FIG.  64    illustrates a BlueForce tracking system in accordance with the principles of the present invention. In embodiments, the BlueForce HWC&#39;s  102  may have directional antenna&#39;s that emit relatively low power directional RF signals such that other BlueForce members within the range of the relatively low power signal can receive and assess its direction and/or distance based on the strength and varying strength of the signals. In embodiments, the tracking of such RF signals can be used to alter the presentation of the virtual markers of persons locations within the FOV of HWC  102 . 
     Another aspect of the present invention relates to monitoring the health of BlueForce members. Each BlueForce member may be automatically monitored for health and stress events. For example, the members may have a watchband as described herein elsewhere or other wearable biometric monitoring device and the device may continually monitor the biometric information and predict health concerns or stress events. As another example, the eye imaging systems described herein elsewhere may be used to monitor pupil dilatations as compared to normal conditions to predict head trauma. Each eye may be imaged to check for differences in pupil dilation for indications of head trauma. As another example, an IMU in the HWC  102  may monitor a person&#39;s walking gate looking for changes in pattern, which may be an indication of head or other trauma. Biometric feedback from a member indicative of a health or stress concern may be uploaded to a server for sharing with other members or the information may be shared with local members, for example. Once shared, the digital content in the FOF that indicates the location of the person having the health or stress event may include an indication of the health event. 
       FIG.  65    illustrates a situation where the primary BlueForce member  6502  is monitoring the location of the BlueForce member  6504  that has had a heath event and caused a health alert to be transmitted from the HWC  102 . As described herein elsewhere, the FOV of the HWC  102  of the primary BlueForce member may include an indication of the location of the BlueForce member with the health concern  6504 . The digital content in the FOV may also include an indication of the health condition in association with the location indication. In embodiments, non-biometric sensors (e.g. IMU, camera, ranger finder, accelerometer, altimeter, etc.) may be used to provide health and/or situational conditions to the BlueForce team or other local or remote persons interested in the information. For example, if one of the BlueForce members is detected as quickly hitting the ground from a standing position an alter may be sent as an indication of a fall, the person is in trouble and had to drop down, was shot, etc. 
     Another aspect of the present invention relates to virtually marking various prior acts and events. For example, as depicted in  FIG.  66   , the techniques described herein elsewhere may be used to construct a virtual prior movement path  6604  of a BlueForce member. The virtual path may be displayed as digital content in the FOV of the primary BlueForce member  6602  using methods described herein elsewhere. As the BlueForce member moved along the path  6604  he may have virtually placed an event marker  6608  such that when another member views the location the mark can be displayed as digital content. For example, the BlueForce member may inspect and clear an area and then use an external user interface or gesture to indicate that the area has been cleared and then the location would be virtually marked and shared with BlueForce members. Then, when someone wants to understand if the location was inspected he can view the location&#39;s information. As indicated herein elsewhere, if the location is visible to the member, the digital content may be displayed in a way that indicates the specific location and if the location is not visible from the person&#39;s perspective, the digital content may be somewhat different in that it may not specifically mark the location. 
     Turning back to optical configurations, another aspect of the present invention relates to an optical configuration that provides digitally displayed content to an eye of a person wearing a head-worn display (e.g. as used in a HWC  102 ) and allows the person to see through the display such that the digital content is perceived by the person as augmenting the see through view of the surrounding environment. The optical configuration may have a variable transmission optical element that is in-line with the person&#39;s see-through view such that the transmission of the see-through view can be increased and decreased. This may be helpful in situations where a person wants or would be better served with a high transmission see-through view and when, in the same HWC  102 , the person wants or would be better served with less see-through transmission. The lower see-through transmission may be used in bright conditions and/or in conditions where higher contrast for the digitally presented content is desirable. The optical system may also have a camera that images the surrounding environment by receiving reflected light from the surrounding environment off of an optical element that is in-line with the person&#39;s see-through view of the surrounding. In embodiments, the camera may further be aligned in a dark light trap such that light reflected and/or transmitted in the direction of the camera that is not captured by the camera is trapped to reduce stray light. 
     In embodiments, a HWC  102  is provided that includes a camera that is coaxially aligned with the direction that the user is looking.  FIG.  67    shows an illustration of an optical system  6715  that includes an absorptive polarizer  6737  and a camera  6739 . The image source  6710  can include light sources, displays and reflective surfaces as well as one or more lenses  6720 . Image light  6750  is provided by the image source  6710  wherein, a portion of the image light  6750  is reflected toward the user&#39;s eye  6730  by a partially reflective combiner  6735 . At the same time, a portion of the image light  6750  may be transmitted by the combiner  6735  such that it is incident onto the absorptive polarizer  6737 . In this embodiment, the image light  6750  is polarized light with the polarization state of the image light  6750  oriented relative to the transmission axis of the absorptive polarizer  6737  such that the incident image light  6750  is absorbed by the absorptive polarizer  6737 . In this way, faceglow produced by escaping image light  6750  is reduced. In embodiments, the absorptive polarizer  6737  includes an antireflection coating to reduce reflections from the surface of the absorptive polarizer  6737 . 
       FIG.  67    further shows a camera  6739  for capturing images of the environment in the direction that the user is looking. The camera  6739  is positioned behind the absorptive polarizer  6737  and below the combiner  6735  so that a portion of light from the environment  6770  is reflected by the combiner  6735  toward the camera  6739 . Light from the environment  6770  can be unpolarized so that a portion of the light from the environment  6770  that is reflected by the combiner  6735  passes through the absorptive polarizer  6737  and it is this light that is captured by the camera  6739 . As a result, the light captured by the camera will have a polarization state that is opposite that of the image light  6750 . In addition, the camera  6739  is aligned relative to the combiner  6735  such that the field of view associated with the camera  6739  is coaxial to the display field of view provided by image light  6750 . At the same time, a portion of scene light  6760  from the environment is transmitted by the combiner  6735  to provide a see-through view of the environment to the user&#39;s eye  6730 . Where the display field of view associated with the image light  6750  is typically coincident to the see-through field of view associated with the scene light  6760  and thereby the see through field of view and the field of view of the camera  6739  are at least partially coaxial. By attaching the camera  6739  to the lower portion of the optical system  6715 , the field of view of the camera  6739  as shown by the light from the environment  6770  moves as the user moves their head so that images captured by the camera  6739  correspond to the area of the environment that the user is looking at. By coaxially aligning the camera field of view with the displayed image and the user&#39;s view of the scene, augmented reality images with improved alignment to objects in the scene can be provided. This is because the captured images from the camera  6739  provide an accurate representation of the user&#39;s perspective view of the scene. As an example, when the user sees an object in the scene as being located in the middle of the see-through view of the HWC, the object will be located in the middle of the image captured by the camera and any augmented reality imagery that is to be associated with the object can be located in the middle of the displayed image. As the user moves their head, the relative position of the object as seen in the see-through view of the scene will change and the position of the augmented reality imagery can be changed within the displayed image in a corresponding manner. When a camera  6739  is provided for each of the user&#39;s eyes, an accurate representation of the 3D view of the scene can be provided as well. This is an important advantage provided by the invention because images captured by a camera located in the frame of the HWC (e.g. between the eyes or at the corners) capture images that are laterally offset from the user&#39;s perspective of the scene and as a result it is difficult to align augmented reality images with objects in the scene as seen from the user&#39;s perspective. 
     In the optical system  6715  shown in  FIG.  67   , the absorptive polarizer  6737  simultaneously functions as a light trap for escaping image light  6750 , a light blocker of the image light  6750  for the camera  6739  and a window for light from the environment  6770  to the camera  6739 . This is possible because the polarization state of the image light  6750  is perpendicular to the transmission axis of the absorptive polarizer  6737  while the light from the environment  6770  is unpolarized so that a portion of the light from the environment  6770  that is the opposite polarization state to the image light is transmitted by the absorptive polarizer  6737 . The combiner  6735  can be any partially reflective surface including a simple partial mirror, a notch mirror and a holographic mirror. The reflectivity of the combiner  6735  can be selected to be greater than 50% (e.g. 55% reflectivity and 45% transmission over the visible wavelength spectral band) whereby a majority of the image light  6750  will be reflected toward the user&#39;s eye  6730  and a majority of light from the environment  6770  will be reflected toward the camera  6739 , this system will provide a brighter displayed image, a brighter captured image with a dimmer see-through view of the environment. Alternatively, the reflectivity of the combiner  6735  can be selected to be less than 50% (e.g. 20% reflectivity and 80% transmission over the visible wavelength spectral band) whereby the majority of the image light  6750  will be transmitted by the combiner  6735  and a majority of light from the environment  6770  will be transmitted to the user&#39;s eye  6730 , this system will provide a brighter see-through view of the environment, while providing a dimmer displayed image and a dimmer captured image. As such, the system can be designed to favor the anticipated use by the user. 
     In embodiments, the combiner  6735  is planar with an optical flatness that is sufficient to enable a sharp displayed image and a sharp captured image, such as a flatness of less than 20 waves of light within the visible wavelengths. However, in embodiments, the combiner  6735  may be curved in which case the displayed image and the captured image will both be distorted and this distortion will have to be digitally corrected by the associated image processing system. In the case of the displayed image, the image is digitally distorted by the image processing system in a direction that is opposite to the distortion that is caused by the curved combiner so the two distortions cancel one another and as a result the user sees an undistorted displayed image. In the case of the captured image, the captured image is digitally distorted after capture to cancel out the distortion caused by the curved combiner so that the image appears to be undistorted after image processing. 
     In embodiments, the combiner  6735  is an adjustable partial mirror in which the reflectivity can be changed by the user or automatically to better function within different environmental conditions or different use cases. The adjustable partial mirror can be an electrically controllable mirror such as for example, the e-Transflector that can be obtained from Kent Optronics (http://www.kentoptronics.com/mirror.html) where the reflectivity can be adjusted based on an applied voltage. The adjustable partial mirror can also be a fast switchable mirror (e.g. a switching time of less than 0.03 seconds) wherein the perceived transparency is derived from the duty cycle of the mirror rapidly switching between a reflecting state and a transmitting state. In embodiments, the images captured by the camera  6739  can be synchronized to occur when the fast switchable mirror is in the reflecting state to provide an increased amount of light to the camera  6739  during image capture. As such, an adjustable partial mirror allows for the transmissivity of the partial mirror to be changed corresponding to the environmental conditions, e.g. the transmissivity can be low when the environment is bright and the transmissivity can be high when the environment is dim. 
     In a further embodiment, the combiner  6735  includes a hot mirror coating on the side facing the camera  6739  wherein visible wavelength light is substantially transmitted while a spectral wavelength band of infrared light is substantially reflected and the camera  6739  captures images that include at least a portion of the infrared wavelength light. In these embodiments, the image light  6750  includes visible wavelength light and a portion of the visible wavelength light is transmitted by the combiner  6735 , where it is then absorbed by the absorptive polarizer  6737 . A portion of the scene light  6760  is comprised of visible wavelength light and this is also transmitted by the combiner  6735 , to provide the user with a see-through view of the environment. The light from the environment  6770  is comprised of visible wavelength light and infrared wavelength light. A portion of the visible wavelength light along with substantially all of the infrared wavelength light within the spectral wavelength band associated with the hot mirror, is reflected by the combiner  6735  toward the camera  6739  thereby passing through the absorptive polarizer  6737 . In embodiments, the camera  6739  is selected to include an image sensor that is sensitive to infrared wavelengths of light and the absorptive polarizer  6737  is selected to substantially transmit infrared wavelengths of light of both polarization states (e.g. ITOS XP44 polarizer which transmits both polarization states of light with wavelengths above 750 nm: see http://www.itos.de/english/polarisatoren/linear/linear.php) so that an increased % of infrared light is captured by the camera  6739 . In these embodiments, the absorptive polarizer  6737  functions as a light trap for the escaping image light  6750  and thereby blocking the image light  6750  that is in the visible wavelengths from the camera  6739  while simultaneously acting as a window for infrared wavelength light from the environment  6770  for the camera  6739 . 
     By coaxially aligning the camera field of view with the displayed image and the user&#39;s view of the scene, augmented reality images with improved alignment to objects in the scene can be provided. This is because the captured images from the camera provide an accurate representation of the user&#39;s perspective view of the scene. In embodiments, the camera that is coaxially aligned with the user&#39;s view captures an image of the scene, the processor then identifies an object in the captured image and identifies a field of view position for the object, which can be compared to the displayed field of view correlated position so digital content is then displayed relative to the position of the object. 
     Another aspect of the present invention relates to an optical assembly that uses a reflective display where the reflective display is illuminated with a front light arranged to direct the illumination at angles around 90 degrees from the active reflective surface of the reflective display. In embodiments, the optical configuration is light weight, small and produces a high quality image in a head-worn see-through display. 
       FIG.  68    provides a cross sectional illustration of the compact optical display assembly for a HWC  102  according to principles of the present invention along with illustrative light rays to show how the light passes through the assembly. The display assembly is comprised of upper optics and lower optics. The upper optics include a reflective image source  6810 , a quarter wave film  6815 , a field lens  6820 , a reflective polarizer  6830  and a polarized light source  6850 . The upper optics convert illumination light  6837  into image light  6835 . The lower optics comprise a beam splitter plate  6870  and a rotationally curved partial mirror  6860 . The lower optics deliver the image light to a user who is wearing the HWC  102 . The compact optical display assembly provides the user with image light  6835  that conveys a displayed image along with scene light  6865  that provides a see-through view of the environment so that user sees the displayed image overlaid onto the view of the environment. 
     In the upper optics, linearly polarized light is provided by the polarized light source  6850 . Where the polarized light source  6850  can include one or more lights such as LEDs, QLEDs, laser diodes, fluorescent lights, etc. The polarized light source  6850  can also include a backlight assembly with light scattering surfaces or diffusers to spread the light uniformly across the output area of the polarized light source. Light control films or light control structures can be included as well to control the distribution of the light (also known as the cone angle) that is provided by the polarized light source  6850 . The light control films can include, for example, diffusers, elliptical diffusers, prism films and lenticular lens arrays. The light control structures can include prism arrays, lenticular lenses, cylindrical lenses, Fresnel lenses, refractive lenses, diffractive lenses or other structures that control the angular distribution of the illumination light  6837 . The output surface of the polarized light source  6850  is a polarizer film to ensure that the illumination light  6837  provided to the upper optics is linearly polarized. 
     The illumination light  6837  provided by the polarized light source  6850  is reflected by a reflective polarizer  6830 . Where the polarizer on the output surface of the polarized light source  6850  and the reflective polarizer  6830  are oriented so that their respective transmission axes are perpendicular to one another. As a result, the majority of the illumination light  6837  provided by the polarized light source  6850  is reflected by the reflective polarizer  6830 . In addition, the reflective polarizer  6830  is angled so that the illumination light  6837  is reflected toward the reflective image source  6810  thereby illuminating the reflective image source  6810  as shown in  FIG.  68   . 
     The illumination light  6837  passes through a field lens  6820  and is then incident onto the reflective image source  6810 . The illumination light  6837  is then reflected by the reflective image source (otherwise referred to as a reflective display herein elsewhere)  6810 . Wherein the reflective image source  6810  can comprise a liquid crystal on silicon (LCOS) display, a ferroelectric liquid crystal on silicon (FLCSO) display, a reflective liquid crystal display, a cholesteric liquid crystal display, a bistable nematic liquid crystal display, or other such reflective display. The display can be a monochrome reflective display that is used with sequential red/green/blue illumination light  6837  or a full color display that is used with white illumination light  6837 . The reflective image source  6810  locally changes the polarization state of the illumination light  6837  in correspondence to the pixel by pixel image content that is displayed by the reflective image source  6810  thereby forming image light  6835 . Wherein if the reflective image source  6810  is a normally white display, the areas of the image light  6835  that correspond to bright areas of the image content end up with a polarization state that is opposite to the polarization state of the illumination light and dark areas of the image light  6835  end up with a polarization state that is the same as the illumination light  6837  (it should be noted that the invention can be used with normally black displays which provide an opposite effect on polarization in the image light). As such, the image light  6835  as initially reflected by the reflective image source  6810  has a mixed polarization state pixel by pixel. The image light  6835  then passes through the field lens  6820  which modifies the distribution of the image light  6835  while preserving the wavefront to match the requirements (such as for example, magnification and focus) of the lower optics. As the image light  6835  passes through the reflective polarizer  6830 , the bright areas of the image light  6835  that have a polarization state that is opposite to the illumination light  6837  are transmitted through the reflective polarizer  6830  and the dark areas of the image light  6835  that have the same polarization state as the illumination light  6837  are reflected back toward the polarized light source  6850 , as a result, the image light  6835  after passing through the reflective polarizer  6830  is linearly polarized with a single polarization state in all the pixels of the image but now with different intensities pixel by pixel. Thus the reflective polarizer  6830  acts first as a reflector for the illumination light  6837  and then second as an analyzer polarizer for the image light  6835 . 
     As such, the optical axis of the illumination light  6837  is coincident with the optical axis of the image light  6835  between the reflective polarizer  6830  and the reflective image source  6810 . The illumination light  6837  and the image light 
       6835  both pass through the field lens  6820 , but in opposite directions. Wherein the field lens acts to expand the illumination light  6837  so it illuminates the entire active area of the reflective image source  6810  and also to expand the image light  6835  so it fills the eyebox  6882  after passing through the rest of the compact optical display system. By overlapping the portion of the compact optical display assembly associated with the illumination light  6837  with the portion of the compact optical display assembly associated with the image light  6835 , the overall size of the compact optical display assembly is reduced. Given that the focal length associated with the field lens  6820  requires some space in the compact optical display assembly, the reflective polarizer  6830  and the polarized light source  6850  are located in space that would otherwise be unused so the overall size of the display assembly is more compact. 
     The reflective polarizer  6830  can be a relatively thin film (e.g. 80 microns) or thin plate (e.g. 0.2 mm) as shown in  FIG.  68   . The reflective polarizer  6830  can be a wiregrid polarizer such as is available from Asahi Kasei under the name WGF, or a multilayer dielectric film polarizer such as is available from 3M under the name DBEF. As previously described, the reflective polarizer  6830  has two functions. First, the reflective polarizer  6830  reflects the illumination light  6837  provided by the polarized light source  6850  and redirects the illumination light  6837  toward the reflective image source  6810 . Second, the reflective polarizer  6830  acts as an analyzer polarizer to the image light  6835  thereby converting the mixed polarization state of the image light  6835  above the reflective polarizer  6830  to linearly polarized light with a single polarization state below the reflective polarizer  6830 . While the illumination light  6837  incident on the reflective polarizer  6830  is incident on a relatively small portion of the reflective polarizer  6830 , the image light  6835  is incident on the majority of the area of the reflective polarizer  6830 . Consequently, the reflective polarizer  6830  extends at least across the entire area of the field lens  6820  and may extend across the entire area between the field lens  6820  and the beam splitter  6870  as shown in  FIG.  68   . In addition, the reflective polarizer  6830  is angled at least in the portion where the illumination light  6837  is incident to redirect the illumination light  6837  toward the reflective image source  6810 . However, since reflective polarizers (such as a wiregrid polarizer) can be relatively insensitive to the incident angle, in a preferred embodiment, the reflective polarizer  6830  is a flat surface angled to redirect the illumination light  6837  toward the reflective image source  6810  wherein the flat surface extends substantially across the entire area between the field lens  6820  and the beam splitter  6870  in one continuously flat surface to make manufacturing easier. The thin film or thin plate of the reflective polarizer  6870  can be retained at the edges to position it at the desired angle and to make the surface flat. 
     The systems and methods described herein with respect to  FIGS.  68  through  71    have a number of advantages. By avoiding grazing angles of the illumination light  6837  and the image light  6835  at all the surfaces in the compact optical display assembly, scattering of light in the assembly is reduced and as a result the contrast of the image presented to the user&#39;s eye  6880  is higher with blacker blacks. In addition, the reflective image source  6810  can include a compensating retarder film  6815  as is known to those skilled in the art, to enable the reflective image source  6810  to provide a higher contrast image with more uniform contrast over the area of the displayed image. Further, by providing an optical display assembly that is largely comprised of air, the weight of the compact optical display assembly is substantially reduced. By using coincident optical axes for the illumination light  6837  and the image light  6835  and overlapping the illumination light  6837  and image light  6835  for a substantial portion of the optical display assembly, the overall size of the compact optical display assembly is reduced. Where the coincident optical axes are provided by passing the illumination light  6837  and the image light  6835  in opposite directions through the field lens  6820 . To maintain a uniform polarization state for the illumination light  6837 , the field lens  6820  is made from a low birefringence material such as glass or a plastic such as OKP4 as available from Osaka Gas Chemicals. By positioning the polarized light source  6850  and the associated illumination light  6837  below the field lens  6820 , and by folding the optical path of both the illumination light  6837  at the reflective polarizer  6830  and the image light  6835  at the beam splitter  6870 , the overall height of the compact optical display assembly is greatly reduced. For example the overall height of the compact optical display assembly can be less than 24 mm as measured from the reflective image source  6810  to the bottom edge of the rotationally curved partial mirror  6860  for a display that provides a 30 degree diagonal field of view with a 6×10 mm eyebox. 
     In a preferred case, the light control structure in the polarized light source  6850  includes a positive lens, such as for example a positive Fresnel lens, a positive diffractive lens or a positive refractive lens. Wherein a positive Fresnel lens or a positive diffractive lens is preferred because they can be very thin. The illumination light  6837  is thereby focused to form a smaller area or pupil at the reflective polarizer  6830  that has a direct relationship to the area of an eyebox  6882  at the other end of the optics wherein image light  6835  is provided to the user&#39;s eye  6880  as shown in  FIG.  68   . Where the positive lens concentrates the illumination light  6837  from the polarized light source  6850  both in terms of intensity and angular distribution to match the etendue of the optical system and thereby fills the eyebox with image light  6835 . By using the positive lens to converge the light from the polarized light source  6850  as provided to the reflective polarizer  6830  and then using the field lens  6820  to expand the illumination light  6837  to illuminate the active area of the reflective image source  6810 , efficiency is improved since illumination light  6837  is substantially delivered only where needed to form image light  6835 . Further, illumination light  6837  outside the pupil can be controlled by the positive lens and clipped by masked edges of the positive lens. By focusing the illumination light  6837  and clipping light outside the pupil, illumination light  6837  is prevented from impinging adjacent surfaces at grazing angles in the compact optical display assembly to reduce scattering of light and thereby increase contrast in the image provided to the user&#39;s eye  6880  by providing blacker blacks. 
     It should be noted that while  FIGS.  68 ,  69  and  70    show optical layouts wherein the illumination light  6837  is provided from behind the rotationally curved partial mirror  6860 , other optical layouts are possible within the invention. The location of the polarized light source  6850  can be changed for example to be at the side of the rotationally curved partial mirror  6860  wherein the reflective polarizer  6830  is oriented to receive the illumination light  6837  from the side. And reflect it toward the reflective image source  6810  (not shown). 
     In a further embodiment, the portion of the image light  6835  that is reflected back toward the polarized light source  6850  is recycled in the polarized light source  6850  to increase the efficiency of the polarized light source  6850 . In this case, a diffuser and a reflective surface is provided behind the polarized light source  6850  so the polarization of the light is scrambled and reflected back toward the reflective polarizer  6830 . 
     In yet another embodiment, another reflective polarizer is provided in the polarized light source  6850  and behind the linear polarizer previously disclosed. Wherein the respective transmission axes of the reflective polarizer and the linear polarizer are parallel to one another. The other reflective polarizer then reflects the light back into the backlight that has the polarization state that would not be transmitted by the linear polarizer. The light that is reflected back into the backlight passes through diffusers associated with the polarized light source  6850  where the polarization state is scrambled and reemitted thereby recycling the light and increasing efficiency. 
     In another embodiment, the system according to the principles of the present invention includes an eye imaging system.  FIG.  69    is an illustration of a compact optical display assembly, which includes an eye imaging camera  6992  that captures an image of the user&#39;s eye  6880  that is coaxial with the displayed image provided to the user so that a full image of the user&#39;s iris can be reliably captured. The eye imaging camera  6992  is reflected into the lower optics by a reflective polarizer  6930  that includes a notch mirror coating, facing the eye imaging camera  6992 , that reflects the wavelengths of light that are captured by the eye imaging camera  6992  (e.g. near infrared wavelengths) while transmitting wavelengths associated with the image light  6835  (e.g. visible wavelengths). Eye light rays  6995  shown in  FIG.  69    illustrate how the field of view associated with the eye imaging camera  6992  is a relatively narrow field of view because it is multiply reflected through the lower optics to capture an image of the user&#39;s eye  6880 . However, to enable the eye imaging camera  6992  to focus onto the user&#39;s eye  6880 , the eye imaging camera  6992  needs to have a very near focus distance (e.g. 35 mm). In addition, the field of view and focus distance of the eye imaging camera must take into account the reducing effect of the optical power provided by the rotationally curved partial mirror  6860 . To increase the efficiency of capturing the light reflected from the user&#39;s eye  6880  and thereby enable a brighter image of the eye, the rotationally curved partial mirror  6860  can be coated with a partial mirror coating that acts as a full mirror in the wavelengths being captured by the eye imaging camera  6992 , for example the coating can reflect 50% of visible light associated with the image light and 90% of near infrared light associated with the eye light  6995 . Where the reflections and associated changes in polarization state are similar to those associated with the image light  6835  but in the opposite order since the eye light rays  6995  are coming from the user&#39;s eye  6880 . LEDs or other miniature lights are provided adjacent to the user&#39;s eye  6880  to illuminate the user&#39;s eye  6880  wherein the wavelengths associated with the LED&#39;s or other miniature lights are different than the wavelengths associated with the image light  6835  such as for example near infrared wavelengths (e.g. 850 nm, 940 nm or 1050 nm). Alternatively, the image light  6835  is used to illuminate the user&#39;s eye  6880  and a reflective polarizer  6930  with a low extinction ratio in reflection (e.g. reflective extinction ratio &lt;15) is used so that some of the eye light rays are reflected toward the eye imaging camera  6992 . 
     In an alternative embodiment, the reflective and partially reflective surfaces can extend laterally to the sides of the areas used for displaying an image to the user. In this case, the eye imaging camera can be located adjacent to the field lens and pointed in a direction to image the user&#39;s eye after reflecting from the beam splitter and the rotationally curved partial mirror as shown in  FIG.  70   . Where  FIG.  70    is an illustration that shows an eye imaging camera  7092  positioned to the side of the field lens  6820  and reflective polarizer  6830 . The eye imaging camera  7092  is pointed such that the field of view captured by the eye imaging camera  7092  includes the user&#39;s eye  6880  as illustrated by the eye light rays  7095 . The quarter wave film  6890  is also extended laterally to change the polarization state of the eye light  7095  in the same way that the polarization state of the image light is changed so that the eye light passes through the beam splitter  6870  and quarter wave  6890 , is partially reflected by the rotationally curved partial mirror  6860  and is then reflected by the beam splitter  6870  and is then captured by the eye imaging camera  7092 . By positioning the eye imaging camera  7092  to the side of the field lens  6820  and reflective polarizer  6830 , the complexity of the optics associated with displaying an image to the user is reduced. In addition, the space available for the eye imaging camera  7092  is increased since interferences with the display optics are reduced. By positioning the eye imaging camera  7092  adjacent to the display optics, the eye image is captured nearly coaxially with the displayed image. 
     In a yet another embodiment, the systems according to the principles of the present invention include a field lens with an internal reflective polarizer and one or more surfaces with optical power.  FIG.  71    is an illustration of the upper optics including a field lens  7121  comprised of upper prism  7122  and lower prism  7123 . The upper prism  7122  and the lower prism  7123  can be molded to shape or grind and polished. A reflective polarizer  7124  is interposed on the flat surface between the upper prism  7122  and the lower prism  7123 . The reflective polarizer  7124  can be a wiregrid polarizer film or a multilayer dielectric polarizer as previously mentioned. The reflective polarizer  7124  can be bonded into place with a transparent UV curable adhesive that has the same refractive index as the upper prism  7122  or the lower prism  7123 . Typically the upper prism  7122  and the lower prism  7123  would have the same refractive index. Wherein upper prism  7122  includes an angled surface for illumination light  6837  to be provided to illuminate the reflective image source  6810 . The illumination light is provided by a light source that includes lights such as LEDs, a backlight  7151 , a diffuser  7152  and a polarizer  7153  as has been previously described. The lower prism  7123  includes a curved surface on the exit surface for controlling the wavefront of the image light  6835  as supplied to the lower optics. The upper prism may also include a curved surface on the upper surface next to the reflective image source  6810  as shown in  FIG.  71    for manipulating the chief ray angles of the light at the surface of the reflective image source  6810 . Illumination light  6837  is polarized by the polarizer  7153  prior to entering the upper prism  7122 . The transmission axes of the polarizer  7153  and the reflective polarizer  7124  are perpendicular to one another so that the illumination light  6837  is reflected by the reflective polarizer  7124  so that the illumination light is redirected toward the reflective image source  6810 . The polarization state of the illumination light  6837  is then changed by the reflective image source  6810  in correspondence with the image content to be displayed as previously described and the resulting image light  6835  then passes through the reflective polarizer  7124  to form the bright and dark areas associated with the image that is displayed to the user&#39;s eye  6880 . 
     In another embodiment, the field lens  7121  of  FIG.  71    comprises a polarizing beam splitter cube including two prisms, upper prism  7122  and lower prism  7123 . In this case, the reflective polarizer  7124  is replaced by a coating that is polarization sensitive so that light of one polarization state (typically S polarized light for example) is reflected and light of the other polarization state is transmitted. The illumination light  6837  is then provided with the polarization state that is reflected by the coating and the image light is provided with the polarization state that is transmitted by the coating. As shown in  FIG.  71   , the beam splitter cube includes one or more curved surfaces in the upper prism  7122  or the lower prism  7123 . The beam splitter cube can also include one or more angled surfaces where the illumination light is supplied. The angled surface can include light control structures such as a microlens array to improve the uniformity of the illumination light  6837 , or a lenticular array to collimate the illumination light  6837 . 
     In yet another embodiment, the curved surface(s) or the angled surface(s) illustrated in  FIG.  71    can be molded onto a rectangularly shaped beam splitter cube by casting a UV curable material (e.g. UV curable acrylic) onto a flat surface of a beam splitter cube, placing a transparent mold with a cavity that has the desired curve onto the flat surface to force the UV curable material into the desired curve and applying UV light to cure the UV curable material. The beam splitter cube can be made of a material that has the same or different refractive index than the UV curable material. 
     In a further embodiment, polarization sensitive reflective coatings such as dielectric partial mirror coatings, can be used in place of reflective polarizers or beam splitters as shown in  FIG.  68   . In this case, the reflective films and plates that comprise the reflective polarizers  6830  and beam splitters  6870  include polarization sensitive coatings that substantially reflect light with one polarization state (e.g. S polarization) while substantially transmitting light with the other polarization state (e.g. P polarization). Since the illumination light source includes a polarizer  7153 , the illumination light  6837  is one polarization state and it is not important that the reflective polarizer  7124  be sensitive to the polarization state in reflection, the polarization state just needs to be maintained and presented uniformly over the surface of the reflective image source  6810 . However, it is important that the reflective polarizer  7124  be highly sensitive to polarization state in transmission (e.g. extinction ratio &gt;200) to be an effective polarizer analyzer and to provide a high contrast image (e.g. contrast ratio &gt;200) to the user&#39;s eye  6880 . 
     In a further embodiment, the field lens  7121  shown in  FIG.  71    can comprise a reflective polarizer  7124  with a curved surface (not shown) instead of a flat surface and wherein the reflective polarizer  7124  is not a film and instead is a polarization sensitive coating, a printed wiregrid polarizer or a molded wiregrid pattern that is then metallized. In this case, the upper prism  7122  and the lower prism  7123  are made as a matched pair with mating curved surfaces that together form the surface of the reflective polarizer. Wherein the polarization sensitive coating, the printed wiregrid or the molded wiregrid pattern are applied to the mating curved surface associated either the upper prism  7122  or the lower prism  7123  and a transparent adhesive is applied to the other mating surface to bond the upper prism  7122  and lower prism  7123  together to form the field lens  7121  with an internal curved reflective polarizer  7121 . 
     Another aspect of the present invention relates to manufacturing and providing an optical element for use in a see-through computer display system. In embodiments, a lightweight low-cost and high optical quality optical element. 
     In a head mounted display, a beam splitter can be used to direct illuminating light from a light source toward a reflective image source such as an LCOS or a DLP. Where it is desirable to have a low weight beam splitter with a flat partially reflective surface to provide good image quality. The flat partially reflective surface is particularly important when an eye camera is provided for eye imaging that utilizes the flat partially reflective surface for directing the field of view of the eye camera toward the user&#39;s eye. 
     Systems and methods provide for a lightweight beam splitter comprised of molded plastic elements and an internal plate element to provide a flat partially reflective surface. Together the pieces form a triplet beam splitter optic including two molded elements and a plate element. By providing the plate element internal to the beam splitter, the matching surfaces of the molded elements do not have to be optically flat, instead the plate element provides the flat surface and an index matching material is used to join the plate element to the molded elements. All three elements can be plastic elements to reduce the weight and cost of the lightweight beam splitter. To provide a more uniform refractive effect, the molded elements and the plate element are preferentially made from plastic materials with similar refractive index and have low birefringence. 
       FIG.  72    shows an illustration of the two molded elements  7210  and  7220 . 
     These molded elements are molded with a relatively uniform thickness to provide uniform flow of the plastic material during molding (either injection molding, compression molding or casting) and thereby enable a low birefringence in the elements as molded. To further reduce birefringence in the molded elements as molded, materials with low viscosity and low stress optic coefficients are preferred including: OKP4 from Osaka Gas Company; Zeonex F52R, K26R or 350R from Zeon Chemical; PanLite SP3810 from Teijin. 
     The molded elements  7210  and  7220  can include flat surfaces and surfaces with optical power, where the surfaces with optical power can include spherical or aspheric curved surfaces, diffractive surfaces or Fresnel surfaces. Flat surfaces, diffractive surfaces or Fresnel surfaces are preferred on the surfaces associated with light that illuminates the image source and flat surfaces, spherical surfaces or aspheric surfaces are preferred on the surfaces associated with image light. Molded element  7210  is shown with a spherical or aspheric surface  7215  and molded element  7220  is shown with a flat surface  7225 , however, any of the surfaces shown can be molded as flat surfaces or surfaces with optical power. 
     After molding the molded elements  7210  and  7220  are machined to provide matching angled surfaces. Molded element  7210  is shown in  FIG.  73    where a milling cutter  7328  is shown machining angled surface  7329 .  FIG.  74    shows an illustration of molded elements  7210  and  7220  after they have been machined to respectively provide beam splitter elements  7430  and  7440  that are prisms. The angled surface of beam splitter elements  7430  and  7440  are machined to have matching angles. Alternatively, beam splitter elements  7430  and  7440  can be machined from sheet material or molded pucks. In either case of using machined angled surfaces or molded angled surface in the beam splitter elements, the surfaces will not be optically flat. 
       FIG.  75    shows an illustration of the assembled triplet beam splitter optic, wherein the beam splitter elements  7430  and  7440  have been assembled with a partially reflecting plate element  7560  to form a beam splitter cube. Wherein the beam splitter elements  7430  and  7440  are made from either the same material or different materials that have a very similar refractive index (e.g. within 0.05 of each other). An index matching material is used at the interfaces between the beam splitter elements and the plate element. The index matching material can be a fluid, a light curing adhesive, a moisture curing adhesive or a thermally curing adhesive. The index matching material should have a refractive index that is very similar to that of the beam splitter elements (e.g. within 0.1). 
     The partially reflective plate element  7560  can be a transparent plate with a partially reflective layer that is either a partially reflective coating or a laminated partially reflective film. The transparent plate is preferably a cast sheet such as cell cast acrylic that has low birefringence, or a molded plaque of a low birefringence material such as OKP4, Zeonex F52R, Zeonex K26R, Zeonex 350R or PanLite SP3810. In addition, the transparent plate should be optically flat (e.g. within 20 microns over the surface and with a surface finish of less than 15 nanometers), however optically flat surfaces are easily obtained in sheet stock. By using an index matching material at the interfaces between the beam splitter elements  7430  and  7440  and the partially reflective plate element  7560 , the lack of optical flatness of the surface of the beam splitter elements  7430  and  7440  can be filled by the index matching material so that the flatness of the reflective surface is determined by the flatness of the more easily obtained partially reflective plate element  7560  thereby providing a manufacturing advantage. The partially reflective layer can be a partial mirror, a reflective polarizer or a wiregrid polarizer where the reflective polarizer can be a coating or a film and the wiregrid polarizer can be a film or a molded structure that is partially coated with a conductive layer. Where a suitable reflective polarizer film can be obtained from 3M available under the trade name of DBEFQ and a wiregrid polarizer film can be obtained from Asahi-Kasei available under the trade name of WGF. In a preferred embodiment, the transparent plate of the partially reflective plate element  7560  has a refractive index that is very similar (e.g. within 0.1) to the refractive indices of the beam splitter elements  7430  and  7440   
       FIG.  76    shows an illustration of an optical system for a head mounted display system. The system includes a reflective display as an image source  7667 , a light source  7665  that can be a white light source or a sequential color light source as appropriate for the image source  7665 . Wherein the light source  7665  provides illumination light  7674  that can be polarized light provided that a quarter wave layer is associated with the image source  7667  or the partially reflecting plate element  7560  so that the polarization of the illumination light  7674  is changed before becoming image light  7672 . The illumination light  7674  is reflected by a surface of the partially reflecting plate element  7560 , and then reflected by the image source  7667 , whereupon it passes through the partially reflective plate element  7560  thereby becoming image light  7672 . The image light  7672  is then reflected by a partially reflective combiner  7682  so that the image light is directed toward the user&#39;s eye  7680  to display an image to the user while simultaneously providing a see-through view of the environment. In the optical system, an index matching material can be used at the interface between the image source  7665  and the beam splitter element  7440  sop that the surface of the beam splitter element  7440  does not have to be flat. It is contemplated by the current inventions that the optical system may include additional lenses and other optical structures that are not shown to improve the image quality or change the form factor of the optical system. 
     In another embodiment, beam splitter elements  7430  and  7440  are molded directly to shape using injection molding or casting. The molded beam splitter elements are then assembled as shown in  FIG.  75    as described previously herein. 
     In further embodiments, surfaces of the beam splitter elements are molded or machined to have additional structures to provide further features.  FIG.  77    shows an illustration of lightweight beam splitter  7750  that includes an extended partially reflective plate element  7760  and an extended beam splitter element  7740 , wherein the partially reflective surface is extended to provide additional area for the illumination light  7674  to be reflected toward the image source  7665 . Where having an extended partially reflective surface is particularly useful when the image source  7665  is a DLP and the illumination light  7665  must be delivered at an oblique angle.  FIG.  78    shows a lightweight beam splitter  7850  that includes an entrance surface  7840  for the illumination light  7674  that is angled so the illumination light  7674  passes substantially perpendicularly through the entrance surface  7840 . 
     In yet further embodiments, beam splitter element elements  7430  and  7440  are machined from a single molded element. Where the single molded element is designed to provide the desired optical surfaces. For example, the molded element  7210  as shown in  FIG.  72    has surfaces that could be used for both surface  7215  and  7225 . A series of molded elements  7210  could then be molded and some would be used to make machined beam splitter elements  7430  and some for beam splitter elements  7440 . A partially reflective plate element  7560  would then be bonded with the beam splitter element  7430  and  7440  using index-matched adhesive as previously described herein. Alternatively, the single molded element  7210  could be designed with extra thickness across the dimension where the partially reflective plate element  7560  will be added, so that a single molded element  7210  could be sawn, machined or laser cut into beam splitter elements  7430  and  7440 . 
     In another embodiment, a first molded optical element is molded in a geometry that enables improved optical characteristics including: low birefringence; more accurate replication of the optical surfaces of the mold (reduced power and irregularity deviation). The first molded optical element is then cut to a different shape wherein the cutting process leaves an optically rough surface finish. A second optical element with an optically smooth surface is then bonded to the optically rough surface of the first molded optical element using an index matched adhesive to provide a combined optical element. The index matched adhesive fills in the optically rough surface on the first molded optical element so that the optically rough surface is no longer visible and an optically smooth surface is provided in the combined optical element by the second optical element. The optical characteristics of the combined optical element are improved as compared to a directly molded optical element that has the geometry of the combined optical element. The cut surface can be flat or curved, as long as the cut surface of the first molded optical element is substantially similar to the bonding surface of the second optical element. In addition, both the first molded optical element and the second optical element can provide optical surface with independent optical features such as optical power, wedge, diffraction, grating, dispersion, filtering and reflection. For example, optically flat surfaces can be difficult to mold on plastic lenses. A lens can be molded to provide a spherically curved surface and another surface that is subsequently milled off to provide a flat surface with a rough surface finish. An optically flat sheet can then be bonded to the milled surface using an index matched adhesive to provide a combined optical element with an optically flat surface. 
     In yet further embodiments, surfaces of the beam splitter elements include molded or machined structures to collimate, converge, diverge, diffuse, partially absorb, redirect or polarize the illumination light  7674  or the image light  7672 . In this way, the number of parts in the lightweight beam splitter is reduced and the cost and manufacturing complexity is reduced. 
     The multi-piece lightweight solid optic has been described in connection with certain embodiments; it should be understood that the multi-piece lightweight solid optic may be used in connection with other optical arrangements (e.g. other see-through head-worn display optical configuration described herein elsewhere). 
     In embodiments, the invention provides methods for aligning images, along with methods and apparatus for controlling light within the optics of the display assembly associated with a HMD to prevent scattering and also to trap excess light to thereby improve the image quality provided to the user. 
       FIG.  79   a    is a schematic illustration of a cross section of a display assembly for a HMD. Wherein, the display assembly includes upper optics  795  and lower optics  797  that operate together to display an image to a user while simultaneously providing a see-through view of the environment. Aspects of the upper optics  795  will be discussed in more detail herein. The lower optics  797  can comprise optical elements to manipulate image light  7940  from the upper optics  795  and thereby present the image light  7940  to the user&#39;s eye  799 . Lower optics  797  can comprise one or more lenses  7950  and a combiner  793 . The combiner  793  presents the image light  7940  to the user&#39;s eye  799  while simultaneously allowing light from the environment  791  to pass through to the user&#39;s eye  799  so that the user sees the displayed image overlaid onto a view of the environment. 
       FIG.  79    is a schematic drawing of a cross section of the upper optics  795  for a HMD. Included are a light source  7910 , a partially reflective layer  7930 , a reflective image source  7935  and a lens  7950 . The light source  7910  provides illumination light  7920  to the HMD. The illumination light  7920  is redirected by the partially reflective layer  7930  to illuminate the reflective image source  7935 . The illumination light  7920  is then reflected by the reflective image source  7935  in correspondence with the image content in the displayed image so that it passes through the partially reflective layer  7930  and thereby forms image light  7940 . The image light  7940  is optically manipulated by the lens  7950  and other optical elements (not shown) in the lower optics  797  so that a displayed image is provided to a user&#39;s eye  799 . Together, the light source  7910 , the partially reflective layer  7930  and the reflective image source  7935  form a frontlighted image source. Where, the reflective image source  7935  can comprise a LCOS, a FLCOS, DLP or other reflective display.  FIGS.  79 ,  80 ,  82  and  83    are shown with the illumination light  7920  provided so that it is incident on the reflective image source  7935  at an oblique angle as is required for a DLP.  FIGS.  84   c ,  84   d   ,  85 ,  86 ,  87 ,  88  and  89  are shown with the illumination light  7920  provided perpendicular to the reflective image source  8535  as is required for an LCOS or FLCOS. The principles of the invention described herein apply to any type of reflective image source where stray reduction is needed. The light source  7910  can include light sources such as LEDs, laser diodes or other light sources (e.g. as described herein) along with various light control elements including: diffusers, prismatic films, lenticular films, Fresnel lenses, refractive lenses and polarizers. Polarizers included in the light source  7910  polarize the light exiting the light source  7910  so that the illumination light  7920  is polarized. The partially reflective layer  7930  can be a partial mirror coating on a substrate or it can be a reflective polarizer film such as a wire grid film supplied by Asahi-Kasei under the name WGF or a multilayer polarizer film supplied by 3M under the name DBEF. When the partially reflective layer  7930  is a reflective polarizer, the illumination light  7920  is supplied as polarized light wherein the polarization axis of the illumination light  7920  is oriented relative to the polarization axis of the reflective polarizer so that the illumination light  7920  is substantially reflected. The reflective image source  7935  then includes a quarter wave retarder (e.g. a quarter wave film) so that the polarization state of the illumination light  7920  is reversed in the process of being reflected by the reflective image source  79345 . This enables the reflected illumination light  7920  to then be substantially transmitted by the reflective polarizer. After passing through the partially reflective layer  7930 , the light becomes image light  7940 . The image light  7940  then passes into a lens  7950  which is part of the lower optics  797  or display optics which manipulates the light to provide a displayed image to the user&#39;s eye. While the partially reflective layer  7930  is illustrated as a flat surface, the inventors have contemplated that the surface may be curved, shaped, have simple or complex angles, etc. and such surface shapes are encompassed by the principles of the present invention. 
     In HMDs that provide images to both eyes of the user, it is desirable to provide the images so that they are aligned to one another. This is particularly important when the images are viewed as stereo images where the perceived alignment of the images seen with each eye is critical to achieving the perception of depth. To provide an accurate alignment of the images, an active alignment of the optics can be performed after the optics have been assembled into a rigid frame of the HMD. Where active alignment includes aligning the images for each eye to one another by moving portions of the display assembly and affixing the portions into position relative to one another. To this end,  FIG.  79    shows space  7952  that extends around the reflective image source  7935  so that the reflective image source  7935  can be moved laterally and rotationally. The light source  7910  and partially reflective layer  7930  are arranged to illuminate the area that includes the reflective image source  7935  and a portion of the adjacent space  7952 . As a result, the reflective image source  7935  can be moved within the space  7952  during the active alignment process without losing illumination or degrading the brightness of the displayed image. Where movements of the reflective image source  7935  during the active alignment can include movements that correspond to horizontal, vertical and rotational movements of the image provided to one eye relative to the image provided to the other eye of the user. The movements can be 0.5 mm in size for example when the reflective image source  7935  is approximately 5×8.5 mm in size (this equates to approximately 10% of the reflective image source dimension) and as such the space  7952  can be 0.5 mm wide or wider. 
     However, by including the space  7952 , in the illuminated area, visible artifacts can occur due to light scattering or reflecting from the edges of the reflective image source  7935  or from structures adjacent to the space  7952 . Consequently, a mask  8055  is provided that extends from the edge of the active area of the reflective image source  7935  across the space  7952  to cover the edges of the reflective image source  7935  and structures adjacent to the space  7952  as shown in  FIG.  80   . The mask  8055  is black and non-reflecting so that incident illumination light  7920  is absorbed. In addition the mask  8055  is designed to not interfere with the movements of the reflective image source  7935  that occur during active alignment. To this end, the mask  8055  can be stiff (e.g. a black plastic or a black coated metal) and designed to slide under the adjacent structures such as the light source  7910 , the edge of the partially reflective layer  7930  and the sides of the housing that contain the frontlight. Alternatively, the mask  8055  can be flexible (e.g. a black plastic film or a black rubber film or tape) so that it deforms when it contacts the adjacent structures.  FIG.  81   a    shows an illustration of the reflective image source  7935 , the light source  7910  and the space  7952  as viewed from above. As is typically found with image source of all kinds, there is a mask  8168  applied to the surface of the image source that surrounds the active area  8165 , however this mask  8168  does not cover the space  7952 .  FIG.  81   b    shows a further illustration of the system shown in  FIG.  81   a    wherein the mask  8055  is applied to the reflective image source  7935  so that it attaches within the mask  8168  in a way that covers the space  7952  and does not block the active area  8165 . 
     In another embodiment, the image produced by the image source does not use all of the active display area of the image source so there is room to shift the image in an x and/or y perspective within the active display area for alignment of the content. For example, if a misalignment is observed (as indicated above) rather than physically moving the image source, or in addition to moving the image source, the image is digitally shifted in the x and/or y direction to create better combined content alignment. The originally inactive display area around the content may be referred to as a content shift buffer zone. 
     In a further embodiment for aligning images in a HMD with see-through, a first image containing features is provided to one eye of the user using a display assembly similar to that shown in  FIG.  79   a    or  FIG.  85   . A second image containing features in the same locations is provided to the other eye of the user. The position of at least one of the image sources is then moved within the space provided for adjustment to align the first image to the second image as seen by the user&#39;s eyes. This image alignment can also be done using cameras in place of the user&#39;s eyes. 
     In the case where the first and second images are smaller in size than the active area of the reflective image source, thereby leaving a digital space adjacent to the images that can be used for digital shifting of the images for further alignment adjustment. This adjustment can be used in combination with physical movements of the reflective image sources to align the first image to the second image. 
       FIG.  82    is an illustration of upper optics  825  that includes the elements of upper optics  795  with the addition of a trim polarizer  8260 . Where the polarization axis of the trim polarizer  8260  is oriented so the image light  7940  is transmitted to the lower optics (not shown). Light that has the opposite polarization state compared to the image light  7940  is absorbed by the trim polarizer  8260 . As such, light that is scattered from surfaces such as the walls of the housing  8262  that typically has a mixed polarization state will be partially absorbed by the trim polarizer  8260 . The trim polarizer  8260  can also absorb a portion of colored light caused by birefringence in the lens  7950  provided the trim polarizer  8260  is located after the lens  7950 . In this case, the trim polarizer  8260  absorbs the light that has the opposite polarization state caused by the birefringence and transmits the light that has the polarization state of the image light  7940  prior to the lens  7950 . In some cases, it is advantageous to change the polarization state of the image light  7940  to improve the reflection of the image light  7940  from the combiner  793  so that a half wave retarder is needed in addition to the trim polarizer  8260 . For proper operation, the half wave retarder is positioned with its fast axis oriented at 45 degrees to the transmission axis of the trim polarizer  8260 . In this case, it is advantageous to position the half wave retarder (not shown) below the trim polarizer  8260  so that the trim polarizer can absorb any elliptical polarization that may be present due to birefringence in the lens  7950  before the image light is acted upon by the half wave retarder. In this way, any variation in retardation with wavelength that may be present in the half wave retarder will not act to increase the elliptical polarization or act to increase color artifacts in the image light  7940  caused by birefringence in the lens  7950 . In an example, the trim polarizer can be a polarizer film that is laminated to a half wave retarder film and antireflection coatings can be applied to the outer surfaces. 
     In  FIG.  83   , the partially reflective layer  8330  is a laminated multiple polarizer film comprised of a reflective polarizer film  8332  laminated to an absorptive polarizer film  8331 . Where, the reflective polarizer film  8332  is only big enough to reflect the illumination light  7920  that illuminates the active area  8165  of the reflective image source  7935 . The absorptive polarizer film  8331  is larger than the reflective polarizer film  8332  and extends across the entire aperture between the reflective image source  7935  and the lens  7950 , so that no edges of the absorptive polarizer film  8331  are visible and all the light reflected from the reflective image source  7935  passes through the absorptive polarizer  8331 . For the case when the reflective image source  7935  is an LCOS, the absorptive polarizer  8331  acts as an analyzer polarizer to only allow the polarization state of the image light to be transmitted. As such, the reflective polarizer film  8332  only covers a portion of the absorptive polarizer film  8331 . The polarization axes of the reflective polarizer film  8332  and the absorptive polarizer film  8331  are aligned so that polarized light that is transmitted by the reflective polarizer film  8332  is also transmitted by the absorptive polarizer film  8331 . In contrast, polarized light that is reflected by the reflective polarizer film  8332  is absorbed by the absorptive polarizer film  8331 . Thereby, illumination light  7920  that is incident onto the reflective polarizer film  8332  is reflected toward the reflective image source  7935  where the polarization state is reversed so that it is transmitted by the reflective polarizer film  8332  and the absorptive polarizer film  8331  as it becomes image light  7940 . At the same time, illumination light  7920  that is incident onto the absorptive polarizer film  8331  in the area surrounding the reflective polarizer film  8332  is absorbed by the absorptive polarizer film  8331 . By absorbing this excess illumination light  7920 , that would not illuminate the active area  8165  of the reflective image source  7935 , stray light is reduced within the display assembly and the contrast in the image presented to the user&#39;s eye is increased as a result. By aligning the polarization axes of the reflective polarizer film  8332  and the absorptive polarizer film  8331 , the transmission is only reduced by approximately 12%, in the regions that include both reflective polarizer film  8332  and absorptive polarizer film  8331  compared to the regions that include just absorptive polarizer film  8331 . Given the location of the partially reflective layer  8330  in the optical system and the fact that it is remote from the reflective image source  7935 , having local differences in transmission on the partially reflective layer  8330  comprised of a laminated multiple polarizer will have a very small effect on the brightness uniformity in the image provided to the user&#39;s eye. In addition, the fact that the partially reflective layer  8330  is remote from the reflective image source  8330  makes the edges of the reflective polarizer film  8332  indistinct as seen by the user. 
       FIGS.  84   a  and  84   b    show illustrations of examples of partially reflective layers  8330 , comprised of a reflective polarizer film  8430  and  8431  laminated to an absorptive polarizer film  8432 . The reflective polarizer films  8430  and  8431  are cut to a shape that covers only the area where illumination light  7920  will be reflected to illuminate the active area  8165  of the reflective image source  7935 . The shape required for the reflective polarizer film will vary depending on the type of frontlight. For the frontlight shown in  FIG.  83    where the partially reflective layer  8330  is located adjacent to the reflective image source  7935 , the shape of the reflective polarizer film  8431  will be rectangular or oval such as shown in  FIG.  84   b   . For the frontlight included in the display assembly shown in  FIG.  85    where the lens  8550  is located between the partially reflective layer  8530  and the reflective image source  8535 , the influence of the illumination light  8520  passing through the lens  8550  changes the distribution of illumination light  8520  needed from the light source  8510 . As a result, the illumination light  8520  can cover only a portion of the partially reflective layer  8530  and the use of a laminated multiple polarizer is advantageous. In embodiments, the reflective polarizer film can cover less than 80% of the area of the absorptive polarizer film in the laminated partially reflective layer. In further embodiments, the reflective polarizer film can cover less than 50% of the area of the absorptive polarizer film in the laminated partially reflective layer. In this case, the partially reflective layer  8530  can include a reflective polarizer film  8430  with a shape similar to that shown in  FIG.  84   a   . In any case, the shape of the reflective polarizer film is selected in concert with the optical elements in the frontlight and display optics associated with the display assembly of the HMD. 
       FIG.  84   c    shows an example illustration of a frontlight for a display assembly similar to that shown in  FIG.  85    wherein a laminated multiple polarizer film  8436  is shown with a complex curved shape that resembles an S with a central flat portion and curved ends. The laminated multiple polarizer  8436  includes a reflective polarizer film  8438  and an absorptive polarizer film  8437 . Illumination light  8520  includes rays  8522  that are incident on the reflective polarizer film  8438  and rays  8521  that are incident on the absorptive polarizer film  8437 . Due to the alignment of the polarization of the illumination light  8520  to the polarization axes of the reflective polarizer film  8438  and the absorptive polarizer film  8437  as previously described herein, rays  8522  are reflected by the reflective polarizer film  8438  and rays  8521  are absorbed by the absorptive polarizer film  8437 . In this way, rays  8521  are prevented from contributing to stray light. It is beneficial to absorb rays  8521  since they cannot contribute to image light  8540  because if they were reflected by the laminated multiple polarizer  8436  they would be incident on the reflective image source  8535  outside of the active area  8165 , and if they were transmitted by the laminated multiple polarizer  8436 , they would be incident on the housing sidewalls  8262 . Consequently, by absorbing rays  8521 , the laminated multiple polarizer  8436  reduces stray light and thereby increases the contrast in the image displayed to the user. 
       FIG.  84   d    shows a further example illustration of a frontlight for a display assembly similar to that shown in  FIG.  79    wherein the partially reflective layer  7930  comprises a laminated multiple polarizer film with a curved surface. The laminated polarizer includes an absorptive polarizer film  8442  with a laminated reflective polarizer film  8441 . The reflective polarizer film  8441  is positioned in the central portion of the absorptive polarizer film  8442  where the illumination light  7920  is reflected toward the reflective image source  7935 . The polarization axes of the reflective polarizer film  8441  and the absorptive polarizer film  8442  are aligned in parallel to each other and perpendicular to the polarization axis of the illumination light  7920  as provided by the polarized light source  7910 . The rays  8421  of the illumination light  7920  that are incident on the partially reflective layer  7930  outside of the reflective polarizer film  8441  are absorbed by the absorptive polarizer film  8442 . The reflective light source  8535  includes a quarter wave layer  8443  so that the polarization axis of the illuminating light  7920  is changed during the process of being reflected from the reflective image source  8535 . As a result, the reflected illumination light  7920  is transmitted by the reflective polarizer film  8441  and the absorptive polarizer film  8442 , thereby becoming image light  7940 . By absorbing the rays  8421 , before they are incident on external surfaces such housing walls or other optical surfaces, stray light is reduced and as a result the contrast in the image provided to the user&#39;s eye is increased. It should be noted that while  FIGS.  84   c  and  84   d    show the reflective polarizer film being positioned to reduce stray light from the left and right sides as shown in the figure, the reflective polarizer can similarly be positioned to reduce stray light in the direction in and out of the paper as shown in the figure.  FIGS.  84   a  and  84   b    show reflective polarizer films  8430  and  8431  positioned in a center portion of the absorptive polarizer  8432  so that stray light can be reduced in all directions. An important aspect of the invention is that this stray light reduction is obtained without a reduction in the brightness of the image provided to the user&#39;s eye since the reflective polarizer films  8430  and  8431  reflect illumination light over the entire area that is needed to fully illuminate the reflective image source. 
       FIG.  85    shows a schematic illustration of a display assembly for a HMD wherein the optical elements of the frontlight are overlapped with the display optics, as the lens  8550  is located between the partially reflective layer  8530  and the reflective image source  8535 . The display assembly is then comprised of upper optics and lower optics. The upper optics include a reflective image source  8535 , a lens  8550 , a partially reflective layer  8530  and a light source  8510 . The upper optics convert illumination light  8520  into image light  8540 . As shown, the lower optics comprise a beam splitter plate  8580 , a quarter wave film  8575  and a rotationally curved partial mirror  8570  (lower optics similar to those shown in  FIG.  79   a    are also possible). The lower optics deliver the image light  8540  to a user&#39;s eye  8582 . As previously stated herein, the display assembly provides the user with image light  8540  that conveys a displayed image along with scene light  8583  that provides a see-through view of the environment so that the user sees the displayed image overlaid onto a view of the environment. 
       FIG.  85    shows a display assembly wherein the partially reflective layer  8530  is a single flat film. However, it can be advantageous to use a segmented partially reflective layer  8630  such as is shown in  FIG.  86   . In this way, the angle of the central portion  8631  of the partially reflective layer  8630  can be selected to position the light source  8610  differently to reduce the clipping of illumination light  8620  by the lens  8550  or other portions of the supporting structure associated with the display assembly and thereby improve brightness uniformity in the displayed image seen by the user&#39;s eye  8582 . To this end, a comparison of  FIG.  85    to  FIG.  86    shows that by changing the angle of the central portion of the partially reflective film, the position of the light source  8610  is moved downward and the clearance of the illumination light  8620  is increased relative to the lens  8550 . 
     Segmented partially reflective layers can be used which a variety of geometries and makeups.  FIG.  86    shows a segmented partially reflective layer  8630  that includes a folded Z shape with three flat sections.  FIG.  87    shows a segmented partially reflective layer that includes an S shape with a central flat section  8731  and ends that are curved similar to that shown in  FIG.  84   c   . The segmented partially reflective layer can comprise a single partially reflective layer such as a reflective polarizer film or a partial mirror film. In addition, illumination light  8620  can be reflected from just the central flat section or it can be reflected from the central flat section plus one or more of the other segments of the segmented partially reflective layer. Alternatively, the partially reflective layer  8630  can comprise a multiple polarizer film to selectively provide a partially reflective layer over just the portions of the partially reflective layer that are actually needed to reflect illumination light to uniformly illuminate the reflective image source  7935  as previously described herein.  FIG.  88    shows a display assembly wherein the partially reflective layer  8830  is comprised of a laminated multiple polarizer film with a central portion  8831  that includes a reflective polarizer film and the remainder of which is an absorptive polarizer as previously described herein. Where the segmented shape of the partially reflective layer  8830  is similar to that shown in  FIG.  86   .  FIG.  89    shows a display assembly wherein the partially reflective layer  8930  is comprised of a laminated multiple polarizer film with a central portion  8931  that includes a reflective polarizer film and the remainder of which is an absorptive polarizer as previously described herein. Where the segmented shape of the partially reflective layer  8930  is similar to that shown in  FIG.  87   . While  FIGS.  88  and  89    show the reflective polarizer film as just occupying the flat central segment of the segmented partially reflective layers  8830  and  8930  respectively, the reflective polarizer can extend into the adjacent segments as needed to reflect the illumination light  8620  in the pattern needed to uniformly illuminate the reflective image source  8535 . Alternatively the segments associated with the segmented partially reflective layers  8830  and  8930  can have three dimensional shapes when the reflective polarizer portion is shaped like that shown in  FIG.  84   a    to keep the reflective polarizer  8430  portion flat. 
     In a further embodiment, the reflective polarizer film is laminated to a flexible transparent carrier film to increase the flexibility and the absorptive polarizer film is a separate layer.  FIG.  90    shows a partially reflective layer  9030  comprised of a reflective polarizer film  8441  laminated to a flexible transparent carrier film  9043 . Where the flexible transparent carrier film  9043  does not reflect the illumination light  7920  or change polarization state of the illumination light  7920  and as a result rays  8421  pass through the flexible transparent carrier film  9043 . The purpose of the flexible transparent carrier film is to support the reflective polarizer film  8441  while allowing the partially reflective layer  9030  to be substantially as flexible as the reflective polarizer film  8441  alone. Absorptive polarizer film  9042  is then provided as a separate layer positioned adjacent to the partially reflective layer  9030 . While the absorptive polarizer film  9042  can be flat or curved as needed to fit within the available space, in a preferred embodiment, the absorptive polarizer film  9042  is curved to be better positioned to absorb rays  8421  that are incident on the partially reflective layer  9030  outside of the reflective polarizer film  8441  as shown in  FIG.  90   . 
     In yet another embodiment, the reflective polarizer film is modified to make the portions transparent and non-reflective where illumination light is incident that is not needed to illuminate the active area of the reflective image source and a separate absorptive polarizer is provided to absorb light that is transmitted through the non-reflective portions.  FIG.  91    is an illustration of a partially reflective layer  9130  comprised of a reflective polarizer film wherein portions  9143  are modified to be transparent and non-reflective while the portion  9141  is a reflective polarizer. As such, polarized illumination light  7920  is reflected by the reflective polarizer portion  9141  and is transmitted by the modified portions  9143 . An absorptive polarizer  9042  is provided as a separate layer adjacent to the partially reflective layer  9130  so that rays  8421  of the illumination light  7920  are transmitted by the modified portions  9143  and absorbed by absorptive polarizer. Wherein the transmission axis of the reflective polarizer portion  9141  is parallel aligned to the transmission axis of the absorptive polarizer  9042 . The modification of the reflective polarizer film can be accomplished by etching the reflective polarizer film, when the reflective polarizer film is a wiregrid polarizer, and thereby removing the metal wires of the wiregrid in the modified portions. Alternatively the wiregrid polarizer can be masked during the metal deposition step to provide shaped portions of wire grid polarizer during manufacturing. An advantage provided by modifying the reflective polarizer film is that the flexibility of the partially reflective layer  9130  is substantially unchanged by the modification and as a result the partially reflective layer  9130  remains uniformly flexible in both the modified portions  9143  and the reflective polarizer portion  9141 . Another advantage provided by using a modified reflective polarizer film is that the transition from the modified portion  9143  to the reflective polarizer portion  9141  does not include a sharp edge that can cause visible artifacts in the image provided to the user&#39;s eye due to scattering by the edge or a change in optical density from a thickness change. This embodiment can also be applied to other types of display assemblies such as for example that shown in  FIG.  85   . 
     In a yet further embodiment, the partially reflective layer comprises a reflective polarizer film laminated to an absorptive polarizer and the partially reflective layer includes a flat portion and a curved portion.  FIG.  92    is an illustration of a frontlight for a display assembly similar to that shown in  FIG.  79   a    with the addition of a laminated partially reflective layer  9230  that has a portion that is a reflective polarizer laminated to an absorptive polarizer  9230 . Where the partially reflective layer  9230  is segmented with a flat segment and a curved segment. By including a flat segment in the portion of the partially reflective layer  9230  that is a reflective polarizer  9241 , the uniformity of illumination light  7920  that is reflected onto the reflective image source  7935  is improved because a larger portion of the light source  7910  is mapped to the image as can be seen in  FIG.  92   . Wherein when using a small scale light source and associated light control films such as diffusers, it is important to map a large portion of the light source area to avoid darker or brighter lines across the image produced by a dark or bright spot on the light source. Including a flat segment in the partially reflective layer  9230  also reduces local distortions in the image provided to the user&#39;s eye that are caused by local changes in optical path length or localized refraction due to changes in the surface angles that the light is exposed to. This embodiment can also be applied to other types of display assemblies such as for example that shown in  FIG.  85   . 
     In head mounted displays that provide a displayed image overlaid onto a see-through view of the environment, it is advantageous to have high see-through transmission both so the user can better interact with the environment and so that people in the environment can see the user&#39;s eyes so they feel more engaged with the user. It is also advantageous to have a thin optics module with low height to make the head mounted display more compact and thereby more attractive. 
       FIG.  93    shows an illustration of an optics module that provides the user with a displayed image while simultaneously providing high see-thru transmission. In this way, the user is provided with a displayed image overlaid onto a clear view of the environment. The optics module includes a combiner  9320  that can have a partial mirror coating that transmits a majority (greater than 50% transmission of visible light) of the available light from the environment, with transmission higher than 70% preferred. For example, the combiner  9320  can have a broadband partial mirror that reflects less than 30% and transmits over 70% of the entire visible wavelength band. Alternatively, the combiner  9320  can have a notch mirror coating where the reflectivity band of the notch mirror coating is matched to the wavelength bands provided by the light source  9340 , where the light source  9340  can include one or more LEDs, QLEDs, diode lasers or other light source, each with narrow wavelength bands (e.g. 50 nm wide bands or less, full width half max). The notch mirror coating can provide for example, greater than 20% reflectivity (e.g. 50% reflectivity) in the wavelengths bands provided by the light source  9340  while providing greater than 80% transmission in the remaining wavelength bands in the visible. For full color images to be provided by the optics module, at least three LEDs with complimentary colors are required such as red, green and blue light or, cyan, magenta and yellow light. In a preferred embodiment, the combiner  9320  has a tristimulus notch mirror that reflects over 50% of the light within the wavelength bands provided by the light source  9340  and transmits an average of over 80% across the entire visible wavelength band. In this way, the tristimulus notch mirror coating provides improved efficiency compared to the partial mirror coating previously described. In an example, if the combiner is to provide 75% transmission of visible light from the environment  9362 , the partial mirror coating will reflect only 25% of image light  9360  so that 75% of the image light will be transmitted through the combiner and will not contribute to the brightness of the image provided to the user&#39;s eye  9310 . In contrast, a tristimulus notch mirror coating can be used to reflect over 50% of the image light  9360  over the wavelengths of light provided by the LEDs in the light source  9340  while transmitting over 90% of the remaining wavelengths of visible light that are not provided by the LEDs so that the average transmission over the entire range of visible light is over 75%. Consequently, the tristimulus notch mirror is twice as efficient as the partial mirror in terms of the ability to reflect image light  9360  toward the user&#39;s eye  9310 . 
     To enable the optics module to operate with a combiner  9320  as shown in  FIG.  93   , image light  9360  is provided to a lens  9330  which focuses the image light  9360  at the user&#39;s eye  9310 . Wherein lens  9330  is shown as a single lens element for simplicity, but multiple lens elements are also possible. The image light  9360  is provided from illumination light  9364  that comes from the light source  9340 . Where, the illumination light  9364  is reflected by a beam splitter  9352  toward a reflective image source  9350 . The image source  9350  can be a liquid crystal on silicon display (LCOS), a ferroelectric liquid crystal display (FLCOS) or other such reflective display. A polarizer  9342  can be associated with the light source  9340  to provide polarized illumination light  9364 . The beam splitter  9352  can then be a reflective polarizer that is oriented to substantially reflect the polarized illumination light  9364 . The image source  9350  changes the polarization state of the illumination light  9364  when the light is reflected by the image source  9350  to form image light  9360  that has a polarization state that is opposite to that of the illumination light  9364 . By changing the polarization state of the illumination light  9364  to the polarization state of the image light  9360 , the image light  9360  can then be transmitted by the reflective polarizer of the beam splitter  9352 . It is important to note that the image light  9360  is polarized to enable a folded illumination system and not because polarized light is required by the combiner  9320 . In fact, to provide a transmission of light from the environment  9362  that is greater than 50%, the combiner  9320  cannot include a polarizer. 
       FIG.  94    is an illustration of an optics module than includes multiply folded optics to reduce the overall height of the optics module. In this case, illumination light  9464  is transmitted by the beam splitter  9452  so that it passes directly toward the image source  9450  wherein the beam splitter  9452  is a reflective polarizer and the light source  9340  includes a polarizer  9342  that is oriented so the transmission axis of the polarizer  9342  is parallel to the transmission axis of the beam splitter  9452 . The illumination light  9464  is then reflected and changed in polarization state by the image source  9450  so that the image light  9360  with its changed polarization state is reflected by beam splitter  9452  toward the lens  9330 . As can be seen by comparing  FIG.  93    to  FIG.  94   , the overall height of the optics module shown in  FIG.  94    is substantially reduced. 
     However, the orientation of the additional fold in the optical path of the image light  9360  in the optics module of  FIG.  94    increases the thickness of the optics module, where thickness is defined as the distance from the closest back surface of the optics module that is nearest to the user&#39;s eye to the farthest front surface of the optics module that is farthest from the user&#39;s eye.  FIGS.  95  and  96    show illustrations of an optical module where the added fold in the optical path of the image light  9360  is oriented perpendicular to the fold shown in  FIG.  94   . In this case, the optics module in  FIGS.  95  and  96    is wider but thinner than that shown in  FIG.  94   .  FIG.  95    shows the optics module from the side and  FIG.  96    shows the optics module from the position of the user&#39;s eye  9310 . As such, in the multiply folded optics shown in  FIGS.  95  and  96   , optical axis  935  associated with the illumination light  9464  is perpendicular to both the optical axis  934  associated with the image light  9360  as it passes through the lens  9330  and the optical axis  933  associated with the image light  9360  as it proceeds toward the user&#39;s eye  9310  in the eyebox. In the case of a head mounted display, it can be very important to have a thin optics module because a thick optics module can cause the head mounted display to stick outward from the user&#39;s forehead, which can be uncomfortable and unattractive. Thus, the multiply folded optics module shown in  FIGS.  95  and  96    are shorter and thinner than the optic module shown in  FIG.  93   . The optics module shown in  FIGS.  95  and  96    is wider than the optics module shown in  FIG.  93   , but in a glasses configuration of the head mounted display, wider optics modules can be better fit into the glasses frames than taller or thicker optics modules. 
     A further advantage that is provided by an optics module that includes multiply folded optics is that twists can be introduced at the fold surfaces to modify the orientation of different portions of the optics module relative to each other. This can be important when the optics module needs to fit into a thin curved glasses frame, a visor or a helmet where the increased width associated with the upper portion of the multiply folded optics module can make it more difficult to fit into structures that are not parallel to the combiner. In this case, the upper portion including for example (based on  FIG.  96   ), the light source  9340 , the polarizer  9342 , the beam splitter  9452  and the image source  9450 , can be twisted relative to the lower portion including the lens  9330  and the combiner  9320 . Where to avoid distortion of the image due to the compound angles between the fold surfaces, a twist of the upper portion about the axis  934  must be combined with a corresponding twist of the lower portion about the axis  933 . In this way, the effects of the increased width of the upper portion of the multiply folded optics can be reduced when fitting the optics module into a curved structure such as glasses frames, a visor frame or a helmet structure. 
       FIG.  99    shows a further embodiment wherein the lens  9930  includes a diffractive surface  9931  to enable a more compact and shorter optical design with reduced chromatic aberration. Where the diffractive surface  9931  can be comprised of a series of small annular sections of a refractive lens curve such as for example in a Fresnel lens. The diffractive surface  9931  can be flat as shown in  FIG.  99    or it can have a base curve to provide additional optical power. The diffractive surface  9931  can be a single order diffractive or a multiple order diffractive. To reduce scattering of wide angle illumination light  9964  that could be incident on the diffractive surface  9931 , an absorptive polarizer  9932  is provided and is oriented with its transmission axis perpendicular to the transmission axis of the reflective polarizer of the beam splitter  9452 . In this way, illumination light  9964  that is transmitted by the beam splitter  9452  in the direction that would cause it to be incident on the diffractive surface  9931  is absorbed by the absorptive polarizer  9932  before it can be scattered by the diffractive surface  9931 . At the same time, image light  9360  has a polarization state that is opposite to that of the illumination light  9964  so that it is reflected by the beam splitter  9452  and transmitted by the absorptive polarizer  9932  as it passes into the lens  9930 . 
       FIG.  100    shows an illustration of an optics module that includes a reduced angle between the beam splitter  9452  and the lens  9930  to reduce the overall height of the optics module. The fold angle of the image light  9360  (the deflection angle between 934 and 1005) is then more than 90 degrees and as a result, the upper edge of the beam splitter is closer to the lens  9330  thereby providing a reduced overall height of the optics module. 
       FIG.  100    also shows a compact planar light source  10040  comprised of a thin edge-lit backlight similar to what is provided in displays used in displays for mobile devices like cellphones. The compact planar light source  10040  is positioned directly behind the beam splitter  9452  to reduce the overall size of the optics module. The compact planar light source can include a light guide film or light guide plate with an edge lit light such as one or more LEDs and a reflector on the side opposite the beam splitter  9452 . The compact planar light source can include a polarizer so the illumination light  10064  is polarized as previously described herein. To direct the illumination light  10064  toward the image source  9450  for improved efficiency, a turning film  10043  is positioned between the compact planar light source  10040  and the beam splitter  9452 . A 20 degree prismatic turning film can be obtained for example, from Luminit 103C (Torrance, Calif.) under the name DTF. To obtain greater degrees of turning, such as 40 degrees, multiple layers of turning film  10043  can be stacked together provided they are oriented such that the turning effect is additive. A diffuser layer (not shown) can be used in addition to the turning film  10043  to reduce artifacts such as linear shadows that can be associated with prismatic structures that are typically associated with turning films  10043 .  FIG.  101    shows an illustration of an optics module as seen from the position of the user&#39;s eye, which is similar to that shown in  FIG.  100    but with a perpendicular orientation of the added fold in the image light  10164  to reduce the thickness of the optics module as previously described herein. As in the optics module shown in  FIGS.  95  and  96   , the multiply folded optics shown in  FIG.  101    have an optical axis  1005  associated with the illumination light  10164  that is perpendicular to both the optical axis  934  associated with the image light  9360  as it passes through the lens  9330  and the optical axis  933  associated with the image light  9360  as it proceeds toward the user&#39;s eye  9310  in the eyebox. As a result, the optics module of  FIG.  101    is thinner and shorter than the optics module of  FIG.  93   .  FIG.  101    also includes a field lens  10130  to improve the optical performance of the optics module. The addition of this second lens element is possible because of the change in fold orientation so that the field lens  10130  does not increase the thickness of the optics module, instead the added length of the optical path from the field lens  10130  occurs in the width of the optics module where space is more readily available in the head mounted display. 
       FIG.  102    shows an illustration of an optics module similar to that shown in  FIG.  99    but with a different orientation of the upper portion of the optics module relative to the combiner so that the combiner  10220  can be more vertical. This rearrangement of the elements within the optics module can be important to achieve a good fit of the head mounted display onto the user&#39;s face. By making the combiner  10220  more vertical, the optics module can be made to have less interference with the user&#39;s cheekbones. 
       FIGS.  103 ,  103     a  and  103   b  show illustrations of optics modules as seen from the position of the user&#39;s eye, that include multiply folded optics and digital light projector (DLP) image sources  10350 . In this case, the illumination light  10364  is provided at an oblique angle to the image source  10350  as required by the micromirrors in the DLP, to reflect image light  9360  along the optical axis  934  of the lens  9930 . Where, in the case of a DLP image source  10350 , image light  9360  is comprised of on-state light reflected by on-state micromirrors in the DLP image source  10350  along optical axis  934 , in correspondence to the brightness of pixels in the image to be displayed to the user&#39;s eye  9310  in the eyebox. The micromirrors in the DLP image source  10350  also reflect off-state light  10371  to the side of the optics module in correspondence to the dark image content and as a result, a light trap  10372  is provided in the optics module to absorb light  10371 . The light trap  10372  can be a black absorptive surface or a textured black surface. The purpose of the light trap  10372  is to absorb incident light  10371  and thereby reduce stray light and subsequently improve the contrast of the image displayed to the user&#39;s eye  9310 . As previously described in other embodiments herein, the light source  10340  is provided to the side of the optics module with a multiply folded optical path to reduce the overall thickness and height of the optics module.  FIG.  103    provides the DLP image source  10350  at the top of the optics module so that the image light  9360  proceeds straight along the optical axis  934 , through the lens  9930  and down to the combiner  9320  where the image light is reflected toward the user&#39;s eye  9310  located in the eyebox. A polarizer  10341  is provided with the light source  10340  so that polarized illumination light  10364  is reflected by the beam splitter  9452  to illuminate the DLP image source  10350 . Where, the beam splitter  9452  in this case, is a reflective polarizer that is aligned with the polarizer  10341  so that the polarized illumination light  10364  is reflected by the beam splitter  9452  and image light  9360  is transmitted by the beam splitter  9452 . A quarter wave film  10351  is located adjacent to the surface of the DLP image source  10350  so that the polarization state of the image light  9360  is opposite to that of the illumination light  10364  after being reflected by the DLP image source  10350 . The light source  10340  and the reflective polarizer  9452  are angularly arranged so that the illumination light  10364  is incident onto the DLP image source  10350  at the oblique angle required so that the image light  9360  when reflected by the on-state pixels in the DLP image source  10350  proceeds along the optical axis  934  of the lens  9930 . A field lens (similar to  10130  as shown in  FIG.  101   ) or other lens elements may be included in the optics of  FIG.  103    but is not shown, in which case, the illumination light  10364  and the image light  9360  may pass thru the field lens or other lens elements in opposite directions. 
       FIG.  103   a    is an illustration of another optics module with a multiply folded optical path that includes a DLP image source  10350  and is shown from the position of the user&#39;s eye. The light source  10340  is again provided to the side of the optics module to reduce the thickness of the optics module. In this case, the light source  10340  is provided on the same side of the lens  9930  and combiner  9320 , as the DLP image source  10350 . Lens  9930  can optionally include one or more diffractive surfaces  9931 . The light source  10340  directly illuminates the DLP image source  10350  where the illumination light  10364  is incident on the DLP image source  10350  at an oblique angle so that the image light  9360 , after being reflected by the on-state micromirrors in the DLP image source  10350 , proceeds along the folded optical axis  934 . At least one light trap  10372  is also provided to absorb light  10371  that is reflected from off-state micromirrors in the DLP and thereby improve the contrast of the displayed image as seen by the user. A field lens  10332  is provided between the DLP image source  10350  and the fold mirror  10352 . The illumination light L 64  in this case can be unpolarized light whereupon the fold mirror  10352  can be comprised of a full mirror coating (e.g. a coating that reflects the entire visible light spectrum) on a substrate. The field lens  10332  can be a single lens element as shown in  FIG.  103   a    or it can include multiple lens elements as needed. The field lens  10332  is designed to provide a large air gap between the field lens  10352  and the DLP image source  10350 , so that the illumination light  10364  can be introduced to the optics module to directly illuminate the active area associated with the DLP image source  10350 . By using unpolarized illumination light  10364 , the optics module shown in  FIG.  103   a    has improved efficiency over the optics module with DLP image sources  10350  shown in  FIGS.  103  and  103     b.    
       FIG.  103   b    is an illustration of another optics module with multiply folded optical path that includes a DLP image source  10350  and is shown from the position of the user&#39;s eye  9310  in the eyebox. As in the optics modules shown in  FIGS.  103  and  103     a , the optics module of  FIG.  103   b    has the light source  10340  positioned at the side of the optics module to reduce the height and thickness of the optics module. The DLP image source  10350  is positioned opposite the light source  10340  however in this embodiment they do not share an optical axis. The illumination light  10364  passes through the beam splitter  10352 , which in this case can be a first reflective polarizer. A second reflective polarizer  10332  is positioned adjacent to the lens  9930  so that the illumination light  10364  is reflected toward the DLP image source  10350 . To reflect the illumination light  10364 , the first reflective polarizer (beam splitter  10352 ) and the second reflective polarizer  10332  are oriented with perpendicular transmission axes. A quarter wave film  10351  (or quarter wave coating on the DLP cover glass) is provided adjacent to the DLP image source  10350  so that the polarization state of the illumination light  10364  is changed upon reflection from the DLP image source  10350  as it becomes image light  9360 . As a result, the polarization of the illumination light  10364  is opposite to that of the image light  9360 . Consequently, the illumination light  10364  is transmitted by the beam splitter  10352  and reflected by the second reflective polarizer  10332 , while the image light  9360  is reflected by the beam splitter  10352  and transmitted by the second reflective polarizer  10332 . The light source  10340  is oriented relative to the second reflective polarizer  10332  so that it is reflected at an oblique angle relative to the DLP image source  10350  as required to provide image light  9360  reflected from on-state micromirrors in the DLP image source  10350  along the folded optical axis  934 . The second reflective polarizer  10332  can be extended beyond the lens  9930  to provide the required oblique angle to fully illuminate the DLP image source  10350  as shown in  FIG.  103   b   . Because the light source  10340  is located behind the beam splitter  10352 , which is a reflective polarizer, the light source  10340  does not affect the image light  9360  and as a result, the light source  10340  can be a different size and orientation than the beam splitter  10352 . One or more light traps  10372  are provided to absorb light  10371  that is reflected from off-state micromirrors in the DLP image source  10350  and thereby improve the contrast of the displayed image. In this case, the light trap  10372  can be positioned under the second reflective polarizer  10332  because the polarization state of the light  10371  is such that it is reflected by the beam splitter  10352  and transmitted by the second reflective polarizer  10332 . The combined orientation of the light source  10340 , the beam splitter  10352  and the DLP image source  10350  provides an optics module that is relatively thin and relatively short compared to optics modules where the image source or the light source are positioned above the fold mirror or beam splitter (e.g. such as the optics module shown in  FIG.  103   ). 
       FIGS.  97  and  98    show illustrations of optics modules similar to those shown in  FIG.  94    but with the addition of an eye imaging camera  979  for capturing images of the user&#39;s eye  9310  during use. In these cases, the light source  9340  and image source  9450  are positioned opposite one another so that the eye imaging camera  979  can be positioned directly above the lens  9340  so that the optical axis  934  is shared between the optics module and the eye imaging camera  979 . By sharing a common optical axis, the eye imaging camera  979  can capture an image of the user&#39;s eye  9310  that has a perspective from directly in front of the user&#39;s eye  9310 . Image light  9360  can then be used to illuminate the user&#39;s eye  9310  during image capture. A portion of the light reflected from the user&#39;s eye  9310 , which can be unpolarized, passes through the beam splitter  9452  before being captured by the eye imaging camera  979 . Because the eye imaging camera  979  is located above the beam splitter  9452 , if the beam splitter  9452  is a reflective polarizer, the polarization state of the image light  9360  will be opposite to that of the light  978  captured by the eye imaging camera  979 . The eye imaging camera  979  can be used to capture still images or video. Where video images can be used to track movements of the user&#39;s eye when looking at displayed images or when looking at a see-through view of the environment. Still images can be used to capture images of the user&#39;s eye  9310  for the purpose of identifying the user based on patterns on the iris. Given the small size of available camera modules, an eye imaging camera  979  can be added to the optics module with little impact on the overall size of the optics module. Additional lighting can be provided adjacent to the combiner  9320  to illuminate the user&#39;s eye. The additional lighting can be infrared, so the user can simultaneously view images displayed with visible light. If the additional lighting is infrared, the eye camera  979  must be capable of capturing images at matching infrared wavelengths. By capturing images of the user&#39;s eye from the perspective of directly in front of the user&#39;s eye, undistorted images of the user&#39;s eye can be obtained over a wide range of eye movement. 
     In an alternative embodiment for the optics module shown in  FIG.  103   a   , the light source  10340  provides polarized illumination light  10364  and the fold mirror  10352  is a reflective polarizer plate so that an eye camera (not shown) can be positioned above the fold mirror  10352  and along the optical axis  934  for capturing images of the user&#39;s eye  9310  similar to that shown in  FIGS.  97  and  98   . The eye camera and the optics module then share a common optical axis  934  so that images of the user&#39;s eye  9310  are captured from directly in front of the eye. In this arrangement, the polarization state of the image light  9360  is opposite to that of the light captured by the eye camera because the image light  9360  is reflected by the fold mirror  10352  and the light captured by the eye camera is transmitted by the fold mirror  10352 . 
       FIG.  104    shows an illustration of the optics module of  FIG.  95    with the additional element of a controllable light blocking element to improve contrast in portions of the displayed image and also to improve the appearance of opacity in displayed objects such as augmented reality objects. Where the controllable light blocking element can operate by absorbing the incident light or scattering the incident light as provided, for example, by an electrochromic element, a polymer stabilized liquid crystal or a ferroelectric liquid crystal. Examples of suitable light blocking elements includes: 3G Switchable Film from Scienstry (Richardson, Tex.); Switchable Mirror or Switchable Glass from Kent Optronics (Hopewell Junction, N.Y.). The controllable light blocking element  10420  is shown in  FIG.  104    as being attached to the lower surface of the combiner  9320  so that it doesn&#39;t interfere with the displayed image while blocking see-thru light from the environment  9362 . Provided the combiner  9320  is flat, the addition of controllable light blocking elements  10420  adjacent to the combiner  9320  is easily done either by attaching directly to the combiner or attaching to the sidewalls of the optics module housing. The controllable light blocking element  10420  can have a single area that can be used to block a selectable portion of the see-through light from the environment over the entire combiner  9320  area thereby enabling a selectable optical density. Alternatively the controllable light blocking element  10420  can provide an array of areas  10520 , as shown in  FIG.  105   , that can be separately selectably controlled to block portions of the combiner  9320  area that correspond to areas in the displayed image where high contrast areas of the image are located.  FIG.  105    shows an illustration of an array of separately controllable light blocking elements  10520 .  FIGS.  106   a ,  106   b  and  106   c    are illustrations of how the array of separately controllable light blocking elements  10520  can be used.  FIG.  106   a    shows how the array of separately controllable light blocking elements  10520  can be put into blocking modes in areas  10622  and non-blocking modes in areas  10623 . Where the blocking mode areas  10622  correspond to areas where information or objects are to be displayed such as is shown in the corresponding areas in the illustration of  FIG.  106   b   .  FIG.  106   c    shows what the user sees when the image of  FIG.  106   b    is displayed with the array of controllable light blocking elements  10520  used in light blocking modes  10622  and non-blocking modes  10623 . The user then sees the displayed information or objects overlaid onto a see-through view of the environment, but in the areas where information of objects are displayed, the see-through view is blocked to improve the contrast of the displayed information or object and provide a sense of solidness to the displayed information or objects. 
     In addition,  FIG.  104    shows a rear optical element  10490  that can be a protective plate or a corrective optic. The protective plate can be connected to sidewalls and other structural elements to stiffen the positioning of the combiner  9320  and to prevent dust and dirt from getting onto the inner surface of the combiner  9320 . The corrective optics can include a prescriptive optic, which includes the ophthalmic prescription (optical power and astigmatism for example) of the user to improve the viewing experience. 
     Although embodiments of HWC have been described in language specific to features, systems, computer processes and/or methods, the appended claims are not necessarily limited to the specific features, systems, computer processes and/or methods described. Rather, the specific features, systems, computer processes and/or and methods are disclosed as non-limited example implementations of HWC. All documents referenced herein are hereby incorporated by reference.