Patent Publication Number: US-11036051-B2

Title: Head wearable display using powerless optical combiner

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The presentation application is a continuation application of U.S. patent application Ser. No. 14/289,498, entitled “HEAD WEARABLE DISPLAY USING POWERLESS OPTICAL COMBINER” and filed on May 28, 2014, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND INFORMATION 
     A head mounted display (“HMD”) or head wearable display is a display device worn on or about the head. HMDs usually incorporate some sort of near-to-eye optical system to create a magnified virtual image placed a few meters in front of the user. Single eye displays are referred to as monocular HMDs while dual eye displays are referred to as binocular HMDs. Some HMDs display only a computer generated image (“CGI”), while other types of HMDs are capable of superimposing CGI over a real-world view. This latter type of HMD typically includes some form of see-through eyepiece and can serve as the hardware platform for realizing augmented reality. With augmented reality the viewer&#39;s image of the world is augmented with an overlaying CGI, also referred to as a heads-up display (“HUD”). 
     HMDs have numerous practical and leisure applications. Aerospace applications permit a pilot to see vital flight control information without taking their eye off the flight path. Public safety applications include tactical displays of maps and thermal imaging. Other application fields include video games, transportation, and telecommunications. There is certain to be newfound practical and leisure applications as the technology evolves; however, many of these applications are limited due to the cost, size, weight, field of view, eye box, and efficiency of conventional optical systems used to implement existing HMDs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles being described. 
         FIG. 1  illustrates an optical system including a lightguide and optical combiner for use with a see-through head wearable display, in accordance with an embodiment of the disclosure. 
         FIGS. 2A-C  illustrate various optical combiners for use with a see-through head wearable display, in accordance with embodiments of the disclosure. 
         FIG. 3  illustrates an optical system including a lightguide and optical combiner for use with a see-through head wearable display, in accordance with an embodiment of the disclosure. 
         FIG. 4  illustrates a demonstrative see-through head wearable display including a lightguide and optical combiner, in accordance with an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of a system, apparatus, and method of operation for a head wearable display including a lightguide and optical combiner are described herein. In the following description numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
       FIG. 1  illustrates an optical system  100  including a lightguide and optical combiner for use with a see-through head wearable display, in accordance with an embodiment of the disclosure. The illustrated embodiment of optical system  100  includes a display module  105 , in-coupling optics  110 , a lightguide  115 , and an optical combiner  120 . The illustrated embodiment of display module  105  includes a display source  125  and collimation optics  130 . The illustrated embodiment of lightguide  115  includes a plurality of internal optical elements  135 . The illustrated embodiment of optical combiner  120  includes an ambient scene side  145 , eye-ward side  150 , and one or more reflective optical elements  155  that impart substantially no optical power on display light  161 . 
     Optical system  100  is a free-space apparatus that delivers an image generated peripherally to the user&#39;s central vision (e.g., temple region) into the user&#39;s eye. This design addresses a number of drawbacks associated with conventional free space designs that use an optical combiner with lensing power to collimate the display light and bring the image into easy focus for the user. Conventionally, the collimation optical power is positioned within the eyepiece optical combiner to bring it as close to the eye as possible. Placing the collimation optics close to the eye generally provides a larger eyebox, which accommodates a larger range of inter-pupillary distances of different users. While this conventional setup provides for a larger eyebox, it has a number of other drawbacks. For example, positioning the collimation optics within the eyepiece optical combiner typically results in larger, bulkier lenses, which are less desirable from an industrial design perspective. Collimation optics positioned directly in front of the eye also affect external light, and therefore disturb the user&#39;s see-through vision. Since the eyepiece optical combiner is typically illuminated from an off-axis or peripheral location, an off-axis lens function must be used when locating the collimation optics within the centrally located eyepiece optical combiner. Off axis lensing suffers from degraded image quality (e.g., comma, field distortions, astigmatisms, etc.). These optical aberrations detract from the user&#39;s experience, or should be compensated for elsewhere within the optical system using costly and sometimes bulking optics. 
     Optical system  100  overcomes many of the above drawbacks associated with conventional free space designs by using a see-through optical combiner  120  positioned in front of the user&#39;s eye that uses reflective optical elements  155  that impart substantially no optical power on display light  161 . Instead collimation optics  130  are repositioned to the periphery (e.g., temple region) outside of the user&#39;s central vision and external to optical combiner  120 . By repositioning collimation optics  130  external to optical combiner  120 , optical combiner  120  can be made thin (e.g., 1 mm) for desirable industrial design. Optical combiner  120  need not provide collimation lensing power to display light  161  and therefore does not distort the user&#39;s see-through vision of ambient scene light  163 . Without need of collimation lensing, reflective optical elements  155  within optical combiner  120  can be simpler optical elements that are easier and less expensive to fabricate. Optical system  100  repositions the lensing function to display module  105 . Collimation optics  130  are centrally located over display source  125  and therefore provide on-axis lensing, which does not suffer from the aberrations typified by off-axis lenses. 
     However, by placing collimation optics  130  within display module  105 , which is further from the user&#39;s eye, the eyebox of the optical system is reduced. To address this concern, optical system  100  positions lightguide  115  between display module  105  and optical combiner  120  to expand the cross-section size of the display light. Lightguide  115  operates as an exit pupil expander by receiving display light  162  having an initial cross-section size  170  and outputting display light  161  having an expanded cross-section size  175  that is larger than initial cross-section size  170 . This expansion serves to offset the negative effects on eyebox associated with displacing collimation optics  130  further from the user&#39;s eye. 
     Accordingly, optical system  100  enables the use of a segmented powerless optical combiner. The use of powerless segments (e.g., reflective optical elements  155 ) is desirable since they can be identical, replicated elements that therefore do not require careful lateral alignment to accommodate different inter-pupillary distances—unlike optical combiners with power. The replication of these powerless segments lends itself to less expensive fabrication techniques. Having selected a powerless optical combiner, the lensing power is moved further away from the eye and placed into display module  105  near the user&#39;s temple region. As mentioned above, this reduces the size of the eye box, which is inversely proportional to the distance between the eye and the collimation optics (e.g., collimation optics  130 ). Optical system  100  compensates for this reduction in eye box using lightguide  115  as an eye box expander. In one embodiment, lightguide  115  is a waveguide imbedded with coated-dichroic-cascaded mirrors (e.g., internal optical elements  135 ). Lightguide  115  does not operate as an optical combiner positioned in front of the user&#39;s forward vision, rather lightguide  115  is configured as an exit pupil expander positioned near the user&#39;s temple region. 
     Optical system  100  operates as follows. Display module  105  generates display light  162  having an initial cross-section size  170  for viewing by the user. Display module  105  may be coupled to a micro-processor for real-time generation of computer generated images. Display module  105  includes display source  125  and collimation optics  130 . Display source  125  may be implemented using a variety of compact display technologies, including liquid crystal displays (“LCDs”), liquid crystal on silicon (“LCoS”) displays, light emitting diode (“LED”) displays, organic LED (“OLED”) displays, pico-projectors, or otherwise. Collimation optics  130  are positioned over the output of display source  125  to collimate, or nearly collimate, the display light to generate display light  162  having initial cross-section size  170 . For example, collimation optics  130  may be configured to virtually displace the display image to appear 1 m to 3 m from the user. Of course, other amounts of collimation may be implemented. In one embodiment, collimation optics  130  are implemented as a refractive on-axis lens. 
     Display light  162  is injected into lightguide  115  via in-coupling optics  110 . In-coupling optics  110  serve to couple display light  162  into lightguide  115  at an angle that promotes propagation via total internal reflection (“TIR”) down lightguide  115  from the proximal end near display module  105  to the opposing distal end. In the illustrated embodiment, in-coupling optics  110  is a prism. 
     In the illustrated embodiment, lightguide  115  is implemented as a planar waveguide with internal optical elements  135  obliquely oriented relative to the planar emission side of lightguide  115 . Internal optical elements  135  are partially reflective planar layers offset from each other along the length of lightguide  115  running from the proximal end to the distal end. As display light  162  propagates down lightguide  115  portions of display light  162  are redirected out of lightguide  115  along the emission surface resulting in display light  161  having an expanded cross-section size  175 . As mentioned above, lightguide  115  operates as a lightguide expander or exit pupil expander. In one embodiment, internal optical elements  135  are partially reflective surfaces with a multi-layer dichroic coating that has an angle selective reflectivity. The dichroic coating permits a portion of the light incident on a surface to be reflected out of lightguide  115  while permitting another portion to continue propagating down lightguide  115  to subsequent surfaces. In this manner, display light  162  is expanded and redirected out of lightguide  115  as display light  161 . Lightguide  115  may be fabricated of glass or plastic with internal optical elements  135  disposed therein. 
     Display light  161  is emitted from lightguide  115  along a direction that is incident upon eye-ward side  150  of optical combiner  120 . Optical combiner  120  may be fabricated using a glass or plastic body having reflective optical elements  155  disposed internally or along the one of side surfaces (e.g., eye-ward side  150  or ambient scene side  145 ). Reflective optical elements  155  operate to reflect at least a portion of display light  161  incident upon the eye-ward side  150  towards an eye-ward direction. Correspondingly, reflective optical elements  155  also operate to permit at least portion of ambient scene light  163  incident on ambient scene side  145  to pass through to eye-ward side  150  and to the user&#39;s eye. In this manner, optical combiner  120  provides a see-through eyepiece that serves to combine ambient scene light  163  with display light  161  for delivery to the eye along an eye-ward direction. 
     Reflective optical elements  155  may be implemented using a variety of different elements that reflect display light  161  substantially without imparting optical power and passing ambient scene light  163  also substantially without imparting optical power thereto. For example, reflective optical elements  155  may include an array of planar reflective surfaces offset from each other and obliquely oriented relative to eye-ward side  150 . In one embodiment, these planar reflective surfaces may be partially reflective surfaces, such as beam splitters or polarization beam splitters. In embodiments, where reflective optical elements  155  are implemented using a diffractive optical element, optical combiner  120  may include a linear diffraction grating or hologram tuned to reflect the display light  161 . 
       FIGS. 2A to 2C  illustrates various possible implementations of optical combiner  120 .  FIG. 2A  illustrates an optical combiner  201  including a linear array of reflective planar surfaces  210  disposed within a lens body  205 . Surfaces  210  are offset from each other and obliquely oriented relative to the eye-ward and ambient scene sides. In one embodiment, surfaces  210  may have partially reflective coatings that permit ambient scene light to pass through. In other embodiments, surfaces  210  may be 100% reflective surfaces that only permit ambient scene light to pass through the offset gaps between the surfaces  210 . In either case, surfaces  210  are planar surfaces that do not impart substantial optical lensing power to display light  161  in reflection. Surfaces  210  are powerless surfaces, due to the optical path difference between the different portions of display light  161  originating from the different facets (internal optical elements  135 ) within lightguide  115 . If surfaces  210  had lensing power, each portion of display light  161  originating from a different facet within lightguide  115  would appear at different planes in space. Accordingly, the reflective optical elements  155  (or surfaces  210 ) do not have optical power. 
       FIG. 2B  illustrates an optical combiner  202  including a diffractive optical element (“DOE”)  215  disposed along the eye-ward side of a lens body  220 . In various other embodiments DOE  215  may be embedded internally or along the ambient scene side. Diffractive optical element  215  may be implemented using a variety of diffractive optic elements. For example, DOE  215  may be a linear grating tuned to reflect the wavelength of display light  161  towards an eye-ward direction. In another embodiment, DOE  215  may be a reflection-mode hologram configured to reflect display light  161  towards an eye-ward direction. In either embodiment, DOE  215  does not impart substantial optical lensing power to display light  161 . 
       FIG. 2C  illustrates an optical combiner  203  including surfaces  210  disposed within a lens body  225  with curved ambient scene and/or eye-ward sides that impart corrective optical power to ambient scene light  163 . It is noteworthy, that while the side surfaces of lens body  225  may impart optical power, the reflective optical elements  155  (e.g., surfaces  210 ) substantially do not impart optical power. Since display light  161  enters and exits the same curved eye-ward side of lens body  225 , the optical power imparted by this surface is significantly negated by the dual-pass over this refractive boundary.  FIG. 2C  illustrates how optical combiner  120  can be incorporated into a head wearable display having a prescription lens. 
       FIG. 3  illustrates an optical system  300  including a lightguide and optical combiner for use with a see-through head wearable display, in accordance with an embodiment of the disclosure. The illustrated embodiment of optical system  300  includes a display module  305 , in-coupling optics  310 , a lightguide  315 , and an optical combiner  120 . Optical system  300  is similar to optical system  100  except the orientations of display module  305 , in-coupling optics  310 , and lightguide  315  relative to optical combiner  120  have been changed. 
     Optical system  100  illustrates a “toe-in” embodiment where display module  105  is closer to optical combiner  120  and lightguide  115  angles towards optical combiner  120  running from the distal end towards the display module  105 . This orientation of the components may be well suited for head wearable displays where the ear-arms or temple arms of eyewear angle out towards a user&#39;s ears. In contrast, optical system  300  places the distal end of lightguide  315  closer to optical combiner  120  and display module  305  further away. This configuration is referred to as a “toe-out” embodiment wherein lightguide  315  angles away from optical combiner  120  running from display module  305  to the distal end. The “toe-out” configuration places the bulk associated with the components of display module  305  further back on the temple region towards a user&#39;s ear and thus opens up their peripheral vision. It should be appreciated that other relative orientations, angles, and positions between optical combiner  120  and the lightguide and display module may be implemented and are contemplated herein. 
       FIG. 4  illustrates a monocular head wearable display  400  using an optical system  401  including an optical combiner  402  and lightguide  403  to provide a see-through eyepiece, in accordance with an embodiment of the disclosure. Optical system  401  may be implemented with embodiments of optical systems  100  or  300 , as discussed herein, where optical combiner  402  would correspond to optical combiner  120  and lightguide  403  would correspond to either of lightguides  115  or  315 . The optical system  401  is mounted to a frame assembly, which includes a nose bridge  405 , left ear arm  410 , and right ear arm  415 . Housing  420  may contain various electronics including a microprocessor, interfaces, one or more wireless transceivers, a battery, a camera, a speaker, a display module (e.g., display modules  105  or  305 ), lightguide  403 , etc. Although  FIG. 4  illustrates a monocular embodiment, head wearable display  400  may also be implemented as a binocular display with two optical systems  401  each having an optical combiner  402  aligned with a respective eye of the user when display  400  is worn. 
     The optical system  401  is secured into an eye glass arrangement or head wearable display that can be worn on the head of a user. The left and right ear arms  410  and  415  rest over the user&#39;s ears while nose bridge  405  rests over the user&#39;s nose. The frame assembly is shaped and sized to position optical combiner  402  in front of an eye of the user. Other frame assemblies having other shapes may be used (e.g., traditional eyeglasses frame, a single contiguous headset member, a headband, goggles type eyewear, etc.). 
     The illustrated embodiment of head wearable display  400  is capable of displaying an augmented reality to the user. Optical combiner  402  permits the user to see a real world image via external scene light  480 . Display light  481  is emitted from lightguide  403  and generated by a display source mounted in peripheral corners outside the user&#39;s central vision. Display light  481  is seen by the user as a virtual image superimposed over external scene light  480  as an augmented reality. In some embodiments, external scene light  480  may be fully, partially, or selectively blocked to provide sun shading characteristics and increase the contrast of image light  481  via. 
     The processes explained above are described in terms of computer software and hardware. The techniques described may constitute machine-executable instructions embodied within a tangible or non-transitory machine (e.g., computer) readable storage medium, that when executed by a machine will cause the machine to perform the operations described. Additionally, the processes may be embodied within hardware, such as an application specific integrated circuit (“ASIC”) or otherwise. 
     A tangible machine-readable storage medium includes any mechanism that provides (i.e., stores) information in a non-transitory form accessible by a machine (e.g., a computer, network device, personal digital assistant, manufacturing tool, any device with a set of one or more processors, etc.). For example, a machine-readable storage medium includes recordable/non-recordable media (e.g., read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.). 
     The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
     These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.