Patent Publication Number: US-11662583-B2

Title: Optical combiner with integrated prescription optical correction and method of manufacturing the same

Description:
BACKGROUND 
     In the field of optics, a combiner is an optical apparatus that combines two light sources, for example, light transmitted from a micro-display and directed to the combiner via a waveguide, and environmental light from outside of the combiner. Optical combiners are used in heads up displays (HUDs), sometimes referred to as head mounted displays (HMDs) or near-eye displays, which allow a user to view computer generated content (e.g., text, images, or video content) superimposed over a user&#39;s environment viewed through the HMD, creating what is known as augmented reality (AR). The HMD enables a user to view the computer-generated content without having to significantly shift his or her line of sight. Conventional near-to-eye displays are not well suited for users that require prescription corrective lenses as HMDs can physically interfere with conventional prescription corrective glasses because they are necessarily worn close to a user&#39;s eye, thus limiting the vertex distance available for corrective and display components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference symbols in different drawings indicates similar or identical items. 
         FIG.  1    illustrates a lateral cross-section of an HMD including a combiner with an integrated prescription mounted within a frame in accordance with at least one embodiment. 
         FIG.  2    is a diagram illustrating expanded cross-section of the layers of an example combiner with integrated prescription in accordance with some embodiments. 
         FIG.  3    is a block diagram of a method of manufacturing a combiner with integrated prescription in accordance with some embodiments. 
         FIG.  4    is an example geometry of the waveguide prism and compensation prism in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Conventional methods for including a corrective optical prescription in an HMD primarily require configuring the display to accommodate a separate prescription lens, either as part of eye-glasses worn by the user or as a lens that is inserted into or attached to a combiner of the HMD. The result is often a bulky system that can be uncomfortable for a user to wear, thus detracting from the user experience. Further, boundary lines of a corrective prescription lens included in a combiner as an insert or attachment are often visible to the user, which also detracts from the user experience. 
     There are also complications in simultaneously correcting both the light from within the combiner and the environmental light such that a user does not experience optical aberrations when viewing an augmented reality scene. For example, if a corrective lens is positioned the world-facing side (i.e., the side facing away from a user) of an optical combiner, then light representing the computer generated content, which is traveling within the combiner, does not receive any prescriptive correction and will appear out of focus to the user. Further, if a corrective lens is positioned over the eye-ward side (i.e., the side facing towards a user) of an optical combiner, the strength of the prescription lens is limited by the vertex distance (i.e., the space available between the combiner and the user&#39;s eye). This is due to the fact that a stronger prescription (i.e., larger diopter) requires the corrective lens to be thicker, whether at the edges of the lens (as in nearsighted vision correction) or in the center of the lens (as in farsighted vision correction), which can potentially bump into a user&#39;s cheek or eyelashes. 
     Using the techniques described herein, a corrective prescription is integrated directly into a combiner of an HMD. This integration can reduce bulk and weight of the HMD, as well as increase the range of prescription diopters that can be accommodated by the HMD. One challenge of integrating the corrective prescription is that, while combiners can be formed from the same material typically used in the manufacturing of prescription lenses, such as, for example, optical grade polycarbonate plastic or a urethane-based monomer material, the combiner also includes specialized layers and components to facilitate transmission of light from a light source, through a volume of the combiner, and then out of the combiner towards a user&#39;s eye. Using the techniques disclosed herein, the manufacturing of a combiner with an integrated corrective prescription allows the layers and components of the combiner to remain unaltered, while also delivering high quality prescription vision correction tailored to the individual user. 
     Prescription eyeglasses lens have two curved surfaces of consequence to the vision of the wearer: the eye-side surface and the world-side surface. The corrective power of a lens is determined by adding the degree of curvature of eye-side surface and the degree of curvature of the world-side surface. For any given corrective power, an infinite number of curve combinations may be used to achieve the same result. Prescription lenses for eyeglasses are typically made from a pre-formed disk of polycarbonate plastic, called a blank, with one side being flat and the other side having a convex curvature corresponding to the world-side curvature described by a user&#39;s specific prescription. Material from the flat side is then cut or ground away utilizing specialized equipment to form the eye-side curvature according to the user&#39;s prescription. The edges of the resulting lens are then shaped to fit into a frame to be worn by the user. 
       FIGS.  1 - 4    illustrate embodiments of optical combiners that include integrated prescription optical correction and methods of manufacturing the same. An optical combiner with an integrated prescription can be manufactured in much the same way as conventional eyeglass lenses. For example, by creating a “blank” formed from layers of material having specialized coatings and/or embedded physical features and then cutting the eye-side and world-side surfaces of the blank according to the specific curvatures called for by a user&#39;s prescription. The edges of the resulting combiner/prescription lens can then be shaped to fit into an HMD or other near-to-eye display system. 
       FIG.  1    illustrates a lateral cross-section of an HMD  100  including a combiner  104  mounted within a frame  102  in accordance with at least one embodiment. The HMD  100  employs an eyeglass form factor with an eyeglass frame  102  in which a combiner  104  is housed. The combiner  104  includes a waveguide prism  106  located at the upper portion of the world-side  110  of the combiner  104  and a compensation prism  114  located at the lower portion of the world-side  110  of the combiner  104 . The waveguide prism  106  is configured to act upon light traveling within the waveguide prism  106  to change at least one of: the direction that the light is traveling, the polarization state of the light, and the angle at which light is refracted or reflected. These changes facilitate conveyance of light within the waveguide prism  106  to an outcoupler region  120 , where the light is then directed out of the waveguide prism  106  towards a user&#39;s eye. 
     The waveguide prism  106  is positioned within the frame  102  to receive display light  130  from a micro-display  108  mounted within a housing  118  at the top of the frame  102 . The micro-display  108  is connected to computing components (not shown) responsible for providing computer generated content to the micro-display  108 . In some embodiments, computer generated content includes video content, images, or text that is intended to be viewed by a user wearing the HMD  100 . Light emitted from the micro-display is conveyed through a field lens  124 , which acts to align the light in a parallel fashion so that the light has minimal spread as it propagates within the waveguide prism  106 . After being collimated at the field lens  124 , the light is transmitted into the combiner  104  at an incoupler region  126  as display light  130 . 
     Coupled to the waveguide prism  106  is the compensation prism  114 , which is shaped to be complementary to the waveguide prism  106  such that the combined waveguide prism  106  and compensation prism  114  form the combiner  104  having a lens-like shape configured to be mounted within the frame  102 . Thus, the world-side  110  of the combiner  104  includes the waveguide prism  106  and the compensation prism  114  and can be configured to have a curvature that corresponds to a user&#39;s corrective prescription. The compensation prism  114  is formed from a transparent optical material, such as that used to form the waveguide prism  106 , which allows light from the environment  128  to be transmitted through the combiner  104  such that the light from the environment  128  is combined with display light  130  conveyed from the waveguide prism  106  to present the user&#39;s with an image overlaying the user&#39;s environment. 
     The eye-side  112  of the combiner is comprised of a correction layer  116  formed from optical grade transparent material and configured to have a curvature corresponding to a user&#39;s prescription. The waveguide prism  106  and compensation prism  114  can be formed of the same or similar material to that of the correction layer  116 . Additionally, as described below with reference to  FIG.  2   , other layers of materials or coatings may be included on or between the waveguide prism  106 , the compensation prism  114 , and the correction layer  116  to impart the combiner  104  with specific light interaction properties. 
     In order to present an image for viewing by a user, the micro-display  108  directs light  130  to the field lens  124 , where the light is collimated and transmitted into the waveguide prism  106  portion of the combiner  104  via the incoupler region  126 . The display light  130  (or representation thereof) is then transmitted within and along the waveguide prism  106  to an outcoupler region  120  of the waveguide prism  106 . The outcoupler region  120  is configured to reflect the representation of the display light  130  at an angle less than the critical angle so that the representation of the display light  130  is directed out of the combiner  104 , through the correction layer  116 , towards a user&#39;s eye  122 . The combination of display light  130  reflected from the outcoupler region  120  and environmental light  128  transmitted through the combiner  104  from the world-side  110  create an AR scene viewable by the user. As the display light  130  representing an image and the environmental light  128  both travel through the correction layer  116 , the user will see both the image and the environmental scene in focus. 
       FIG.  2    illustrates an expanded cross-section of the layers of an example combiner  200  in accordance with some embodiments. The combiner may be similar to the combiner  104  illustrated in  FIG.  1    and is described with reference to the world-side  110  and the eye-side  112  of the combiner  200  when employed in an HMD  100  such as illustrated in  FIG.  1   . Starting from the eye-side  112  of the combiner  200 , a first layer  202  is provided that is formed from transparent optical grade material and configured to have a curvature, facing a user&#39;s eye, that corresponds to the diopter of user&#39;s prescription. The first layer  202  is also has a convex curvature, with respect to the eye-side  112  of the combiner  200 , on its world-side  110  surface. Disposed on the world-side  110  surface of the first layer is a partial mirror coating  238 . A second layer  204 , formed from transparent optical grade material, is disposed on the world-side  110  surface of the first layer  202  and configured to have a concave curvature on its eye-side  112  surface that corresponds to the convex curvature of the first layer  202 . A third layer  206  comprising a quarter wave plate (QWP) and an anti-reflective film is disposed on the world-side  110  surface of the second layer  204 . The QWP serves to alter the polarization state of a light wave as it is transmitted through the QWP. While the first  202 , second  204 , and third 206 layers may differ in thickness, each of the layers is configured to span the vertical height (h) of the combiner. 
     Continuing from the eye-side  112  of the combiner  200 , a fourth layer  208  or outermost layer on the world-side  110  of the combiner  200 , includes a waveguide prism  220  vertically coupled to a compensation prism  222  with a PBS film layer  210  and a linear polarization film layer  212  disposed therebetween at an outcoupling region  224 . The waveguide prism  220  and the compensation prism  222  each have a vertical height that is less than the vertical height (h) of the combiner  200  but such that the total vertical height of the fourth layer  208  is equal to the height of the combiner  200 . In order to maintain an air gap  236  between the third layer  206  and fourth layer  208 , microspheres  214  are placed between the third layer  206  and fourth layer  208 . 
     According to some embodiments, an output film stack layer  218  is disposed on the eye-side  112  surface of the first layer  202 . The output film stack layer  218  is composed of linear polarization film  226 , PBS film  228 , and QWP film  230 . In addition, a linear polarization film layer  232  can be bonded to the top edge  234  of the waveguide prism  220  such that, when the combiner  200  is employed in an HMD, such as the HMD  100  illustrated in  FIG.  1   , the linear polarization film layer  232  is disposed between the field lens  124  and the waveguide prism  220 . Thus, display light from a micro-display is linearly polarized before entering into the waveguide prism  220 . 
     With the described configuration of  FIG.  2   , in an embodiment where display light  240  is provided to the combiner  200  from a micro-display (not shown), the display light  240  is linearly polarized as it is transmitted through the linear polarization film layer  232  into the waveguide prism  220 . Though the information carried by the display light  240  (i.e., the computer generated content) remains unchanged, at least one property of the display light  240  is altered by the linear polarization film layer  232 , thus light within the waveguide prism  220  will be referred to as a representation of the display light  240 . The representation of the display light  240  travels through the volume of the waveguide prism  220  until it is incident upon the world-side  110  surface of the waveguide prism  220  at an angle greater than the critical angle for the representation of the display light  240  to be totally internally reflected, which is determined based on the material from which the waveguide prism is formed and the environmental medium (e.g., air or water). The reflected representation of the display light  240  travels back through the volume of the waveguide prism  220  and is reflected from the eye-side  112  surface of the waveguide prism  220 . Depending on the vertical length of the waveguide prism  220  and the angles at which the representation of the display light  240  is reflected, multiple reflections of the representation of the display light  240  can occur before the representation of the display light  240  is incident on the polarization film layer  212  disposed at the outcoupling region  224 . 
     The representation of the display light  240  is then transmitted through the polarization film  212  to PBS film  210 , where it is reflected toward the eye-side  112  surface of the waveguide prism  220  at an angle less than the critical angle for the material from which the waveguide prism  220  is formed and the air within the air gap  236 . Accordingly, the representation of the display light  240  is transmitted through the eye-side  112  surface of the waveguide prism  220 , through the air gap  236 , and through the third layer  206  where the polarization state of the representation of the display light  240  is converted from linear to circular polarization. The circularly polarized representation of the display light  240  then continues through the second layer  204 , and through the first layer  202  to the QWP film  230 . As the representation of the display light  240  passes through the QWP film  230  it is linearly polarized such that upon incident at PBS film  228 , the linearly polarized representation of the display light  240  is reflected back through the QWP film  230  where it is again circularly polarized. The circularly polarized representation of the display light  240  travels through the first layer  202  and is reflected by the partial mirror coating  238 , which results in reversal of the handedness of the circular polarization. The representation of the display light  240  travels back through the first layer  202  and through the QWP film  230 , where its circular polarization is converted to a linear polarization state that is orthogonal to the linear polarization state when the representation of the display light first passed through the QWP film  230 . The representation of the display light  240 , having a linear polarization which is transmissible though PBS film  228 , passes through the PBS film  228  and the linear polarization film  226  to exit the combiner towards a user&#39;s eye. 
     The angles at which the representation of the display light  240  travels and is reflected between the eye-side  112  surface and world-side  110  surface depicted in  FIG.  2    are exemplary only and may vary based on the configuration of the combiner  200 . Furthermore, the curvatures of the first layer  202 , second layer  204 , third layer  206 , and output film stack layer  218  are exemplary only and may vary based on an individual user&#39;s prescription. 
       FIG.  3    is a block diagram of a method  300  of manufacturing a combiner, such as the combiner  200  illustrated in  FIG.  2   . At block  302 , a plano-convex component (PCX), a plano-concave component (PCC), a waveguide prism component, and a compensation prism component are formed. Injection molding can be used to form the components, though other techniques for molding plastics may be utilized as well. The components can each be formed from the same optical grade transparent material or from a variety of optical grade transparent materials and may be formed as discs or other shapes. The curvatures of the PCX component and PCX component are formed to be complementary to one another such that when bonded, the convex surface of the PCX component fits within the concave surface of the PCX component without gaps. The waveguide prism component is configured to have at least one edge that is complementary to a corresponding edge of the compensation prism component, as further described below with reference to  FIG.  4   , such that when bonded they form a component having a shape and size that is approximately equal to that of the PCX and PCX components. 
     At block  304 , a partial mirror coating is applied to the convex surface of the PCX component. At block  306 , the PCX component is then bonded to the PCX component. A layer of QWP film is then adhered to the planar surface of the PCX component at block  308 . A pressure sensitive adhesive can be used to adhere the QWP film to the PCX component. At block  310 , a layer of PBS film and a layer of linear polarization film are adhered to a connection edge of the waveguide prism formed at block  302 . The PBS film and linear polarization film can be adhered to the waveguide prism using a pressure sensitive adhesive similar to that used to adhere the QWP film to the PCX component. The waveguide prism and compensation prism are then bonded at their connection edges so that the PBS film and linear polarization film are between the two prisms at block  312 . The bonded waveguide prism and compensation prism form a complete component having approximately the same size and shape as the PCX and PCX components. At block  314 , the waveguide/compensation prism component is bonded to the PCX/PCC component assembly to form a lens blank having a world-side corresponding to the waveguide/compensation prism component and an eye-side corresponding to a planar side of the PCX component. 
     Optical lens cutting equipment, such as a generator, can be used to cut, or grind, the eye-side of the lens blank to have a curvature corresponding to a user&#39;s individual prescription at block  316 . Similar equipment can be used to cut the world-side of the lens blank to have a curvature corresponding to the user&#39;s individual prescription at block  318 . The resulting shaped lens blank can be referred to as a combiner as it contains the features required to convey display light and combine the display light with environmental light to be viewed by the user. Once the eye-side and world-side of the combiner have been shaped, an output film stack layer  218  can be adhered to the eye-side of the combiner at block  320 . The completed combiner can then be fitted into an HMD, such as HMD  100  illustrated in  FIG.  1   , or other near-to-eye display device. 
       FIG.  4    illustrates an example configuration  400  of a waveguide prism  402  and compensation prism  412 , such as the waveguide prism and compensation prism formed at block  302  of  FIG.  3   . The waveguide prism  402  is formed as a partial disc having a top surface  404 , a bottom surface  406 , an outer edge  408 , and a connection edge  410  at an acute angle to the top surface  404 . Though the connection edge  410  is shown as being straight, the connection edge  410  could be curved, wavy, or configured to have protruding features. Furthermore, the connection edge  410  is shown having a consistent angle, with respect to the top surface  404 , over the length of the edge. However, the angle may vary, while not exceeding ninety degrees, along the length of the connection edge  410 . 
     The compensation prism  412  is formed as a partial disc having a top surface  414 , a bottom surface  416 , an outer edge  418 , and a connection edge  420  at an obtuse angle to the top surface  414 . Though the connection edge  420  of the compensation prism  412  is shown as being straight, the connection edge  420  could be curved, wavy, or configured to have protruding features. Furthermore, the connection edge  420  is shown having a consistent angle, with respect to the top surface  414  of the compensation prism  412 , over the length of the edge, but the angle may vary, while not being less than ninety degrees, along the length of the connection edge  420 . The angles and shapes given to the connection edge  410  of the waveguide prism  402  and the connection edge  420  of the compensation prism  412  are complementary to each other, such that the surfaces of the connection edges  410 ,  420  can be fit together flush, without gaps, to form a complete disc, as when bonded at block  312  illustrated in  FIG.  3   . While the connected compensation prism  412  and waveguide prism  402  are shown as a disc, the compensation prism  412  and the waveguide prism  402  may be formed in any other shape suitable for cutting by optical lens cutting equipment. 
     In some embodiments, certain aspects of the techniques described above may be implemented by one or more processors of a processing system executing software. The software comprises one or more sets of executable instructions stored or otherwise tangibly embodied on a non-transitory computer readable storage medium. The software can include the instructions and certain data that, when executed by the one or more processors, manipulate the one or more processors to perform one or more aspects of the techniques described above. The non-transitory computer readable storage medium can include, for example, a magnetic or optical disk storage device, solid state storage devices such as Flash memory, a cache, random access memory (RAM) or other non-volatile memory device or devices, and the like. The executable instructions stored on the non-transitory computer readable storage medium may be in source code, assembly language code, object code, or other instruction format that is interpreted or otherwise executable by one or more processors. 
     A computer readable storage medium may include any storage medium, or combination of storage media, accessible by a computer system during use to provide instructions and/or data to the computer system. Such storage media can include, but is not limited to, optical media (e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media (e.g., floppy disc, magnetic tape, or magnetic hard drive), volatile memory (e.g., random access memory (RAM) or cache), non-volatile memory (e.g., read-only memory (ROM) or Flash memory), or microelectromechanical systems (MEMS)-based storage media. The computer readable storage medium may be embedded in the computing system (e.g., system RAM or ROM), fixedly attached to the computing system (e.g., a magnetic hard drive), removably attached to the computing system (e.g., an optical disc or Universal Serial Bus (USB)-based Flash memory), or coupled to the computer system via a wired or wireless network (e.g., network accessible storage (NAS)). 
     Note that not all of the activities or elements described above in the general description are required, that a portion of a specific activity or device may not be required, and that one or more further activities may be performed, or elements included, in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure. 
     Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. Moreover, the particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. No limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.