Composite polymer for light guide

Abstract

An optical system including an optical structure and a method for forming the optical structure are described. The optical structure can include a light guide having two major surfaces. The optical structure can further include a transparent plate, a first polymer layer, and a second polymer layer. The first polymer layer can be disposed on one of the two major surfaces of the light guide. The material of the first polymer layer can maintain the total internal reflectance in the light guide, and the refractive index of the first polymer layer is smaller than the refractive index of the light guide. The second polymer layer can be disposed between the first polymer layer and the transparent plate. The material of the second polymer layer can have a Young's modulus lower than that of the first polymer layer and can have a refractive index higher than the refractive index of the first polymer layer.

Description

Technical Field

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 436,634, filed on January 2, 2023, U.S. Provisional Patent Application No. 63 / 425,329, filed on November 15, 2022, and U.S. Provisional Patent Application No. 63 / 341,004, filed on May 12, 2022. The disclosures of U.S. Provisional Patent Application No. US63 / 436,634, U.S. Provisional Patent Application No. US63 / 425,329, and U.S. Provisional Patent Application No. US63 / 341,004 are hereby incorporated by reference.

Background Art

[0002] The present disclosure generally relates to devices including, but not limited to, optical systems, light guide optical elements, and optical structures, as well as methods including, but not limited to, methods of manufacturing light guide optical elements and methods of manufacturing optical structures.

[0003] Light guides for near-eye or head-up displays propagate light by total internal reflection (TIR). To prevent dirt on the surface of the light guide from disturbing TIR, a low refractive index material (such as a polymer) is applied to the outside of the light guide. Unfortunately, such low refractive index materials are sensitive to human contamination and tend to suffer from fatigue due to stress induced by their low coefficient of thermal expansion relative to the light guide. Directly attaching a rigid transparent plate to the light guide serves to protect the low refractive index material for safety reasons, and it is also possible to attach an optical plastic lens if necessary. However, rigid polymers have a relatively large coefficient of thermal expansion (CTE) compared to light guide glass.

Summary of the Invention

[0004] In one embodiment, an optical system is generally described. The optical system can include a projection optical device configured to generate a light beam. The optical system can further include a light guide optical element. The light guide optical element can include a light guide having two major surfaces. The light beam generated by the projection optical device and coupled to the light guide can travel through the light guide by reflecting at the two major surfaces. The light guide optical element can further include a transparent plate. The light guide optical element can further include a first polymer layer disposed on one of the two major surfaces of the light guide. The material of the first polymer layer can be selected to maintain the total internal reflectance in the light guide, and the refractive index of the first polymer layer can be made smaller than the refractive index of the light guide. The light guide optical element can further include a second polymer layer disposed between the first polymer layer and the transparent plate. The material of the second polymer layer can be selected to have a Young's modulus lower than that of the first polymer layer, and the refractive index of the second polymer layer can be made larger than the refractive index of the first polymer layer.

[0005] In one embodiment, a light guide optical element is generally described. The light guide optical element can include a light guide having two major surfaces. A light beam generated by a projection optical element and coupled to the light guide travels through the light guide by reflecting at the two major surfaces. The light guide optical element can further include a transparent plate. The light guide optical element can further include a first polymer layer disposed on one of the two major surfaces of the light guide. The material of the first polymer layer can be selected to maintain the total internal reflectance in the light guide, and the refractive index of the first polymer layer can be made smaller than the refractive index of the light guide. The light guide optical element can further include a second polymer layer disposed between the first polymer layer and the transparent plate. The material of the second polymer layer can be selected to have a Young's modulus lower than that of the first polymer layer, and the refractive index of the second polymer layer can be made larger than the refractive index of the first polymer layer.

[0006] In one embodiment, a method of manufacturing a light guide optical element is generally described. The method can include providing a light guide consisting of two major surfaces. The light guide can be configured such that a light beam generated by a projection optical element and coupled to the light guide travels through the light guide by reflecting at the two major surfaces. The method can further include providing a transparent plate. The method can further include disposing a first polymer layer on one of the two major surfaces of the light guide. The material of the first polymer layer can be selected to maintain the total internal reflectance in the light guide, and the refractive index of the first polymer layer can be made smaller than the refractive index of the light guide. The method can further include disposing a second polymer layer between the first polymer layer and the transparent plate. The material of the second layer can be selected to have a Young's modulus lower than that of the first polymer layer, and the refractive index of the second polymer layer can be made larger than the refractive index of the first polymer layer.

[0007] In one embodiment, an optical structure in an optical system is generally described. The optical structure can include a light guide having two major surfaces. A light beam generated by a projection optical device and coupled into the light guide can travel through the light guide by reflecting off the two major surfaces. The optical structure can further include a first polymer layer disposed on one of the two major surfaces of the light guide. The material of the first polymer layer can be selected to maintain the total internal reflectance in the light guide, and the refractive index of the first polymer layer can be made smaller than the refractive index of the light guide. The optical structure can further include a second polymer layer disposed on the first polymer layer. The material of the second layer can be selected to have a Young's modulus lower than that of the first polymer layer, and the refractive index of the second polymer layer can be made larger than the refractive index of the first polymer layer.

[0008] In one embodiment, a method of manufacturing an optical structure is generally described. The method can include providing a light guide having two major surfaces. The light guide can be configured such that a light beam generated by a projection optical device and coupled into the light guide can travel through the light guide by reflecting off the two major surfaces. The method can further include disposing a first polymer layer on one of the two major surfaces of the light guide. The material of the first polymer layer can be selected to maintain the total internal reflectance in the light guide, and the refractive index of the first polymer layer can be made smaller than the refractive index of the light guide. The method can further include disposing a second polymer layer on the first polymer layer. The material of the second layer can be selected to have a Young's modulus lower than that of the first polymer layer, and the refractive index of the second polymer layer can be made larger than the refractive index of the first polymer layer.

[0009] The following further details the features, as well as the structure and operation of various embodiments, with reference to the accompanying drawings. In the drawings, the same reference numerals denote the same or functionally similar elements.

Brief Description of the Drawings

[0010]

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DETAILED DESCRIPTION OF THE INVENTION

[0011] In the following description, in order to provide an understanding of various embodiments of the present application, numerous specific details are shown, such as specific structures, components, materials, dimensions, processing steps, and techniques. However, those skilled in the art will understand that various embodiments of the present application can be implemented without these specific details. In other instances, well-known structures or processing steps are not described in detail to avoid obscuring the present application.

[0012] FIG. 1 is a schematic diagram of an exemplary optical system 100 according to one embodiment. The optical system 100 can include at least an image projection assembly 110 and a controller 140. The controller 140 can include a computing device having one or more processing devices, memories, or other components. For example, the controller 140 can include a central processing unit (CPU), a field programmable gate array (FPGA), a microcontroller, an application specific circuit, or any other component. The controller 140 can be configured to control a projection optical device (described later) to generate and output an image for projection onto the eye 180 through a light guide optical element (LOE) (described later).

[0013] In some embodiments, the controller 140 can be integrated with the image projection assembly 110, or can be integrated with a device comprising the image projection assembly 110, such as, for example, glasses, a head-mounted display, or another device. In some embodiments, the controller 140 can be located at a location remote from the image projection assembly 110. For example, the image projection assembly 110 can include a wired or wireless communication device configured to communicate with the controller 140. As an example, the controller 140 can be included as a separate mobile device from the image projection assembly 110 or a device comprising the image projection assembly 110, or as part of another computing device.

[0014] The image projection assembly 110 can include a projection optical device (POD) 112 and a light guide optical element (LOE) 114, and is configured to project an image onto the user's eye 180. The POD 112 can include an image generator 150, a collimating optical system 152, or other components that can be included in an image projection assembly, such as, for example, a spatial light modulator (SLM). Some or all of these components may be disposed on the surface of one or more polarization beam splitter (PBS) cubes or other prism configurations in some embodiments. The image generator 150 comprises one or more components that provide illumination corresponding to the image projected onto the user's eye 180, such as, for example, a light beam, a laser beam, or other forms of illumination. For example, the image generator 150 comprises a light emitting diode (LED) display, an organic light emitting diode (OLED) display, a backlit liquid crystal display (LCD) panel, a micro-LED display, a digital light processing (DLP) chip, a liquid crystal on silicon (LCOS) chip, or other components.

[0015] Alternatively, POD 112 can include a scanning device, such as a high-speed scanning mirror, that scans illumination from a light source across the image plane of POD 112 and varies the intensity of the illumination in synchronization with movement on a pixel-by-pixel basis to project a desired intensity for each pixel. POD 112 can also optionally include a coupling-in arrangement, such as a coupling-in reflector, an angled coupling prism, or other coupling-in arrangement, for injecting the illumination of the image into LOE 114. In some embodiments, the coupling between POD 112 and LOE 114 can include a direct connection. For example, POD 112 may contact a portion of LOE 114, or may include a coupling via an additional aperture expansion configuration for expanding the dimensions of an aperture through which the image is incident into the plane of LOE 114.

[0016] LOE 114 can include first and second parallel major LOE surfaces 116 and 118 and a light guide that includes optically inactive edges. In an exemplary embodiment, the various light guides described herein may be composed of a geometric light guide, a diffractive light guide, or any other type of light guide. LOE 114 also includes a coupling-out device 120 configured to direct illumination outside of LOE 114 for projection onto the user's eye 180. In some embodiments, the coupling-out device 120 is illustrated as a plurality of embedded partial reflectors (also referred to as facets) 1221, 1222, 1223, 1224, and 1225 disposed within LOE 114 at an oblique angle with respect to the major LOE surfaces 116 and 118 of LOE 114. Five embedded partial reflectors 1221, 1222, 1223, 1224, and 1225 are shown in FIG. 1, but in an exemplary embodiment, LOE 114 can alternatively include a greater or fewer number of embedded partial reflectors in other embodiments.

[0017] In some embodiments, each embedded partial reflector is configured to couple and output a light beam having a specific propagation angle in the LOE 114 to the eye 180. For example, in some embodiments, each embedded partial reflector is configured to couple and output light beams having different propagation angles in the LOE 114. In some embodiments, one or more embedded partial reflectors may be selectively operable by the controller 140 between a state in which the embedded partial reflector has a high light transmittance and a state in which the embedded partial reflector has a high light reflectivity. The expansion or multiplication of the aperture may be two-dimensional in which another set of facets reflect laterally to perform the multiplication of the aperture.

[0018] As shown in FIG. 1, for example, the light beam L travels through the LOE 114 towards the embedded partial reflector by reflecting off the major LOE surfaces 116 and 118. For example, the major LOE surfaces 116 and 118 may provide TIR for any light beam traveling through the LOE 114. When the light beam L strikes a right-angled embedded partial reflector, or an active embedded partial reflector, the light beam L is redirected by the embedded partial reflector. The light that strikes the embedded partial reflector is redirected outside the LOE 114, for example, in the direction of the eye 180.

[0019] FIG. 2 is a diagram showing a layer of adhesive used to attach a layer of material to a light guide. In the example shown in FIG. 2, a layer of material such as a polycarbonate plate 204 (e.g., a transparent plate) can be disposed on the light guide 202 using a layer of adhesive 206. In one or more embodiments, the layer of material shown as the polycarbonate plate 204 can be or a polymer, glass, or other material that forms a transparent plate or a transparent layer of material. The adhesive 206 can be used to attach the surface of the light guide 202 to the surface of the polycarbonate plate 204. The light guide 202 can be a light guide optical element such as the LOE 114 shown in FIG. 1. In the example shown in FIG. 2, the dashed arrows represent the (TIR) guided light reflected by the reflector in the light guide 202. The polycarbonate plate 204 is shown as having a flat upper surface, but the upper surface of the polycarbonate plate 204 can also be curved. In one aspect, the adhesive 206 can have a lower refractive index with respect to the light guide 202 while being sufficiently flexible with respect to thermal expansion so that TIR within the light guide 202 is maintained.

[0020] The polycarbonate plate 204 and the light guide 202 can expand, such as expanding horizontally in the ±x direction. Since the CTEs of the polycarbonate plate 204 and the light guide 202 are different, the surface of the adhesive 206 adhered to the polycarbonate plate 204 can expand faster than the surface of the adhesive 206 adhered to the light guide 202. For example, if both the polycarbonate plate 204 and the light guide 202 are subjected to a temperature change of 30 degrees Celsius, the light guide 202 expands approximately 3 microns laterally (along the x-axis), and the polycarbonate plate 204 expands approximately 32 microns laterally. Thus, the expansion difference between the polycarbonate plate 204 and the light guide 202, i.e., the relative expansion amount, is approximately 29 microns, as shown by the relative expansion 228 in FIG. 2.

[0021] The relative expansion 228 can stretch the upper surface of the adhesive 206 and stretch and deform the side surfaces of the adhesive 206 in a diagonal direction (e.g., the xy direction and the -xy direction) as indicated by the extension 232. In one aspect, a particular type of polymer may exhibit signs of fatigue after stretching laterally (e.g., along the x-axis) by about 18% of the polymer's thickness (e.g., along the y-axis). Thus, if the length of the extension 232 is greater than a particular threshold (e.g., 18% of the polymer's thickness) by more than the thickness 230 of the adhesive 206, the adhesive 206 may break, and the polycarbonate plate 204 may fall towards the light guide 202, potentially reducing the transparency of the light guide 202 and allowing unwanted substances (e.g., dirt) to adhere to the light guide 202. Now, when the relative expansion 228 is about 29 microns, for the 29-micron relative expansion (e.g., 232) not to be more than 18% greater than the thickness 230, the thickness 230 of the adhesive needs to be about 45 microns. Thus, increasing the thickness of the adhesive layer can increase the amount of lateral expansion of the polycarbonate plate 204.

[0022] However, as the adhesive layer thickens, the device size becomes significantly larger, and the light passing through the thick adhesive layer may become unstable. For example, the occurrence of internal scattering and external scattering may increase as the thickness of the adhesive layer increases. The scattered light due to the thick adhesive layer may also disrupt the TIR within the light guide 2. Reducing the thickness of the adhesive 206 is beneficial because it can reduce the risk of scattering and perturbation and maintain the TIR within the light guide 202. However, simply reducing the thickness of the adhesive 206 alone may increase the risk of breakage (for example, reducing the thickness makes it easier to pass the 18% threshold or other thresholds for other types of polymers). Therefore, in order to attach the polycarbonate plate 204 to the light guide 202 while preventing the breakage of the adhesive, it is necessary to optimize the thickness of the polymer used as the adhesive and make the refractive index of the material of the adhesive 206 relatively low with respect to the light guide 202 so that the TIR within the light guide 202 is maintained. Furthermore, in order to maintain the TIR, it is difficult to use a single material that can provide both 1) mechanical flexibility and adhesiveness corresponding to the CTE difference between the polycarbonate plate 204 and the light guide 202, and 2) a low refractive index with respect to the light guide 202.

[0023] FIG. 3 is a diagram showing a structure 300 including a plurality of polymer layers used to attach a layer of material (e.g., polycarbonate plate 204) to a light guide (e.g., light guide 202) in one embodiment. In order to maintain TIR in the light guide 202 and reduce the thickness of the adhesive used to bond the polycarbonate plate 204 and the light guide 202, a plurality of polymer layers can be used instead of the adhesive 206 of FIG. 2. In the structure 300 shown in FIG. 3, a polymer layer 308 (or polymer layer 308) is directly attached to the light guide 202, and another polymer layer 310 (or polymer layer 310) is directly attached to the polymer layer 308 and the polycarbonate plate 204. In one embodiment, the polymer layers 308, 310 can be composed of different types of adhesive materials. In another embodiment, an adhesive can be pre-applied to at least one surface of the polymer layers 308, 310.

[0024] The polymer layer 308 can be a relatively thin layer of a low refractive index polymer that retains the TIR of the light guide 202. The thickness of the polymer layer 308 can be less than 10 microns, such as a thickness of 1-2 microns, for example. In one embodiment, in order to maintain TIR in the light guide 202, the refractive index of the polymer layer 308 can be made smaller than the refractive index of the light guide 202. The polymer layer 310 can be a flexible layer of a polymer having an elongation of 140% before breakage, for example (e.g., the 140% elongation is in the same direction as the extension 324 shown in FIG. 3). The polycarbonate plate 204 can be disposed on the polymer layer 310. In one embodiment, the polymer layer 310 functions as a damping choke between the polycarbonate plate 204 and the light guide 202 and can absorb vibrations received by the structure 300. In one embodiment, the thickness of the polymer layer 310 can be about 13 microns, which is significantly thinner than the example shown in FIG. 2 where the layer of adhesive 206 can be about 45 microns. The polymer layer 310 can function as a layer of adhesive that bonds the polycarbonate plate 204. The above parameters and dimensions are for illustrative purposes, and other dimensions are possible.

[0025] To prevent damage to the polymer layer 308, the polymer layer 310 can have a lower Shore hardness than the polymer layer 308. Alternatively, the Young's modulus of the material of the polymer layer 310 can also be made lower than the Young's modulus of the material of the polymer layer 308. The polymer layer 310 having a Shore hardness and a Young's modulus lower than those of the polymer layer 308 can accommodate the different expansion rates of the polycarbonate plate 204 and the light guide 202. In one embodiment, the CTEs of the flexible polymer layers 308, 310 can be negligible when compared to the CTEs of the polycarbonate plate 204 and the light guide 202. As an example, when the polycarbonate plate 204 and the light guide 202 expand in response to a temperature change, the expansion of the polycarbonate plate 204 can stretch the upper (e.g., +x direction) surface of the polymer layer 310 at a first rate proportional to the CTE of the polycarbonate plate 204, and the light guide 202 can stretch the polymer layer 308 at the bottom (e.g., -x direction) surface at a second rate lower than the first rate and proportional to the CTE of the light guide 202.

[0026] As an example, the relative expansion 320 between the polycarbonate plate 204 and the polymer layer 308 is shown in FIG. 3. The relative expansion 320 can be made smaller than the relative expansion between the polycarbonate plate 204 and the light guide 202 by the independent stretching of the polymer layers 308, 310. The relative expansion 320 in FIG. 3 can control the size or length of the extension 324 instead of the relative expansion between the polycarbonate plate 204 and the light guide 202. The extension 324 can be measured from the surface of the polymer layer 308 instead of measuring from the surface of the light guide 202 as compared with a configuration where there is a single layer of polymer between the polycarbonate plate 204 and the light guide 202 (e.g., FIG. 2). Therefore, the extension 324 can be reduced when compared with the configuration shown in FIG. 2. By reducing the elongation, the breakage of the adhesive layer (e.g., the polymer layer 310) can be delayed. As shown in FIG. 3, by using a plurality of polymer layers between the polycarbonate plate 204 and the light guide 202, while the polymer layer 308 provides a low refractive index for maintaining TIR, the polymer layer 310 can provide mechanical flexibility and adhesiveness for corresponding to the CTE difference between the polycarbonate plate 204 and the light guide 202, so that functional separation can be provided.

[0027] In one embodiment for manufacturing the structure 300, before adhesion, the light guide 202 can undergo physical and chemical pretreatment (e.g., plasma / corona using silane, etc.) to induce high adhesiveness of the polymer layer 308 to the light guide 202. The polymer layer 308 can be applied to the surface of the light guide 202, for example, by spin coating and cured in an external air environment.

[0028] In a modification of the embodiment, the polymer of the polymer layer 308 does not contain a component that suppresses oxygen inhibition in its formulation. Under this embodiment, oxygen inhibition occurs on the surface layer of the polymer layer 308 (e.g., about 1 to 2 microns thick) such that the bulk of the polymer of the polymer layer 308 undergoes complete curing while the upper layer of the polymer layer 308 remains uncured.

[0029] The adhesion of the polycarbonate plate 204 to the polymer layer 308 can include applying the polymer of the polymer layer 310 as an intermediate adhesive having a specific CTE and elongation to the wet uncured surface of the polymer layer 308. Two separate adhesives (e.g., polymer layers 308, 310) between the polycarbonate plate 204 and the light guide 202 can assimilate, diffuse, interact, and interbond when exposed to curing conditions (e.g., UV, heat, etc.), achieving high adhesion strength without the need for additional pretreatment.

[0030] FIG. 4A is a diagram showing the pre-integration of a plurality of polymer layers in one embodiment. In one embodiment shown in FIG. 4A, the polycarbonate plate 402 can be attached to the lower surface of the light guide 202 via the polymer structure 401, and another polycarbonate plate 404 can be attached to the upper surface of the light guide 202 via the polymer structure 403. The polymer structure 401 can be a stack of polymer layers including the polymer layers 308L, 410L, 412L. The polymer structure 403 can be a stack of polymer layers including the polymer layers 308U, 410U, 412U.

[0031] Returning to FIG. 3, the polymer layers 308U and 308L in the polymer structures 401 and 403 can be composed of the same material as the polymer layer 308 shown in FIG. 3. Also, the polymer layers 410U and 410L within the polymer structures 401 and 403 can be composed of the same material as the polymer layer 310 shown in FIG. 3. Further, the polymer layer 310 in FIG. 3 and the polymer layers 410U and 410L in FIG. 4A can be composed of the same material, such as a flexible polymer having a shore hardness lower than that of the polymer layer 308 and a Young's modulus lower than that of the polymer layer 308. In one embodiment, the polymer layers 412U and 412L can be composed of a polymer material different from the materials of the polymer layers 308U, 308L, 410L, and 410U. The polymer layer 412U can function as an adhesive for adhering the polymer layer 410U to the polycarbonate plate 404, and the polymer layer 412L can function as an adhesive for adhering the polymer layer 410L to the polycarbonate plate 402. The polymer layers 412U and 412L may be optically transparent, may have a refractive index between the polymer layer 410U and the polycarbonate plate 404, may have a refractive index between the polymer layer 410L and the polycarbonate plate 402, may include an AR coating, and / or may be mechanically flexible.

[0032] In one embodiment, the polymer structure 401 can be formed or constructed by laminating the polymer layer 410L on the polymer layer 412L and then laminating the polymer layer 308L on the polymer layer 410L. In another embodiment, the polymer structure 401 can be formed or constructed by laminating the polymer layer 410L on the polymer layer 308L, then laminating the polymer layer 412L on the polymer layer 410L, and then inverting the entire laminated structure to complete the formation of the polymer structure 401.

[0033] In one embodiment, the polymer structure 403 can be formed or constructed by laminating a polymer layer 410U onto a polymer layer 412U and then laminating a polymer layer 308U onto the polymer layer 410U. In another embodiment, the polymer structure 403 can be formed or constructed by laminating a polymer layer 410U onto a polymer layer 308U, then laminating a polymer layer 412U onto the polymer layer 410U, and then inverting the entire laminated structure to complete the formation of the polymer structure 403.

[0034] Each of the polymer layers 410L, 410U (e.g., flexible polymer layers) can be separately fabricated as foils (sometimes referred to as "laminates"). For example, the polymer layer 308U can be applied directly to one surface (e.g., the top or bottom surface) of this foil, and additional layers such as the polymer layer 412U can be applied to the opposing surface (e.g., the bottom or top surface) of this foil. Each of the polymer layers 410L, 410U can also function as a protective layer for holding the remainder of the light guide 202 in the event that the light guide 202 is damaged, thus improving safety for the user.

[0035] The polymer structures 401, 403 can be manufactured separately and can form the structure 420 shown in FIG. 4B before being integrated with the light guide 202 and the polycarbonate plates 402, 404. In FIG. 4B, the polymer structure 401 can be positioned between the bottom surface of the light guide 202 and the polycarbonate plate 402. The polymer structure 403 can be positioned between the top surface of the light guide 202 and the polycarbonate plate 404. In one embodiment, the structure 420 can be formed by laminating the polymer structure 401 onto the polycarbonate plate 402, then laminating the light guide 202 onto the polymer structure 401, then laminating the polymer structure 403 onto the light guide 202, and then laminating the polycarbonate plate 404 onto the polymer structure 404.

[0036] FIG. 5A is a diagram showing a pre-laminated configuration in which a foil is used as a protective surface in one embodiment. In the embodiment shown in FIG. 5A, a polymer layer 410L can be adhered to a polymer layer 308 to form a first protective structure 501, and a polymer layer 410U can be adhered to another polymer layer 308 to form a second protective structure 503. The polymer layers 410L, 410U can function as foils that protect the user in case of breakage. After forming the first and second protective structures 501, 503, the first and second protective structures 501, 503 can be attached to the light guide 202 and laminated with the light guide 202 to form a laminated structure 510 shown in FIG. 5B. In one embodiment, since the polymer layers 410U, 410L are flexible, the polymer layers 410U, 410L are also stretchable and can reduce problems caused by thermal expansion.

[0037] FIG. 6A is a diagram showing a light guide having a non-smooth surface coated with an anti-reflection (AR) coating. In the example shown in FIG. 6A, the light guide 202 can have a non-smooth surface coated with an anti-reflection (AR) coating 657A. The deviation from smoothness that forms the non-smooth surface is, for example, the result of a component 650 in the light guide 202 causing a deviation 652, or an embedded partial reflector 654 causing a deviation 656. The deviations 652, 656 are shown as bumps in FIG. 6A, but the deviations 652, 656 can also be depressions on the surface of the light guide 202. The reflection 658 in FIG. 6A shows an optimal reflection where the beam is reflected by TIR and the reflection angle is equal to the incident angle measured locally from the surface apex 620 (vertical dashed line). The transmittance 660 represents a transmitted beam without disturbance. In one aspect, a transmitted beam without disturbance can also be generated by reflection from the embedded partial reflector 654.

[0038] Internal reflections 662 at the surface of the escape 652 can deflect the beam at slightly different angles, as indicated by another surface vertex 622 (the inclined dotted line), thereby scattering it in a way that degrades the quality of the TIR-guided light and the image within the light guide 202. Also, the transmitted beam 664 can be scattered both inside the light guide 202 and outside the surface of the light guide 202, thus degrading the quality of the TIR-guided image. Since the AR coating 657A essentially follows the surface pattern, it cannot suppress these scatterings and may cause further scatterings and image degradation.

[0039] FIG. 6B is a diagram showing a low refractive index polymer layer laminated on a non-smooth surface of a light guide in one embodiment. FIG. 6B shows that by laminating a polymer layer 603 on the surface of the light guide 202, scattering of the transmitted beam 664 can be substantially suppressed. The polymer layer 603 may be a low refractive index layer and may be the same as or similar to the polymer layer 308 shown in FIG. 3. The polymer layer 603 can have a refractive index n2, and n2 can be made smaller than the refractive index n1 of the light guide 202. The refractive index n2 can be made smaller than the refractive index n1 in order to maintain TIR within the light guide 202. The outer surface of the polymer layer 603 may be polished so that an optimal and smooth AR coating 657B can be mounted on the polymer layer 603 (for example, an object similar to the component 650 or the embedded portion reflector 654 is not embedded in the polymer layer 603).

[0040] FIG. 7 is a diagram showing an example of a beam that undergoes total internal reflection in a light guide. A plot of the phase change of a light beam undergoing TIR within the light guide 202 is shown in FIG. 7, and the light guide 202 can have a smooth surface. The x-axis of FIG. 7 represents the angle of incidence of the beam undergoing TIR within the light guide 202, and the y-axis represents the phase change of the TIR beam in degrees (e.g., 360 degrees corresponding to 2π). FIG. 7 also shows three different configurations of the light guide 202 having a smooth or flat surface (e.g., in an ideal case) that can direct an image under a limited angular range 769.

[0041] The first plot 770 corresponds to the first case where the light beam refracts at the surface of the light guide 202 interfacing with air. The first plot 770 represents the change in the phase change of the light beam with respect to the angle of incidence from the vertex forming the interface between the surface of the light guide 202 and air. The refractive index n1 of the light guide 202 can be, for example, 1.52. The range 779 of the plot 770 represents the angular range of TIR for the first case, and in the first case, a beam refracting at an angle of incidence lower than the critical angle of about 41 degrees may not undergo TIR and may not remain within the light guide 202.

[0042] The second plot 772 corresponds to the second case where the light beam refracts at the surface of the polymer layer 603 (see FIG. 3) interfacing with air. The second plot 772 represents the change in the phase change of the light beam with respect to the angle of incidence from the vertex forming the interface between the surface of the polymer layer 603 and air. The refractive index n2 of the polymer layer 603 may be, for example, 1.35. The range 778 of the plot 770 represents the angular range of TIR for the second case, and in the second case, a beam refracting at an angle of incidence lower than the critical angle of about 48 degrees may not undergo TIR and may not remain inside the polymer layer 603.

[0043] The third plot 774 corresponds to a third case where the light beam refracts at the surface of the light guide 202 interfacing with the polymer layer 603. The third plot 774 represents the change in the phase change of the light beam with respect to the incident angle from the vertex forming the interface between the surface of the light guide 202 and the polymer layer 603. The range 777 of plot 770 represents the angle range of TIR in the third case. In the third case, a beam refracting at an incident angle lower than the critical angle of about 63 degrees may not undergo TIR and may not remain inside the light guide 202. In one embodiment, the value of n2, or the material constituting the polymer layer 603, can be selected to fall within the range 777 in order to guide the light beam under a limited angle range 769.

[0044] FIG. 8 is a diagram showing an example of laminating a polymer layer on a light guide to suppress a beam that may be scattered due to surface deviation in one embodiment. A plot of the phase change of light undergoing TIR in the light guide 202 is shown in FIG. 8, and the light guide 202 may have a non-smooth surface. The x-axis in FIG. 8 represents the incident angle of the beam undergoing TIR within the light guide 202, and the y-axis represents the phase change of the TIR beam in degrees (for example, 360 degrees corresponding to 2π). FIG. 8 also shows two different configurations of the light guide 202 having a non-smooth surface.

[0045] In the example shown in FIG. 8, the non-smooth surface of the light guide 202 can cause a vertex deviation 879 of about 5 degrees. In the first case 880 where the vertex deviation 879 interfaces with air, the phase change of the light beam is about 8 degrees. In the second case 882 where the polymer layer 603 is laminated on the non-smooth surface of the light guide 202, the phase change of the light beam at the vertex deviation 879 is about 2 degrees. Therefore, by adding the polymer layer 603 to the non-smooth surface of the light guide 202, scattering of the light beam in the non-smooth portion of the light guide 202 can be suppressed, and TIR in the light guide 202 can be maintained.

[0046] FIG. 9 shows an example of attaching a polymer layer on a light guide to suppress a beam that may be scattered due to surface deviation and filter the scattering in one embodiment. In the first case 902, the optimal TIR 984 on the smooth portion of the surface of the light guide 202 and the perturbed TIR 990 on the non-smooth portion of the surface of the light guide 202 are shown in FIG. 9. The reflected beam in the perturbed TIR 990 is at a different angle from the optimal TIR 984, but continues to be guided to perturb the light beam.

[0047] In the second case 904, different polymer layers 603A, 603B having a refractive index n2 are attached to both surfaces (e.g., top and bottom) of the light guide 202. The polymer layers 603A, 603B can be composed of the same material as the polymer layer 603 in FIG. 6 and the polymer layer 308 in FIG. 3. A medium 910 having a refractive index n3 is attached to the bottom surface under the polymer layer 603B. In the second case 904, reflection 992 (which may be the same as 990) can occur at the non-smooth portion of the surface of the light guide 202 that interfaces with the polymer layer 603A. The reflection 992 can reflect the deflected beam at a different angle so that the deflected beam is emitted from the light guide 202 at a point 993 that is the interface between the light guide 202 and the polymer layer 603B. The deflected beam exiting from the point 993 may couple to the medium 910 in some cases, or be shallowly guided along the polymer layer 603B. In either case, the distortion of the beam in the light guide 202 can be reduced as shown in FIG. 9, and the original beam angle 986 guided in the light guide 202 is reflected by perturbation as angles 988, 989 outside the guiding range of the light guide 202.

[0048] Figure 10 is a diagram showing the prevention of non-guided light beams exiting a light guide in one embodiment. In the first case 1002, an unguided beam 1106 (e.g., from a scene or reflected by a facet) is shown exiting or passing through the smooth portion of the surface of the light guide 202 coated with the AR coating 657A. At the non-smooth portion of the surface of the light guide 202, this beam can be made to be guided by the perturbation 1108.

[0049] In the second case 1004, the polymer layer 603 is directly laminated on the light guide 202, and the surface of the polymer layer 603 is coated with the AR coating 657B. In the second case 1004, the perturbation 108 can deflect the beam without maintaining the guidance within the light guide 202. The deflected beam can couple out of the polymer layer 603 for the smooth AR coating 657B or another medium, or deflect at a very shallow angle within the polymer layer 603. The perturbed beam is not guided within the light guide 202, so the image degradation is reduced. As shown in Figure 10, the unguided beam 1100 is guided under the first case 1002 but is redirected to 1102 or 1104 that are not guided under the second case 1004.

[0050] Figure 11 is a flowchart showing the manufacturing process of a light guide optical element in one embodiment. Step 1100 may include one or more operations, actions, or functions as indicated by one or more of blocks 1102, 1104, 1106, and / or 1108. Although shown as discrete blocks, the various blocks can be divided into additional blocks, combined into fewer blocks, deleted, or executed in parallel, and / or executed in a different order depending on the desired embodiment.

[0051] Process 1100 can be carried out to manufacture light guide optical elements such as the structures 300 and 420 of FIGS. 3 and 4B. Process 1100 can start at block 1102. At block 1102, a light guide can be provided, and the light guide can include two major surfaces. The light guide is generated by a projection optical device and can be configured such that a light beam coupled to the light guide can move through the light guide by reflecting at the two major surfaces. In one embodiment, a coupling-out device can be provided to the light guide, and the coupling-out device can be configured to derive the light guided by the light guide from the light guide. In one embodiment, the coupling-out device can include a plurality of surfaces disposed inside the light guide at one or more oblique angles with respect to the major surface of the light guide.

[0052] Process 1100 can proceed from block 1102 to block 1104. At block 1104, a transparent plate may be provided. In one embodiment, this transparent plate can have a larger coefficient of thermal expansion than the light guide.

[0053] Process 1100 can proceed from block 1104 to block 1106. At block 1106, a first polymer layer can be disposed on one of the two major surfaces of the light guide. The material of the first polymer layer can be selected to maintain the total internal reflectance in the light guide, and the refractive index of the first polymer layer can be made smaller than the refractive index of the light guide. In one embodiment, the first polymer layer can be disposed on one of the two major surfaces by adhering the first polymer layer to one of the two major surfaces of the light guide. In one embodiment, the material of the first polymer layer can be selected such that oxygen inhibition occurs at the surface layer of the first polymer layer that is not in contact with one of the two major surfaces of the light guide.

[0054] Process 1100 can proceed from block 1106 to block 1108. At block 1108, a second polymer layer can be disposed between the first polymer layer and the transparent plate. The material of the second layer can be selected to have a Young's modulus lower than that of the first polymer layer, and the refractive index of the second polymer layer can be made greater than that of the first polymer layer. In one embodiment, the Shore hardness of the second polymer layer can be selected to be lower than that of the first polymer layer. In one embodiment, while the surface layer of the first polymer layer remains uncured, a portion of the first polymer layer can be cured, and the second polymer layer can be applied to the uncured surface layer of the first polymer layer.

[0055] In one embodiment, a third layer can be provided and disposed between the second polymer layer and the transparent plate. In one embodiment, the first polymer layer, the second polymer layer, and the third layer can be formed as a laminate structure with the first polymer layer disposed on one of the two major surfaces of the light guide before disposing the transparent plate on the third layer.

[0056] FIG. 12 is a flowchart showing the process of manufacturing an optical structure in one embodiment. Process 1200 can include one or more operations, actions, or functions, as exemplified by one or more of blocks 1202, 1204, and / or 1206. Although shown as discrete blocks, the various blocks can be divided into additional blocks, combined into fewer blocks, deleted, or executed in parallel, and / or executed in a different order, depending on the desired embodiment.

[0057] Process 1200 can be executed to manufacture a light guide optical element such as the structure 510 of FIG. 5B. Process 1200 can start at block 1202. At block 1202, a light guide can be provided, and the light guide can include two major surfaces. The light guide can be configured such that a light beam generated by a projection optical device and coupled to the light guide can move through the light guide by reflecting at the two major surfaces. In one embodiment, a coupling-out device can be provided in the light guide, and the coupling-out device can be configured to guide the light guided by the light guide out of the light guide. In one embodiment, the coupling-out device can include a plurality of surfaces disposed within the light guide at one or more oblique angles with respect to the major surface of the light guide.

[0058] Process 1200 can proceed from block 1202 to block 1204. At block 1204, a first polymer layer can be disposed on one of the two major surfaces of the light guide. The material of the first polymer layer can be selected to maintain the total internal reflectance in the light guide, and the refractive index of the first polymer layer can be made smaller than the refractive index of the light guide. In one embodiment, the first polymer layer can be disposed on one of the two major surfaces by adhering the first polymer layer to one of the two second major surfaces of the light guide. In one embodiment, the material of the first polymer layer can be selected such that oxygen inhibition occurs at the surface layer of the first polymer layer that is not in contact with one of the two major surfaces of the light guide. In one embodiment, the first polymer layer and the second polymer layer can form a laminated structure before the first polymer layer is disposed on one of the two major surfaces of the light guide.

[0059] Process 1200 can proceed from block 1204 to block 1206. At block 1206, the second polymer layer can be disposed on the first polymer layer. The material of the second layer can be selected to have a Young's modulus that can be lower than the Young's modulus of the first polymer layer, and the refractive index of the second polymer layer can be greater than the refractive index of the first polymer layer. In one embodiment, the Shore hardness of the second polymer layer can be selected to be lower than the Shore hardness of the first polymer layer. In one embodiment, while the surface layer of the first polymer layer remains uncured, a portion of the first polymer layer can undergo curing, and the second polymer layer can be applied to the uncured surface layer of the first polymer layer.

[0060] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagram can represent one or more executable instructions that form a module, segment, or portion of instructions for implementing the specified logical function. In some alternative implementations, the functions noted in the blocks may occur out of the order shown in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending on the functions involved. It should be noted that each block of the block diagrams and / or flowchart diagrams, as well as combinations of blocks in the block diagrams and / or flowchart diagrams, can be implemented by a dedicated hardware-based system that performs the specified function or operation, or a combination of special purpose hardware and computer instructions.

[0061] The terms used in this specification are for the purpose of describing particular embodiments only and are not intended to limit the invention. As used in this specification, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, as used in this specification, the terms "comprises" and / or "comprising" identify the presence of the recited features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0062] In the following claims, all means or step plus function elements corresponding structures, materials, acts, and equivalents, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Claims

1. An optical system comprising: a projection optical device configured to generate a light beam; a light guide optical element; wherein the light guide optical element comprises: a light guide having two major surfaces, wherein a light beam generated by the projection optical device and coupled into the light guide is reflected at the two major surfaces and travels through the light guide; a transparent plate; a first polymer layer disposed on one of the two major surfaces of the light guide, wherein the material of the first polymer layer is selected to maintain total internal reflectance in the light guide, and the refractive index of the first polymer layer is less than the refractive index of the light guide; a second polymer layer disposed between the first polymer layer and the transparent plate, wherein the material of the second polymer layer is selected to have a Young's modulus lower than the Young's modulus of the first polymer layer, and the refractive index of the second polymer layer is greater than the refractive index of the first polymer layer; An optical system having the above components.

2. The Shore hardness of the second polymer layer is lower than the Shore hardness of the first polymer layer. The optical system according to Claim 1.

3. The transparent plate has a higher coefficient of thermal expansion than the light guide. The optical system according to Claim 1.

4. The light guide optical element further comprises a third layer disposed between the second polymer layer and the transparent plate. The optical system according to Claim 1.

5. The light guide comprises a coupling-out device configured to extract light guided by the light guide from the light guide. The optical system according to Claim 1.

6. The coupling-out device comprises a plurality of surfaces disposed within the light guide at one or more oblique angles with respect to the two major surfaces of the light guide. The optical system according to Claim 5.

7. A light guide optical element comprising: a light guide having two major surfaces, wherein a light beam generated by a projection optical device and coupled into the light guide travels through the light guide by being reflected at the two major surfaces; a transparent plate; A first polymer layer disposed on one of the two major surfaces of the light guide, wherein the material of the first polymer layer is selected to maintain total internal reflectance in the light guide, and the refractive index of the first polymer layer is lower than the refractive index of the light guide, the first polymer layer; A second polymer layer disposed between the first polymer layer and the transparent plate, wherein the material of the second polymer layer is selected to have a Young's modulus lower than the Young's modulus of the first polymer layer, and the refractive index of the second polymer layer is higher than the refractive index of the first polymer layer, the second polymer layer; A light guide optical element having the same. **Claim 8** The Shore hardness of the second polymer layer is lower than the Shore hardness of the first polymer layer. The light guide optical element according to claim 7. **Claim 9** The transparent plate has a higher coefficient of thermal expansion than the light guide. The light guide optical element according to claim 7. **Claim 10** The light guide optical element further includes a third layer disposed between the second polymer layer and the transparent plate. The light guide optical element according to claim 7. **Claim 11** The light guide includes a coupling-out device configured to derive light guided by the light guide from the light guide. The light guide optical element according to claim 7. **Claim 12** The coupling-out device includes a plurality of surfaces disposed in the light guide at one or more oblique angles with respect to the two major surfaces of the light guide. The light guide optical element according to claim 11. **Claim 13** A method of manufacturing a light guide optical element, Providing a light guide having two major surfaces, wherein the light guide is generated by a projection optical device and configured such that a light beam coupled to the light guide can travel through the light guide by reflecting at the two major surfaces; Providing a transparent plate; Disposing a first polymer layer on one of the two major surfaces of the light guide, wherein the material of the first polymer layer is selected to maintain total internal reflectance in the light guide, and the refractive index of the first polymer layer is lower than the refractive index of the light guide; A step of disposing a second polymer layer between the first polymer layer and the transparent plate, wherein the material of the second polymer layer has a Young's modulus lower than that of the first polymer layer and is selected such that the refractive index of the second polymer layer is higher than that of the first polymer layer, the step; A method including the above.

14. The shore hardness of the second polymer layer is selected to be lower than that of the first polymer layer. The method according to claim 13.

15. The transparent plate has a higher coefficient of thermal expansion than the light guide. The method according to claim 13.

16. Further including providing a third layer disposed between the second polymer layer and the transparent plate. The method according to claim 13.

17. The first polymer layer, the second polymer layer, and the third layer are formed as a laminated structure before disposing the transparent plate on the third layer, with the first polymer layer disposed on one of the two major surfaces of the light guide. The method according to claim 16.

18. Providing a coupling-out device to the light guide, the coupling-out device being configured to derive the light guided by the light guide from the light guide. The method according to claim 13.

19. The coupling-out device has a plurality of surfaces disposed in the light guide at one or more oblique angles with respect to the two major surfaces of the light guide. The method according to claim 18.

20. Disposing the first polymer layer on one of the two major surfaces includes adhering the first polymer layer to one of the two major surfaces of the light guide. The method according to claim 13.

21. The material of the first polymer layer is selected to cause oxygen inhibition in the surface layer of the first polymer layer that is not in contact with one of the two major surfaces of the light guide. The method is as follows: While the surface layer of the first polymer layer remains uncured, further including curing a part of the first polymer layer so that the surface layer of the first polymer layer undergoes curing, and applying the second polymer layer to the uncured surface layer of the first polymer layer. The method according to claim 20.

22. An optical structure, A light guide having two major surfaces, wherein a light beam generated by a projection optical device and coupled into the light guide travels through the light guide by reflecting on the two major surfaces, a light guide, A first polymer layer disposed on one of the two major surfaces of the light guide, wherein the material of the first polymer layer is selected to maintain total internal reflectance in the light guide, and the refractive index of the first polymer layer is lower than the refractive index of the light guide, a first polymer layer, and, A second polymer layer disposed on the first polymer layer, wherein the material of the second polymer layer is selected to have a Young's modulus lower than the Young's modulus of the first polymer layer, and the refractive index of the second polymer layer is higher than the refractive index of the first polymer layer, a second polymer layer, An optical structure having.

23. The Shore hardness of the second polymer layer is lower than the Shore hardness of the first polymer layer, The optical structure according to claim 22.

24. The light guide includes a coupling-out device configured to derive light guided by the light guide from the light guide, The optical structure according to claim 22.

25. The coupling-out device includes a plurality of surfaces disposed in the light guide at one or more oblique angles with respect to the two major surfaces of the light guide, The optical structure according to claim 24.

26. A method for manufacturing an optical structure, comprising: Providing a light guide having two major surfaces, the light guide being configured such that a light beam generated by a projection optical device and coupled into the light guide can travel through the light guide by reflecting on the two major surfaces, Disposing a first polymer layer on one of the two major surfaces of the light guide, wherein the material of the first polymer layer is selected to maintain total internal reflectance in the light guide, and the refractive index of the first polymer layer is smaller than the refractive index of the light guide, a step, A step of disposing a second polymer layer on the first polymer layer, wherein the material of the second polymer layer is selected to have a Young's modulus lower than that of the first polymer layer, and the refractive index of the second polymer layer is higher than that of the first polymer layer, the step; A method comprising.

27. The shore hardness of the second polymer layer is selected to be lower than that of the first polymer layer, The method according to claim 26.

28. The first polymer layer and the second polymer layer are formed as a laminated structure before disposing the first polymer layer on one of the two major surfaces of the light guide, The method according to claim 26.

29. A coupling-out device is provided in the light guide, and the coupling-out device is configured to derive light guided by the light guide from the light guide, The method according to claim 26.

30. The coupling-out device includes a plurality of surfaces disposed in the light guide at one or more oblique angles with respect to the two major surfaces of the light guide, The method according to claim 29.

31. Disposing the first polymer layer on one of the two major surfaces includes adhering the first polymer layer to one of the two major surfaces of the light guide, The method according to claim 26.

32. The material of the first polymer layer is selected to cause oxygen inhibition on the surface layer of the first polymer layer that is not in contact with one of the two major surfaces of the light guide, The method is, Curing a part of the first polymer layer so that the surface layer of the first polymer layer undergoes curing while remaining uncured, and Applying the second polymer layer to the uncured surface layer of the first polymer layer, Further including, The method according to claim 26.

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