Compact head-mounted display system with small input port and large output port

Abstract

An optical device includes: a first light-transmitting substrate having at least two parallel principal surfaces; a light wave input aperture; a light wave output aperture located adjacent to one of the principal surfaces of the substrate; a light wave output pupil; a light wave input element for coupling a light wave with a field of view and a central light wave into the substrate to achieve total internal reflection from the principal surfaces of the substrate; and at least one reflective surface having an active region and located between the two principal surfaces of the light-transmitting substrate for coupling light waves out of the substrate, wherein light waves trapped inside the substrate are reflected at least twice by the active region of the reflective surface before being coupled out of the substrate, substantially reflected from one of the principal surfaces between first and second reflectivities from the reflective surface, and then reflected from the reflective surface and through the output aperture toward the output pupil. An optical device for transmitting light waves is also provided.

Description

Technical Field

[0001] This invention relates to substrate-based optical waveguide devices, and more particularly to devices including a reflective surface supported by a light-transmitting substrate.

[0002] This invention can be implemented to gain advantages in a wide range of imaging applications, such as head-mounted displays, head-up displays, cellular phones, compact displays, and 3D displays. Background Technology

[0003] One of the key applications of compact optics is in head-mounted displays (HMDs), where the optical module acts as both an imaging lens and a combiner, in which a two-dimensional display is imaged to infinity and reflected into the observer's eye. The display can be obtained directly from a spatial light modulator (SLM) (such as a cathode ray tube (CRT), liquid crystal display (LCD), organic light-emitting diode array (OLED), scanning source, and similar devices), or indirectly via a relay lens or fiber optic bundle. The display comprises an array of elements (pixels) imaged to infinity by a collimating lens and transmitted into the observer's eye via reflective or partially reflective surfaces that act as a combiner for non-perspective and perspective applications, respectively. Typically, conventional free-space optical modules are used for these purposes. As the desired field of view (FOV) of the system increases, these conventional optical modules become larger, heavier, and bulkier, and are therefore impractical even for medium-performance devices. This is a major drawback for all types of displays, but especially for HMDs where the system should be as light and compact as possible.

[0004] The need for tightness has led to several different complex optical solutions. On the one hand, all of these optical solutions are still not tight enough for most practical applications, and on the other hand, all of these optical solutions suffer from major defects in terms of manufacturability, price and performance.

[0005] The teachings included in International Patent Publication Nos. WO2017 / 141239, WO2017 / 141240, WO2017 / 141242, WO2019 / 077601 and WO2020 / 157747 are incorporated herein by reference. Summary of the Invention

[0006] This invention facilitates the provision of compact substrates for applications such as HMDs. The invention allows for a relatively wide field of view (FOV) combined with a relatively large eye movement box (EMB) value. The resulting optical system supplies large, high-quality images while also accommodating large eye movements. The optical system according to the invention is particularly advantageous because it is substantially more compact than prior art implementations; however, it can even be readily incorporated into optical systems with various specialized configurations.

[0007] Therefore, the broad objective of this invention is to mitigate the shortcomings of existing compact optical display devices and to provide other optical components and systems with improved performance according to specific requirements.

[0008] Therefore, according to the present invention, an optical device is provided, comprising: a first light-transmitting substrate having at least two parallel principal surfaces; an input aperture; an output aperture located adjacent to one of the principal surfaces of the substrate; an output pupil; an input element for coupling a light wave having a field of view and a central light wave into the substrate to achieve total internal reflection from the principal surfaces of the substrate; and at least one flat reflective surface having an active region and located between the two principal surfaces of the light-transmitting substrate for coupling light waves out of the substrate, wherein light waves trapped inside the substrate are reflected at least twice by the active region of the reflective surface before being coupled out of the substrate, substantially reflected from one of the principal surfaces between a first and a second reflectance ratio from the reflective surface, and then reflected from the reflective surface and through the output aperture directly toward the output pupil.

[0009] According to the present invention, an optical device for transmitting light waves is further provided, comprising: a first light-transmitting substrate having at least two parallel principal surfaces and at least one edge; an input aperture; an output aperture located next to one of the principal surfaces of the substrate; an output pupil; an input surface for coupling light waves having a first field of view and a central light wave into the substrate to achieve total internal reflection from the principal surfaces of the substrate; and at least one flat reflective surface having an active area and located between the two principal surfaces of the light-transmitting substrate for coupling light waves out of the substrate, wherein light waves coupled into the substrate substantially normally to the principal surfaces of the substrate through the input aperture are reflected at least twice by the input surface before being coupled into the substrate, and are reflected substantially between a first and a second reflectance ratio from the input surface from one of the principal surfaces. Attached Figure Description

[0010] The invention will be described with reference to the following illustrative figures and certain preferred embodiments, so that it may be more fully understood.

[0011] Referring specifically to the accompanying drawings, it should be emphasized that the details shown are merely illustrative and for the purpose of a discussion of preferred embodiments of the invention, and are presented to provide a description of the principles and concepts of the invention that are considered most useful and readily understood. In this respect, no attempt is made to show the structural details of the invention in more detail than necessary for a basic understanding of the invention. The description taken in conjunction with the drawings is intended to serve as a direction for those skilled in the art regarding how the invention can actually be embodied in several forms.

[0012] In the attached diagram:

[0013] Figure 1 is a side view of an exemplary transparent substrate of the prior art;

[0014] Figure 2 is a side view of another prior art exemplary light-transmitting substrate;

[0015] Figures 3A and 3B illustrate the desired reflectance and transmittance characteristics of selective reflective surfaces for two ranges of incident angles used in exemplary transparent substrates of the prior art.

[0016] Figure 4 illustrates the reflectance curve as a function of the incident angle for an exemplary dielectric coating;

[0017] Figures 5A, 5B, and 5C illustrate cross-sectional views of a prior art transparent substrate with coupling-in and coupling-out surfaces and a partial reflection redirection element.

[0018] Figure 6A and 6B The diagram illustrates the creation of gaps and ghost images in the coupled image.

[0019] Figure 7 This is a schematic cross-sectional view of an embodiment of the present invention, which guides a substrate having a single coupling-in element and a single coupling-out element, wherein all light rays are coupled toward the output pupil;

[0020] Figure 8A , 8B Figure 8C is a schematic cross-sectional view of an embodiment of the present invention, which is guided by a substrate having a single coupling-in element and a single coupling-out element, wherein all light rays for the entire coupling field of view are coupled toward the output pupil;

[0021] Figure 9 This is a schematic cross-sectional view of an embodiment of the present invention, which has a single coupling-in element and two coupling-out elements;

[0022] Figure 10 This is a schematic cross-sectional view of an embodiment of a substrate guide with a single coupling-in element and a single coupling-out element according to the present invention, wherein the coupling-out image is tilted about the normal to the substrate plane;

[0023] Figure 11 is a diagram illustrating a prior art method for augmenting an image with a limited field of view along two axes using a dual-light-guide optical element configuration.

[0024] Figure 12 This is a schematic cross-sectional view of a substrate-guided beam expander with a single partial reflective coupling-in element and two coupling-out elements according to the present invention.

[0025] Figure 13This is a schematic cross-sectional view of a substrate-guided beam expander with a single partial reflective coupling-in element and a single coupling-out element according to the present invention;

[0026] Figure 14 This is a schematic cross-sectional view of a substrate-guided beam expander according to the present invention, having two partially reflective coupling-in elements and two coupling-out elements arranged in a symmetrical configuration;

[0027] Figure 15 This is a schematic cross-sectional view of a substrate-guided beam expander according to the present invention having two partially reflective coupling-in elements and two coupling-out elements arranged in a symmetrical configuration, wherein only a portion of the coupled light reaches the output pupil;

[0028] Figure 16 Another schematic cross-sectional view of a substrate-guided beam expander according to the invention, having two partially reflective coupling-in elements and two coupling-out elements arranged in a symmetrical configuration;

[0029] Figure 17 This is yet another schematic cross-sectional view of a substrate-guided beam expander according to the invention, having two partially reflective coupling-in elements and two coupling-out elements arranged in a symmetrical configuration.

[0030] Figure 18 This is a schematic cross-sectional view of a substrate-guided beam expander according to the present invention, having four partial reflective coupling-in elements and four coupling-out elements arranged in a two-step symmetrical configuration.

[0031] Figure 19 This is a schematic cross-sectional view of an embodiment of the present invention having a substrate guide with three coupling-in elements and three coupling-out elements arranged in a three-step asymmetric configuration, wherein the coupling-out image is tilted about the normal to the substrate plane.

[0032] Figure 20 The diagram schematically illustrates the creation of gaps and ghosting in the coupled image of the beam expander;

[0033] Figure 21A and 21B A schematic cross-sectional view of a substrate-guided beam expander according to the invention, having two partially reflective coupling-in elements and two coupling-out elements arranged in a symmetrical configuration, wherein the edge portions of the coupling-out elements are immobile; and

[0034] Figure 22A and 22B A schematic cross-sectional view of a substrate-guided beam expander according to the invention, having two partially reflective coupling-in elements and two coupling-out elements arranged in a symmetrical configuration, wherein the edge portions of the coupling-out and coupling-in elements are truncated. Detailed Implementation

[0035] Figure 1 illustrates a cross-sectional view of a prior art light-transmitting substrate, wherein a first reflective surface 16 is illuminated by a collimated light wave 12 emitted from a display source 4 and collimated by a lens 6 located between the source 4 and the substrate 20 of the device. The reflective surface 16 reflects the incident light from the source 4, causing the light wave to be trapped within the planar substrate 20 by total internal reflection. After several reflections from the main surfaces 26, 27 of the substrate 20, the trapped light wave reaches a partial reflective element 22, which couples the light emanating from the substrate into the viewer's eye 24, located within an output pupil 25. In this text, the input aperture 17 of the substrate 20 is defined as the aperture through which the input light wave enters the substrate, and the output aperture 18 of the substrate is defined as the aperture through which the trapped light wave exits the substrate. In the case of the substrate illustrated in Figure 1, both the input and the input aperture coincide with the lower surface 26. However, other configurations are conceivable, where the input and image light waves from the displacement source 4 are located on opposite sides of the substrate or on one of the edges of the substrate. As illustrated, the active areas of the input and output apertures, which are approximations of the projections of the input element 16 and the output element 22 on the main surface 26, are similar to each other.

[0036] In HMD systems, the entire area of ​​the EMB must be illuminated by all light waves emanating from the display source so that the viewer's eye can simultaneously view the entire FOV of the projected image. Therefore, the system's output aperture must be correspondingly enlarged. On the other hand, the optical module must be lightweight and compact. Since the lateral extension of the collimating lens 6 is determined by the lateral dimension of the substrate's input aperture, it is desirable that the input aperture be as small as possible. In systems such as those illustrated in Figure 1, where the lateral dimension of the input aperture is similar to the lateral dimension of the output aperture, there is an inherent contradiction between these two requirements. Most systems based on this optical architecture suffer from a small EMB and a small achievable FOV, and suffer from a large and bulky imaging module.

[0037] Figure 2 illustrates an embodiment that at least partially solves this problem, wherein the elements coupling light waves from the substrate are an array of partially reflective surfaces 22a, 22b, etc. The output aperture of this configuration can be expanded by increasing the number of partially reflective surfaces embedded within the substrate 20. Therefore, it is possible to design and construct an optical module with a small input aperture and a large output aperture. As can be seen, the trapped light rays reach the reflective surfaces from two different directions 28, 30. In this particular embodiment, the trapped light rays reach the partially reflective surface 22a from one of these directions 28 after an even number of reflections from the main surfaces 26 and 27 of the substrate, wherein the angle of incidence between the trapped light rays and the normal to the reflective surface is β. ref .

[0038] The trapped light ray, after an odd number of reflections from substrate surfaces 26 and 27, reaches the partially reflective surface 22b from the second direction 30, wherein the angle of incidence between the trapped light ray and the normal to the reflective surface is β. ref .

[0039] As further illustrated in Figure 2, for each reflective surface, each ray of light first arrives at the surface from direction 30, with some of the rays then striking the surface again from direction 28. To prevent undesirable reflections and ghosting, it is important that the reflectance be negligible for rays striking the surface from the second direction 28.

[0040] A solution to this requirement utilizing the angular sensitivity of a thin-film coating was previously proposed in the disclosure mentioned above. The desired discrimination between the two incident directions can be achieved if one angle is significantly smaller than the other. It is possible to provide a coating with very low reflectivity at high incident angles and high reflectivity for low incident angles. This property can be utilized to prevent unwanted reflections and ghosting by eliminating reflectivity in one of the two directions.

[0041] Referring now specifically to Figures 3A and 3B, these figures illustrate the desired reflectivity behavior of a portion of the reflecting surface 34. Despite having an off-axis angle β... ref The light ray 32 (Fig. 3A) is partially reflected and coupled out from the substrate 20, but at an off-axis angle β' ref Light ray 36 (Fig. 3B) reaching the reflective surface 34 is transmitted through the reflective surface 34 without any significant reflection.

[0042] Figure 4 illustrates the reflectance curve of a typical partially reflective surface of this specific system as a function of the angle of incidence for S-polarized light with a wavelength λ = 550 nm. For full-color displays, a similar reflectance curve should be achieved for all other wavelengths in the relevant visible spectrum, typically for most display sources between 430 nm and 660 nm. Two significant regions exist in this curve: between 65° and 85°, where the reflectance is very low; and between 10° and 40°, where the reflectance increases monotonically with increasing angle of incidence. As can be seen in Figures 3 and 4, the requested reflectance behavior of the partially reflective surface 22 of the embodiment illustrated in Figure 2 is not conventional. Furthermore, to maintain low reflectance in the higher angle regions, the reflectance in the lower angle regions cannot exceed 20%–30%. Moreover, to achieve uniform brightness throughout the FOV, the reflectance of the partially reflective surface is required to gradually increase towards the edges of the substrate. Therefore, the maximum achievable efficiency is relatively low and typically cannot exceed 10%.

[0043] Figures 5A and 5B illustrate embodiments for overcoming the problems described above. Instead of using a single element (22 in Figure 2) that performs the dual function of coupling light waves out of substrate 20 and directing light waves into the user's eye 24, the requested function is divided into two different elements. That is, an element embedded inside the substrate couples light waves out of the substrate, while a second conventional partially reflective element located outside the substrate redirects the light waves into the viewer's eye. As illustrated in Figure 5A, two rays 63 (dashed lines) from a plane light wave emitted from a display source and collimated by a lens (not shown) have angles of incidence relative to the main surfaces 70 and 72 of the substrate. Light enters through input hole 86 onto a light-transparent substrate 64 having two parallel principal surfaces 70 and 72. Light rays striking the reflective surface 65 travel at an angle α to the principal surfaces of the substrate. sur1 The reflective surface 65 reflects the incident light, trapping it inside the planar substrate 64 by total internal reflection from the main surface. To distinguish between the various "propagation orders" of the trapped light wave, the superscript (i) indicates order i. The input light wave striking the substrate with zero order is indicated by the superscript (0). After each reflection from the coupled reflective surface, the order of the trapped light increases from (i) to (i+1). The off-axis angle between the first-order trapped light wave and the normal to the main surfaces 70, 72 is... yes:

[0044]

[0045] After several reflections from the surface of the substrate, the trapped light reaches the second flat reflective surface 67, which couples the light out of the substrate. It is assumed that surface 67 is inclined at the same angle to the main surface as the first surface 65, that is, surfaces 65 and 67 are parallel and α... sur2 =α sur1 Then the angle α between the coupled ray and the normal to the substrate plane is... out yes:

[0046]

[0047] Therefore, the coupled light ray is tilted towards the substrate at the same angle as the incident light ray. So far, the coupled light wave has behaved in a manner similar to the light wave illustrated in Figure 1. However, Figure 5A illustrates a different behavior, where the incident angle is the same as that of light ray 63. Two light rays 68 (dashed line) strike the right side of the reflective surface 65. After two reflections from surface 65, the light waves are coupled into the substrate 64 by total internal reflection, and the off-axis angle of the light rays trapped inside the substrate is now:

[0048]

[0049] After several reflections from the main surface of the substrate, the trapped ray reaches the second reflective surface 67. Ray 68 is reflected twice from the coupling surface 67, at the same off-axis angle α as the other two rays 63. out Coupled from the substrate, the other two rays 63 are reflected only once from substrates 65 and 67, at an off-axis angle α. out These four rays also share the same incident angle on the main plane of the substrate. Although all four rays strike the substrate and couple out of it at the same off-axis angle, there are fundamental differences between them: the two rays 68 incident on the right side of the reflective surface 65 are closer to the right edge 66 of the substrate 64, are reflected twice from surfaces 65 and 67, and couple out of the substrate at the left side of surface 67, which is closer to the opposite left edge 69 of the substrate. On the other hand, the two rays 63 incident on the left side of the reflective surface 65 are closer to the center of the substrate 64 and are reflected once from surfaces 65 and 67. They couple out of the substrate at the right side of surface 67, which is closer to the center of the substrate.

[0050] As further illustrated in Figures 5A and 5B, an angle α of 72° to the surface of the substrate can be added. red The tilted reflective surface 79 is used to adjust the tilt angle α of the image. out As shown, the image coupled through the output aperture 89 of the substrate is reflected and rotated so that it passes through the substrate again substantially normally to the main surface of the substrate and reaches the viewer's eye 24. To minimize distortion and chromatic aberration, it is preferable to embed surface 79 in the redirection prism 80 and use a second prism 82 to complete the shape of the substrate 64, both made of the same material, which should not necessarily be similar to the material of prism 80. To minimize the thickness of the system, as illustrated in FIG5B, it is possible to use an array of parallel partially reflective surfaces 79a, 79b, etc., instead of a single reflective surface 79, wherein the number of partially reflective surfaces can be determined according to the requirements of the system. Another way to redirect the coupled light waves to the viewer's eye is to use flat metasurfaces structured using patterns at the subwavelength scale.

[0051] As shown in equation (20) of the previously mentioned public WO2017 / 141239, the following condition must be met:

[0052] In other words, the incident angle of the coupled light rays relative to the normals to the principal surfaces 70 and 72 It should be less than the tilt angle of the coupled surface 67 relative to the normal. Figure 6A and 6BAn embodiment in which the condition of equation (4) is violated is illustrated, that is, instead, the relationship for at least one of the coupled light waves is satisfied:

[0053]

[0054] like Figure 6A As illustrated, the coupled light ray 81 has its first incident point at surface 67 originating from the lower main surface 72. Consequently, the coupled light ray is reflected twice from surface 67, and after the second reflection, it is coupled out of the substrate at the following output angle:

[0055] It is the "appropriate" output angle.

[0056] Figure 6B The illustration shows different rays 84 from the same coupled light wave that first strikes surface 67 from the upper main surface 70 at point 85. Thus, the coupled rays 84 are reflected from surface 67 at the following off-axis angle:

[0057]

[0058] Light 84 now strikes surface 67 from the lower main surface 72, is reflected twice from the surface, and after the second reflection is coupled out of the substrate at the following output angle:

[0059]

[0060] This angle is not necessarily the required angle. Assume, for example, α sur2 =18° and The actual light rays coupled from substrate 64 then have α out (act) = -10°. In other words, not only is the “correct” ray that should be coupled out as ray 84 lost from the image and thus creates a gap in the image, but instead, there is another ray originating from the “wrong” direction, which creates a ghosting.

[0061] As shown in equations (23) and (24) of WO2017 / 141239, the result of equation (5) in this specification is: the maximum tilt angle of surface 67 is determined by α sur2 The value is less than 16°, and therefore, the minimum output angle of the central output light wave is... That is, the coupled image is tilted substantially about the normal to the substrate plane. However, it is generally required that the coupled image projected onto the viewer's eye be oriented substantially normally to the substrate plane. Therefore, the tilt of the image not coupled from the substrate toward the system's output pupil should be adjusted by adding a partially reflective surface 79 at an angle to the surface 72 of the substrate. Tilt, as shown in Figures 5A-5C.

[0062] Alternative methods according to the invention for overcoming the problems described above are then illustrated. That is, at least a portion of the light wave trapped inside the substrate is reflected at least twice by the coupling element in a manner similar to the embodiments of Figures 5A-5C before being coupled out of the substrate through the output aperture. However, the light wave is reflected from the coupling surface in the direction of the output pupil. Inevitably, the condition given in equation (5) will be violated, but as illustrated below, there are embodiments in which ghosting and gaps in the image can be avoided.

[0063] Figure 7 The first example illustrated is primarily suitable for optical systems with small to medium FOV and EMB. As illustrated, the optical device includes a light-transmitting substrate 83 having at least two parallel principal surfaces: a reflective surface 65 for coupling light waves passing through an input aperture 86 into the substrate; and a reflective surface 67, parallel to surface 65, for coupling light waves exiting the substrate through an output aperture 89 toward the system's output pupil 90. For a perspective system where light from an external scene needs to pass through the substrate to reach the viewer's eye, surface 67 should be partially reflective. Three rays—two marginal light waves and a central light wave from the image—are coupled out of the substrate to the center of the output pupil 90. As shown, rays 91R, 91M, and 91L, having incident angles that are the largest, central, and smallest angles in the FOV, are coupled out from the right, central, and left portions of the coupling surface 67, respectively. Although rays 91M and 91L are coupled out after two reflections, ray 91R is coupled out after a single reflection from surface 67.

[0064] Figure 6B The possible approach to minimizing gap and ghosting effects, as illustrated in the diagram, is to separate the conditions that cause these undesirable effects. As explained above, a ray must meet two different requirements to deviate from its specified direction: it should be reflected at least twice from the coupling surface, and it should satisfy the relationship of equation (5). As illustrated here, ray 91R does not satisfy the first condition. It is reflected only once from surface 67. Therefore, it can be allowed to satisfy equation (5). On the other hand, rays 91M and 91L are reflected twice from surface 67, and therefore, they should not be allowed to satisfy equation (5). A possible way to achieve these requirements is by selecting constraints for the central ray 91M, that is:

[0065]

[0066] therefore

[0067]

[0068] Assuming the central light wave couples out normally to the main plane of the substrate, this results in:

[0069] α sur2 =18° (11).

[0070] Figure 8A , 8B The system is illustrated in Figure 8C, where equation (11) is satisfied, and the zero-order incident angle is... and The angles in the air are +10°, 0°, and -10°, and the refractive index of the substrate is 2.0. The substrate thickness is 4mm, the eyedropper distance is 18mm, and the output pupil diameter is 6mm. Figure 8A , 8B As shown in 8C, all rays with the maximum angle of incidence are reflected only once from surface 65, and therefore also once from surface 67, and thus, rays with the "wrong" direction cannot be formed. Rays with the minimum angle of incidence ( Figure 8C All rays are reflected twice from surface 65, and therefore twice from surface 67. However, since they all satisfy the condition of equation (4), all rays are coupled out in the appropriate direction. Regarding the central incident angle ( Figure 8B The light rays, partially reflected only once from surfaces 65 and 67, but those reflected twice propagate parallel to surface 67 within the substrate, and therefore cannot directly strike the upper surface 70. Thus, Figure 8A , 8B All the drawn rays shown in Figure 8C are coupled out of the substrate in the appropriate direction.

[0071] Obviously, Figure 8A , 8B The embodiment illustrated in Figure 8C is similar to the embodiment in Figure 1. However, it has a significant advantage over the prior art. The tilt angle of surface 22 is approximately 30°, and therefore, the size of the output aperture is approximately 1.5·d, where d is the thickness of the substrate. On the other hand, the tilt angle of surface 67 is 18°, and therefore, the size of the output aperture in this embodiment is approximately 3·d. Therefore, for a given substrate thickness, the output aperture can be doubled, or alternatively, for a given output aperture, the substrate thickness in this embodiment can be reduced to half.

[0072] However, there are applications that require further enlarging of the output aperture while still maintaining the substrate as thin as possible. Figure 9An embodiment in which the output aperture is enlarged without increasing the thickness of the substrate is illustrated. As shown, a partial reflective surface 93 is embedded within the substrate 83. Surface 93 is parallel to the coupling-in surface 65 and the coupling-out surface 67. That is, the tilt angle of surface 93 with respect to the main surface of the substrate 83 is α. sur2 For the entire field of view (FOV) of an image propagating within substrate 83, surface 93 is partially reflective. That is, it partially reflects and partially transmits coupled-in light waves with the following incident angles:

[0073] Furthermore, it undergoes total internal reflection for light waves with the following angles of incidence:

[0074]

[0075] A possible method to achieve relationships (12) and (13) is to apply an optical adhesive with a refractive index much lower than that of the substrate 83 onto the partially reflective surface 93. The critical angle α is set by the refractive indices of the substrate 83 and the surface 93. cr For the entire FOV of the light wave trapped inside the substrate 83, the following relationship must be satisfied:

[0076]

[0077] For those with Figure 8A , 8B An optical system with the same parameters as the embodiment of 8C. and The critical angle α was generated using Norland NA-148 optical adhesive with a refractive index of 1.48. cr =47.7°, and therefore, the condition of Equation 14 is satisfied.

[0078] like Figure 9 As shown in the diagram, light ray 95 (dashed line) is coupled into substrate 83 after a single reflection from surface 67, and thus propagates within substrate 83 with a first-order off-axis angle. After several reflections from the main surface of substrate 83, light 95 strikes surface 93. Since the light strikes the surface from the right, it behaves in a similar manner to the light striking surface 67, and therefore...

[0079]

[0080] Thus, the condition of equation (12) is satisfied, and ray 95 is split by surface 93. That is, a portion of the intensity of ray 95 is reflected from surface 93 as having an off-axis angle. The light ray 95a is thus coupled out of the substrate 83 through the lower surface 72. In another part, the intensity of the light ray 95 passes through the surface 93 as light ray 95b and continues to propagate within the substrate 83, having the same off-axis angle. After one reflection from the upper main surface 70, light ray 95b strikes surface 93 again. Now, light ray strikes the surface from the left, and it behaves similarly to the light ray striking surface 67, and therefore,

[0081]

[0082] Thus, the condition of equation (13) is satisfied, and the ray 95b is totally internally reflected from the surface 93 and continues to propagate inside the substrate 83, having the following off-axis angle:

[0083]

[0084] Specifically, the light ray 95b propagates inside the substrate 83 and has a second-order off-axis angle. After two reflections from the coupling surface 67, ray 95b is coupled out from the substrate 83 with the same off-axis angle as ray 95a.

[0085] Similarly, Figure 9 As illustrated, another ray 96 (solid line) couples into the substrate 83 after two reflections from surface 67, and thus propagates within the substrate with a second-order off-axis angle. After several reflections from the main surface of substrate 83, light 96 strikes surface 93. Since the light strikes the surface from the left and behaves in a similar manner to the light striking surface 67, therefore...

[0086]

[0087] Thus, the condition of equation (13) is satisfied, and the ray 96 undergoes total internal reflection from surface 93 and continues to propagate inside substrate 83, having the following off-axis angle:

[0088]

[0089] Specifically, the light ray 96 propagates inside the substrate 83 and has a first-order off-axis angle. After a single reflection from the lower main surface 72 of the substrate 83, ray 96 strikes surface 93 again. Similar to the behavior of ray 95, ray 96 is split by surface 93. A portion of the intensity of ray 96 is reflected from surface 93 as having an off-axis angle. The light ray 96a is thus coupled out of the substrate 83 through the lower surface 70. Another portion of the intensity of the light ray 96 passes through surface 93 as light ray 96b and continues to propagate within the substrate 83, having the same off-axis angle. After one reflection from the coupling surface 67, ray 96b is coupled out from the substrate 83 with the same off-axis angle as rays 95a, 95b, and 96a. Therefore, the output hole of substrate 83 is a combination of surfaces 93 and 67. Thus, the actual active area of ​​the output hole of substrate 83 is related to... Figure 8A , 8B The actual active area of ​​the substrate 83 shown in Figure 8C has been doubled, while the substrate thickness remains the same. On the other hand, the brightness of the light waves coupled from the substrate 83 has been reduced by the reflectivity of the surface 93.

[0090] Figure 10 The illustration shows another embodiment of the invention. Here, the coupled image projected onto the viewer's eye is not oriented normally to the principal plane of the substrate, but rather at an angle α. inc Tilt. This configuration can be used in applications where the image is required to be outside the viewer's visual axis. That is, the image is shifted upwards or laterally for top-down and eyeglass configurations, respectively. An alternative use could be in a top-down configuration where the image is at the viewer's visual axis, but the substrate is tilted at an angle α. inc Rotate to reduce the system's eye level while keeping the upper edge of the substrate away from the user's forehead.

[0091] Figure 10 The embodiment shown has the following parameters: α sur2 =12.5°; the refractive index of the substrate is 2.0, and therefore, α Cr =30°; zero-order incident angle and In the air, the angles are 10°, 20°, and 30°, and therefore inside the substrate, they are 5°, 9.8°, and 14.5°; respectively, the first-order incident angles and The angles are 30°, 34.8°, and 39.5°, and the second-order incident angles are... and The angles are 55°, 59.8°, and 64.5°. For all coupled light waves in the substrate, the condition of equation (4) is satisfied. As shown, three rays from the two edge light waves and the central light wave from the image are coupled out from the substrate to the center of the output pupil 90. Rays 97L, 97M, and 97R, with incident angles that are the minimum, central, and maximum angles in the FOV, are coupled out from the left, central, and right portions of the coupling surface 67, respectively. Although rays 97M and 97L are coupled out after two reflections, ray 97R is coupled out after a single reflection from the surface 67. Since equation (4) is satisfied for the entire FOV, ghosting and gaps are avoided. In addition, since for the entire FOV and Therefore, light waves from the entire FOV can be reflected from the coupling surface 67 in the direction of the output pupil 90 without using the redirection element 79.

[0092] Figure 9 The illustration depicts a method for expanding an output aperture of a substrate along the propagation direction ξ by embedding a partially reflective surface 93 within the substrate 83. The output aperture can be further expanded along the ξ axis by embedding more partially reflective surfaces within the substrate. In many applications, it is required to further expand the aperture along the orthogonal axis η.

[0093] Figure 11 illustrates how a beam can be expanded along two axes using a dual-substrate configuration. The input wave 110 is coupled to a reflective surface 116a through a first reflecting surface 116a. Figure 9 In the first substrate 120a, which has a similar structure to the one illustrated in the diagram, the light propagates along the η-axis. A partially reflective surface 122a couples the light out of substrate 120a, and then the light is coupled into the second substrate 120b via a reflective surface 116b. The light then propagates along the ξ-axis and is coupled out via the partially reflective surface 122b. As shown, the original beam 110 is expanded along both axes η and ξ, where the overall expansion is determined by the ratio between the lateral dimensions of elements 116a and 122b.

[0094] In order to find a suitable configuration for the lateral expansion of the input light wave, it is important to note that the lateral expander 120a does not necessarily have to be partially transparent, as the main substrate 120b would have to be in the case of a transparent application.

[0095] Figure 12 The diagram shows... Figure 9The modified version. As shown, surface 116a here is a partially reflective surface that also satisfies the conditions of equations (12) and (13). Thus, the output aperture of substrate 83 is a combination of surfaces 116a, 122a1, and 112a2. Therefore, the actual active area of ​​the output aperture of substrate 120b along the η-axis is three times that of the embodiment using only a single substrate. The reflectance of surfaces 116a, 122a1, and 112a2 for the incident angle satisfying equation (12) should be set to achieve a uniform image along the η-aperture axis. Figure 12 The configuration shown in the diagram has surfaces with reflectances of 67%, 50%, and 100% respectively for incident angles satisfying equation (12) (that is, surface 112a2 can be a simple mirror). Thus, the luminance efficiency of the lateral expander 120a is approximately 33%.

[0096] Figure 13 The diagram illustrates a lateral expander in which the brightness of the output light wave is increased due to lateral expansion. As shown, only two surfaces are embedded inside the substrate 120a: a partially reflective coupling surface 116a, which satisfies the conditions of equations (12) (having a reflectivity of 50%) and (13); and a reflective coupling out element 122a. Here, the brightness efficiency of element 120a is increased to 50%, and the expansion along the η-axis is reduced to 1 / 2.

[0097] exist Figure 12 and 13 In the system described, light from the display source is coupled into the substrate at the ends of the substrate. However, there are systems in which, preferably, symmetrical systems are used, i.e., the input light is coupled into the substrate at the central portion of the substrate.

[0098] Figure 14 The diagram illustrates the combination of two such... Figure 13 The method uses identical substrates, which are joined to create a symmetrical optical module 124. As can be seen, a portion of the light from the display source (not shown) passes directly through the partial reflective surfaces and exits from the substrate. The remaining portion of the light is coupled into small portions of the substrate, 120R on the right and 120L on the left, respectively, through partial reflective surfaces 116R and 116L. The trapped light is then coupled out through reflective surfaces 122R and 122L, respectively. The output aperture is twice the size of the system's input aperture, which is consistent with... Figure 13 The same amplification described in [the text]. However, unlike this system, Figure 14 The system in the diagram is symmetrical about the central line 125. Module 124 can be constructed as follows: Figure 13The diagram shows a combination of two identical substrates 120R and 120L, which are optically attached at the edge 123 of the substrates. The module can also be constructed from an isosceles triangular prism 126M, which is optically bonded to two identical parallelepipeds 126R and 126L.

[0099] remove Figure 14 In addition to the preferred external shape of the optical system illustrated in the figure, the symmetrical configuration also has advantages over... Figure 12 and 13 Other advantages of the system illustrated in the diagram. When considering the viewpoint, it should be noted that different segments of the resulting image emerge from different regions of the coupled elements. For example... Figure 15 As illustrated, a single plane wave 127 representing a specific viewing angle 128 emerges from the output pupil 90 and illuminates only a portion 129 of the overall array of coupled elements 122a.

[0100] Figure 16 The illustration shows how this perspective analysis can simplify the optical design of a symmetrical substrate. Based on the examination of the input plane wave 133 emerging from the right side of the display source, it is clear that only the right portion of wave 133R, partially coupled to the right portion 120R, reaches the system's output pupil 90. In contrast, the left portion of wave 133L, coupled to the left LOE 20L, does not reach the output pupil. Similarly, only the left portion 134L of wave 134 emerging from the left side of the display source reaches the output pupil, while the right portion 134R of the wave does not reach the output pupil.

[0101] There are two main consequences for this phenomenon. The first consequence is related to the symmetrical structure of the substrate. Assume the required FOV angle inside the substrate is α. FOV =α max =α min Therefore, for asymmetric substrates, such as Figure 12 and 13 As shown in the diagram, the maximum and minimum angles of the wave trapped inside the substrate are α and α, respectively. max and α min Therefore, the substrate should be designed to couple into and out of this angle range. However, for Figure 17 In the symmetrical substrate diagram, it is evident that, for the right portion 120R, only the lower portion of FOV 140RL is coupled into the system's output pupil, while the higher portion of FOV 140RH is coupled outside the output pupil and is not utilized by the viewer. Therefore, only the α portion, which is the lower half of the original FOV... min and The angular bandwidth between them is utilized by the right portion 120R. Similarly, only the lower portion of the FOV 140LL is utilized by the left facet 120L, and again, due to the symmetrical structure of the components, only... With αmin The lower angular bandwidth between them is utilized by the user here. Therefore, both sections of the substrate, 120R and 120L, must be coupled into and out with... The same element with the same FOV of the wave. Because the FOV of the light wave coupled within each of sections 120R and 120L is coupled in... Figure 12 and 13 The FOV inside the substrate 120a is half of that inside the substrate, so verifying that all the light rays encountered by the double reflections from surfaces 116a and 122a also satisfy the condition of equation (4) will now be much simpler. Figure 17 The design and manufacturing process of the two parts shown in the diagram are as follows: Figure 12 and 13 The design and fabrication processes for a single substrate, as illustrated in the diagram, are much easier.

[0102] Similar results relate to collimating lens 6. Since only the right half of the FOV is utilized by the right portion 120R, it can be inferred that this is the only relevant portion of the FOV for the right side of collimating lens 6R. Similarly, only the left side of the FOV relates to the left side of collimating lens 6L. Therefore, it is now possible to design much simpler collimating lenses, even for systems with very wide FOVs.

[0103] Figures 14 to 17 The diagram illustrates a method for expanding the output aperture by a factor of 2; however, systems with wide FOV and large EMB require a significantly greater expansion ratio. (Using...) Figure 12 It is possible to expand the output aperture through a similar approach as illustrated in the diagram. The number of beam splitters 122ai (i = 1, 2, ...) inserted inside the substrate 120a is not limited to 1. A larger number of beam splitters, n+2, can be used to expand the aperture, thus reducing the output brightness by the same ratio. However, the main drawback of this approach is that the FOV that can be coupled inside the substrate is limited due to the asymmetric structure of the substrate. Furthermore, the use of several different beam splitters makes the embodiment complex and challenging to manufacture.

[0104] Figure 18 The diagram illustrates the use of all of them. Figure 14The diagram illustrates an alternative embodiment of two different substrates with the same structure to improve the expansion ratio. As illustrated, the optical module 144 includes a primary substrate 124M and a secondary substrate 124S, wherein the lateral dimensions of substrate 124M along the ζ and η axes are twice as large as the lateral dimensions of substrate 124S. Typically, both substrates have the same lateral dimension along the ξ axis. The output surface 72S of substrate 124S is located adjacent to the input surface 70M of substrate 124M. The lateral extension of the incoming light wave along the η axis is expanded by a factor of 2 by substrate 124S, and then again by a factor similar to the overall expansion of 4. Therefore, the brightness of the output light wave is similarly reduced to 1 / 4. Ultimately, Figure 18 The approach illustrated in the diagram is more specific than... Figure 12 The approach shown in the diagram is much simpler, and it can encompass a much wider field of view (FOV). The number of elements 124 combined to form the expansion device is not limited to 2. A larger number of n different elements 124 can be connected to form an expansion ratio of 2. n Optical equipment.

[0105] Figure 8A , 8B 8C to Figure 18 The diagram shows what can be added. Figure 7 The diagram illustrates various features of the basic configuration, including: off-axis optical system ( Figure 10 ); Single coupled-out element ( Figure 8A , 8B and 8C) and multiple coupling elements ( Figure 9 Asymmetric lateral expansion ( Figure 12 and 13 ) and symmetrical lateral expansion ( Figures 14 to 18 ), and the device comprises a single component ( Figure 8A , 8B 8C to Figure 17 ) and multiple components ( Figure 18 Ultimately, any combination of any number of these features can be added to meet the specific requirements of the optical system. Figure 7 The basic embodiment is shown in the figure.

[0106] Figure 19 The diagram illustrates an optical device that processes several of the characteristics described above. As shown, device 146 is an off-axis multi-stage beam expander comprising three substrates 148A, 148B, and 148C. The lateral dimensions along the ξ-axis of substrates 148A and 148B are twice as large as those of substrates 148B and 148C, respectively. The output surfaces 72B and 72C of substrates 148B and 148C are positioned adjacent to the input surfaces 70A and 70B of substrates 148A and 148B, respectively. The lateral extension of the input light wave 150 is increased by eight times by device 146, while its brightness is reduced by the same factor.

[0107] As explained above, in Figures 7 to 19 In all embodiments illustrated in the figure, it is assumed that the coupled light rays inside the substrate must satisfy at least one of the following requirements: they should be reflected from the coupling surface no more than once or they should satisfy the relationship of equation (4). Otherwise, gaps and ghosting will occur. However, there are optical systems, primarily those with extremely wide FOVs, where this requirement is difficult to achieve. Assuming an optical system with a lateral FOV of 40° along the ξ axis in the air, then in Figure 7 and 8A In the embodiments illustrated in 8B and 8C, the tilt angle of the coupling surface is α. sur2 =18° and the refractive index of the substrate is 2.0. The minimum FOV in the air is And inside the substrate is After a single reflection from the coupled element, the off-axis angle of the light trapped inside the substrate is:

[0108]

[0109] The propagation angle is less than the critical angle α. cr =30°, and therefore, light waves cannot be trapped inside the substrate by TIR. This problem can be solved for some optical systems by tilting the substrate, such as... Figure 10 The diagram is shown in the image. However, the field of view (FOV) that can be trapped inside an asymmetric system is usually finite. Furthermore, for systems like... Figure 16 In the symmetrical system shown, the trapped field of view (FOV) can be doubled, but the substrate cannot tilt about its axis of symmetry due to its symmetrical structure. Therefore, to encompass the entire FOV of 40°, the tilt angle of the coupled element should be increased to at least α. sur2 =19.9°.

[0110] The main problem with the embodiment with this tilt angle is that the requirement for terminating unwanted artifacts as defined above no longer exists. Figure 20 The illustration shows the backward tracing (from EMB to input aperture) of ray 152, which has an off-axis angle of -16.1° in the air and -8° inside the substrate. The tilt angle of the coupled element is α. sur2 =20°. Since the light ray is located in the left segment of the FOV, it illuminates the left portion of the coupled element 122, and therefore reflects twice from the surface before being coupled into the substrate 120. The off-axis angle of the second-order propagating ray is:

[0111]

[0112] And therefore

[0113]

[0114] In other words, the conditions of equation (4) are not met. For example... Figure 20 As shown, because both conditions stated above are met simultaneously, the light ray enters the coupled element 116 from the lower surface 72 in the "wrong" direction. Therefore, it couples out with a different off-axis angle than the incoming light ray. Since the "wrong" light ray originates at the edge portion of the coupled-out surface 122, a possible solution is to render that portion of the substrate inactive.

[0115] Figure 21A and 21B The illustration shows a method for mechanical removal (e.g., by cutting the edge of the substrate). Figure 21A Alternatively, the edges of surfaces 112L and 112R can be coupled out by using mechanical stops 127L and 127R respectively (e.g.) Figure 21B The method shown in the figure is to concretize the solution.

[0116] The main problem with the proposed solution is that immobilizing the edge portions reduces the active area of ​​the coupled surface. The precise reduction is typically determined by the device's FOV and EMB, but for most relevant systems, it is around 25%. That is, the usable area of ​​the coupled surface is approximately 75% of its original size. Figure 14 The embodiment shown in the figure has an expansion ratio of A. r yes:

[0117]

[0118] Where S in and S out These are the active areas of the coupling-in and coupling-out surfaces, respectively.

[0119] For conventional equipment, when the active areas of the two surfaces are equal, the expansion ratio is 2. Figure 21A and 21B In the modified device, this ratio was reduced to ~1.75. This reduction remains acceptable for some systems; however, for systems with a very large FOV, the input aperture must be as small as possible. Furthermore, a single expansion may not be sufficient for these systems, and requirements such as… Figure 18 and 19 The diagram shows a double or even triple expansion. In this case, partially immobilizing the coupling surfaces of the substrate would reduce the expansion ratio from 4 and 8 to 3 and 5.4, respectively.

[0120] exist Figure 22A and 22BThe diagram illustrates a possible solution to the problem of reduction. Due to the partial inactivity of the coupled-out surface, along with the satisfaction of the conditions given in Equation 5, the edge portions of the coupled-in surface also become unusable and can also be inactive. For example... Figure 22A As shown, the edge portion of the coupled-in element is removed in the same way as the edge of the coupled-out surface. The active areas of the coupled-in and coupled-out surfaces of the truncated substrate 160 are now equal. Figure 22B The diagram illustrates a symmetrical device 164 with the following parameters: the tilt angle is α. sur2 =20°, FOV is 40°, and the refractive index of the substrate is 2.0. Without suffering phenomena such as black streaks or ghosting, the lateral dimension of the light wave is doubled throughout the entire FOV. Module 164 can be configured as follows: Figure 22B The figure shows a combination of two identical substrates 160R and 160L, which are optically attached at the edge 123 of the substrates.

[0121] like Figure 22C As shown, the module can also be constructed as a combination of two identical truncated parallelepipeds 166R and 166L, which are optically bonded to two different isosceles triangular prisms 167M and 167S.

[0122] It will be apparent to those skilled in the art that the present invention is not limited to the details of the embodiments described above, and that the invention may be embodied in other specific forms without departing from the spirit or essential nature of the invention. Therefore, these embodiments should be considered illustrative rather than restrictive in all respects, and the scope of the invention is indicated by the appended claims rather than by the foregoing description; and thus, all changes falling within the equivalent meaning and scope of the claims are intended to be covered herein.

[0123] Specifically, it should be noted that the features described with reference to one or more embodiments are described as examples and not as limitations on those embodiments. Therefore, unless otherwise stated or unless a particular combination is clearly unacceptable, the optical features described with reference to only some embodiments are assumed to be equally applicable to all other embodiments.

Claims

1. An optical device, comprising: The first light-transmitting substrate has at least two parallel principal surfaces; Optical wave input port; The light wave output aperture is located next to one of the main surfaces of the substrate; Light waves are emitted from the pupil; An optical wave input element is used to couple a light wave with a field of view and a central light wave into the substrate to achieve total internal reflection from the main surface of the substrate; as well as At least a first reflective surface, having an active area and located between the two main surfaces of the light-transmitting substrate, is used to couple light waves out of the substrate. The first reflective surface is configured to have a critical angle relative to the light wave trapped inside the substrate, and is oriented inside the substrate such that: for the entire field of view, the light wave trapped inside the substrate is reflected by at least first and second reflections by the active region of the first reflective surface before being coupled out of the substrate, is reflected substantially from one of the main surfaces between the first and second reflectivities from the first reflective surface, and then reflected from the first reflective surface and passes through the output aperture in the direction of the output pupil. For the entire field of view, the incident angle of the coupled light wave at the first reflective surface is above the critical angle at the first reflection and below the critical angle at the second reflection. At the second reflection, the light wave incident at the first reflective surface is split into two parts by the first reflective surface. One part of the light wave is coupled out from the first light-transmitting substrate in the direction of the output pupil without any redirection element, and the other part passes through the first reflective surface.

2. The optical device of claim 1, wherein an optical adhesive having a refractive index lower than that of the light-transmitting substrate is applied at the first reflective surface, and the critical angle is determined by the ratio between the refractive index of the optical adhesive and the refractive index of the corresponding substrate.

3. The optical device according to claim 1, further comprising a second reflective surface, wherein a portion of the light wave passing through the first reflective surface propagates within the first light-transmitting substrate and is coupled out toward the output pupil via the second reflective surface.

4. The optical device of claim 2, wherein the light wave trapped inside the substrate is reflected the same number of times from the input element and the first reflective surface.

5. The optical device of claim 3, wherein the light wave trapped inside the substrate after a single reflection from the input element is totally reflected by the second reflective surface with a first reflectance ratio, and is reflected from the second reflective surface toward the output pupil portion with a second reflectance ratio.

6. The optical device of claim 1, wherein the first reflective surface is configured such that the central wave of the field of view is coupled from the substrate substantially normally to the principal surface of the substrate.

7. The optical device of claim 4, wherein the input element partially reflects light waves that arrive directly from the input aperture and totally reflects light waves that are reflected once from the input element and once from one of the main surfaces of the substrate.

8. The optical device of claim 7, wherein light waves from the input aperture partially pass through the input surface toward the output aperture of the optical device.

9. An optical device for transmitting light waves, comprising: A first light-transmitting substrate has at least two parallel main surfaces and at least one edge; Optical wave input port; The light wave output aperture is located next to one of the main surfaces of the first light-transmitting substrate; Light waves are emitted from the pupil; A first input surface is used to couple light waves with a first field of view and a central light wave into the first light-transmitting substrate to achieve total internal reflection from the main surface of the first light-transmitting substrate, and At least a first reflective surface, having an active area and located between the two main surfaces of the first light-transmitting substrate, is used to couple light waves out of the first light-transmitting substrate. The first input surface is configured to have a critical angle relative to light waves trapped inside the first light-transmitting substrate, and is oriented inside the first light-transmitting substrate such that light waves coupled into the first light-transmitting substrate substantially normal to the main surface of the first light-transmitting substrate through the input aperture are reflected by the first input surface by at least first and second reflections before being coupled into the first light-transmitting substrate, and are reflected from one of the main surfaces substantially between the first and second reflectance ratios from the first input surface. For the entire field of view, the incident angle of the coupled light wave on the first input surface is below the critical angle at the first reflection and above the critical angle at the second reflection. At the first reflection, the light wave incident on the first reflective surface is split into two parts by the first reflective surface. One part of the light wave passes through the first input surface and is coupled out from the first light-transmitting substrate through the output aperture, while the other part is reflected by the first input surface and coupled into the first light-transmitting substrate. The light waves trapped inside the first light-transmitting substrate are reflected at least twice by the active area of ​​the first reflective surface before being coupled out of the first light-transmitting substrate substantially normally to the main surface of the first light-transmitting substrate through the output hole, and the light waves passing through the input hole substantially normally to the main surface of the first light-transmitting substrate are reflected once by the first input surface before being coupled into the first light-transmitting substrate.

10. The optical device according to claim 9, further comprising: The second light-transmitting substrate has at least two parallel main surfaces and at least one edge; A second input surface is used to couple light waves with a second field of view into the second light-transmitting substrate to achieve total internal reflection from the main surface of the second light-transmitting substrate, and At least a second reflective surface, having an active area and located between the two main surfaces of the second light-transmitting substrate, is used to couple light waves out of the second light-transmitting substrate. Light waves coupled into the second light-transmitting substrate substantially normally from the input aperture are reflected at least twice by the second input surface before being coupled into the second light-transmitting substrate, and are reflected substantially from one of the main surfaces between the first and second reflectance ratios from the second input surface, and the first and second light-transmitting substrates are optically attached at their edges, and the first and second input surfaces of the first and second light-transmitting substrates are disposed adjacent to each other.

11. The optical device of claim 9, wherein an optical adhesive having a refractive index lower than that of the light-transmitting substrate is applied at the input surface, and the critical angle is determined by the ratio between the optical adhesive and the refractive index of the corresponding light-transmitting substrate.

12. The optical device of claim 9, wherein a portion of the light wave passing through the first input surface is coupled out from the first light-transmitting substrate through the output aperture in the direction of the output pupil.

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