Compact display system with a wide output aperture

Abstract

The optical device comprises a first light-transmitting substrate, an input aperture, an output aperture, an eye-motion box, a first flat reflective surface, a second flat reflective surface, and a first redirection mechanism. The first light-transmitting substrate has at least two parallel principal surfaces and an edge. A principal propagation direction axis is defined parallel to the principal surfaces, a first reference plane is defined parallel to the principal propagation direction axis, and an orthogonal axis is defined perpendicular to the principal propagation direction axis and parallel to the first reference plane. The first flat reflective surface is located between the two principal surfaces of the light-transmitting substrate and causes internal total internal reflection on the principal surfaces of the light-transmitting substrate. The second flat reflective surface is parallel to the first flat reflective surface and located between the two principal surfaces of the light-transmitting substrate and couples out light waves from the substrate. The first redirection mechanism comprises at least one pair of first and second mutually perpendicular flat reflective surfaces and redirects the light waves coupled out through the output aperture to the eye-motion box. The light waves coupled out from the substrate are reflected by the first and second flat reflective surfaces before reaching the eye motion box.

Description

Field of Invention

[0001] The present invention relates to an optical guide device using a substrate, and more particularly to a device including a reflective surface supported by a light-transmitting substrate.

[0002] The present invention can be advantageously applied to numerous imaging applications, including head-mounted displays, head-up displays, mobile phones, compact displays, and 3D displays. Background of the Invention

[0003] One important application area for compact optical elements is head-mounted displays (HMDs). The optical module acts as both an imaging lens and a combiner, focusing a two-dimensional display at infinity and reflecting it back to the viewer's eye. Displays range from spatial light modulators (SLMs) to, for example, cathode ray tubes (CRTs), liquid crystal displays (LCDs), and organic light-emitting diodes (OLEDs). ( Displays can be obtained directly from OLED arrays, scanning light sources, etc. Alternatively, they can be obtained indirectly via relay lenses or bundles of optical fibers. A display consists of an array of elements (pixels) that are imaged at infinity by collimating lenses and transmitted to the viewer's eye. For transmission to the viewer's eye, a reflective surface is used as a coupler in non-see-through displays, and a partially reflective surface in see-through displays. Conventional free-space optical modules are typically used for these purposes. As the field of view (FOV) required of the system increases, such conventional optical modules become large, heavy, and bulky. As a result, even devices with moderate performance become impractical. Therefore, these are significant drawbacks for all types of displays, especially HMDs. In HMDs, the system needs to be as lightweight and compact as possible.

[0004] Due to the need for miniaturization, several different and complex optical solutions have been proposed. However, none of these are sufficiently compact for most practical applications, and they also present significant problems in terms of manufacturability, cost, and performance. [Prior art documents]

Patent Document

[0005] The disclosures of International Patent Publications WO2017 / 141239, WO2017 / 141240, WO2017 / 141242, WO2019 / 077601, WO2020 / 157747, WO2022 / 029764, and WO2022 / 054047 are incorporated herein.

Summary of the Invention

[0006] In the present invention, it is made easy to provide a compact substrate for applications such as HMDs. In the present invention, it is possible to simultaneously achieve a relatively wide field of view (FOV) and a relatively large eye motion box (EMB) value. The resulting optical system provides large and high-quality images that can cope even when the line of sight moves significantly. The optical system according to the present invention is significantly more compact than prior art implementations and can be easily incorporated into optical systems with various special configurations.

[0007]

[0008] ​The optical device of the present invention includes a first light-transmitting substrate having at least two parallel main surfaces and edges, thereby constituting a main propagation direction axis parallel to the main surfaces and a first reference plane parallel to the main propagation direction axis. The optical device of the present invention also includes a first orthogonal axis perpendicular to the first reference plane, a second orthogonal axis perpendicular to the main propagation direction axis and parallel to the first reference plane, an input aperture, an output aperture, and an eye motion box. The optical device of the present invention further includes a first flat reflecting surface disposed between two main surfaces of the light-transmitting substrate, which couples light waves into the light-transmitting substrate and generates total reflection on the main surface of the light-transmitting substrate, and a second flat reflecting surface parallel to the first flat reflecting surface and disposed between two main surfaces of the light-transmitting substrate, which extracts (couples out) light waves from the light-transmitting substrate, and at least one pair of first and second flat reflecting surfaces perpendicular to each other for redirecting the light waves coupled out from the light-transmitting substrate to the eye motion box through the output aperture. In the present invention, the light waves coupled out from the substrate are reflected at least once by the first and second flat reflecting surfaces before reaching the eye motion box.

Brief Description of the Drawings

[0009] To enable a full understanding of the present invention, preferred embodiments will be described below with reference to the following drawings.

[0010] The details of the drawings are for example only and are for explaining the preferred embodiments of the present invention. The drawings are for facilitating an easy understanding of the principles and concepts of the invention. In this regard, they do not show detailed structures beyond the scope necessary for a basic understanding of the invention. The drawings and their descriptions are a guide for those skilled in the art on how to actually embody various forms of the present invention.

[0011] In the figures: FIG. 1 is a side view of an example of a light-transmitting substrate in the prior art. FIG. 2 is a side view of a light-transmitting substrate in another prior art. Figure 3 is a schematic cross-sectional view of a conventional light-transmitting substrate in which the couple-in and couple-out portions are optical diffraction elements. Figures 4A and 4B show cross-sectional views of a transparent substrate in the prior art, which has a coupling-in surface, a coupling-out surface, and a partially reflective redirection element. Figure 5 is a schematic diagram showing the unfolded substrate guide system projected onto the main plane. Figure 6 is a schematic diagram showing a deployable substrate guide system equipped with a lateral field of view (FOV) reversal mechanism, projected onto the main plane. Figure 7A is a schematic diagram of an inversion mechanism according to the present invention, which consists of two mutually perpendicular reflective surfaces. Figure 7B is a schematic diagram of a reversal mechanism according to the present invention, which combines two mutually perpendicular reflective surfaces on a transparent substrate, the transparent substrate having an incident surface, an exit surface, and a partially reflective direction-changing element. Figures 8A and 8B are plan views of an inversion mechanism having two mutually perpendicular reflective surfaces according to the present invention. Figures 9A and 9B are front views of an inversion mechanism according to the present invention, having two mutually perpendicular reflective surfaces. Figure 10 is a front view of an inversion mechanism according to the present invention, which includes two mutually perpendicular reflective surfaces and two complementary prisms. Figures 11A and 11B are schematic cross-sectional views of an inversion mechanism according to the present invention, which includes an array of pairs of mutually perpendicular reflective surfaces. Figure 12 is a schematic cross-sectional view of an inversion mechanism according to the present invention, which consists of an array of pairs of mutually perpendicular reflective surfaces inclined at a predetermined angle with respect to the system's reference plane. Figures 13A and 13B are front views of another inversion mechanism according to the present invention, which includes two mutually perpendicular reflective surfaces. Figures 14A and 14B are front views of an inversion mechanism according to the present invention, which includes two mutually perpendicular reflective surfaces having an asymmetrical structure. Figure 15 is a front view of an inversion mechanism according to the present invention, which consists of an arrangement of pairs of mutually perpendicular reflective surfaces having an asymmetrical structure. Figures 16A, 16B, and 16C are side views, bottom views, and front views, respectively, of an optical system including a main substrate, an inversion mechanism, and a redirection element according to the present invention. Figure 17 is a schematic cross-sectional view of the inversion mechanism according to the present invention, which includes two mutually perpendicular reflective surfaces oriented at a predetermined angle with respect to a reference plane. Figure 18 is a schematic cross-sectional view of the inversion mechanism according to the present invention, which consists of a two-dimensional array of pairs of mutually perpendicular reflective surfaces oriented at a predetermined angle with respect to a reference plane. Figures 19A and 19B show a method for manufacturing an inversion element according to the present invention. [Modes for carrying out the invention] [Examples]

[0012] Figure 1 shows a cross-section of a conventional light-transmitting substrate. The first reflective surface 16 is illuminated by parallel light waves 12 emitted from a display light source 4 and collimated by a lens 6 placed between the light source 4 and the substrate 20 of the device. The reflective surface 16 reflects the incident light from the light source, so that the light waves are confined inside the planar substrate 20 by total internal reflection. After being reflected several times by the main surfaces 26,27 of the substrate 20, the confined light waves reach a partial reflecting element 22, which couples the light out of the substrate and guides it to the pupil 25 of the viewer's eye 24. Here, the input aperture 17 of the substrate is the aperture through which the input light waves enter the substrate 20, and the output aperture 18 of the substrate is the aperture through which the confined light waves exit the substrate. In the case of the substrate in Figure 1, both the input aperture 17 and the output aperture 18 coincide with the bottom surface 26. However, other configurations are also possible in which the input light waves and the imaging light waves from the light source 4 enter on the opposite side of the substrate or at one of the edges of the substrate. As shown in the figure, the effective regions of the input aperture and the output aperture are similar to each other and correspond to the couple-in reflective surface 16 and the couple-out partial reflective element 22 projected onto the main surface 26, respectively.

[0013] In HMD systems, the entire EMB (Earth-Motion Field of View) must be illuminated by the total light waves emitted from the display light source. This allows the viewer's eye to simultaneously capture the entire field of view of the projected image. As a result, the system's output aperture needs to be enlarged accordingly. On the other hand, the optical module must be lightweight and compact. Since the lateral spread of the collimating lens 6 is determined by the lateral size of the input aperture of the substrate, it is desirable to make the input aperture as small as possible. As shown in Figure 1, in systems where the lateral size of the input aperture is similar to that of the output aperture, an inherent contradiction arises between these two requirements. Many systems based on this optical structure suffer from the problems of a small EMB, a small FOV, and a large, unwieldy imaging module. Consequently, to obtain a practical imaging system, the output aperture needs to be expanded laterally compared to the input aperture.

[0014] A method to solve this problem, at least partially, is shown in Figure 2. The element that couples the light wave out from the substrate consists of an array of partial reflectors 22a, 22b, etc. Clearly, the output aperture in this configuration can be enlarged by increasing the number of partial reflectors embedded inside the substrate 20. As a result, optical modules with small input apertures and large output apertures can be designed and manufactured. As shown in the figure, the confined light ray reaches the reflectors from two different directions 28 and 30. In this particular embodiment, the confined light ray reaches the partial reflector 22 from the second direction 30 after an even number of reflections from the substrate surfaces 26 and 27. At this time, the angle of incidence between the confined light ray and the normal to the reflector is βref. As shown in Figure 2, at each reflector, each light ray first reaches the surface from direction 30. A portion of this is irradiated onto the surface from direction 28. To prevent unwanted reflections and ghost images, the reflectance for the light ray irradiated onto the surface from the second direction 28 is made negligible.

[0015] To meet this requirement, a solution utilizing the angular sensitivity of thin-film coatings has been previously proposed in the aforementioned literature. Desired discrimination between two incident directions can be achieved when one angle is significantly smaller than the other. It is possible to provide a coating that exhibits very low reflectivity at high incident angles and high reflectivity at low incident angles. By utilizing this property and eliminating reflection from one of the two directions, undesirable reflections and ghost images can be prevented.

[0016] The main problem with the example shown in Figure 2 is that the required reflective properties of the partial reflective surface 22 differ from those of conventional designs. Furthermore, in order to maintain low reflectivity in the high-angle region, the reflectivity in the required angular region cannot be increased to 20% to 30% or higher. In addition, in order to achieve uniform brightness across the entire field of view, it is necessary to gradually increase the reflectivity of the partial reflective surface toward the edges of the substrate. As a result, the maximum achievable efficiency is relatively low and usually cannot exceed 10%.

[0017] Another method for achieving incidence and emission to an optical waveguide element is to utilize a diffracting element. As shown in Figure 3, light rays 34 and 36 are incident on the transparent substrate 20 via a diffracting element 48. After total internal reflection at the outer surface of the substrate, the light rays are emitted from the substrate by a second diffracting element 50. As shown in the figure, the light ray 38 is coupled out at least twice at two different points 52 and 54 on the element 50. Therefore, in order to obtain a uniform output light wave, it is necessary to gradually increase the diffraction efficiency of the element 50 along the ξ axis. As a result, the overall efficiency of the optical system becomes even lower than that of the system in Figure 2, and usually does not exceed a few percent. That is, in Figures 2 and 3, the output aperture is significantly larger than the input aperture, which drastically reduces the brightness efficiency of the optical module and also complicates the substrate manufacturing process.

[0018] Figures 4A and 4B show examples of prior art that overcome the problems that the present invention aims to solve. Instead of assigning the dual role of coupling light waves from the substrate 20 and directing the light waves to the user's eye 24 to a single element (element 22 in Figure 2, or element 50 in Figure 3), the two required functions are assigned to two different elements. That is, one element embedded in the substrate couples light waves from the substrate, and a second conventional partial reflecting element located outside the substrate redirects the light waves to the viewer's eye. As shown in Figure 4A, two planar light rays 63 (dashed lines) emitted from a display light source and collimated by a lens (not shown) enter the light-transmitting substrate 64 through an input aperture 86. The substrate 64 has two parallel main surfaces 70, 72, and the light rays are incident at an angle α of incidence relative to the main surfaces 70, 72 of the substrate. in (0) The light beam enters at a certain angle. The light ray reaches the bonding surface 65. The bonding surface 65 is at an angle α with respect to the main surface of the substrate. surl It is only slightly inclined. The bonding surface 65 reflects the incident light ray, and the light ray is trapped inside the planar substrate 64 by total internal reflection from the main surface.

[0019] As shown in Figure 4A, the tilt angle α of the image outThis can be adjusted by adding a partial reflective surface 79 tilted at an angle αr with respect to the substrate surface 72. As shown in the figure, the image is reflected, rotated, passes through the substrate almost perpendicular to the main surface of the substrate, and reaches the viewer's eye 24 through the output aperture 89 of the substrate. To minimize distortion and chromatic aberration, it is preferable to embed the surface 79 in a redirection element such as a prism, and to complete the shape of the redirection mechanism 80 with a second prism 82. Both are manufactured from the same material and do not necessarily have to be the same material as the substrate. There are several options for the material that realizes partial reflection of the surface. For example, dielectrics, metals, or hybrid beam splitters can be considered. In the case of a polarized light source, a polarized beam splitter is used. In the case of a laser-based display light source, a dichroic coating is used that reflects only specific wavelengths of the light source and is transparent to other spectra. Furthermore, a multiple reflection phase hologram that is sensitive to only three narrowband spectral regions corresponding to the specific color of the light source, or one that is sensitive to only a single band for a monochromatic display light source, can also be considered. To minimize the system thickness, a single reflective surface 79 can be replaced with an array of parallel partial reflective surfaces 79a, 79b, etc., as shown in Figure 4B. The number of partial reflective surfaces can be determined according to the system requirements, and the specific type of beam splitter can be determined similarly.

[0020] To simplify the analysis, the following symbols are defined. The main axis ξ is defined as the propagation direction of the central light wave of the field of view (FOV) within the substrate. The orthogonal axis η is perpendicular to the axis ξ and is oriented parallel to the main transverse axis of the FOV. The reference plane is parallel to the axes ξ and, and the normal axis? is perpendicular to the reference plane. Usually, the reference plane coincides with the main surfaces 70, 72 of the substrate 64. However, there are also systems in which the substrate is oriented at a pantoscopic angle with respect to the viewer's line of sight. In this case, the reference plane is inclined about the axis ξ with respect to the main surface. As shown in FIGS. 9A?9D of WO2020 / 157747, it is possible to realize a substrate guide element in which the input aperture along the main axis ξ of the substrate is at least three times smaller than the original input aperture 86 and output aperture 89 of the substrate, and moreover, the luminance of the projected image does not decay. That is, the light transmission efficiency within the substrate 64 is kept close to 100%, and the necessary lateral expansion of the output aperture along the light propagation direction ξ inside the substrate is achieved. However, in many applications, an expansion of the aperture along the orthogonal axis η direction is required.

[0021] In a single substrate structure, the achievable FOV and EMB along the η axis do not depend on the couple-out element and depend on the lateral size of the input aperture of the substrate along the η axis.

[0022] FIG. 5 shows a substrate guide system projected onto and developed in the main plane. When the light rays are traced backward from the EMB 24, the light passes through the projection of the EMB on the output aperture 89 and reaches the input aperture 86. JPEG2026525415000002.jpg29150 Here, 90, 91, 93 are the projections of the upper, central, and lower parts of the FOV, respectively. The maximum FOV in the η axis direction is as shown in Equation (1). Here, D η is the lateral size of the input aperture in the η axis direction, d eye is the EMB in the η axis direction, R eye is the eye relief, l is the distance between the far ends of the input aperture and the output aperture of the substrate, ν is the refractive index of the substrate, α in min is the minimum off-axis angle of the light wave coupled inside the substrate. Equation (2) JPEG2026525415000003.jpg28150 For the case of the parameters of the substrate: The lower limit of the lateral size is 42 mm. In systems with a wide field of view (FOV) and large embola (EMB), the required lateral size for the output aperture is approximately 25 mm. Therefore, by using the expansion method shown in Figures 4A-4B, the input aperture along the principal axis ξ can be reduced to 6-8 mm. As a result, the lateral size of the substrate becomes more than six times larger than the vertical size. This asymmetry necessitates a collimating lens with a high numerical aperture or a very large display light source, which is problematic. With such values, it is impossible to realize the desired compact system.

[0023] As shown in Figure 30 of Publication WO2020 / 157747, beam expansion along two axes is possible by utilizing a dual-substrate configuration. However, this expansion method still has several drawbacks. The expansion ratio in the lateral direction is limited, resulting in an overly wide lens aperture after expansion. Furthermore, the lateral size of the substrate 64 is not reduced, and it remains too large to significantly miniaturize the substrate input aperture required for the spectacle structure. Therefore, it is necessary to find an alternative method to maintain a small input aperture along the orthogonal axes of the substrate 64.

[0024] As shown in Figure 6, the optimal means of achieving the required method is to add a reflection or inversion mechanism 100 near the output aperture 89 of the substrate. As shown in the figure, the purpose of this mechanism is to invert the direction of the η component of each coupled light wave while preserving its absolute value. In this case, the divergent light waves 90, 91, and 93 converge in the modified directions 95, 96, and 97, respectively, and focus into a new input aperture 86' that is significantly smaller than the original input aperture 86 and output aperture 89.

[0025] Figure 7A shows a possible reflection or reversal mechanism 100. As shown, a ray 101 is coupled from the substrate 64 via the bottom surface 72 (see Figures 4A and 4B). However, instead of being reflected to the viewer's eye by the redirection element 80 (see Figures 4A and 4B), this ray enters another redirection element consisting of first and second flat reflective surfaces 106 and 107 perpendicular to each other. Each reflective surface is inclined at an angle of approximately 45 degrees with respect to the reference plane 105. The ray is reflected by the first surface 106, then by the second reflective surface 107, and enters the substrate 64 again (not shown). To evaluate the effect of double reflection, a reflection vector analysis is referred to here. Given that the unit vector of the incident light wave and the unit vector in the direction normal to the reflective surface are given by equations (3) and (4), JPEG2026525415000004.jpg44150 The unit vector of the reflected light wave is given by equation (5). JPEG2026525415000006.jpg61150 Substituting equations (6) and (7) into equation (5), JPEG2026525415000007.jpg61160 The unit vector of the light wave reflected by the first reflecting surface is given by equation (8), and the unit vector of the light wave reflected by the second reflecting surface is given by equation (9). Here V out2 → This is the unit vector of the light wave that couples out from mechanism 100 and is re-incident onto substrate 64.

[0026] Coupled in vector V in → and couple out vector V out → When you combine them, you get results a to d: a. The absolute values ​​of the three components are preserved. b. The ξ component retains its original direction. That is, the light wave continues to propagate in the same direction along the principal axis. c. Similar to reflection at the reference plane, the direction of the zeta component is reversed. d. As required by the inversion mechanism, the direction of the η component is also inverted.

[0027] The same result occurs even if the incident light wave is first reflected by the second reflecting surface and then reflected by the first reflecting surface.

[0028] Figure 7B shows a combination of the inversion mechanism 100 and the configuration shown in Figure 4A. As shown, this combination is configured as follows: A light-transmitting substrate 64 having at least two parallel main surfaces and edge portions defines a main propagation direction axis ξ parallel to the main surfaces. A reference plane 105 parallel to the main propagation direction axis is parallel to the main propagation direction axis and perpendicular to the orthogonal axis η. The orthogonal axis is perpendicular to the main propagation direction axis and parallel to the first reference plane. An input aperture 17, an output aperture 18, and an eye motion box 24 are provided, along with a first flat reflective surface 65 positioned between the two main surfaces 70 and 72 of the light-transmitting substrate and coupling the light wave 101 to the substrate, causing total internal reflection of the light wave at the main surface of the substrate. A second flat reflective surface 67 parallel to the first flat reflective surface is positioned between the two main surfaces of the light-transmitting substrate 70 and 72, extracting the light wave from the substrate and redirecting it to the optical mechanism 100. The optical mechanism 100 comprises at least one pair of first and second mutually perpendicular and flat reflective surfaces 106, 107 that redirect light waves coupled out from the substrate through an output aperture to the eye motion box 24.

[0029] As shown in the figure, the light ray 101, which is coupled out from the substrate 64 by the surface 67, is reflected once by the first and second flat reflective surfaces 106, 107 before reaching the eye motion box 24.

[0030] In the two examples shown in Figures 8A-8B (side view and front view) and 9A-9B (side view and front view), the incident light wave is first reflected at the first reflecting surface and then at the second reflecting surface (Figures 8A, 9A), or vice versa (Figures 8B, 9B). As illustrated, the final effect is the same in both cases. In summary, the light wave 101 is reflected in mechanism 100 in the same way as it is reflected on a flat plane parallel to the reference plane, but a significant difference exists: the transverse component of the reflected wave along the η-axis is inverted.

[0031] To minimize distortion and chromatic aberration, it is preferable to embed the reflective surfaces 106 and 107 in the prism 109, as shown in Figure 10, and to complete the shape of the mechanism 100 with the second prism 110. Both of these prisms are manufactured from the same material, but do not necessarily have to be made of a material similar to the substrate material. Furthermore, to minimize the thickness of the system, a single pair of reflective surfaces is embedded in the arrangement of the pair ((106 i , 107 i ),(106 i+1 , 107 i+1 These can be replaced with ),…), etc. For all pairs, the first and second reflective surfaces are parallel to each other, and the number of pairs is determined according to the requirements of the system. To further reduce the volume of the system, the upper surface 112 of the mechanism 100 is attached to the lower surface 72 of the substrate 64. To achieve a highly rigid system, it is preferable to apply an optical adhesive to the interface between the two surfaces and fix the redirection mechanism 100 to the substrate 64. As illustrated in Figure 5D of Publication WO2017 / 141242, the refractive index of the adhesive must be significantly lower than the refractive index of the substrate.

[0032] Up until now, we have assumed that the reference plane is parallel to the main surface of the substrate 64. However, especially in spectacle-type optical systems, the substrate has a pan angle b with respect to the viewer's line of sight axis. pan It is tilted. Normally, the vertical field of view is centered on the line of sight, so the reference plane is also at the same angle b with respect to the main surface of the substrate. pan It tilts. As a result, the mechanism 100 in Figure 11B pans at an angle b around the ξ axis with respect to the substrate. pan It only needs to be rotated by a certain amount. Therefore, surface 112 and surface 72 cannot be optically joined. However, in order to ensure rigidity and compactness, it is necessary to bond both surfaces together.

[0033] Figure 12 shows how to solve this problem. As shown, the reflective surface is rotated slightly around the ξ axis compared to the configuration in Figure 11B, but the reflective surface is still tilted at an angle of approximately 45 degrees with respect to the reference plane 105. Nevertheless, the first reflective surface 106 and the second reflective surface 107 are tilted at 45°-β, respectively, with respect to the upper surface 112 which is parallel to the surface 72.pan and 45°+β pan It is tilted at this angle, which facilitates the optical bonding of surfaces 72 and 112.

[0034] The symmetrical design shown in Figures 8A, 8B, 9A, 9B, 10, 11A, and 11B is suitable for systems with small to medium fields of view along the η-axis. However, for systems with wide fields of view, this architecture presents problems at the edges of the field of view. To improve the architecture at the edges of the FOV, refer to Figures 13A and 13B. The light wave first reflected by the second reflecting surface 107 has a negative component on the ∫-axis, and the light wave first reflected by the first reflecting surface 106 has a positive ∫-component. Referring to equation (8), from Figures 8A and 8B, the incident light wave V in → η component b i It can be seen that is negative. Therefore, the ? component -b of the light wave first reflected at surface 106 i This becomes positive. That is, the light wave is reflected upward. Similarly, the ? component b of the light wave first reflected at surface 107 i The value becomes negative and is reflected downward. The practical implications are that the light wave first reflected at surface 107 always intersects with surface 106. However, the light wave reflected at the right edge of surface 106 avoids intersecting with surface 107, and this ray is lost as shown in Figure 13B.

[0035] Figures 14A-14B illustrate one possible method for improving the behavior of the light wave at its edges. By enlarging and rotating the output aperture of mechanism 100, the light wave reflected at the right edge of the first surface 106 intersects with the second surface 107. As shown, in all pairs located at the right edge of mechanism 100, the second surface 107 is wider than the first surface 106. Clearly, this configuration is reversed at the left edge of mechanism 100, i.e., the positive η component b i The light wave 102 having this property is reflected downward at the first surface and upward at the second surface. Therefore, this correction enlarges the first surface 106.

[0036] As shown in Figure 15, the pair 106r,107r at the right end of mechanism 100 has a larger second reflective surface, and the pair 106l,107l at the left end has a larger first reflective surface. In contrast, the central pair 106c,107c, where the incident light wave 103 has a small η component, is configured symmetrically. For systems with a wide lateral field of view and a wide panthescopic angle, the embodiment in Figure 12 and the embodiment in Figure 15 are combined. The precise parameters of the reflective pairs, depending on their position on mechanism 100, are determined based on various optical system parameters, such as the required output aperture size, the system's lateral field of view, the substrate tilt angle, and the eye relief.

[0037] Another issue to consider is the reflection mechanism of surfaces 106 and 107. Apparently, these surfaces exhibit partial reflection in see-through systems and total reflection in non-see-through systems. However, the actual situation is more complex. As equation (9) shows, the light waves reflected by mechanism 100 are directed at a large off-axis angle relative to the main substrate surface. Therefore, a second mechanism 80 is required to reflect the light waves towards the viewer's eye.

[0038] Figures 16A, 16B, and 16C show the side, bottom, and front views (not to scale) of the system. For simplicity, before coupling to the substrate, the tracked light wave 101 has a zero initial component in the ξ-axis direction and a negative initial component in the η-axis direction. As shown, the light wave coupled out from the substrate 64 by the couple-out element 67 is reflected by the reflection pair 106i,107i in Figure 16C, and its components along the η and ζ axes are reversed. The light wave 101 passes through the substrate 64 and surface 67 without significant reflection and is reflected towards the viewer's eye by the second mechanism 80. After passing through the substrate 64 and surface 67 again, the light wave 101 reaches the reflection surface 107j, at which point the transmission rate should be as high as possible. Furthermore, in the see-through system, light waves 83 from the external scene pass through mechanism 100. Here again, reflections from surfaces 106,107 should be minimized.

[0039] Therefore, surfaces 106 and 107 present conflicting requirements: high reflectivity during the first incident and low reflectivity during the second incident. To optimize the efficiency of the projection system and increase the transmission rate of the composite substrate, an appropriate reflection mechanism is employed. The first option is a naive solution using conventional partial reflective surfaces, in which case the optimal reflection / transmission ratio is 50%:50%. However, even without considering losses in the second mechanism 80, the maximum efficiency of the projected image remains at 12.5%. Furthermore, the maximum transmission rate of the substrate to light waves from the external scene falls below 50% (again, without considering losses in the second mechanism). This solution results in an inefficient system.

[0040] Another suitable solution for polarized images is to use a polarizing beam splitter. For example, the reflectivity for s-polarized and p-polarized light would be 100% and 0%, respectively. Furthermore, a quarter-wave plate is inserted adjacent to the reference plane 85 between the substrate 64 and the second mechanism 80, or alternatively, adjacent to the top surface 112 of mechanism 100 (Figure 16C). In this case, the overall efficiency exhibited by mechanism 100 for projected light waves becomes very high. However, the transmission rate for unpolarized light from the external scene in mechanism 100 becomes less than 50%, and the transmission rate becomes very low for displays outputting s-polarized light. In addition, this solution becomes quite complex to implement because the incident light waves have a large oblique angle of incidence with respect to the reflective surfaces 106,107.

[0041] To find a more efficient solution, the light wave V irradiated onto the pair of reflective surfaces during the aforementioned inversion process in → Then, the light wave V, which is reflected by element 80 and then incident on these reflective surfaces, heads towards the viewer's eye. eye → We will treat them as distinct. As shown in Figure 16A, light wave V out2 → It is reflected by the redirect plane 79i, which is at an angle a with respect to the reference plane. r It is rotating in that direction. The normal to face 79i has negative components along the x and z axes. Therefore, the unit vector of this normal is given by equation (10). JPEG2026525415000008.jpg14150 JPEG2026525415000009.jpg18150 For simplicity, we assume that mechanisms 80 and 100 have the same refractive index. Although this is not necessarily required, similar calculations can be performed for different materials. The unit vector of the reflected wave redirected to the viewer's eye is given by equation (11). Here, equation (12) holds true. Combining equations (11) and (12) yields equation (13). JPEG2026525415000010.jpg40150 Therefore, the three components of the reflected light wave are given by equations (14) to (16). JPEG2026525415000011.jpg45150

[0042] Refer to Figure 16, and the light wave V in → It is reflected from surfaces 106,107, and the light wave V eye → The mechanism by which light passes through them is described. In this case, surfaces 106 and 107 have angle-dependent reflectivity. One way to realize this mechanism is to provide an intermediate dielectric material with a refractive index smaller than that of mechanism 100 on surfaces 106 and 107 between elements 109 and 110. This material is, for example, an optical adhesive that bonds elements 109 and 110. Alternatively, a layer of thin film material may be formed on the surface by a process such as spin coating. Because there is a difference between the refractive indices of elements 109 and 110 and the refractive index of the intermediate material, these reflective surfaces have a critical angle α cr It has. In order to verify the required mechanism, light wave V is irradiated onto the reflective surfaces 106 and 107. in → The critical angle is α cr With a higher angle of incidence, V eye → The critical angle is α r A lower angle of incidence is required.

[0043] From equations (6) to (8) and equations (14) to (16), the input light wave V in →Regarding this, the following requirements are derived: JPEG2026525415000012.jpg26150 JPEG2026525415000013.jpg26150 JPEG2026525415000014.jpg31150 JPEG2026525415000015.jpg31150 Light wave V redirected to the viewer's eye eye → Regarding this, equations (19) and (20) are derived. In order for the conditions of equations (17) to (20) to be satisfied, the condition of equation (21) must be satisfied across the entire field of view (C in (Note that it is negative.) JPEG2026525415000016.jpg15150 Because the coupled light wave is significantly tilted with respect to the reference plane along the ξ axis, equation (21) can be achieved even in systems with a wide lateral field of view along the η axis.

[0044] Figure 17 shows another embodiment in which mechanism 120 combines the inversion mechanism of mechanism 100 and the ray redirection effect of mechanism 80. As shown in the figure, element 120 has a pair of first reflective surfaces 116 and second reflective surfaces 117 perpendicular to each other, so that their surfaces are not inclined at an angle of about 45 degrees with respect to the reference plane 105. Instead, the intersection line of these surfaces is at an angle β with respect to the reference plane 105. r It is sloped. As a result, the unit normal vector to these surfaces is, JPEG2026525415000017.jpg38150 It is given by equations (22) and (23). The unit vector of the output light wave from the first reflecting surface 116 is, JPEG2026525415000018.jpg18150 is given by equation (24). Equations (3) and (22) are given by equation Substituting this into (24), we obtain equation (25). JPEG2026525415000019.jpg25150 Output Vector V RO1 → The three components are given by equations (26) to (28). JPEG2026525415000020.jpg59150 Similarly to JPEG2026525415000021.jpg30150, the output vector from the second reflective surface 117 is given by equation (29). JPEG2026525415000022.jpg18150 Combining equations (29) and (30) yields equation (31). JPEG2026525415000024.jpg24150 Output vector V RO2 → The three components are given by equations (32) to (34). JPEG2026525415000025.jpg45150

[0045] β γ =a γ Assuming this, juxtaposing the components of the light waves output from mechanism 80 and coupling element 120 (see equations (14) to (16) and equations (32) to (34)) yields equations (35) to (37). JPEG2026525415000026.jpg53150 That is, the light wave is redirected to the viewer's eye in the appropriate direction as needed. The minus sign in equation (37) indicates that the output light wave is reflected downward and upward in Figures 16A, 17A, and 17B, respectively. To reduce the volume of the system, the inversion / redirection element 120 is arranged as a one-dimensional array of pairs of reflective surfaces perpendicular to each other along the η axis, as shown in Figure 18, or as pairs 116 arranged along the ξ and η axes. i,j, 117 i,j This can be arranged as a two-dimensional array. This array can also be arranged in an asymmetrical structure, similar to the examples in Figures 12 and 15.

[0046] There are several ways to achieve reflection on surfaces 116 and 117. In non-see-through systems, these can be perfectly reflective surfaces. In transmission systems with polarized display light sources, these can be polarized beam splitters, for example, with reflectivity of 100% and 0% for s-polarized and p-polarized light, respectively. In this case, the efficiency of the projected image and the transmitted external scene are 100% and 50%, respectively. Reducing the reflectivity for s-polarized light reduces the efficiency of the projected image and improves the efficiency of the external scene. In the case of laser display light sources, the surfaces can be color-sensitive reflective surfaces with a dichroic coating that reflects only specific wavelengths and transmits other wavelengths. In this case, since the reflected light waves do not pass through surfaces 116 and 117 again in this embodiment, the overall efficiency of the projected image is very high. Furthermore, for light waves from the external scene, the efficiency of the external scene is also high because the surface has high transmission capability for most of the bright-vision range. As a similar solution, the surface can be composed of multiple reflective phase holograms that are sensitive to only three narrowband spectral regions depending on the specific color of the light source. In see-through systems with non-polarized display light sources, these become partially reflective surfaces, and the specific reflectivity of the surface is set according to the system requirements.

[0047] Figures 19A and 19B show a method for manufacturing the required inversion mechanisms 100 and 120. First, a pair of prisms 109 and 110 of a predetermined size are manufactured. These prisms can be manufactured from silicate materials using conventional techniques such as grinding, polishing, and bonding, or from polymer or sol-gel materials using injection molding or casting techniques. Next, the necessary optical coatings are applied to the appropriate surfaces of these prisms. In systems where reflection is set by total internal reflection at the substrate-adhesive interface, an anti-reflective coating is applied. In systems where reflection is set by total internal reflection at the substrate-layer interface, a material with the required refractive index is applied. In this case, different materials can be applied to different pairs, or even to two surfaces of the same pair. Depending on the situation, various options for the mechanism 120 can be applied, such as total internal reflection coatings, beam splitters, or partial internal reflection coatings. Finally, the prisms are bonded together with a suitable optical adhesive to form the desired mechanisms 100 and 120. In applications where the quality of the optical surface is critical, a final step of polishing the outer surface or at least a portion thereof can be added to the process.

[0048] Figures 11A, 11B, 12, 13A, 13B, 14A, 14B, 15, 16A, 16B, 16C, 17, and 18 show various features that can be added to the basic configuration shown in Figures 7A, 7B, 8A, 8B, 9A, 9B, and 10. These include: arrangement of the system by one-dimensional and two-dimensional arrays of pairs (Figures 11A, 11B, and 18); rotation of pairs relative to the main surface (Figure 12); generation of symmetrical structures (Figures 14A, 14B, and 15); and combination of inversion and reversal mechanisms (Figures 17-18). Ultimately, any combination of these features can be added to the basic embodiments shown in Figures 7A, 7B, 8A, 8B, 9A, 9B, and 10, according to the specific requirements of the optical system.

[0049] Those skilled in the art will understand that the present invention is not limited to the details of the embodiments described above and can be embodied in other specific forms without departing from its spirit or essential attributes. Therefore, these embodiments are considered illustrative and non-limiting in all respects, and the scope of the invention is indicated by the appended claims rather than the foregoing description. Accordingly, all modifications equivalent to the scope of the claims are incorporated herein.

Claims

1. A first light-transmitting substrate comprising at least two parallel main surfaces and edges, defining a main propagation direction axis parallel to the main surfaces, a first reference plane parallel to the main propagation direction axis, and an orthogonal axis perpendicular to the main propagation direction axis and parallel to the first reference plane, Input aperture and, Output aperture and i-motion box and, A first flat reflective surface is located between the two main surfaces of the light-transmitting substrate, which couples light waves into the substrate and causes internal total internal reflection at the main surfaces of the light-transmitting substrate, A second flat reflective surface is located parallel to the first flat reflective surface and between the two main surfaces of the light-transmitting substrate, and couples out light waves from the substrate. The device comprises a first redirection mechanism which includes at least one pair of mutually perpendicular flat reflective surfaces, and redirects light waves coupled out through an output aperture to an eye motion box. The light waves coupled out from the substrate are reflected by the first and second flat reflective surfaces before reaching the i-motion box. Optical devices.

2. The optical device according to claim 1, characterized in that the first flat reflective surface and the second flat reflective surface are each inclined at an angle of approximately 45° with respect to the first reference plane.

3. The optical device according to claim 2, characterized in that the first flat reflective surface and the second flat reflective surface are substantially parallel to the main propagation direction axis.

4. The propagation direction of the light wave coupled within the first redirection mechanism is determined by three orthogonal components: the first component is parallel to the main propagation direction axis, the second component is perpendicular to the first reference plane, and the third component is parallel to the aforementioned orthogonal axis. The optical device according to claim 3, characterized in that, after being reflected by the first and second flat reflective surfaces, respectively, the absolute values ​​of the three components are substantially preserved, the first component retains its original direction, and the second and third components have their directions reversed.

5. The optical device according to claim 1, characterized in that the first redirection mechanism comprises at least one flat main surface optically fixed to one main surface of the substrate.

6. The optical device according to claim 1, characterized in that the first redirection mechanism comprises at least two transparent elements, fixed by an optical adhesive that defines an interface, and the first and second mutually perpendicular flat reflective surfaces are located at the interface.

7. The optical device according to claim 6, characterized in that the refractive index of at least two transparent elements is significantly higher than the refractive index of the optical adhesive.

8. The optical device according to claim 6, characterized in that the first and second flat reflective surfaces are covered with a thin transparent material having a refractive index significantly lower than that of the two transparent elements.

9. The optical device according to claim 8, characterized in that the first and second flat reflective surfaces are covered with different transparent materials.

10. The optical device according to claim 6, characterized in that the first and second flat reflective surfaces are covered with an anti-reflective coating.

11. The optical device according to claim 1, wherein the first redirection mechanism comprises an array of pairs of first and second mutually perpendicular reflective surfaces, wherein for all pairs, the first mutually perpendicular reflective surfaces are parallel and the second mutually perpendicular reflective surfaces are parallel.

12. The optical device according to claim 11, characterized in that, for at least some pairs, the active area of ​​the first reflective surface is wider than the active area of ​​the second reflective surface.

13. The optical device according to claim 12, characterized in that, for at least some pairs, the active area of ​​the second reflective surface is wider than the active area of ​​the first reflective surface.

14. The optical device according to claim 1, further comprising a second redirection mechanism located outside the substrate and having at least two surfaces, which redirects the light waves reflected by the first redirection mechanism and causes them to enter the eye motion box through an output aperture.

15. The optical device according to claim 1, further comprising a second reference plane rotated by a first predetermined angle with respect to the first reference plane, wherein the first and second reference planes are each inclined by approximately 45° with respect to the second reference plane.

16. The optical device according to claim 15, characterized in that the light wave is reflected by a first redirection mechanism and directly reflected to an eye motion box via an output aperture.

17. The propagation direction of the light wave coupled within the first redirection mechanism is determined by three orthogonal components: the first component is parallel to the main propagation direction axis, the second component is perpendicular to the first reference plane, and the third component is parallel to the aforementioned orthogonal axis. The optical device according to claim 15, characterized in that, after being reflected by the first and second reflective surfaces respectively, the three components have their absolute values ​​substantially preserved and their orientations reversed, and the direction of the vector sum of the second and third components is rotated by a second predetermined angle.

18. The optical device according to claim 1, characterized in that each of the aforementioned reflective surfaces is a polarizing beam splitter.

19. The optical device according to claim 1, characterized in that each of the reflective surfaces is reflective in a small portion of the photopic region and substantially transparent elsewhere.

20. The optical device according to claim 19, characterized in that each of the reflective surfaces is a color-sensitive hologram.

Images