Increased field of view for near-eye displays

Abstract

A method for generating an image in a near-eye display may include splitting an image into a first sub-image and a second sub-image, sequentially transmitting the first sub-image and the second sub-image through a channel, extracting light corresponding to the first sub-image in a first polarization and light corresponding to the second sub-image in a second polarization, deflecting a first order of light in the first polarization in a first direction, and deflecting an opposite order of light in the second polarization in an opposite direction different from the first direction. The resulting image width corresponds to a wider field of view.

Description

Technical Field

[0001] The present disclosure relates to an optical system for use within a near-eye display (NED) having a relatively wide field of view (FOV).

Background Art

[0002] Near-eye displays (NEDs) are now standard in augmented reality (AR) and virtual reality (VR) applications. An augmented reality display typically includes, for example, a transparent or semi-transparent display close to the eye through which a user can view the surrounding environment and simultaneously also view virtual objects (such as text, graphics, video, etc.) that appear as part of and / or overlaid on the surrounding environment.

[0003] NED devices often utilize optical waveguides to reproduce the virtual images presented for the user to view within the augmented reality environment. Such optical waveguides often present limitations regarding the performance and / or form factor of such devices. In particular, in NED devices that utilize optical waveguides, such as, for example, head-mounted displays (HMDs), light propagates through the optical waveguide over a limited range of internal angles. Light propagating to the inner surface of the optical waveguide at an incident angle will travel within the optical waveguide and bounce between its surfaces only if the angle of incidence with respect to the surface normal is greater than a certain critical angle associated with the material in which the optical waveguide is fabricated. Light propagating at other angles of incidence will escape from the optical waveguide. Thus, the angular width of light in an NED device that uses an optical waveguide is essentially limited by the optical waveguide. These and other factors inherent to optical waveguides tend to limit the field of view (FOV) that can be supported by waveguide-based displays.

[0004] Attempts to increase the field of view (FOV) of optical waveguide-based displays have traditionally come at the cost of size compromises. To improve the FOV, designers have had to make NED devices bulky and unwieldy, which is an undesirable attribute for consumers. Therefore, there is a need in this art for NEDs with improved FOV that are less bulky and easier to handle. [Overview of the Initiative]

[0005] This disclosure relates to an optical system for use in a NED having a relatively wide field of view (FOV). According to one embodiment, the optical system includes an optical guide optical element (LOE) comprising an optical transmission substrate. The optical transmission substrate includes a first primary surface and a second primary surface parallel to each other, one or more optical input coupling elements configured to couple incident light into the optical transmission substrate, thereby confining the light between the first primary surface and the second primary surface by total internal reflection, and one or more optical output coupling elements configured to couple light out of the substrate. In this embodiment, the optical system further includes a pair of complementary polarizing diffraction gratings. The first polarizing diffraction grating from this pair is disposed on a first side surface of the optical transmission substrate corresponding to the first primary surface, and the second polarizing diffraction grating from this pair is disposed on a second side surface of the optical transmission substrate corresponding to the second primary surface. In this embodiment, the optical system further includes at least one switching polarizing element configured to switch the polarization of light between a first polarization and a second polarization different from the first polarization, such that a second polarization diffraction grating deflects light of the first polarization in a first direction and light of the second polarization in a second direction different from the first direction.

[0006] A polarization diffraction grating deflects polarized light from an image in two different directions according to a time-division multiplexing scheme. At a first time point, the first sub-image light, polarized with a first polarization, is deflected in the first direction, and at a second subsequent time point, the second sub-image light, polarized with a second polarization, is deflected in the second direction. The effective combination of light deflected in the first direction and light deflected in the second direction by time-division multiplexing significantly expands the image's field of view (FOV).

[0007] This technique enables the use of compact optical waveguides, projectors, and the like. Therefore, the present invention disclosed herein enables an improved field of view (FOV) for NEDs without significantly increasing their size.

[0008] In one embodiment, the optical system includes a projector configured to emit polarized light in a direction centered on the normals of a first and a second main surface.

[0009] In one embodiment, at least one switching polarizer is positioned between the projector and a first main surface such that incident light is switched between a first polarization and a second polarization before it is coupled to the optical transmission substrate.

[0010] In one embodiment, at least one switching polarizing element includes a first switching polarizing element and a second switching polarizing element, the first switching polarizing element being disposed between the LOE and a first polarization diffraction grating, and the second switching polarizing element being disposed between the LOE and a second polarization diffraction grating such that incident light remains polarized with the first polarization when coupled into the optical transmission substrate.

[0011] In one embodiment, the optical system includes a second pair of complementary polarizing diffraction gratings, a third polarizing diffraction grating from the second pair disposed on a first side surface of the optical transmission substrate corresponding to a first main surface, and a fourth polarizing diffraction grating from the second pair disposed on a second side surface of the optical transmission substrate corresponding to a second main surface. At least one switching polarizing element includes a third switching polarizing element and a fourth switching polarizing element, the third switching polarizing element disposed between the first polarizing diffraction grating and the third polarizing diffraction grating, and the fourth switching polarizing element disposed between the second polarizing diffraction grating and the fourth polarizing diffraction grating.

[0012] In one embodiment, at least one switching polarizing element includes first, second, and third switching polarizing elements, the first switching polarizing element being disposed between the LOE and a first polarization diffraction grating, the second switching polarizing element being disposed between the LOE and a second polarization diffraction grating, and the third switching polarizing element being disposed between the projector and the first polarization diffraction grating, and the first switching polarizing element being configured to switch to the opposite side of the second and third switching polarizing elements.

[0013] In one embodiment, the optical system includes a processor operably connected to a projector and at least one switching polarizer, and configured to time-division multiplex at least once the polarization of light between a first polarization and a second polarization into an image frame.

[0014] In one embodiment, the projector is configured to project an image frame divided into at least two subframes, and the optical system includes a processor operably connected to the projector and at least one switching polarizer, and configured to time-division multiplex the polarization of light between a first polarization and a second polarization, synchronized with the projection of a first subframe and a second subframe from at least two subframes, respectively.

[0015] In one embodiment, the projector is configured to project a multicolor image in which light of a first color is projected in a field of view different from that of light of a second color, which is different from that of the first color. In one embodiment, a first polarization diffraction grating splits unpolarized light incident on it into orthogonal polarizations, which are incident on a first main surface, propagate through the substrate, and are incident on a second polarization diffraction grating that deflects the orthogonal polarizations to light having the same angular direction as the light incident on the first polarization diffraction grating.

[0016] The accompanying drawings incorporated herein and constituting part thereof illustrate various exemplary systems, methods, etc., illustrating various exemplary embodiments of aspects of the present invention. It will be understood that the boundaries of elements illustrated in the drawings (e.g., boxes, groups of boxes, or other shapes) represent examples of such boundaries. Those skilled in the art will understand that one element may be designed as multiple elements, or multiple elements may be designed as one element. An element shown as an internal component of another element may be implemented as an external component, and vice versa. Furthermore, elements may not be drawn to scale. [Brief explanation of the drawing]

[0017] [Figure 1] A schematic diagram of a typical optical system for a near-eye display (NED) is shown. [Figure 2A] A schematic diagram is shown to typically demonstrate the operation of a polarizing diffraction grating pair. [Figure 2B] A schematic diagram illustrating the typical operation of a polarizing diffraction grating pair is shown. [Figure 3] A schematic diagram of another typical optical system for NED is shown. [Figure 4] A schematic diagram of yet another typical optical system for NED is shown. [Figure 5A] A schematic diagram illustrating a typical FOV for NED is shown. [Figure 5B] A schematic diagram illustrating a typical FOV for NED is shown. [Figure 6] A schematic diagram of yet another typical optical system for NED is shown. [Figure 7] A schematic diagram of yet another typical optical system for NED is shown. [Figure 8] A flowchart shows a typical method for generating an enlarged FOV image in NED. [Figure 9] A typical system block diagram for an extended field of view (FOV) in NED is shown. [Modes for carrying out the invention]

[0018] Figure 1 shows a schematic diagram of a typical optical system 100 for a near-eye display (NED).

[0019] This optical system 100 includes a light guide optical element (LOE) 50. Examples of the LOE 50 are described in significant detail, for example, in U.S. Patent Nos. 7,643,214 and 7,724,442 by Amitai. The LOE 50 includes an optical transmission substrate 52 having a first major surface 52a and a second major surface 52b that are parallel to each other, and edge portions 52c, 52d. The first major surface 52a is also described herein as the front major surface or the front face, and elements related to the major surface 52a are also described as related to the front face. Similarly, the second major surface 52b may be described herein as the rear major surface or the rear face, and elements related to the major surface 52b are also described as related to the rear face. This is because in a NED application, the front major surface 52a and related elements are disposed on the front face of the NED lens away from the user's eye, while the rear major surface 52b and its related elements are disposed on the rear face of the NED lens near the user's eye. The LOE 50 also includes a planar surface 54 that is non-parallel to the first major surface 52a and the second major surface 52b. The surface 54 couples the light incident thereon (represented by the light ray 31) to the optical transmission substrate 52. The surface 54 can be reflective or diffractive, and thus can reflect or diffract the light 31 (reflection represented by the light ray 32), thereby confining the light between the first major surface 52a and the second major surface 52b by total internal reflection. In the illustrated embodiment, the surface 54 is used as a light input coupling element, but in other embodiments, the light can be coupled to the LOE 50 using a light input coupling element other than or in addition to a reflective or diffractive surface such as the surface 54. For example, the edge portions 52c, 52d can be used as light input coupling elements. That is, the light can be directly injected into the LOE 50 at one or more of the edge portions 52c, 52d. In another example, the light can be coupled to the LOE 50 using refraction techniques, and thus the light input coupling element can include a refractive element.

[0020] The LOE50 may also include one or more light output elements. In the illustrated embodiment, the LOE50 includes, as a plurality of partially reflecting light output elements, on a surface 56 that is non-parallel to the first major surface 52a and the second major surface 52b. The surface 56 couples the light 32 out of the substrate 52 (output light represented by the light ray 33).

[0021] The optical system 100 also includes a pair of complementary polarization diffraction gratings 3, 5. The first polarization diffraction grating 3 is disposed on the front side surface of the optical transmission substrate 52 corresponding to the first major surface 52a, and the second polarization diffraction grating 5 is disposed on the rear side surface of the optical transmission substrate 52 corresponding to the second major surface 52b. The polarization diffraction grating is an optical device used to deflect light as a function of the polarization of the light. Examples of polarization-sensitive diffraction gratings include diffraction gratings based on the Pancharatnam Berry phase (geometric phase). One specific example is a diffraction grating made of liquid crystal molecules, which can deflect light as a function of the circular polarization of the light. Such a diffraction grating can generate deflection angles on opposite sides for light having right circular polarization (RHCP) and left circular polarization (LHCP), and in most cases, the polarization of the deflected light will be switched (rotated). That is, for such a diffraction grating, light with right polarization (RHCP) results in light with left circular polarization (LHCP) deflected in a first direction, while light with left circular polarization (LHCP) will result in right circular polarization (RHCP) deflected in a second direction different from the first direction. In this specification, a circular polarization diffraction grating is used to achieve light deflection, but it should be noted that other polarization diffraction gratings, such as linear polarization diffraction gratings, can have different deflections for two orthogonal polarizations and can also be used in the systems disclosed herein. Furthermore, the polarization diffraction grating can be realized in various ways including active or passive liquid crystal elements, polymers, sub-wavelength spatially varying diffraction gratings, or spatially varying polarizers, but is not limited thereto.

[0022] As a means of explanation, Figure 2A illustrates a schematic diagram of a single circular polarization diffraction grating 3. A ray 1 (RHCP) and a ray 2 (LHCP) are incident on the polarization diffraction grating 3. The polarization diffraction grating 3 deflects rays 1 and 2 according to their polarization states, switching their polarization states. As a result, ray 1 (RHCP) is deflected in one direction using LHCP, and ray 2 (LHCP) is deflected in the opposite direction using RHCP. Rays 11 and 12 are deflected to certain diffraction orders m and -m of the polarization diffraction grating 3. In the case of incident unpolarized light, the polarization diffraction grating functions as a polarization beam splitter. In this case, half of the incident intensity is deflected in one direction with RHCP, and the other half is deflected in the opposite direction with LHCP.

[0023] Figure 2B illustrates a configuration of two complementary polarization diffraction gratings, 3 and 5, arranged alternately. Both perpendicularly incident rays 2 and obliquely incident rays 2' with LHCP are deflected by polarization diffraction grating 3 into rays 12 and 12' with RHCP. Rays 12 and 12' then strike polarization diffraction grating 5, where they propagate as polarized rays 22 and 22' with RHCP. Rays 22 and 22' are deflected to the zeroth order of diffraction of polarization diffraction grating 5; therefore, the angular orientation of these rays is the same as that of the incident rays 2 and 2'. While the deflection angle of the diffraction grating depends on the wavelength, because the orientation of rays 22 and 22' is the same as that of rays 2 and 2', chromatic color corruption is not expected for the transmitted image.

[0024] It should be noted that some more unusual or unconventional polarization gratings may be designed such that rays 11 and 12 will have the same polarization as incident rays 1 and 2, respectively. These elements may also be used in the inventors' manner to rotate the polarization of rays 11 and 12, if an additional waveplate is included behind each polarization grating. Alternatively, these elements may be used if they are designed to deflect light in opposite directions from each other, i.e., grating 3 deflects the RHCP ray to some order m, and grating 5 deflects the RHCP in the opposite direction to the opposite order -m. Physically, such a grating may be fabricated as a conventional polarization grating that rotates polarization as the elements in Figure 2A, but then also has another half-waveplate that rotates polarization relative to the original incident polarization. The inventors propose this description of more unusual / unconventional polarization gratings to indicate that the invention is not limited to conventional polarization gratings.

[0025] Returning to Figure 1, in system 100, the polarization-sensing diffraction gratings 3 and 5 may be arranged on the respective sides (front and rear) of the LOE 50.

[0026] A typical system 100 also includes a projection optical device (POD) 60 which may include a spatial light modulator (SLM) such as a liquid crystal display (LCD), a liquid crystal on silicon (LCOS) modulator, or a digital micromirror device of a digital light processing (DLP) system, an OLED array, or an inorganic LED array. Alternatively, it may include a laser beam scanning system (LBS). The POD 60 can produce a collimated image, i.e., the light from each image pixel generates a parallel beam collimated to infinity in the angular direction corresponding to the pixel position in the image. Thus, the image illumination extends to an angular range corresponding to a two-dimensional field of view, all of which can be confined within the LOE 50 by internal reflection and then coupled outward. The POD 60 includes at least one light source, typically an LED or a laser, which may be deployed to illuminate an SLM such as an LCOS chip. The SLM modulates the projection intensity of each pixel of the image, thereby generating the image. In system 100, POD60 can generate a polarization wave of light in the first polarization.

[0027] A typical system 100 also includes a switching polarizer (SPE) 61, which is a device configured to controllly / dynamically switch or rotate the polarization of light incident on it from a first polarization to a second polarization different from the first polarization.

[0028] For example, an SPE61 could be a device in which the polarization direction of its output light can be controlled as a function of the applied voltage. In such a case, the SPE61 can be considered a voltage-controlled waveplate. An example of such an SPE61 is a liquid crystal (LC) polarization rotor, a device that can rotate the polarization state of a linearly polarized input beam without mechanical movement. Such an LC polarization rotor may consist of a liquid crystal variable delay and a quartz zero-order quarter-waveplate. Using linearly polarized light incident on the polarization rotor from the liquid crystal cell side, the rotation of the output polarization can be achieved by adjusting the liquid crystal delay. The liquid crystal delay can then be controlled as a function of the applied voltage.

[0029] In other examples, SPE61 may be a device in which the polarization direction of the output light can be controlled as a function of other variables (e.g., current, sound, etc.). Thus, SPE61 may be an electro-optical device, an acoustic-optical device, or even a mechanically movable element that functions as a modulator for dynamically switching or rotating the polarization of light incident on top.

[0030] System 100 can be presented in front of the eye motion box (EMB) 70, which corresponds to the position of the user's eyes, relative to the NED on which System 100 is mounted.

[0031] During operation, the POD 60 projects light (represented by ray 30) polarized in a first polarization. The POD 60 will cause the light beam to illuminate in multiple directions (fields of view), but for simplicity of explanation, a single ray 30 is shown. Light 30 propagates through the SPE 61, which can dynamically change the polarization of light 30. In the illustrated embodiment, the output of the SPE 61 is light 31, which is injected into the LOE 50 and coupled to the LOE 50 by the surface 54 to become ray 32. This ray 32 is coupled outward from the LOE 50 by the facet 56 to become ray 33. Finally, ray 33 propagates through the diffraction grating 5 and is deflected in a first direction or a second direction represented by ray 34 or ray 35, respectively, depending on its polarization. When SPE61 operates to sequentially change the polarization of light 30 in synchronization with the projection of the image POD60 (at least one polarization switch per frame), light 33 is sequentially polarized in the first direction 34 and the second direction 35, respectively. Therefore, by switching the polarization in SPE61, the direction of the FOV reaching EMB70 can be changed.

[0032] Simultaneously, light 1 incident on the LOE 50 from the scenery (around the user) is split into rays 10 and 11 by the diffraction grating 3, but due to the complementary effect caused by the diffraction grating 5, it ultimately emerges parallel to the incoming ray 1 as rays 12 and 13. As a result, the scenery FOV ultimately remains unchanged by the system 100.

[0033] The principle of FOV deflection is disclosed herein in the context of LOE50, i.e., a 1D expanded optical waveguide with reflective facets. However, system 100 can also be implemented using other types of optical waveguides, such as holographic diffraction gratings or optical waveguides with diffraction gratings, liquid crystal optical waveguides, optical waveguides that expand the FOV to two or more dimensions, and even systems without optical waveguides, such as free-form optical elements with beam splitters or water basins, or any other method used for NED. Although these principles are disclosed herein in the context of AR, they are equally applicable to VR applications and other NED applications (e.g., by removing scenery elements such as forward diffraction gratings 3).

[0034] With respect to the continuous polarization of SPE61 synchronized with the projection of the projected image on POD60, the projected image can be effectively divided into two sub-images: a first sub-image (ray 34) to be deflected in the direction of some diffraction order m, and a second sub-image (ray 35) to be deflected in the opposite direction of diffraction order -m. For example, the AR system may display an image 30 with a 20-degree FOV along the deflection axis of PG centered on the normal to LOE50 (perpendicular to the main surfaces 52a, 52b). As described above, by controlling SPE61 for the first polarization P1, the polarization diffraction grating 5 is deflected to the direction of diffraction order m=1, which is approximately +10 degrees. The P1 image will reach the eye with an FOV distribution of 0 to 20 degrees, rather than -10 to 10 degrees emerging from LOE50 (represented by EMB70). By changing the polarization to a second polarization P2 orthogonal to P1, the light 35 is deflected in the direction of diffraction order m = -1, which is approximately -10 degrees. When SPE61 operates to sequentially change the polarization of the light 30 in synchronization with the projection of the first and second sub-images on POD60, the overall image perceived by the user expands from -20 degrees to 20 degrees, i.e., to a 40-degree FOV, doubling the FOV of the original image. For the sake of simplicity, this explanation ignores the effect of dispersion. The effect of dispersion will be discussed below.

[0035] Figures 3-5 illustrate other possible embodiments.

[0036] Figure 3 illustrates a schematic diagram of a typical optical system 200 for NED. Some optical waveguides and other NED systems cannot propagate or display light in two polarizations. In such cases, system 200 can be used so that light propagating through LOE 50 is always in one polarization. In system 200, SPE 61 is no longer between POD 60 and LOE 50. Therefore, rays 30, 32, and 33 are in a specific polarization (i.e., the first polarization) that does not dynamically change as the light propagates through LOE 50. Instead of one SPE 61, system 200 uses two SPEs 62 and 63. SPE 62 dynamically switches or rotates the polarization of incident light 33 to produce light 36. Light 36 then enters the diffraction grating 5, and in this case, as in system 100, ray 36 is sequentially deflected into rays 34 and 35 depending on the polarization of light 36.

[0037] With respect to the view, SPE63 is controlled in sync with SPE62 so that rays 12 and 13 have the same angle as ray 1. Since rays 10 and 11 are generally transmitted by the internal structure of 50, which is sensitive to polarization, SPE63 is controlled in sync with SPE62 so that SPE63 cancels out the effect of SPE62 together with the internal structure of 50. In this way, the light entering system 200 as ray 1 first hits diffraction grating 3 and SPE63, which is modified, then hits SPE62 and diffraction grating 5, whose effect is canceled out, resulting in rays 12 and 13 having the same angle as ray 1. As a result, the view FOV is ultimately not changed by system 200.

[0038] Some NED systems can only display light in linearly polarized form. If diffraction gratings 3 and 5 deflect the angle corresponding to circularly polarized light, a quarter-wave plate (QWP) can be used as part of the diffraction grating structure to convert it to linearly polarized light.

[0039] The above example describes an embodiment having only one single polarization of the image projected on the polarization diffraction grating 5, but in other embodiments, multiple consecutive polarizations are possible by stacking several polarization diffraction gratings together and inserting SPEs between them as needed.

[0040] Figure 4 illustrates a schematic diagram of a typical optical system 300 for NED. This system 300 can further increase the FOV compared to system 200 in Figure 3. In Figure 4, in addition to diffraction gratings 3 and 5, and SPE62 and SPE63 of system 200 in Figure 3, two additional diffraction gratings 7 and 9, and SPE64 and SPE65 are introduced. However, the principle of operation is similar. In particular, diffraction grating pairs 3 and 5 will always have a complementary effect on each other. The same is true for diffraction grating pairs 7 and 9, which will always have a complementary effect on each other. Similarly, SPE pairs 62 and 63 will dynamically have complementary SPE effects on each other, and SPE pairs 64 and 65 will also dynamically have complementary SPE effects on each other. This does not result in a change to the scene FOV, but it can achieve controlled and continuous deflection of the projected image. The level of continuous polarization can be controlled by separately controlling SPE62 and SPE64 for the first polarization P1 or the second polarization P2.

[0041] As an example, both SPE62 and SPE64 are set for a first polarization P1, the diffraction grating 5 deflects the light 36 by +10 degrees, and the diffraction grating 9 deflects the resulting light by an additional +5 degrees, resulting in an overall deflection of +15 degrees. As another example, SPE62 is set for a first polarization P1 and SPE64 is set for a second polarization P2, the diffraction grating 5 deflects the light 36 by +10 degrees, and the diffraction grating 9 deflects the resulting light by -5 degrees, resulting in an overall deflection of +5 degrees. Thus, different deflections can be achieved by controlling the SPEs to change the polarization at each diffraction grating. In the exemplary system 300, the deflection as a function of polarization at each diffraction grating is as follows:

[0042] [Table 1]

[0043] Therefore, system 300 can be configured in at least four different configurations, and if the original FOV of the system is 10 degrees (+5 to -5), then, as described above, the FOV of system 300 can be controlled by time multiplexing to bring the overall FOV down to +20 to -20 degrees. Diffraction gratings may have the same deflection angle, or even different directions of deflection, and a greater number of diffraction gratings are also conceivable. Furthermore, although the deflection is expressed above in discrete steps (e.g., 5, 10, 15, 20, ...), it may be possible to control the FOV continuously rather than simply discretely by continuously changing the polarization in the SPE from a first polarization to a second polarization.

[0044] Generally, the deflection angle of a polarization grating depends nonlinearly with respect to the incident angle. Therefore, different fields of the projected image will be deflected at different angles, resulting in image distortion. Consequently, this distortion needs to be corrected by projecting a distorted image that synchronously compensates for the nonlinear response of the polarization grating.

[0045] For most diffraction gratings, the deflection angle is wavelength-dependent. Therefore, there may be advantages to using the techniques disclosed herein with a single, narrow-wavelength light source. In the case of a monochromatic system, the system's FOV may be 2α, the deflection of the diffraction grating may be ±α, and the resulting FOV will double to 4α. However, in most NEDs, the light source is multicolored (e.g., RGB), which will lead to different results.

[0046] For example, suppose the NED displays red and blue light (630 and 450 nm). The red wavelength will be deflected at a specific angle, i.e., α degrees, while the blue light will be deflected by only about 0.7α degrees (under linear approximation). This means that the minimum width of the FOV is 2α, while the FOV for blue light can be expanded by 1.4α. Therefore, the resulting FOV is approximately 3.4α. Thus, when the image is divided into different sub-images as described above, only about 85% of the image can be displayed, preserving the FOV between all colors. For colors with smaller deflections (generally shorter wavelengths), only about 85% can be displayed, preventing the overlap of two images that would cause an uneven brightness distribution. Furthermore, for colors with larger deflection angles, only the internal 85% area can be displayed, preventing the FOV of colors with larger deflection angles from being wider than the FOV of colors with smaller deflection angles.

[0047] Figures 5A and 5B illustrate schematic diagrams illustrating typical FOVs for NEDs. Figure 5A illustrates the FOV for red light, while Figure 5B illustrates the FOV for blue light. In both Figures 5A and 5B, rectangles represent the left and right FOVs, and the outer frame of the combined rectangles represents the width that the NED can display. As shown in Figure 5A, for red light, a relatively larger deflection is obtained, and the inner portion of its display is shown at the top. This is indicated by filling in the inner portion of the rectangle. As shown in Figure 5B, for blue light, a relatively smaller deflection is obtained, and therefore the outer portion of the FOV is used instead. The outer portion of the FOV is filled in.

[0048] Using two or more pairs of diffraction gratings, as shown in Figure 4, can also be helpful in making the deflection achromatic. Assume that the NED is illuminating with red and blue wavelengths (630 nm and 450 nm). As shown in Figure 3, using a single pair of diffraction gratings, the red wavelength will be deflected at a specific angle, e.g., 8.5 degrees, while the blue light will be deflected at a smaller angle, e.g., only 5.95 degrees. However, as shown in Figure 4, using two pairs of diffraction gratings, a second pair of diffraction gratings can be introduced, resulting in smaller deflection angles, e.g., 1.5 degrees for red and 1.05 degrees for blue. If the second pair of diffraction gratings is adjusted to deflect the red light in the opposite direction to the first pair of diffraction gratings, and to deflect the blue light in the same direction as the first pair of diffraction gratings, then for both colors, we obtain α = 8.5 - 1.5 = 5.95 + 1.05 = 7. The deflection for both colors is the same. Therefore, by switching the effect of a single diffraction grating between the red and blue images, a smaller diffraction difference can be achieved.

[0049] In one embodiment, the RGB light source has a narrow bandwidth to reduce chromatic aberration within a single monochromatic subimage. For example, the technique disclosed herein may be implemented using a light source with a full width at half maximum (FWHM) of less than 1 nm so as to have an arc FOV dispersion of less than 1 minute for a red image of about 633 nm.

[0050] Another way to overcome the diffraction effect is to use two diffraction gratings on the light from the POD60, as shown in Figure 6.

[0051] Figure 6 illustrates a schematic diagram of a typical optical system 400 for NED. The illustrated configuration is similar to that shown in Figure 3, except for the extension of diffraction grating 3 to receive light from POD 60 so that the light of the projected image travels through both diffraction gratings 3 and 5. Other differences from Figure 3 are the addition of SPE 66 at the exit of the light from POD 60, and the extension of SPE 63 between the extension of diffraction grating 3 and LOE 50. Similar to system 200 in Figure 3, in system 400, the light coming out of POD 60 passes through diffraction grating 5, which deflects the direction of the light according to its polarization. However, here the light first passes through diffraction grating 3, which deflects the light so that its angular width is reduced. Finally, the light reaching EMB 70 (rays 34, 35) has the same angular width as the light coming out of POD 60 (rays 44, 45). However, inside LOE50, the angular distribution of light will be smaller (rays 30-33).

[0052] Typically, LOEs such as LOE50 propagate light with only one polarization. Similarly, PODs such as POD60 illuminate with light with only one polarization. To address this, SPE63 and SPE66 are introduced at the illustrated positions and controlled synchronously. This provides the polarization shift required for light deflection while maintaining a constant polarization from POD60 to LOE50.

[0053] During operation, polarized light 44, 45 from POD60 is set to either the first or second polarization by SPE66. The diffraction grating 3 deflects the light, reducing its angular width. Since SPE63 operates on the opposite side from SPE66, the light entering LOE50 is in its original polarization state from POD60. The light travels through LOE50 (rays 30, 32, 33) and is coupled outward. SPE62 is operated to change the polarization of the LOE output light from the first polarization to the second polarization. The polarization diffraction grating 5 deflects the light in the opposite direction according to its polarization.

[0054] This disclosure describes using a combination of a polarization grating and an SPE to switch the operation of the grating / SPE set (i.e., the SPE controls the polarization, resulting in the polarization grating deflecting light in one direction or another). Other possible structures may be used to achieve similar results. For example, switchable gratings may be used. Switchable gratings are gratings whose optical effects can be dynamically switched on and off, and are primarily part of a system that can dynamically deflect light. Such switchable gratings may be used in complementary pairs, as described above, resulting in a dynamic complementary grating pair, i.e., two gratings that cancel out the effects of one grating and can also be dynamically switched on and off.

[0055] Figure 7 illustrates a schematic diagram of a typical optical system 500 for NED. This system 500 is similar to system 200 described above, except that active transparent liquid crystal elements (such as SLM and LCOS) 103, 105 can be used instead of SPE and polarization diffraction gratings. Using element 105, a controlled linear phase can be applied to the incident polarized light represented by ray 33 to deflect the incident field to different angular orientations, resulting in polarized light represented by rays 34, 35. Using such element 105, the incident light can be deflected in time-dynamically to two or more angular orientations. A similar complementary second element 103 can be placed before the optical waveguide 50 to compensate for the effect of the first element 105, so that the transmitted image will not be distorted.

[0056] method A typical method can be better understood by referring to the flowchart in Figure 8. For the sake of simplicity, the illustrated methodologies are illustrated and described as a series of blocks, but please understand that these methodologies are not limited by the order of the blocks, as some blocks may occur in a different order or simultaneously with other blocks illustrated and described. Furthermore, fewer blocks than all of the illustrated blocks may be required to implement a typical methodology. In addition, additional methodologies, alternative methodologies, or both may employ additional blocks that are not illustrated.

[0057] In a flowchart, a block represents a “processing block” that can be implemented using logic. A processing block may represent a method step or device element for executing a method step. Flowcharts do not depict syntax for any particular programming language, methodology, or style (e.g., procedural, object-oriented). Rather, they illustrate functional information that a person skilled in the art could adopt to develop logic and execute the illustrated process. It will be understood that in some examples, program elements such as temporary variables and routine loops are not shown. It will be further understood that electronic and software applications may involve dynamic and flexible processes, and as a result, the illustrated blocks may be executed in a different order than those shown, or the blocks may be combined or separated into multiple components. It will be understood that processes may be implemented using various programming techniques such as machine language, procedural, object-oriented, or artificial intelligence techniques.

[0058] Figure 8 illustrates a flowchart for a typical method 700 for generating an image in NED. In method 710, method 700 may include dividing the image to be projected by NED into a first sub-image and a second sub-image. For example, a video consists of a series of still images called frames. A frame can be effectively divided into two or more subframes, that is, the same frame image may be transmitted first in synchronization with a first polarization, and second in synchronization with a second polarization, and so on. This step may also include calculating and implementing the necessary correction distortion, which must be applied to the sub-images to correct or compensate for the resulting chromatic aberration and nonlinear deflection as a function of the incident angle (for a given color).

[0059] In 720, Method 700 includes sequentially transmitting a first subimage and a second subimage through a channel. This channel may be, for example, an LOE such as LOE50 described above. Method 700 may also include, in 730, extracting light corresponding to the first subimage in a first polarization and light corresponding to the second subimage in a second polarization. For example, an SPE may be used to dynamically control the polarization of the light, as described above.

[0060] In 740, if the light is in a first polarization state, method 700, in 750, deflects the first-order light in the first polarization in a first direction. However, if the light is in a second polarization state, in 760, the first-order light is deflected in a second direction, different from the first direction, in the second polarization. For example, a polarization grating may be used to deflect the light in the first polarization in a first direction and the light in the second polarization in a second direction. In the illustrated embodiment, the image or frame is effectively divided into two sub-images, but in other embodiments, any image or frame may be divided into more (e.g., four, six, etc.) sub-images. In other words, the same frame image can be transmitted first in synchronization with a first polarization, second in synchronization with a second polarization, third in synchronization with a first polarization (or some other polarization), fourth in synchronization with a second polarization (or some other polarization), and so on. Dividing an image into sub-images does not necessarily require changing the original timing or length of the image or frame. Dividing an image into sub-images means that the image can be transmitted during its original time, but for part of that time the image is transmitted in synchronization with a first polarization, and for part of that time the image is transmitted in synchronization with a second polarization, and so on.

[0061] In one embodiment, deflecting light includes a back-polarizing diffraction grating receiving the extracted light and deflecting the light in the first polarization in a first direction, and deflecting the light in the second polarization in a second direction.

[0062] In one embodiment, the method further includes extracting and deflecting light, while simultaneously transmitting unpolarized light incident on a forward-polarizing diffraction grating through a forward-polarizing diffraction grating, a channel, and a back-polarizing diffraction grating, so that the unpolarized light exits the back-polarizing diffraction grating having the same angular direction as the unpolarized light when incident on the forward-polarizing diffraction grating.

[0063] In one embodiment, light corresponding to the first subimage in the first polarization and light corresponding to the second subimage in the second polarization are transmitted sequentially through the LOE using a time-division multiplexing scheme.

[0064] In one embodiment, sequentially transmitting a first sub-image and a second sub-image includes time-division multiplexing the polarization of light between the first polarization and the second polarization into an image frame at least once.

[0065] In one embodiment, sequentially transmitting a first sub-image and a second sub-image involves time-division multiplexing the polarization of light between a first polarization and a second polarization synchronized with the projection of the first sub-image and the second sub-image, respectively.

[0066] In one embodiment, light corresponding to a first sub-image and light corresponding to a second sub-image are transmitted through the LOE with a common polarization, and the polarization of the light corresponding to the first sub-image in the first polarization, or the polarization of the light corresponding to the second sub-image in the second polarization, is subsequently generated.

[0067] In one embodiment, deflecting light in a first polarization and deflecting light in a second polarization occur in steps involving multiple deflections that lead to an overall deflection.

[0068] In one embodiment, sequentially transmitting a first sub-image and a second sub-image involves projecting a multicolor image in which the light of the first color is projected in a field of view different from that of the second color, which is different from that of the first color.

[0069] Each figure illustrates various operations occurring sequentially, but it should be understood that these illustrated operations may occur substantially in parallel, and although operations may be shown as occurring in parallel, it should be understood that these operations may occur substantially sequentially. In relation to the illustrated methods, several processes are described, but it should be understood that more or fewer processes may be employed, and that lightweight processes, normal processes, threads, and other techniques may be employed. It should also be understood that other typical methods may also, in some cases, include operations that occur substantially in parallel. The illustrated typical methods and other embodiments may operate in real time, faster than real time in software or hardware, or hybrid software / hardware implementations, or slower than real time in software or hardware, or hybrid software / hardware implementations.

[0070] system Figure 9 illustrates a block diagram of a typical system 800 for NED. System 800 may include a processor 80, such as a microprocessor or microcontroller. The processor 80 may be operably connected to the POD 60 and applicable SPEs 61-66, as described in systems 100, 200, 300, and 400 described above. The processor is configured to control, or at least adjust overall, the projection of the image together with the POD 60, and to control the SPEs 61-66 for a first or second polarization to implement the time-division multiplexing scheme described above.

[0071] definition The following includes definitions of selected terms used herein. These definitions include various examples or constituent forms that fall within the scope of the terms and may be used for embodiments. These examples are not intended to be limiting. Both singular and plural forms of the terms may be present within their definitions.

[0072] A “workable connection,” or a connection to which an entity is “workable connected,” is a connection to which signals, physical communications, or logical communications can be transmitted or received. Typically, a workable connection includes a physical interface, an electrical interface, or a data interface, but it should be noted that a workable connection may include different combinations of these or other types of connections, as long as they are sufficient to enable workable control. For example, two entities can be workable connected by being able to communicate signals with each other directly or through one or more intermediate entities such as a processor, operating system, logic, software, or other entities. A workable connection can be created using logical or physical communication channels.

[0073] To the extent that the terms “includes” or “including” are used in the detailed description or claims, they are intended to be encompassed in the same way as the term “comprising,” as they are interpreted when used as an adjective in the claims. Furthermore, to the extent that the term “or” is used in the detailed description or claims of the invention (e.g., A or B), it is intended to mean “A or B, or both.” If the applicant intends for “A or B only, but not both,” the term “A or B only, but not both” would be used. Thus, the use of the term “or” in this specification is inclusive, not exclusive. See Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995).

[0074] Exemplary systems, methods, etc., are illustrated by the illustration of examples, and these examples are described in considerable detail, but it is not the applicant's intention to limit or restrict in any way the scope of such detail. Naturally, for the purpose of illustrating the systems, methods, etc., described herein, it is impossible to describe every conceivable combination of components or methodologies. Additional advantages and modifications will be readily conceived by those skilled in the art. Therefore, the present invention is not limited to the specific details, typical apparatus, and illustrative examples illustrated and described herein. Accordingly, this application is intended to include changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the foregoing description is not intended to limit the scope of the present invention. Rather, the scope of the present invention should be determined by the appended claims and their equivalents.

Claims

1. An optical system for a near-eye display (NED), wherein the optical system is An optical guide optical element (LOE) including an optical transmission substrate, wherein the optical transmission substrate is A first main surface and a second main surface that are parallel to each other, An optical guide optical element having one or more optical input coupling elements configured to couple incident light into the optical transmission substrate, thereby confining the light between the first main surface and the second main surface by total internal reflection, and one or more optical output coupling elements configured to couple the light out of the substrate via the second main surface, A pair of polarization diffraction gratings distinct from the one or more optical output coupling elements, comprising a first polarization diffraction grating from the pair disposed on a first side surface of the optical transmission substrate corresponding to the first main surface, and a second polarization diffraction grating from the pair disposed on a second side surface of the optical transmission substrate corresponding to the second main surface, wherein the second polarization diffraction grating is disposed between the one or more optical output coupling elements and a position corresponding to the user's eye of the NED, The second polarization diffraction grating is configured to switch the polarization of the light from a first polarization to a second polarization different from the first polarization, so that the second polarization diffraction grating deflects the light with the first polarization in a first direction and the light with the second polarization in a second direction different from the first direction, and A projector configured to emit the aforementioned incident light, and configured to project an image frame divided into at least two subframes, A processor operably connected to the projector and the at least one switching polarizer, and configured to time-division multiplex the polarization of the light between the first polarization and the second polarization, synchronized with the projection of the first subframe and the second subframe from the at least two subframes, respectively, comprises: The projector is further configured to project a multicolor image, wherein in the multicolor image, light of a first color is projected only in a first field of view, and light of a second color different from the first color is projected only in a second field of view different from the first field of view, in an optical system.

2. The optical system according to claim 1, wherein the at least one switching polarizer is disposed between the projector and the first main surface such that the incident light switches between the first polarization and the second polarization before the incident light is coupled into the optical transmission substrate.

3. The optical system according to claim 1, wherein the at least one switching polarizing element includes a first switching polarizing element and a second switching polarizing element, the first switching polarizing element is disposed between the LOE and the first polarization diffraction grating, and the second switching polarizing element is disposed between the LOE and the second polarization diffraction grating.

4. The present invention comprises a second pair of polarization diffraction gratings, a third polarization diffraction grating from the second pair disposed on the first side surface of the optical transmission substrate corresponding to the first main surface, and a fourth polarization diffraction grating from the second pair disposed on the second side surface of the optical transmission substrate corresponding to the second main surface, The optical system according to claim 3, wherein the at least one switching polarizing element includes a third switching polarizing element and a fourth switching polarizing element, the third switching polarizing element is disposed between the first polarizing diffraction grating and the third polarizing diffraction grating, and the fourth switching polarizing element is disposed between the second polarizing diffraction grating and the fourth polarizing diffraction grating.

5. The optical system according to claim 1, wherein the at least one switching polarizing element includes first, second, and third switching polarizing elements, the first switching polarizing element is disposed between the LOE and the first polarization diffraction grating, the second switching polarizing element is disposed between the LOE and the second polarization diffraction grating, and the third switching polarizing element is disposed between the projector and the first polarization diffraction grating, and the first switching polarizing element is configured to synchronously switch the second switching polarizing element and the third switching polarizing element.

6. The optical system according to claim 1, comprising a processor operably connected to the projector and the at least one switching polarizing element, and configured to time-division multiplex the polarization of the light between the first polarization and the second polarization at least once into an image frame.

7. The optical system according to claim 1, wherein the first polarizing diffraction grating divides unpolarized light incident thereon into several parts, and the parts are incident on the first main surface, propagate through the substrate, and are incident on a second polarizing diffraction grating which deflects the parts to light having the same angular direction as the light incident on the first polarizing diffraction grating.

8. An optical system for a near-eye display (NED), wherein the optical system is An optical guide optical element (LOE) including an optical transmission substrate, wherein the optical transmission substrate is A first main surface and a second main surface that are parallel to each other, An optical guide optical element having one or more optical input coupling elements configured to couple incident light into the optical transmission substrate, thereby confining the light between the first main surface and the second main surface by total internal reflection, and one or more optical output coupling elements configured to couple the light out of the substrate via the second main surface, Unlike the one or more optical output coupling elements, a first active transparent liquid crystal element disposed on a first side surface of the optical transmission substrate corresponding to the first main surface, wherein the first active transparent liquid crystal element is configured to switch the polarization of the light from a first polarization to a second polarization different from the first polarization, such that the first active transparent liquid crystal element deflects light of a first polarization in a first direction and light of a second polarization in a second direction different from the first direction, Optically, a second active transparent liquid crystal element is disposed adjacent to the second main surface between one or more optical output coupling elements and a position corresponding to the user's eye of the NED, wherein the second active transparent liquid crystal element is configured to switch the polarization of light incident on it in synchronization with the first active transparent liquid crystal element, A projector configured to emit the aforementioned incident light, and configured to project an image frame divided into at least two subframes, The system comprises a processor operably connected to the projector and the first active transparent liquid crystal element, and configured to time-division multiplex the polarization of the light between the first polarization and the second polarization, synchronized with the projection of the first subframe and the second subframe from the at least two subframes, respectively. The projector is further configured to project a multicolor image, wherein in the multicolor image, light of a first color is projected only in a first field of view, and light of a second color different from the first color is projected only in a second field of view different from the first field of view, in an optical system.

9. The optical system according to claim 8, comprising a processor operably connected to the projector and the first active transparent liquid crystal element, and configured to time-division multiplex the polarization of the light between the first polarization and the second polarization at least once into an image frame.

10. An optical system for a near-eye display (NED), wherein the optical system is: A projector configured to emit light corresponding to an image, An optical guide optical element (LOE) including an optical transmission substrate, wherein the optical transmission substrate is A first main surface and a second main surface that are parallel to each other, An optical guide optical element having one or more optical input coupling elements configured to couple light from the projector into the optical transmission substrate, thereby confining the light between the first main surface and the second main surface by total internal reflection, and one or more optical output coupling elements configured to couple the light out of the substrate via the second main surface, A pair of polarization diffraction gratings distinct from the one or more optical output coupling elements, comprising a first polarization diffraction grating from the pair disposed between the projector and the first main surface, and a second polarization diffraction grating from the pair disposed between the second main surface and a position corresponding to the user's eye of the NED, The system comprises at least one switching polarizing element configured to switch the polarization of the light from a first polarization to a second polarization different from the first polarization, so that the second polarization diffraction grating deflects the light with the first polarization in a first direction and the light with the second polarization in a second direction different from the first direction, The projector is further configured to project an image frame divided into at least two subframes, The optical system further comprises a processor operably connected to the projector and the at least one switching polarizer, and configured to time-division multiplex the polarization of the light between the first polarization and the second polarization, synchronized with the projection of the first subframe and the second subframe from the at least two subframes, respectively. The projector is further configured to project a multicolor image, wherein in the multicolor image, light of a first color is projected only in a first field of view, and light of a second color different from the first color is projected only in a second field of view different from the first field of view, in an optical system.

11. The optical system according to claim 10, wherein the at least one switching polarizing element is disposed between the projector and the first polarizing diffraction grating.

12. The optical system according to claim 10, wherein the at least one switching polarizing element includes first, second, and third switching polarizing elements, the first switching polarizing element is disposed between the LOE and the first polarization diffraction grating, the second switching polarizing element is disposed between the LOE and the second polarization diffraction grating, and the third switching polarizing element is disposed between the projector and the first polarization diffraction grating, and the first switching polarizing element is configured to synchronously switch the second switching polarizing element and the third switching polarizing element.

Images