Optical device and augmented reality display equipment

Abstract

The utility model discloses an optical device and augmented reality display equipment, and the optical device comprises a projection light source which emits unpolarized image light; the diffraction optical waveguide comprises a polarization selection coupling grating; the polarization conversion assembly comprises a polaroid and a quarter-wave plate, and the included angle between the polarization direction of the polaroid and the fast axis direction of the quarter-wave plate is 45 degrees or-45 degrees; wherein image light emitted by the projection light source is converted into first linearly polarized light through the polarizer, then is converted into circularly polarized light through the quarter-wave plate, and then enters the polarization selection coupling-in grating; moreover, after being diffracted by the polarization selection coupling-in grating, image light returned to the projection light source is converted into second linearly polarized light through the quarter-wave plate, the second linearly polarized light enters the polaroid and is absorbed by the polaroid, and the polarization directions of the first linearly polarized light and the second linearly polarized light are perpendicular to each other. According to the technical scheme disclosed by the invention, ghosting images can be prevented from being formed.

Description

Technical Field

[0001] The present application relates to the field of augmented reality, and in particular to an optical device and an augmented reality display device. Background Art

[0002] Waveguide display technology is one of the most challenging and complex problems in the field of augmented reality. Diffraction waveguide is a type of waveguide commonly used in waveguide display technology. Usually, the image light emitted by the projection light source is diffracted after being incident on the coupling grating. Among them, the diffraction 1st order light is transmitted to the coupling grating through total internal reflection of the diffraction waveguide and coupled out to the human eye, so that the human eye can see the display image; at the same time, the reflected 0th order light will be reflected back to the projection light source and reflected again by the projection light source before being incident on the coupling grating again. After the same total internal reflection and coupling out, it is incident on the human eye, so that the human eye can see the artifact corresponding to the normal image, also known as the ghost image. The existence of the ghost image seriously affects the display effect and the user experience. Utility Model Content

[0003] In order to solve the above problems, the present application provides an optical device and an augmented reality display device that can avoid the formation of ghost images.

[0004] Specifically, an optical device includes:

[0005] A projection light source, wherein the projection light source emits non-polarized image light;

[0006] a diffractive optical waveguide comprising a polarization selective incoupling grating; and

[0007] A polarization conversion component, the polarization conversion component comprising a polarizer and a quarter wave plate, wherein the angle between the polarization direction of the polarizer and the fast axis direction of the quarter wave plate is 45° or -45°;

[0008] The image light emitted by the projection light source is converted into a first linear polarized light by the polarizer, and then converted into a circular polarized light by the quarter wave plate before being incident on the polarization selective coupling grating; and the image light returned to the projection light source after being diffracted by the polarization selective coupling grating is converted into a second linear polarized light by the quarter wave plate, and then is incident on the polarizer and absorbed by the polarizer, and the polarization directions of the first linear polarized light and the second linear polarized light are perpendicular to each other.

[0009] In practice, the polarization selective coupling-in grating includes a single birefringent material layer or a multi-layer stacked birefringent material layer; the birefringent material layer includes a helical structure formed by birefringent material molecules of the birefringent material.

[0010] Practically, the angle between the polarization direction of the polarizer and the fast axis direction of the quarter wave plate is 45°, the circularly polarized light is left-handed circularly polarized light, and the rotation direction of the birefringent material molecules is left-handed; or, the angle between the polarization direction of the polarizer and the fast axis direction of the quarter wave plate is -45°, the circularly polarized light is right-handed circularly polarized light, and the rotation direction of the birefringent material molecules is right-handed.

[0011] Practically, the refractive index of the birefringent material layer is in the range of 1.5-2.5, and the refractive index difference of the birefringent material layer is in the range of 0.05-1.

[0012] Practically, the birefringent material layer has a thickness ranging from 50 nm to 5 μm.

[0013] Practically, the tilt angle of the periodically tilted refractive index plane in the birefringent material layer is in the range of 5°-85°.

[0014] In practice, the polarization selective coupling-in grating has angle selectivity, and the propagation angle of the image light after being diffracted and coupled into the diffraction optical waveguide by the polarization selective coupling-in grating is outside the angle selection range of the polarization selective coupling-in grating.

[0015] In practice, the diffraction optical waveguide further includes an outcoupling grating, and the outcoupling grating is a surface relief grating or a polarization selective volume holographic grating.

[0016] In practice, the quarter wave plate, the polarizer and the polarization selective incoupling grating are arranged in parallel.

[0017] An augmented reality display device comprises any one of the optical devices described above.

[0018] The present application provides an optical device and an augmented reality display device, in which a polarization-selective volume holographic grating is selected as a coupling element of a diffraction light waveguide. The polarization-selective volume holographic grating can have extremely high diffraction efficiency for light of a specific polarization state within a certain angle range. Based on this, a polarization conversion component including a polarizer and a quarter-wave plate is used in combination. On the one hand, the unpolarized light emitted by the projection light source is converted into circularly polarized light as the incident light for coupling into the grating, so as to greatly improve the coupling efficiency. On the other hand, the light reflected back to the projection light source will first pass through the polarization conversion component. The light has passed through the action of the quarter-wave plate once. At this time, after passing through the quarter-wave plate again, the polarization direction is rotated by 90°. When it is incident on the polarizer again, the polarization direction is perpendicular to the polarization direction of the polarizer, so that it is blocked and absorbed to prevent it from being incident on the projection light source and also to prevent it from being reflected back to the coupling-in grating, which can effectively reduce or even avoid unwanted ghost images. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 A schematic diagram of light diffraction of a polarization-selective volume holographic grating provided in an embodiment of the present application;

[0021] Figure 2 A schematic diagram comparing the reflection first order (R1) diffraction efficiency of the polarization-selective volume holographic grating provided in an embodiment of the present application for left-handed circularly polarized light and right-handed circularly polarized light;

[0022] Figure 3 A schematic diagram comparing the reflected 1st order (R1) diffraction efficiency and the transmitted 0th order (T0) diffraction efficiency of the polarization-selective volume holographic grating provided in an embodiment of the present application for left-handed circularly polarized light;

[0023] Figure 4 A schematic diagram of the structure of an optical device provided in an embodiment of the present application;

[0024] Figure ID:

[0025] 101: Polarization-selective volume holographic grating;

[0026] 401: projection light source;

[0027] 402: non-polarized image light;

[0028] 403: image light reflected once;

[0029] 404: lens group;

[0030] 405: polarization selective coupling grating;

[0031] 406: Diffractive optical waveguide;

[0032] 407: outcoupling grating;

[0033] 409: image light reflected again;

[0034] 410: Polarizer;

[0035] 411: Quarter wave plate. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] The technical solution of the present application is described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0038] The present application provides an optical device, which includes: a projection light source, which emits non-polarized image light; a diffraction light waveguide, which includes a polarization selective coupling grating; and a polarization conversion component, which includes a polarizer and a quarter wave plate, and the angle between the polarization direction of the polarizer and the fast axis direction of the quarter wave plate is 45° or -45°; wherein the image light emitted by the projection light source is converted into a first linear polarized light by the polarizer, and then converted into a circular polarized light by the quarter wave plate, and then incident on the polarization selective coupling grating; and the image light returned to the projection light source after diffraction by the polarization selective coupling grating is converted into a second linear polarized light by the quarter wave plate, and then incident on the polarizer and absorbed by the polarizer, and the polarization directions of the first linear polarized light and the second linear polarized light are perpendicular to each other.

[0039] Among them, the polarization selective coupling grating is a polarization selective volume holographic grating (Polarization Volume Grating, PVG), which has angle selectivity and polarization selectivity and can have extremely high diffraction efficiency for light with a specific polarization state within a certain angle range.

[0040] In practice, the polarization selective coupling-in grating comprises a single birefringent material layer or a multi-layer stacked birefringent material layer; the birefringent material layer comprises a helical structure formed by birefringent material molecules of the birefringent material, wherein the birefringent material may be a liquid crystal material, and the birefringent material molecules are liquid crystal material molecules.

[0041] refer to Figure 1-3 , Figure 1 A schematic diagram of light diffraction of a polarization-selective volume holographic grating provided in an embodiment of the present application; Figure 2 A schematic diagram comparing the reflection first order (R1) diffraction efficiency of the polarization-selective volume holographic grating provided in an embodiment of the present application for left-handed circularly polarized light and right-handed circularly polarized light; Figure 3 A schematic diagram comparing the reflected 1st order (R1) diffraction efficiency and the transmitted 0th order (T0) diffraction efficiency of the polarization-selective volume holographic grating provided in an embodiment of the present application for left-handed circularly polarized light. Figure 1The polarization-selective volume holographic grating 101 shown in FIG. 1 is a reflective grating. When light is incident on the polarization-selective volume holographic grating at an angle θ, diffraction occurs, and at least diffraction light of the reflection 0th order (R0), reflection 1st order (R1), and transmission 0th order (T0) is generated. When light is incident on the polarization-selective volume holographic grating at an angle θ, and the rotation direction of the birefringent material molecules of the polarization-selective volume holographic grating is left-handed, the diffraction efficiency of the polarization-selective volume holographic grating for the reflection 1st order (R1) of left-handed circularly polarized light and right-handed circularly polarized light is as follows: Figure 2 As shown, the reflected 1st order (R1) diffraction efficiency and the transmitted 0th order diffraction efficiency of the polarization selective volume holographic grating for left-handed circularly polarized light are as follows: Figure 3 As shown. Figure 2 It can be seen from the figure that the polarization-selective volume holographic grating has polarization selectivity. The left-handed polarization-selective volume holographic grating has diffraction efficiency only for left-handed circularly polarized light, and has basically no diffraction efficiency for right-handed circularly polarized light. Similarly, the right-handed polarization-selective volume holographic grating has diffraction efficiency only for right-handed circularly polarized light, and has basically no diffraction efficiency for left-handed circularly polarized light. Figure 3 It can be seen that the diffraction efficiency is basically concentrated in the reflection order 1 (R1) and the transmission order 0 (T0), and the diffraction efficiency of the reflection order 0 (R0) is very low.

[0042] Generally, a diffraction optical waveguide is used to guide the image light emitted by a projection light source to the human eye. Specifically, the diffraction optical waveguide includes a waveguide substrate, on which at least a coupling-in element and a coupling-out element are arranged. The coupling-in element couples the image light emitted by the microdisplay into the waveguide substrate, and after the image light is totally reflected in the waveguide substrate and transmitted to the coupling-out element, the coupling-out element couples the image light out of the waveguide substrate and into the human eye.

[0043] Practically, the coupling element (i.e., polarization selective coupling grating) provided by the present application can use a right-handed polarization selective volume holographic grating or a left-handed polarization selective volume holographic grating; when the right-handed polarization selective volume holographic grating is used, the right-handed polarization selective volume holographic grating is designed to provide right-handed circularly polarized light as incident image light; when the left-handed polarization selective volume holographic grating is used, the left-handed circularly polarized light is designed to be incident image light. This can greatly improve the coupling efficiency of the diffraction optical waveguide.

[0044] In practice, the polarization conversion component is used to change the polarization state of the image light. The polarizer is located between the projection light source and the quarter wave plate, and is used to pass the light along the polarization direction of the polarizer, and block and absorb the light that is inconsistent with the polarization direction of the polarizer. The quarter wave plate is located between the polarizer and the polarization selective coupling grating, and can be used to convert linear polarized light into circular polarized light or elliptically polarized light, or to convert circular polarized light or elliptically polarized light into linear polarized light, wherein the rotation direction of the circular polarized light or elliptically polarized light depends on the angle between the fast axis direction of the quarter wave plate and the polarization direction of the linear polarized light.

[0045] Further, based on the polarization selectivity of the polarization-selective volume holographic grating, a polarization conversion component is used in combination, and optionally, the circularly polarized light is left-handed circularly polarized light, the rotation direction of the birefringent material molecules is left-handed, and the angle between the polarization direction of the polarizer and the fast axis direction of the quarter-wave plate is 45°; or, the angle between the polarization direction of the polarizer and the fast axis direction of the quarter-wave plate is -45°, the circularly polarized light is right-handed circularly polarized light, and the rotation direction of the birefringent material molecules is right-handed. Wherein, taking the fast axis direction of the quarter-wave plate as the reference direction, the counterclockwise rotation angle is positive, and the clockwise rotation angle is negative.

[0046] In this way, a polarization conversion component is added between the projection light source and the coupling element of the diffraction light waveguide. On the one hand, based on the non-polarized image light emitted by the projection light source, the coupling element with polarization selection can be provided with image light of a matching polarization state, which can not only improve the coupling efficiency of the coupling element, but also enhance the flexibility of selecting the projection light source. On the other hand, the image light returned to the projection light source generated at the coupling element will also pass through the polarization conversion component. After the linear polarized light passes through the quarter-wave plate twice, the polarization state remains unchanged, but the polarization direction will change and rotate 90°. In this way, after passing through the quarter-wave plate, the returned image light will just become linear polarized light with a polarization direction perpendicular to the polarization direction of the polarizer, and will be blocked and absorbed by the polarizer and can no longer be reflected back to the coupling element, thereby avoiding the formation of ghost images.

[0047] Optionally, the optical device may further include a lens group, which may be located between the quarter wave plate and the polarization selective coupling grating, and is used to collimate the image light emitted by the projection light source. Practically, the projection light source, the polarizer, the quarter wave plate and the lens group may be packaged as a projection light engine, which facilitates the miniaturization of the optical device.

[0048] For example, reference Figure 4 , Figure 4Schematic diagram of the structure of the optical device provided in the embodiment of the present application, wherein the rotation direction of the polarization selective coupling grating 405 is left-handed, and the angle between the polarization direction of the polarizer 410 and the fast axis direction of the quarter-wave plate 411 is 45°. Specifically, the non-polarized image light 402 emitted by the projection light source 401 becomes the first linear polarized light after passing through the polarizer 410, and the polarization direction is consistent with the polarization direction of the polarizer 410 and is the first direction. After the first linear polarized light passes through the quarter-wave plate, the angle between the fast axis direction of the quarter-wave plate and the polarization direction of the polarizer is 45°, so that the light becomes left-handed circularly polarized light. The left-handed circularly polarized light is collimated by the lens group 404 and incident on the polarization selective coupling grating 405, and diffracts. Due to the characteristics of the left-handed polarization volume holographic grating, most of the energy is diffracted and coupled. After entering the diffraction light waveguide 406 or being transmitted, a small portion of the energy is reflected back to the projection light source 401, that is, the reflected 0th order light, that is, the image light 403 reflected once, which is still left-handed circularly polarized light. The image light 403 reflected once passes through the quarter-wave plate 411 again and becomes a second linear polarized light, and the polarization direction is perpendicular to the first direction, that is, perpendicular to the polarization direction of the polarizer 410. The polarizer 410 can block and absorb the second linear polarized light, that is, block and absorb the image light 403 reflected once and reflected back to the projection light source 401, so as to avoid the formation of ghost images.

[0049] Optionally, the refractive index of the birefringent material layer is in the range of 1.5-2.5, and the refractive index difference of the birefringent material layer is in the range of 0.05-1.

[0050] Optionally, the birefringent material layer has a thickness in the range of 50 nm to 5 μm.

[0051] Optionally, the tilt angle of the periodically tilted refractive index plane in the birefringent material layer is in the range of 5°-85°.

[0052] In the optical device provided in the above embodiment, a polarization-selective volume holographic grating is selected as the coupling element of the diffraction light waveguide. The polarization-selective volume holographic grating can have extremely high diffraction efficiency for light of a specific polarization state within a certain angle range. Based on this, a polarization conversion component including a polarizer and a quarter-wave plate is used in combination. On the one hand, the unpolarized light emitted by the projection light source is converted into circularly polarized light as the incident light for the coupling grating, which greatly improves the coupling efficiency. On the other hand, the light reflected back to the projection light source will first pass through the polarization conversion component. After the quarter-wave plate, the polarization direction of the light when incident on the polarizer is perpendicular to the polarization direction of the polarizer, so that it is blocked and absorbed to prevent it from being incident on the projection light source and also prevent it from being reflected back to the coupling grating, which can effectively reduce or even avoid unwanted ghost images.

[0053] Further, optionally, the polarization selective coupling-in grating has angle selectivity, and the propagation angle of the image light after being diffracted and coupled into the diffraction optical waveguide by the polarization selective coupling-in grating is outside the angle selection range of the polarization selective coupling-in grating.

[0054] Specifically, the light coupled into the diffractive optical waveguide via the coupling element may be incident on the coupling element again and coupled out from the diffractive optical waveguide, resulting in a great loss of the coupled energy, especially when the coupling element has a higher coupling efficiency. Usually, in order to balance this loss, the upper limit of the coupling efficiency of the coupling element is limited. The polarization-selective volume holographic grating has angle selectivity, and has extremely high diffraction efficiency for light at a certain angle, but almost no diffraction efficiency for light at another part of the angles. The present application cleverly utilizes the angle selectivity of the polarization-selective volume holographic grating, and designs so that the diffraction angle of the image light coupled into the waveguide substrate (i.e., the incident angle of the second incident into the coupling element) is not within the efficient angular spectrum range of the polarization-selective coupling grating. In this way, the image light coupled into the waveguide substrate will not be diffracted again by the coupling element and lost. Then, when the polarization-selective volume holographic grating is used as the coupling element, the upper limit of the coupling efficiency is no longer limited, and can be designed to be very high, thereby greatly enhancing the coupling efficiency of the diffraction waveguide.

[0055] For example, continue to refer to Figure 2 or Figure 3 , it can be seen that when the incident angle θ is in the angular spectrum range of -10°—10°, there is diffraction efficiency, and the diffraction efficiency is relatively high; when the incident angle θ is in the angular spectrum range of -20°—-10°, there is diffraction efficiency, and the diffraction efficiency is relatively low; when the incident angle θ is in the angular spectrum range of -20°—-55°, the diffraction efficiency is basically zero. In this example, the angle selection range of the polarization selective coupling grating can be -20°—10° or, further, -10°—10°, and the diffraction angle of the image light coupled into the waveguide substrate can be designed to be within the angular spectrum range of "-20°—-55°" outside the angle selection range.

[0056] Continue to refer Figure 4 After the left-handed circularly polarized light is diffracted and coupled into the diffraction optical waveguide 406, it is transmitted in the diffraction optical waveguide 406 with the diffraction angle as the total reflection angle, and when it is incident on the polarization selective coupling grating 405 again, it generates an out-coupled light (i.e., the image light 409 reflected again) that is coupled out of the diffraction optical waveguide 406. Since the diffraction angle of the left-handed circularly polarized light coupled into the waveguide substrate is designed to be within the angular spectrum range of -20° to -55°, the energy of the image light 409 reflected again is almost zero, that is, no out-coupling loss will be generated due to the re-diffraction.

[0057] It should be noted that, in the present application, the re-reflection at the coupling element generally refers to all reflections except the first reflection, and is not limited to the second reflection.

[0058] Optionally, the diffraction optical waveguide further includes an outcoupling grating, and the outcoupling grating is a surface relief grating or a polarization selective volume holographic grating.

[0059] Optionally, the diffraction optical waveguide further includes a turning grating, and the turning grating is a surface relief grating or a polarization selective volume holographic grating.

[0060] Optionally, the quarter wave plate, the polarizer and the polarization selective coupling-in grating are arranged in parallel.

[0061] Optionally, the projection light source in the present application is not limited and can be a micro display such as digital light processing (DLP), laser beam scanner (LBS), liquid crystal on silicon (LCOS), digital micro-mirror device (DMD), organic light-emitting diode (OLED), micro electro mechanical system (MEMS), etc.

[0062] The present application also provides an augmented reality display device, which includes the optical device in the aforementioned embodiments. It can be understood that the augmented reality display device has the optical device in the aforementioned embodiments, and thus also has the advantages of the optical device in the aforementioned embodiments.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An optical device, characterized in that: include: A projection light source, wherein the projection light source emits non-polarized image light; A diffractive optical waveguide, the diffractive optical waveguide comprising a polarization selective incoupling grating; as well as A polarization conversion component, the polarization conversion component comprising a polarizer and a quarter wave plate, wherein the angle between the polarization direction of the polarizer and the fast axis direction of the quarter wave plate is 45° or -45°; The image light emitted by the projection light source is converted into a first linear polarized light by the polarizer, and then converted into a circular polarized light by the quarter wave plate before being incident on the polarization selective coupling grating; and the image light returned to the projection light source after being diffracted by the polarization selective coupling grating is converted into a second linear polarized light by the quarter wave plate, and then is incident on the polarizer and absorbed by the polarizer, and the polarization directions of the first linear polarized light and the second linear polarized light are perpendicular to each other.

2. The optical device according to claim 1, characterized in that The polarization selective coupling-in grating comprises a single birefringent material layer or a multi-layer stacked birefringent material layer; the birefringent material layer comprises a helical structure formed by birefringent material molecules of the birefringent material.

3. The optical device according to claim 2, characterized in that: The angle between the polarization direction of the polarizer and the fast axis direction of the quarter wave plate is 45°, the circularly polarized light is left-handed circularly polarized light, and the rotation direction of the birefringent material molecules is left-handed; or, the angle between the polarization direction of the polarizer and the fast axis direction of the quarter wave plate is -45°, the circularly polarized light is right-handed circularly polarized light, and the rotation direction of the birefringent material molecules is right-handed.

4. The optical device according to claim 2, characterized in that: The refractive index of the birefringent material layer is in the range of 1.5-2.5, and the refractive index difference of the birefringent material layer is in the range of 0.05-1.

5. The optical device according to claim 2, characterized in that: The thickness of the birefringent material layer is in the range of 50 nm to 5 μm.

6. The optical device according to claim 2, characterized in that: The tilt angle of the periodically tilted refractive index plane in the birefringent material layer is in the range of 5°-85°.

7. The optical device according to claim 1, characterized in that: The polarization selective coupling-in grating has angle selectivity, and the propagation angle of the image light after being diffracted and coupled into the diffraction optical waveguide by the polarization selective coupling-in grating is outside the angle selection range of the polarization selective coupling-in grating.

8. The optical device according to claim 1, characterized in that: The diffraction optical waveguide further comprises an outcoupling grating, which is a surface relief grating or a polarization selective volume holographic grating.

9. The optical device according to claim 1, characterized in that: The quarter wave plate, the polarizer and the polarization selective coupling-in grating are arranged in parallel.

10. An augmented reality display device, characterized in that: An optical device comprising any one of claims 1 to 9.

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