A diffraction optical waveguide device capable of eliminating rainbow effect

Abstract

The present invention discloses a diffraction optical waveguide device capable of eliminating the rainbow effect, comprising an optical engine, an in-coupling grating, a waveguide component, an adjusting mechanism and an out-coupling grating, wherein the in-coupling grating, the adjusting mechanism and the out-coupling grating are all arranged in affixed with the waveguide component, wherein: the in-coupling grating is used to couple the light emitted by the optical engine into the waveguide component; the adjusting mechanism is a volume Bragg grating, and is arranged relative to the out-coupling grating, and is used to reflect the light within a preset angle range in the external ambient light, so that the external ambient light entering the waveguide component appears as zero-order diffraction light after passing through the out-coupling grating, so as to eliminate the rainbow effect; the out-coupling grating is used to couple the light conducted by the waveguide component to the human eye. The device can not only ensure the brightness of the ambient light in the user's field of view, but also eliminate the rainbow effect, ensure the uniformity and brightness of the out-coupling image, and provide a better experience for the user.

Description

Technical Field

[0001] The invention belongs to the technical field of waveguide display, and in particular relates to a diffraction light waveguide device capable of eliminating rainbow effect. Background Art

[0002] Augmented reality (AR) and mixed reality (MR) systems include a micro-projection engine, a transparent optical waveguide, and a diffractive optical element (DOE) to achieve the coupling in, pupil expansion, and out-coupling of the micro-projection engine image, allowing users to effectively observe the real-world scenes while receiving the virtual images projected by the micro-projection engine.

[0003] The current diffraction display technology used in near-eye display systems (NED) or head-up displays usually includes an input grating, an exit pupil expansion grating, an output grating, and an optical waveguide element, wherein the grating is a binary grating. The input grating generates diffraction orders in opposite directions, couples the light into the optical waveguide at a suitable angle, and transmits the light in the optical waveguide by total reflection. Then, the exit pupil expansion gratings on both sides respectively expand the positive and negative diffraction orders in one direction (such as the Y direction) and transmit them in orthogonal directions. After reaching the output grating, the light is expanded in another direction (such as the X direction) and coupled out of the waveguide. In this process, in addition to the desired image A input by the light engine and coupled out by the output grating, there is also an undesired image C that is input from the external real world and diffracted by the output grating after passing through the optical waveguide and reaching the human eye, i.e., the rainbow effect in the diffraction optical waveguide system, such as Figure 1 As shown, it presents a colorful pattern on the desired image, causing the imaging quality of the diffractive light waveguide to deteriorate or even become unusable in some cases.

[0004] In view of the above problems, the following technical solutions are proposed in the prior art:

[0005] 1) Patent announcement number US09625717B2 "Optical device with diffractive grating" proposes a method of using a double-layer transparent grating on a transparent optical waveguide, wherein the second layer of grating is located above the first layer of grating, and the two have the same period, but have different refractive index blocks, wherein the low refractive index block of the second layer of grating is aligned or partially aligned with the high refractive index block of the first layer of grating, and vice versa, and the second layer of grating is used to reduce the non-zero-order diffraction light generated by the external environment through the outcoupling area, so as to reduce the partial rainbow effect in the system. However, this method will reduce the outcoupling efficiency and uniformity of the desired image, thereby reducing the imaging quality of the entire system.

[0006] 2) Patent announcement No. US10234686B2 "Rainbow removal in near-eye display using polarization-sensitive grating" proposes the use of polarization filters to convert natural light in the external environment into polarized or partially polarized light, such as TM light. Since the designed outcoupling grating is sensitive to TE polarized light, the light in the external environment will not undergo diffraction effects after passing through the outcoupling grating, thereby avoiding partial rainbow effects in the system. By using a polarization filter to change the polarization state of natural light in the external environment, such as generating TM linear polarization, the outcoupling grating that is sensitive to TE polarization light will not undergo diffraction effects on TM linear polarization, thereby avoiding the rainbow effect. However, this method, on the one hand, converts the natural light of the external environment into linear polarized light through the polarization filter, which will cause the brightness of the natural light passing through the optical waveguide to be reduced by half, making the transparent optical waveguide lose some of its light transmittance advantages; on the other hand, although the image output by the microlight engine is linearly polarized, after passing through the coupling grating and the exit pupil expansion grating, the polarization state of the light interacting with the coupling grating includes linear polarization in different directions, circular polarization, and elliptical polarization, etc. Therefore, if the coupling grating is designed to be sensitive only to TE linear polarization to eliminate the rainbow effect, the coupling efficiency and uniformity of the desired image will be greatly reduced, affecting the imaging quality of the entire system. Summary of the invention

[0007] The purpose of the present invention is to address the above-mentioned problem and propose a diffraction light waveguide device that can eliminate the rainbow effect, which not only ensures the brightness of the ambient light in the user's field of view, but also eliminates the rainbow effect, ensures the uniformity and brightness of the outcoupled image, and can provide a better experience for AR or HMD users.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] The present invention provides a diffraction light waveguide device capable of eliminating rainbow effect, comprising a light engine, an in-coupling grating, a waveguide component, an adjustment mechanism and an out-coupling grating, wherein the in-coupling grating, the adjustment mechanism and the out-coupling grating are all arranged in contact with the waveguide component, wherein:

[0010] A coupling grating, used for coupling light emitted by the optical engine into the waveguide component;

[0011] The adjustment mechanism is a volume Bragg grating and is arranged opposite to the outcoupling grating, and is used to reflect light within a preset angle range in the external ambient light, so that the external ambient light entering the waveguide component appears as zero-order diffraction light after passing through the outcoupling grating, so as to eliminate the rainbow effect;

[0012] The outcoupling grating is used to couple the light transmitted through the waveguide component out to the human eye.

[0013] Preferably, the volume Bragg grating satisfies the following conditions:

[0014]

[0015] Where Λ is the period of the volume Bragg grating, λ is the central wavelength of the interference beam, and θ is the angle of the interference beam.

[0016] Preferably, the preset angle range is -30° to 30°, the thickness range of the volume Bragg grating is 10 um to 100 um, and the refractive index modulation range is 0.16 to 0.2.

[0017] Preferably, the preset angle range is -15° to 15°, the thickness range of the volume Bragg grating is 70um to 100um, and the refractive index modulation range is 0.01 to 0.03.

[0018] Preferably, the volume Bragg grating and the outcoupling grating have the same footprint on the waveguide component.

[0019] Preferably, the photopolymer material of the volume Bragg grating is an acrylic copolymer.

[0020] Preferably, the waveguide assembly comprises a single-layer or multi-layer waveguide sheet.

[0021] Preferably, the volume Bragg grating is processed by a holographic exposure method.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention places a volume Bragg grating on the waveguide component, and the volume Bragg grating is arranged opposite to the outcoupling grating. Through the angle selection characteristics of the volume Bragg grating, all light within a preset angle range in the external ambient light is reflected, while light incident at other angles passes through the waveguide component and only has zero-order diffraction light after the outcoupling grating. This not only ensures the brightness of the ambient light in the user's field of view, but also eliminates the rainbow effect, does not affect the performance of the outcoupling grating, ensures the uniformity and brightness of the outcoupling image, and can provide a better experience for AR or HMD users. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a diffraction optical waveguide device in the prior art;

[0024] Figure 2 It is a schematic structural diagram of the diffraction optical waveguide device of the present invention;

[0025] Figure 3 is a graph showing the relationship between the incident angle and the efficiency in the R0 diffraction order of the first embodiment of the present invention;

[0026] Figure 4 is a graph showing the relationship between the incident angle and the efficiency at the T0 diffraction order in the first embodiment of the present invention;

[0027] Figure 5 is a graph showing the relationship between the incident angle and the efficiency in the T+1 diffraction order of the first embodiment of the present invention;

[0028] Figure 6 is a graph showing the relationship between the incident angle and the efficiency in the R0 diffraction order of the second embodiment of the present invention;

[0029] Figure 7 is a graph showing the relationship between the incident angle and the efficiency at the T0 diffraction order of the second embodiment of the present invention;

[0030] Figure 8 FIG. 1 is a graph showing the relationship between the incident angle and the efficiency at the T+1 diffraction order of the second embodiment of the present invention.

[0031] Explanation of the reference numerals: 1. optical engine; 2. coupling-in grating; 3. waveguide assembly; 4. coupling-out grating; 5. adjustment mechanism; 6. human eye. DETAILED DESCRIPTION

[0032] 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.

[0033] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0034] like Figure 2 As shown, a diffraction optical waveguide device capable of eliminating rainbow effect comprises an optical engine 1, an in-coupling grating 2, a waveguide component 3, an adjustment mechanism 5 and an out-coupling grating 4, wherein the in-coupling grating, the adjustment mechanism and the out-coupling grating are all arranged in contact with the waveguide component, wherein:

[0035] A coupling grating 2, used for coupling the light emitted by the light engine 1 into the waveguide component 3;

[0036] The adjustment mechanism 5 is a volume Bragg grating and is arranged opposite to the outcoupling grating 4, and is used to reflect the light within a preset angle range in the external ambient light, so that the external ambient light entering the waveguide component 3 appears as zero-order diffraction light after passing through the outcoupling grating, so as to eliminate the rainbow effect;

[0037] The outcoupling grating 4 is used to couple the light transmitted through the waveguide component 3 to the human eye 6 .

[0038] The diffractive optical waveguide device of the present application is mainly used in AR or HMD diffractive waveguide display systems. The outcoupling grating 4 is transmissive and is placed on one side of the waveguide component 3, and an adjustment mechanism 5, i.e., a volume Bragg grating, is placed on the other side of the waveguide component 3. Figure 2 The outcoupling grating 4 is located on the upper surface of the waveguide component 3, and the volume Bragg grating is located on the lower surface of the waveguide component 3. The outcoupling grating 4 and the volume Bragg grating are arranged opposite to each other, and the specific orientation is not limited. Figure 2 In the figure, A is the desired image, B1 is the light within the preset angle range of the external ambient light, B2 is the light incident at other angles (outside the preset angle range) in the external ambient light, and C1 is the zero-order diffraction light. Through the angle selectivity of the volume Bragg grating, the light within the preset angle range in the external ambient light is reflected to avoid it passing through the waveguide component 3 and entering the coupling grating 4, and interacting with the coupling grating 4 to produce high-order diffraction orders (such as the first-order diffraction order, etc.), thereby generating an undesired image, allowing the user to observe a rainbow effect; for the light incident at other angles in the external ambient light, it can directly pass through the volume Bragg grating, the waveguide component 3 and the coupling grating 4 to avoid the generation of high-order diffraction orders, and only zero-order diffraction light exists, so it can be directly integrated with the virtual image projected by the micro-projection engine to realize the function of combining virtual and real in AR or HMD, ensuring the brightness of the ambient light in the user's field of view and the uniformity and brightness of the coupled image, providing users with good imaging quality.

[0039] In one embodiment, the volume Bragg grating satisfies the following conditions:

[0040]

[0041] Where Λ is the period of the volume Bragg grating, λ is the central wavelength of the interference beam, and θ is the angle of the interference beam.

[0042] In order to make the volume Bragg grating have good angular selectivity, the grating period Λ needs to be reasonably set. The volume Bragg grating is a grating structure with a specific refractive index distribution formed by using at least two beams of light (i.e., interference beams) to interfere at a certain angle on a photosensitive material, and has angular selectivity. It is well known to those skilled in the art and will not be described in detail here.

[0043] In one embodiment, the volume Bragg grating and the outcoupling grating have the same coverage area on the waveguide component. The volume Bragg grating and the outcoupling grating have the same coverage area on the waveguide component and are arranged in alignment. The angle selectivity of the volume Bragg grating can be used to filter the external ambient light, so that all light at a specific incident angle (within a preset angle range) is reflected, and all light at other incident angles is transmitted, thereby avoiding the interaction between the external ambient light and the outcoupling grating 4 to produce non-zero diffraction so that the user observes a rainbow effect, and good imaging quality can be obtained.

[0044] In one embodiment, the photopolymer material of the volume Bragg grating is an acrylic copolymer, or other materials well known to those skilled in the art, such as dichromated gelatin (DCG), photothermorefractive (PTR) glass, etc.

[0045] In one embodiment, the waveguide component 3 includes a single-layer or multi-layer waveguide sheet.

[0046] In one embodiment, the volume Bragg grating is processed by a holographic exposure method.

[0047] The invention is described in detail below through specific embodiments.

[0048] Embodiment 1:

[0049] like Figure 3-5 As shown, in this embodiment, the preset angle range is -15° to 15°, the thickness range of the volume Bragg grating is 70um to 100um, and the refractive index modulation range is 0.01 to 0.03.

[0050] By reasonably setting the thickness and refractive index modulation of the volume Bragg grating, the volume Bragg grating can have good angular selectivity. External ambient light generates R0 diffraction order, T0 diffraction order and T+1 diffraction order correspondingly through the volume Bragg grating, such as realizing that the incident light with a preset angle range of -15° to 15° in the external ambient light of -45° to 45° is completely reflected through the volume Bragg grating, and the incident light at other angles is completely transmitted through the volume Bragg grating, and no high-order diffraction order, i.e., the first-order diffraction order, is generated. The thickness range of the volume Bragg grating is 70um to 100um, the refractive index modulation range is 0.01 to 0.03, the average efficiency of the R0 diffraction order is greater than 48.2%, and the average efficiency of the T0 diffraction order is greater than 51.8%.

[0051] Specifically, λ=530nm, θ=7.5°, then Λ=4.06um, and the photopolymer material of the volume Bragg grating is selected as an acrylic copolymer. By using the optimized thickness and refractive index modulation of the volume Bragg grating, the external ambient light within the angle of -15° to 15° is completely reflected, and the external ambient light at other angles is the T0 diffraction order, which can pass through the waveguide component 3 and enter the human eye 6. At the same time, no diffraction light of the T+1 diffraction order is generated. Through this method, the non-zero-order diffraction light generated by the external ambient light passing through the outcoupling grating 4 can be reduced, and the rainbow effect introduced by the external ambient light can be effectively eliminated. In actual use, the preset angle range is set based on the field of view borne by the diffraction light waveguide device, and specifically satisfies the following formula:

[0052]

[0053] Where β is the preset angle, λ1 is the incident wavelength (same as the central wavelength λ of the interference beam), i is the incident field angle, T is the period of the outcoupling grating, and n is the refractive index of the waveguide component, which is generally 1.7 to 2.0. Assuming n = 2, i = -10° to 10°, λ = 500nm, T = 380nm, the preset angle range is 34.82° to 48.137°, and the specific preset angle range is determined according to actual needs.

[0054] Based on the above data, the Fourier modal method (FMM) is used to analyze and verify the R0 diffraction order, T0 diffraction order and T+1 diffraction order at different incident angles. Figure 3 It can be seen that for the external ambient light incident at -15° to 15°, the R0 diffraction order efficiency is 100%, and for the external ambient light incident at -45° to 45°, the average efficiency of the R0 diffraction order is 48.2%. Figure 4 It can be seen that for the incident light from the external environment at -15° to 15°, the efficiency of the T0 diffraction order is 0, and the average efficiency of the T0 diffraction order in the external environment at -45° to 45° is 51.7%. Figure 5 It can be seen that the efficiency of the T+1 diffraction order is 0, and no diffraction light of the T+1 diffraction order is generated.

[0055] Embodiment 2:

[0056] like Figure 6-8 As shown, in this embodiment, the preset angle range is -30° to 30°, the thickness range of the volume Bragg grating is 10um to 100um, and the refractive index modulation range is 0.16 to 0.2.

[0057] By reasonably setting the thickness and refractive index modulation of the volume Bragg grating, the volume Bragg grating can have good angular selectivity. External ambient light generates R0 diffraction order, T0 diffraction order and T+1 diffraction order correspondingly through the volume Bragg grating, such as realizing that the incident light with a preset angle range of -30° to 30° in the external ambient light of -45° to 45° is completely reflected through the volume Bragg grating, and the incident light at other angles is completely transmitted through the volume Bragg grating, and no high-order diffraction order, i.e., the first-order diffraction order, is generated. The thickness range of the volume Bragg grating is 10um to 100um, the refractive index modulation range is 0.16 to 0.2, the average efficiency of the R0 diffraction order is greater than 77.2%, and the average efficiency of the T0 diffraction order is greater than 22.8%.

[0058] Specifically, λ=530nm, θ=20°, then Λ=1.55um, and the photopolymer material of the volume Bragg grating is selected as an acrylic copolymer. By using the optimized thickness and refractive index modulation of the volume Bragg grating, the external ambient light within the angle of -30° to 30° is completely reflected, and the external ambient light at other angles is the T0 diffraction order, which can pass through the waveguide component 3 and enter the human eye 6. At the same time, no diffraction light of the T+1 diffraction order is generated. Through this method, the non-zero-order diffraction light generated by the external ambient light passing through the outcoupling grating 4 can be reduced, and the rainbow effect introduced by the external ambient light can be effectively eliminated. In actual use, the preset angle range is set based on the field of view borne by the diffraction light waveguide device, and specifically satisfies the following formula:

[0059]

[0060] Where β is the preset angle, λ1 is the incident wavelength (same as the central wavelength λ of the interference beam), i is the incident field angle, T is the period of the outcoupling grating, and n is the refractive index of the waveguide component, which is generally 1.7 to 2.0. Assuming n = 2, i = -10° to 10°, λ = 500nm, T = 380nm, the preset angle range is 34.82° to 48.137°, and the specific preset angle range is determined according to actual needs.

[0061] Based on the above data, the Fourier modal method (FMM) is used to analyze and verify the R0 diffraction order, T0 diffraction order and T+1 diffraction order at different incident angles. Figure 6 It can be seen that for the external ambient light incident at -30° to 30°, the R0 diffraction order efficiency is 100%, and for the external ambient light incident at -45° to 45°, the average efficiency of the R0 diffraction order is 77.2%. Figure 7 It can be seen that for the incident light from the external environment at -30° to 30°, the efficiency of the T0 diffraction order is 0, and the average efficiency of the T0 diffraction order in the external environment at -45° to 45° is 22.7%. Figure 8 It can be seen that the efficiency of the T+1 diffraction order is 0, and no diffraction light of the T+1 diffraction order is generated.

[0062] The present invention places a volume Bragg grating on a waveguide component and uses the angle selection characteristics of the volume Bragg grating to reflect all light within a preset angle range in the external ambient light, while light incident at other angles passes through the waveguide component and only has zero-order diffraction light after the out-coupling grating. This not only ensures the brightness of the ambient light in the user's field of view, but also eliminates the rainbow effect without affecting the performance of the out-coupling grating, ensuring the uniformity and brightness of the out-coupled image, and providing a better experience for AR or HMD users.

[0063] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above-described embodiments only express the more specific and detailed embodiments described in this application, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of this application, which all belong to the protection scope of this application. Therefore, the protection scope of the patent application shall be based on the attached claims.

Claims

1. A diffraction light waveguide device capable of eliminating rainbow effect, comprising a light engine, characterized in that: The diffraction light waveguide device capable of eliminating the rainbow effect further comprises an in-coupling grating, a waveguide component, an adjustment mechanism and an out-coupling grating, wherein the in-coupling grating, the adjustment mechanism and the out-coupling grating are all arranged in contact with the waveguide component, wherein: The coupling grating is used to couple the light emitted by the light engine into the waveguide component; The adjustment mechanism is a volume Bragg grating, and is arranged opposite to the outcoupling grating, and is used to reflect light within a preset angle range in the external ambient light, so that the external ambient light entering the waveguide component appears as zero-order diffraction light after passing through the outcoupling grating, so as to eliminate the rainbow effect; The outcoupling grating is used to couple the light transmitted through the waveguide component out to the human eye; The thickness of the volume Bragg grating is in the range of 10um to 100um, and the refractive index modulation range is 0.16 to 0.2; or the thickness of the volume Bragg grating is in the range of 70um to 100um, and the refractive index modulation range is 0.01 to 0.03; The diffraction optical waveguide device capable of eliminating the rainbow effect also satisfies the following formula: Wherein, β is a preset angle, λ1 is the incident wavelength and is the same as the central wavelength λ of the interference light beam, i is the incident field angle, T is the period of the outcoupling grating, and n is the refractive index of the waveguide component.

2. The diffractive light waveguide device capable of eliminating the rainbow effect as claimed in claim 1, characterized in that: The volume Bragg grating satisfies the following conditions: Wherein, Λ is the period of the volume Bragg grating, λ is the central wavelength of the interference light beam, and θ is the angle of the interference light beam.

3. The diffractive light waveguide device capable of eliminating the rainbow effect as claimed in claim 1, characterized in that: The volume Bragg grating and the outcoupling grating have the same coverage area on the waveguide component.

4. The diffractive light waveguide device capable of eliminating the rainbow effect as claimed in claim 1, characterized in that: The photopolymer material of the volume Bragg grating is an acrylic copolymer.

5. The diffractive light waveguide device capable of eliminating the rainbow effect as claimed in claim 1, characterized in that: The waveguide component includes a single-layer or multi-layer waveguide sheet.

6. The diffractive light waveguide device capable of eliminating the rainbow effect as claimed in claim 1, characterized in that: The volume Bragg grating is processed by a holographic exposure method.

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