Achromatic grating and preparation method therefor, and optical waveguide apparatus and ar near-eye display device

Abstract

An achromatic grating (10) and a preparation method therefor, and an optical waveguide apparatus (20) and an AR near-eye display device. The structure of the achromatic grating (10) is configured to respectively match different higher-order diffractions on the basis of the wavelengths of red light, green light and blue light in image source light, so as to perform modulation, such that the product of the wavelength of the red light and a diffraction order thereof, the product of the wavelength of the blue light and a diffraction order thereof, and the product of the wavelength of the green light and a diffraction order thereof are the same constant, thereby making the modulated red light, green light and blue light have the same diffraction angle. Thus, multi-wavelength achromatism is realized by means of the grating (10), and the problem of poor uniformity of colors displayed by existing diffractive optical waveguides is also solved.

Description

Achromatic grating, preparation method thereof, optical waveguide device and AR near-eye display device

[0001] The present application claims priority to the Chinese patent application No. CN2024104330659, filed on April 11, 2024, and entitled "Achromatic grating, preparation method thereof, optical waveguide device and AR near-eye display device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of display, in particular to an achromatic grating, an optical waveguide device and an AR display device. BACKGROUND

[0003] AR (Augmented Reality) display devices superimpose virtual images onto real images, which can achieve a display effect of combining virtual and real. Diffractive optical waveguides have the advantages of ultra-light and ultra-thin, large pupil expansion range, high transparency and low mass production cost, and are one of the mainstream solutions for realizing AR display at present.

[0004] In order to provide a more high-quality visual experience for the wearer, full-color display is the development trend of augmented reality technology. When performing full-color display, the traditional diffractive optical waveguide will produce chromatic aberration and affect the display quality due to the different diffraction angles and diffraction efficiencies of different wavelengths of light by the grating as a waveguide coupler.

[0005] In order to solve the problem of chromatic aberration, current AR products mostly use a multi-waveguide scheme, i.e., coupling red, green and blue (RGB) lights as three primary colors of optical display into three different waveguides for transmission to eliminate chromatic aberration. Although this scheme can alleviate the chromatic aberration of the optical waveguide, it will introduce inter-sheet crosstalk, interface reflection, and increase the system volume and weight, which will affect the wearing comfort, and the efficiencies of different colors of light are difficult to keep consistent, making it difficult to achieve good display effect. SUMMARY

[0006] The present application provides an achromatic grating and a preparation method thereof, an achromatic optical waveguide device and an AR near-eye display device to solve the problems of chromatic dispersion and chromatic aberration in traditional AR waveguides.

[0007] To solve the above technical problems, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides an achromatic grating, characterized in that it comprises:

[0009] The structure of the achromatic grating is configured to enable different high-order diffraction of red light, green light and blue light in the image source light, so that the diffraction angles of the modulated red light, green light and blue light are the same; the wavelength of the red light, the wavelength of the green light, the wavelength of the blue light and the corresponding diffraction order satisfy:

[0010]

[0011] M R is the diffraction order of red light;

[0012] M G is the diffraction order of green light;

[0013] M B is the diffraction order of blue light;

[0014] λ R is the wavelength of red light;

[0015] λ G is the wavelength of green light;

[0016] λ B is the wavelength of blue light;

[0017] wherein, when the difference between the maximum value and the minimum value of the product of the wavelength of the red light and its corresponding diffraction order, the product of the wavelength of the blue light and its corresponding diffraction order, and the product of the wavelength of the green light and its corresponding diffraction order does not exceed 5% of the minimum value, it is considered to satisfy the above formula.

[0018] In one embodiment, the wavelength of the red light is 663 nm, the wavelength of the green light is 530 nm, and the wavelength of the blue light is 442 nm. The +4th order diffraction angle of the red light, the +5th order diffraction angle of the green light and the +6th order diffraction angle of the blue light after modulation by the achromatic grating are the same.

[0019] In one embodiment, the ratio of the period of the achromatic grating to the wavelength of the red light, the ratio of the period of the achromatic grating to the wavelength of the green light, and the ratio of the period of the achromatic grating to the wavelength of the blue light are all greater than 2.

[0020] In a second aspect, the present application provides a method for preparing an achromatic grating, comprising the following steps:

[0021] selecting image source light having red light, green light and blue light;

[0022] According to the wavelength of the red light, the wavelength of the green light, and the wavelength of the blue light, the structure of the achromatic grating is configured so that the red light, the green light, and the blue light can have different high-order diffractions at the achromatic grating, and the wavelength of the red light, the wavelength of the green light, the wavelength of the blue light, and the corresponding diffraction order satisfy:

[0023]

[0024] M R is the diffraction order of the red light;

[0025] M G is the diffraction order of the green light;

[0026] M B is the diffraction order of the blue light;

[0027] λ R is the wavelength of the red light;

[0028] λ G is the wavelength of the green light;

[0029] λ B is the wavelength of the blue light;

[0030] wherein when the difference between the maximum value and the minimum value of the product of the wavelength of the red light and the corresponding diffraction order, the product of the wavelength of the blue light and the corresponding diffraction order, and the product of the wavelength of the green light and the corresponding diffraction order does not exceed 5% of the minimum value, it is considered to satisfy the above formula.

[0031] In a third aspect, the present application provides an optical waveguide device, comprising a coupling-in structure, a waveguide substrate, and a coupling-out structure, the coupling-in structure is arranged on the waveguide substrate and is used for coupling image source light into the waveguide substrate and reflecting to the coupling-out structure in the waveguide substrate, the coupling-out structure is arranged on the waveguide substrate and is used for coupling the image source light propagating in the waveguide substrate out of the waveguide substrate; at least one of the coupling-in structure and the coupling-out structure is the achromatic grating or the achromatic grating prepared by the preparation method.

[0032] In one embodiment, the coupling-in structure and the coupling-out structure are both the achromatic grating, and the period of the coupling-in structure and the period of the coupling-out structure are the same.

[0033] In one of the embodiments, the optical waveguide device further comprises a polarization assembly, the polarization assembly comprises a polarization mirror, a phase retarder and a total reflection mirror, the polarization mirror is arranged between the image source of the image source light and the coupling-in structure and is located on the light emitting path of the image source, the phase retarder is arranged on the side of the coupling-in structure away from the polarization mirror, and the total reflection mirror is arranged on the side of the phase retarder away from the coupling-in structure.

[0034] After the image source light enters the coupling-in structure through the polarization mirror, part of the image source light is coupled into the waveguide substrate by the coupling-in structure, and the remaining light is reflected by the total reflection mirror after being converted by the phase retarder passing through the coupling-in structure, and the remaining light after reflection enters the coupling-in structure again through the phase retarder and is at least partially coupled into the waveguide substrate by the coupling-in structure, so that the image source light is coupled into the waveguide substrate at least four times by the coupling-in light.

[0035] In one of the embodiments, the coupling-in structure is a non-diffractive optical element for coupling the image source light into the waveguide substrate, and the coupling-out structure is the achromatic grating.

[0036] In one of the embodiments, the waveguide substrate has a first surface and a second surface parallel to each other, the extension direction of the optical element is arranged at an angle with the first surface, and the optical element can couple the image source light into the waveguide substrate by reflection or refraction, so that the image source light is reflected between the first surface and the second surface of the waveguide substrate to the coupling-out structure.

[0037] In a fourth aspect, the application provides an AR near-eye display device, comprising:

[0038] A wearable support; and

[0039] The above waveguide device is arranged in the wearable support.

[0040] According to the above technical solution, the embodiments of the application have at least the following advantages and positive effects:

[0041] In the achromatic grating and the preparation method thereof, the optical waveguide device and the AR near-eye display device, different wavelengths of incident light are matched with different diffraction orders, so that the product of the wavelength of the incident light and the diffraction order is a constant, thereby realizing multi-wavelength achromatism of the grating, and solving the problem of poor color uniformity of the existing diffractive optical waveguide display. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to make the technical solutions of the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only need to be some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0043] Fig. 1 is a schematic diagram of an achromatic grating according to an embodiment of the present application;

[0044] Fig. 2 is a structural diagram of an achromatic grating according to an embodiment of the present application;

[0045] Fig. 3 is a structural diagram of an achromatic grating according to an embodiment of the present application;

[0046] Fig. 4 is a diagram of a conventional diffraction grating and the existing chromatic aberration and distortion phenomenon;

[0047] Fig. 5 is a flow chart of a preparation method of an achromatic grating according to an embodiment of the present application;

[0048] Fig. 6 is a schematic diagram of a structural design principle of the achromatic grating shown in Fig. 2;

[0049] Fig. 7 is a diagram of the relationship between the incident angle and the exit angle of the red, green and blue light diffracted by the achromatic grating shown in Fig. 2;

[0050] Fig. 8 is a structural diagram of an optical waveguide device according to an embodiment of the present application;

[0051] Fig. 9 is a structural diagram of a coupling-out grating of the optical waveguide device shown in Fig. 8;

[0052] Fig. 10 is an efficiency distribution diagram of the red, green and blue light in the +4, +5 and +6 diffraction orders in the optical waveguide device shown in Fig. 8;

[0053] Fig. 11 is an efficiency distribution diagram of the red, green and blue light in the zero diffraction order in the optical waveguide device shown in Fig. 8;

[0054] Fig. 12 is an efficiency distribution diagram of the red, green and blue light in the -4, -5 and -6 diffraction orders in the optical waveguide device shown in Fig. 8;

[0055] Fig. 13 is a structural diagram of an optical waveguide device according to another embodiment of the present application;

[0056] Fig. 14 is a structural diagram of an optical waveguide device according to another embodiment of the present application;

[0057] Fig. 15 is another state diagram of the optical waveguide device shown in Fig. 14;

[0058] Fig. 16 is a diagram of the relationship between the reflection angle and the coupling-in angle in the waveguide of the optical waveguide device shown in Fig. 15;

[0059] FIG. 17 is a diagram of the relationship between the coupling-out angle and the coupling-in angle of the optical waveguide device shown in FIG. 15;

[0060] FIG. 18 is a diagram of the relationship between the coupling-in angle and the coupling-out angle of the optical waveguide device shown in FIG. 15 at different tilt angles;

[0061] FIG. 19 is a flowchart of an image correction process.

[0062] The reference signs are explained as follows:

[0063] 10, achromatic grating; 20, optical waveguide device; 210, coupling-in structure; 220, waveguide substrate; 221, first surface; 222, second surface; 230, coupling-out structure; 240, optical element. DETAILED DESCRIPTION

[0064] The typical embodiments embodying the features and advantages of the present application will now be described in detail. It should be understood that the application can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, which are presented by way of example only, and that the description and drawings are to be regarded as illustrative in nature and not as restrictive.

[0065] In addition, the terms "first", "second", and the like, do not denote any quantity or importance, but are used to distinguish one element from another, and are not intended to specify a particular order or sequence. Accordingly, a first element discussed above can be termed a second element without departing from the teachings of the application. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an overly literal or overly formal sense unless expressly so defined herein.

[0066] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "set", "connected", "connection" should be understood broadly, for example, can be fixed connection, can also be detachable connection, or integrally connected; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0067] Referring to FIGS. 1-3, in a first aspect, the present application provides an achromatic grating 10, which is arranged in an optical waveguide and used to couple in or out red, green and blue (RGB) light from the optical waveguide to eliminate chromatic aberration.

[0068] The structure of the achromatic grating 10 is configured to enable different high-order diffraction of red light, green light and blue light in the image source light, so that the diffraction angles of the modulated red light, green light and blue light are the same. Specifically, the wavelengths of red light, green light and blue light and their corresponding diffraction orders satisfy:

[0069] Equation (1)

[0070] In the full text of the present application, M R is the diffraction order of red light; M G is the diffraction order of green light; M B is the diffraction order of blue light; λ R is the wavelength of red light; λ G is the wavelength of green light; λ B is the wavelength of blue light.

[0071] It should be noted that the structure of the achromatic grating 10 of the present application is established according to the grating equation and the rigorous coupled wave grating theory, a model is simulated numerically and the grating parameters satisfying equation (1) are obtained. The grating parameters include the efficiency, order, period, duty cycle, ridge height, depth ratio, corresponding light wavelength, corresponding light waveguide material, etc. of the grating, which are not limited. The specific structure of the achromatic grating 10 includes but is not limited to the one-dimensional grating, two-dimensional cross grating and two-dimensional columnar grating shown in FIG. 3. The specific structure of the achromatic grating 10 includes but is not limited to the relief grating and the volume holographic grating. As long as the technical solutions satisfying equation (1) are within the protection scope of the present application.

[0072] According to the grating equation:

[0073] Equation (2)

[0074] In the full text of the present application, n s represents the refractive index of the exit medium, n i represents the refractive index of the incident medium, θ i represents the incident angle of the incident light, m represents the diffraction order, θ m represents the angle of the mth order diffracted light, λ represents the wavelength of the incident light, and Λ represents the period of the grating.

[0075] The inverse trigonometric function of equation (2) can be obtained as:

[0076] Equation (3)

[0077] From equation (3), for the first order diffraction (m=±1) of the grating, the diffraction exit angle of the grating depends on the wavelength of the incident light, and the exit angles of light beams of different wavelengths are different. Therefore, for red, green and blue three-color lights with the same incident angle, they have different exit angles after first order diffraction, which leads to the dispersion phenomenon and affects the display quality.

[0078] Referring to FIG. 4, FIG. 4(a) schematically shows that when a diffractive coupling-out unit adopts first-order diffraction to couple out light rays, different color light rays have different diffraction directions, and the sum of diffraction vectors generated by the light rays in the entire propagation process is not zero, which causes the color difference and distortion shown in FIG. 4(b) to appear in a display picture.

[0079] To solve the color difference problem, current AR products mostly adopt a multi-waveguide scheme, that is, red, green and blue (RGB) light serving as three primary colors of optical display is coupled into three different waveguides for transmission, so as to eliminate the color difference. Although this scheme can alleviate the color difference of the optical waveguide, it introduces inter-sheet crosstalk, interface reflection, and increases the system volume and weight, which affects the wearing comfort, and the efficiencies of different color lights are difficult to keep consistent, which is difficult to achieve good display effect.

[0080] In the scheme of the present application, different high-order diffractions are matched according to different wavelengths of incident light, so that the wavelength of the incident light and the diffraction order satisfy formula (1), formula (1) is substituted into formula (3), and the red, green and blue three-color light has the same exit angle. That is, a color difference elimination grating 10 can be designed by using the existing technology, so that the color difference elimination grating 10 can make the incident light of different wavelengths have the same or extremely close diffraction angle. The present application only needs a single optical waveguide and a single grating to achieve the function of eliminating color difference. Of course, manufacturers can also set multiple optical waveguides and multiple gratings according to their own needs to meet other display requirements.

[0081] Referring to FIG. 5, the present application also provides a preparation method of a color difference elimination grating, which comprises the following steps:

[0082] S1: selecting image source light rays with red light, green light and blue light.

[0083] S2: configuring the structure of the color difference elimination grating according to the wavelength of the red light, the wavelength of the green light and the wavelength of the blue light, so that the red light, the green light and the blue light can undergo different high-order diffractions at the color difference elimination grating, and the wavelength of the red light, the wavelength of the green light and the wavelength of the blue light and the corresponding diffraction order satisfy:

[0084]

[0085] M R is the diffraction order of the red light;

[0086] M G is the diffraction order of the green light;

[0087] M B is the diffraction order of the blue light;

[0088] λ Ra wavelength of red light;

[0089] λ G a wavelength of green light;

[0090] λ B a wavelength of blue light.

[0091] wherein, when the difference between the maximum value and the minimum value of the product of the wavelength of the red light and the diffraction order corresponding thereto, the product of the wavelength of the blue light and the diffraction order corresponding thereto, and the product of the wavelength of the green light and the diffraction order corresponding thereto does not exceed 5% of the minimum value, it is considered that the above formula is satisfied.

[0092] For a specific image source light, the optical parameters (wavelength, etc.) of the red, green and blue light in the image source light can be determined, and then the grating is designed and simulated according to the optical parameters of the red, green and blue light to obtain a grating structure that meets formula (1), which has the effect of achromatism for the selected image source light. Exemplarily, in the present embodiment, according to the grating equation, the period of the achromatic grating 10 is determined to be 1900 nm, the red light with a wavelength of 663 nm is diffracted by +4 order at the achromatic grating 10, the green light with a wavelength of 530 nm is diffracted by +5 order at the achromatic grating 10, and the blue light with a wavelength of 442 nm is diffracted by +6 order at the achromatic grating 10.

[0093] Specifically, referring to FIG. 6, which exemplarily provides a method of designing a grating structure, a topology optimization algorithm based on the variable density method is used for grating design, and the design requirements of the grating are determined according to the optical indicators. In the present embodiment, the efficiency of each diffraction order of the grating is taken as the optimization target, the structure of the grating is taken as the optimization variable, and the gradient is obtained by running electromagnetic simulation, and then the grating structure is updated by using the gradient descent method. Through multiple iterations of optimization, the achromatic grating 10 that meets formula (1) and has the highest diffraction efficiency is obtained.

[0094] The period of the achromatic grating 10 is selected according to the grating equation based on the incident angle of the image source light, the wavelength of the monochromatic light in the image source light, and the refractive index of the achromatic grating 10.

[0095] With reference back to FIG. 2, in an embodiment, the period of the achromatic grating 10 is 1900 nm, the refractive index of the incident medium n i is 1, the refractive index of the exit medium n s is 1.9, the refractive index of the grating is 2.0, the incident angle is 0°, and the exit angle is 0°. In the incident light, the wavelength of red light is 663 nm, the wavelength of green light is 530 nm, and the wavelength of blue light is 442 nm. The corresponding matching diffraction order of red light is +4th order, the corresponding matching diffraction order of green light is +5th order, and the corresponding matching diffraction order of blue light is +6th order. Therefore, the wavelength of red light, the wavelength of green light, the wavelength of blue light, and the corresponding diffraction order satisfy formula (1). It can be understood that the corresponding matching diffraction order of red light can also be -4th order, the corresponding matching diffraction order of green light can also be -5th order, and the corresponding matching diffraction order of blue light can also be -6th order.

[0096] It should be noted that the wavelength of red light, the wavelength of green light, the wavelength of blue light, and the corresponding diffraction order satisfying formula (1) means that the product of the wavelength of red light and the corresponding diffraction order, the product of the wavelength of green light and the corresponding diffraction order, and the product of the wavelength of blue light and the corresponding diffraction order are the same number or approximately the same constant, that is, the difference between the maximum value and the minimum value of the three products does not exceed 5% of the minimum value, and it is considered to satisfy formula (1).

[0097] Referring to FIG. 7, FIG. 7 schematically shows that when the incident angle is within -22.5° to 22.5°, red, green, and blue light has the same exit angle, and the achromatic function is achieved.

[0098] Specifically, the ratio of the period of the achromatic grating 10 to the wavelength of red light, the ratio of the period of the achromatic grating 10 to the wavelength of green light, and the ratio of the period of the achromatic grating 10 to the wavelength of blue light are all greater than 2.

[0099] Referring to FIG. 8, in a second aspect, the present application also provides an optical waveguide device 20, which comprises a coupling-in structure 210, a waveguide substrate 220, and a coupling-out structure 230. The coupling-in structure 210 is arranged on the waveguide substrate 220 and is used for coupling image source light into the waveguide substrate 220 and reflecting the image source light in the waveguide substrate 220 to the coupling-out structure 230. The coupling-out structure 230 is arranged on the waveguide substrate 220 and is used for coupling the image source light propagating in the waveguide substrate 220 out of the waveguide substrate 220. At least one of the coupling-in structure 210 and the coupling-out structure 230 is the above-mentioned achromatic grating 10. That is, the arrangement of the coupling-in structure 210 and the coupling-out structure 230 includes three cases: (1) the coupling-in structure 210 and the coupling-out structure 230 are both arranged as the above-mentioned achromatic grating 10; (2) the coupling-in structure 210 is arranged as the above-mentioned achromatic grating 10, and the coupling-out structure 230 is arranged as other components; and (3) the coupling-out structure 230 is arranged as the above-mentioned achromatic grating 10, and the coupling-in structure 210 is arranged as other components.

[0100] Specifically, the diffraction angle of the image source light rays after being modulated by the coupling-in structure 210 is greater than the total reflection angle of the waveguide substrate 220, so that the image source light rays can be reflected by total reflection to the coupling-out structure 230 after being coupled into the waveguide substrate 220.

[0101] In an embodiment, the coupling-in structure 210 and the coupling-out structure 230 are both composed of the achromatic grating 10 described above, and the periods of the coupling-in structure 210 and the coupling-out structure 230 are the same to achieve the best coupling effect.

[0102] In the embodiment, the coupling-in structure 210 is attached to the bottom of the waveguide substrate 220 to receive the image source light rays, which are light beams emitted by an external micro display or other display device. After being diffracted by the coupling-in structure 210, the image source light rays are coupled into the waveguide substrate 220, and the angle of the coupled-in light is greater than the total reflection angle of the waveguide substrate 220, so that the image source light rays can propagate in the waveguide substrate 220 by total reflection. The coupling-out structure 230 is attached to the bottom of the side of the waveguide substrate 220 away from the coupling-in structure 210. When the image source light rays propagating in the waveguide substrate 220 pass through the coupling-out structure 230, the zero-order diffracted light continues to propagate in the waveguide substrate 220, and the corresponding high-order diffracted image source light rays are coupled out of the waveguide substrate 220 by the coupling-out structure 230 and enter the human eye.

[0103] It should be noted that FIG. 8 only exemplarily describes the positions of the coupling-in structure 210 and the coupling-out structure 230. In other embodiments, the coupling-in structure 210 and the coupling-out structure 230 can also be arranged at other positions of the waveguide substrate 220, for example, the coupling-in structure 210 and the coupling-out structure 230 can be arranged at the top of the waveguide substrate 220 (i.e., at the side of the waveguide substrate 220 close to the image source light rays). In addition, the coupling-in structure 210 and the coupling-out structure 230 include but are not limited to reflective gratings and transmissive gratings, and the corresponding positions can be arranged as needed.

[0104] In the embodiment, the glass with a refractive index of 1.9 is used as the waveguide substrate 220 of the optical waveguide device 20, and the corresponding critical angle of total internal reflection of the waveguide substrate 220 is about 30°. At the same time, the maximum angle of the image source light rays propagating in the waveguide substrate 220 by total reflection is set to 75°, so that the coupled-out image source grating can support a horizontal field of view angle of more than 45°.

[0105] With reference to FIGS. 2, 8 and 9, specifically, the coupling-in structure 210 adopts the achromatic grating 10 as shown in FIG. 2, the coupling-out structure 230 adopts the achromatic grating 10 as shown in FIG. 9, the height of the coupling-in structure 210 and the coupling-out structure 230 is 160 nm, and the period is 1900 nm. In the incident light, the wavelength of red light is 663 nm, the wavelength of green light is 530 nm, the wavelength of blue light is 442 nm, the corresponding diffraction order of red light is +4, the corresponding diffraction order of green light is +5, and the corresponding diffraction order of blue light is +6. Therefore, the wavelength of red light, the wavelength of green light, the wavelength of blue light and the corresponding diffraction order satisfy formula (1).

[0106] With reference to FIGS. 10 to 12, a model is established to obtain the corresponding efficiency of red, green and blue light through simulation calculation.

[0107] FIG. 10 shows the efficiency distribution of red, green and blue light in +4, +5 and +6 diffraction orders of the coupling-in structure 210. In the range of -22.5° to 22.5° horizontal field of view, the diffraction efficiency of +4 order of red light, +5 order of green light and +6 order of blue light of the coupling-in structure 210 maintains high uniformity, thereby realizing achromatism of the incident light.

[0108] FIG. 11 shows the efficiency distribution of red, green and blue light in zero diffraction order of the coupling-out structure 230. In the range of -22.5° to 22.5° horizontal field of view, the efficiency of zero diffraction order of red, green and blue light of the coupling-out structure 230 maintains high uniformity, thereby realizing achromatism of the waveguide total internal reflection light.

[0109] FIG. 12 shows the efficiency distribution of red, green and blue light in -4, -5 and -6 diffraction orders of the coupling-out structure 230. In the range of -22.5° to 22.5° horizontal field of view, the diffraction efficiency of -4 order of red light, -5 order of green light and -6 order of blue light of the coupling-out structure 230 maintains high uniformity, thereby realizing achromatism of the exit light.

[0110] For the same light waveguide device 20 and the same image source light, the high-order diffraction of the diffraction grating has lower efficiency than the low-order diffraction, so that the use efficiency of the incident light is low. In order to improve the use efficiency of the incident light, the light waveguide device 20 further includes a polarization assembly for improving the use efficiency of the incident light in an embodiment. The polarization assembly includes a polarization mirror, a phase delay plate and a total reflection mirror.

[0111] Referring to Fig. 13, specifically, the polarization assembly forms a folded light path in the optical waveguide device 20, a TM polarized mirror is arranged between the image source and the coupling-in structure 210 and on the light emitting path of the image source, the coupling-in structure 210 is attached to the bottom of the waveguide substrate 220, a quarter wavelength phase retarder and a TE / TM polarized total reflection mirror are arranged in sequence on the side of the coupling-in structure 210 opposite to the TM polarized mirror, and the TE / TM polarized total reflection mirror can be a metal total reflection mirror or a total reflection mirror made of other materials.

[0112] The image source light in the TE polarization state is diffracted by the coupling-in structure 210 for the first time after passing through the TM polarized total reflection mirror, part of the image source light is coupled into the waveguide substrate 220, the remaining light passes through the quarter wavelength phase retarder, is converted into left-handed or right-handed circularly polarized light, and is reflected back by the TE / TM polarized total reflection mirror, the reflected image source light passes through the quarter wavelength phase retarder again and is converted into TM polarized light, is diffracted by the coupling-in structure 210 for the second time, part of the image source light is coupled into the waveguide substrate 220, the remaining light is reflected back by the TM polarized total reflection mirror, is diffracted by the coupling-in structure 210 for the third time, the remaining light passes through the quarter wavelength phase retarder and is converted into right-handed / left-handed circularly polarized light, and is reflected back by the TE / TM polarized total reflection mirror, passes through the quarter wavelength phase retarder and is converted into TE polarized light, and is diffracted by the coupling-in structure 210 for the fourth time.

[0113] Therefore, the folded light path formed by the polarization assembly makes the image source light diffracted by the coupling-in structure 210 at least four times, improves the diffraction light flux, and improves the coupling-in light efficiency.

[0114] Referring to Fig. 14, in another embodiment, the coupling-in structure 210 of the optical waveguide device 20 is a non-diffractive optical element 240, and the coupling-out structure 230 is the achromatic grating 10 described above. The problem of low incidence efficiency caused by using a diffractive element as the coupling-in structure 210 is avoided, and the overall efficiency of the optical waveguide device 20 is improved.

[0115] The coupling-in structure 210 can adopt a reflective inclined surface, a prism or other optical element 240 having a coupling-in surface. By adjusting the incidence angle or shape of the image source light, the image source light can satisfy the total internal reflection condition of the waveguide substrate 220, the image source light is totally internally reflected in the waveguide substrate 220 to the coupling-out structure 230, part of the image source light is diffracted out of the waveguide substrate 220 by the coupling-out structure 230 into the human eye, and the remaining light continues to propagate in the waveguide substrate 220.

[0116] Specifically, the waveguide base 220 has a first surface 221 and a second surface 222 which are parallel to each other, and the diffraction direction of the optical element 240 is arranged at an angle with the first surface 221, and the optical element 240 can couple the image source light into the waveguide base 220 by reflection or refraction, so that the image source light is reflected between the first surface 221 and the second surface 222 of the waveguide base 220 to the coupling-out structure 230.

[0117] Since the coupling-in structure 210 adopts a non-diffraction element and the coupling-out structure 230 adopts the achromatic grating 10 described above, the light waveguide device 20 of the embodiment has two advantages: (1) overcomes the chromatic aberration, distortion and other problems that may occur when the existing diffraction grating adopts first-order diffraction, and (2) the coupling-in structure 210 adopts a non-diffraction element, which is more efficient than the light waveguide device 20 in which both the coupling-in structure 210 and the coupling-out structure 230 adopt diffraction gratings.

[0118] Referring to FIGS. 15 and 16, for the light waveguide device 20 shown in FIG. 15, the coupling-in angle range is set to -22.5° to 22.5°, and according to the geometric relationship, the waveguide internal reflection angle and the coupling-in angle have the corresponding relationship shown in FIG. 16. As can be seen from FIG. 16, the waveguide internal reflection angle is always greater than the critical angle of total internal reflection, so the coupled-in image source light can propagate in the waveguide base 220, and the efficiency is close to 100%. When the image source light propagates to the coupling-out structure 230, the image source light is coupled out of the waveguide base 220 by diffraction and enters the human eye. Since the grating uses high-order diffraction to eliminate chromatic aberration, the red, green and blue light will have the same coupling-out angle.

[0119] The coupling-out angle and the coupling-in angle have the corresponding relationship shown in FIG. 17, in which the normal image is represented by a solid line and the image distortion is represented by a dashed line. As can be seen from FIG. 17, the coupling-out angle and the coupling-in angle are not completely linear, indicating that the incident field cannot be completely restored without distortion by the light waveguide device 20, so there is a problem of image distortion.

[0120] Further, for the distortion problem, the light waveguide device 20 is also provided with an image correction module, which can adjust the incident angle of the image source light according to the grating equation and the geometric relationship, and can compensate for the distortion caused by the non-zero diffraction vector of the light in the propagation process, thereby improving the display quality.

[0121] With reference to FIG. 15 and FIG. 18, the optical engine emits image source light into the optical waveguide device 20. According to the grating equation and geometric relationship, the image correction module obtains the relationship between the in-coupling angle and the out-coupling angle of the optical element 240 at different tilt angles a (the angle between the optical element 240 and the second surface 222), as shown in FIG. 18. A curve with the best linearity of the in-coupling angle and the out-coupling angle is selected, and the corresponding in-coupling slope angle a is found. Then, the image emitted by the optical engine is fine-tuned according to the curve, so that the image is displayed without distortion.

[0122] With reference to FIG. 19, FIG. 19 illustrates a specific image correction process. According to the above principle, the image correction module adjusts the tilt angle a of the optical element 240, and then fine-tunes the image source light emitted by the optical engine according to the curve relationship between the in-coupling angle and the out-coupling angle, so that the image coupled out of the optical waveguide device 20 is displayed without distortion. The image correction process can be applied to laser scanning optical engines, OLED optical engines, etc.

[0123] In a third aspect, the present application provides an AR near-eye display device, which comprises a wearable support and the optical waveguide device 20 described above, and the optical waveguide device 20 is arranged on the wearable support. The AR near-eye display device includes, but is not limited to, AR glasses, AR headgear, and AR game cabin.

[0124] Although the present application has been described with reference to several exemplary embodiments, it is understood that the words that have been used are words of description and illustration, rather than words of limitation. Since the application can be embodied in various forms without departing from the spirit or essential characteristics thereof, it is understood that the embodiments are not limited to any particular details, but are capable of changes in form and details without losing the spirit of the application. By the same manner, the above-described embodiments are intended to be illustrative only and not restrictive. Therefore, it is intended to fall within the scope of the appended claims and their equivalents, all changes and modifications that come within the spirit of the application are therefore intended to be embraced by the following claims.

Claims

1. An achromatic grating, characterized in that: include: The structure of the achromatic grating is configured to cause red light, green light, and blue light in the image source light to undergo different high-order diffraction, respectively, so that the diffraction angles of the modulated red light, green light, and blue light are the same; the wavelength of the red light, the wavelength of the green light, the wavelength of the blue light, and their corresponding diffraction orders satisfy: M R is the diffraction order of red light; M G is the diffraction order of green light; M B is the diffraction order of blue light; λ R is the wavelength of red light; λ G is the wavelength of green light; λ B is the wavelength of blue light; Among them, when the difference between the maximum and minimum values ​​of the product of the wavelength of the red light and the corresponding diffraction order, the product of the wavelength of the blue light and the corresponding diffraction order, and the product of the wavelength of the green light and the corresponding diffraction order does not exceed 5% of the minimum value, the above formula is deemed to be satisfied.

2. The achromatic grating according to claim 1, wherein The wavelength of the red light is 663 nm, the wavelength of the green light is 530 nm, and the wavelength of the blue light is 442 nm. After being modulated by the achromatic grating, the +4th order diffraction angle of the red light, the +5th order diffraction angle of the green light, and the +6th order diffraction angle of the blue light are the same.

3. The achromatic grating according to claim 1, wherein The ratio of the period of the achromatic grating to the wavelength of the red light, the ratio of the period of the achromatic grating to the wavelength of the green light, and the ratio of the period of the achromatic grating to the wavelength of the blue light are all greater than 2.

4. A method for preparing an achromatic grating, characterized in that: The steps include: Select image source light with red light, green light, and blue light; The structure of the achromatic grating is configured according to the wavelength of the red light, the wavelength of the green light, and the wavelength of the blue light, so that the red light, the green light, and the blue light can undergo different high-order diffraction at the achromatic grating, and the wavelength of the red light, the wavelength of the green light, and the wavelength of the blue light and their corresponding diffraction orders satisfy: M R is the diffraction order of red light; M G is the diffraction order of green light; M B is the diffraction order of blue light; λ R is the wavelength of red light; λ G is the wavelength of green light; λ B is the wavelength of blue light; Among them, when the difference between the maximum and minimum values ​​of the product of the wavelength of the red light and the corresponding diffraction order, the product of the wavelength of the blue light and the corresponding diffraction order, and the product of the wavelength of the green light and the corresponding diffraction order does not exceed 5% of the minimum value, the above formula is deemed to be satisfied.

5. An optical waveguide device, characterized in that: The invention comprises a coupling-in structure, a waveguide matrix and a coupling-out structure, wherein the coupling-in structure is arranged in the waveguide matrix and is used to couple the image source light into the waveguide matrix and reflect the image source light from the waveguide matrix to the coupling-out structure, and the coupling-out structure is arranged in the waveguide matrix and is used to couple the image source light propagating in the waveguide matrix out of the waveguide matrix; at least one of the coupling-in structure and the coupling-out structure is the achromatic grating according to any one of claims 1 to 2 or the achromatic grating obtained by the preparation method according to claim 3.

6. The optical waveguide device according to claim 5, wherein The diffraction angle of the image source light after being modulated by the coupling-in structure is greater than the total reflection angle of the waveguide matrix, so that the image source light can be reflected to the coupling-out structure by total reflection after being coupled into the waveguide matrix.

7. The optical waveguide device according to claim 5, wherein The optical waveguide device further includes a polarization component, which includes a polarization mirror, a phase retarder, and a total reflection mirror. The polarization mirror is disposed between the image source of the image source light and the coupling structure and is located on the light emission path of the image source. The phase retarder is disposed on a side of the coupling structure facing away from the polarization mirror. The total reflection mirror is disposed on a side of the phase retarder facing away from the coupling structure. After the image source light enters the coupling structure through the polarizing reflector, part of the image source light is coupled into the waveguide base by the coupling structure, and the remaining light passes through the coupling structure and is converted by the phase delay plate and then reflected by the total reflection mirror. The remaining light after reflection enters the coupling structure again through the phase delay plate and is at least partially coupled into the waveguide base by the coupling structure, so that the image source light is coupled into the waveguide base at least four times by the coupled light.

8. The optical waveguide device according to claim 5, wherein The coupling-in structure is a non-diffraction optical element used to couple the image source light into the waveguide matrix, and the coupling-out structure is the achromatic grating.

9. The optical waveguide device according to claim 8, wherein The waveguide matrix has a first surface and a second surface parallel to each other. The extension direction of the optical element is set at an angle to the first surface. The optical element can couple the image source light into the waveguide matrix by reflection or refraction, so that the image source light is reflected between the first surface and the second surface of the waveguide matrix to the outcoupling structure.

10. An AR near-eye display device, characterized in that: include: wearable stents; as well as The optical waveguide device according to any one of claims 5 to 9 is provided on the wearable support.

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