Optical waveguide and augmented reality display device
By controlling the optical path difference between the grating area and the blank area, the problem of abrupt phase change of light in the optical waveguide was solved, improving the imaging quality and promoting the development of augmented reality display devices.
Patent Information
- Application Number
- CN202520272966.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-19
- Publication Date
- 2025-12-30
- Estimated Expiration
- 2035-02-19
AI Technical Summary
Existing optical waveguides suffer from a phase abrupt change when light enters the blank area from the grating area, resulting in poor image quality and affecting the use of augmented reality display devices.
By controlling the optical path difference between the grating area and the blank area to be between 0.8 and 1.2 times the target optical path difference, or an integer multiple of the light wavelength, the height of the dielectric layer in the grating area and the height of the blank area are adjusted to eliminate phase abrupt changes.
It significantly improves the imaging quality of diffractive waveguides, enhances the imaging effect of augmented reality display devices, and improves the user experience.
Smart Images
Figure CN223742786U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of display, in particular to a light waveguide and an augmented reality display device. BACKGROUND
[0002] There is an augmented reality display device realized by using light waveguide technology in the art. In the prior art light waveguide, the phase jump occurs when the light enters the blank area from the grating area in the light waveguide, which leads to poor imaging quality. There is no good way to solve this phase jump phenomenon in the prior art, which leads to that the light waveguide in the prior art cannot well meet the needs of users, and affects its further wide application. Therefore, there is an urgent need in the art for a light waveguide which can solve the problem of phase jump when light passes through the grating area and the blank area, and improve the imaging quality. CONTENT OF THE UTILITY MODEL
[0003] Therefore, the present application is committed to providing a light waveguide and an augmented reality display device which can solve the problem of phase jump when light passes through the grating area and the blank area, and improve the imaging quality.
[0004] In one aspect, the present application provides a light waveguide, comprising: a light waveguide substrate, the light waveguide substrate comprising a grating area and a blank area; a grating, the grating being located in the grating area; wherein the light has a first optical path when passing through the grating area, and has a second optical path when passing through the blank area, the optical path difference between the first optical path and the second optical path is between 0.8 and 1.2 times of a target optical path difference, and the target optical path difference is zero or an integer multiple of the wavelength of the light.
[0005] In a possible implementation manner of the present application, the optical path difference is equal to the target optical path difference.
[0006] In a possible implementation manner of the present application, the second optical path is determined according to the refractive index of the light waveguide substrate and the height of the blank area.
[0007] In a possible implementation manner of the present application, the height of the blank area is adjusted to adjust the optical path difference.
[0008] In a possible implementation manner of the present application, the light waveguide further comprises a medium layer, the medium layer being located in the grating area and below the grating.
[0009] In a possible implementation manner of the present application, the first optical path is the sum of a first sub-optical path of the light passing through the medium layer and a second sub-optical path of the light passing through the grating, the first sub-optical path is determined according to the height of the medium layer and the refractive index of the medium layer, and the second sub-optical path is determined according to the height of the grating and the equivalent refractive index of the grating.
[0010] In a possible implementation manner of the present application, the height of the medium layer is adjusted to adjust the optical path difference, or the height of the medium layer and the height of the blank area are adjusted at the same time to adjust the optical path difference.
[0011] In a possible implementation of the present application, the equivalent refractive index of the grating comprises a second-order equivalent refractive index of the grating.
[0012] In a possible implementation of the present application, the second-order equivalent refractive index of the grating comprises a second-order equivalent refractive index of a TE wave and / or a second-order equivalent refractive index of a TM wave.
[0013] In another aspect, the present application provides an augmented reality display device comprising the optical waveguide described above. BRIEF DESCRIPTION OF DRAWINGS
[0014] Hereinafter, a specific embodiment of the present application will be described in detail with reference to the accompanying drawings, in which:
[0015] Figure 1 A structural schematic diagram of an optical waveguide according to an embodiment of the present application is shown;
[0016] Figure 2 A structural schematic diagram of an optical waveguide according to an embodiment of the present application is shown;
[0017] Figure 3 A top view structural schematic diagram of an optical waveguide according to an embodiment of the present application is shown;
[0018] Figure 4 A side view cross-sectional structural schematic diagram of an optical waveguide according to an embodiment of the present application is shown; Figure 3
[0019] A result schematic diagram of an X direction of a Strehl ratio of an optical waveguide according to an embodiment of the present application is shown; Figure 5A Figure 3 A result schematic diagram of a Y direction of a Strehl ratio of an optical waveguide according to an embodiment of the present application is shown;
[0020] Figure 5B Figure 3 A result schematic diagram of an X direction of an MTF of an optical waveguide according to an embodiment of the present application is shown;
[0021] Figure 6A A result schematic diagram of a Y direction of an MTF of an optical waveguide according to an embodiment of the present application is shown; Figure 3
[0022] Figure 6B A result schematic diagram of a Y direction of an MTF of an optical waveguide according to an embodiment of the present application is shown; Figure 3
[0023] A structural schematic diagram of an optical waveguide according to an embodiment of the present application is shown; Figure 7
[0024] A result schematic diagram of an X direction of a Strehl ratio of an optical waveguide according to an embodiment of the present application is shown; Figure 8A Figure 7 A result schematic diagram of an X direction of a Strehl ratio of an optical waveguide according to an embodiment of the present application is shown;
[0025] Figure 8B Results of the X direction of the Strehl ratio of the optical waveguide according to Figure 7 Example 1;
[0026] Figure 9A Results of the X direction of the MTF of the optical waveguide according to Figure 7 Example 1;
[0027] Figure 9B Results of the Y direction of the MTF of the optical waveguide according to Figure 7 Example 1;
[0028] Figure 10 Structure diagram of the optical waveguide according to an embodiment of the present application;
[0029] Figure 11A Results of the X direction of the Strehl ratio of the optical waveguide according to Figure 10 Example 1;
[0030] Figure 11B Results of the Y direction of the Strehl ratio of the optical waveguide according to Figure 10 Example 1;
[0031] Figure 12A Results of the X direction of the MTF of the optical waveguide according to Figure 10 Example 1;
[0032] Figure 12B Results of the Y direction of the MTF of the optical waveguide according to Figure 10 Example 1. DETAILED DESCRIPTION
[0033] In order to make the concept and thought of the present application more clearly understood by those skilled in the art, the present application is described in detail below in combination with specific embodiments. It should be understood that the embodiments given herein are only a part of all the embodiments that the present application can have. Those skilled in the art can make improvements, modifications or replacements to part or whole of the following embodiments after reading the description of the present application, and these improvements, modifications or replacements are also included in the scope of protection claimed by the present application.
[0034] In this document, the terms "one," "an," and other similar words are not intended to indicate that only one of the described things exists, but rather that the description refers only to one of the described things, which may have one or more. In this document, the terms "comprising," "including," and other similar words are intended to indicate a logical relationship, not a spatial relationship. For example, "A includes B" means that logically B belongs to A, not that spatially B is located inside A. Furthermore, the meanings of the terms "comprising," "including," and other similar words should be considered open-ended, not closed-ended. For example, "A includes B" means that B belongs to A, but B does not necessarily constitute all of A; A may also include other elements such as C, D, and E.
[0035] In this document, the terms "first," "second," and other similar terms are not intended to imply any order, quantity, or importance, but are merely used to distinguish different elements. In this document, the terms "embodiment," "this embodiment," "an embodiment," or "an example" do not indicate that the description applies only to one specific embodiment, but rather that such description may also be applicable to one or more other embodiments. Those skilled in the art will understand that any description made herein with respect to one embodiment can be substituted, combined, or otherwise combined with the descriptions in one or more other embodiments, and the new embodiments resulting from such substitutions, combinations, or other combinations are readily conceived by those skilled in the art and fall within the scope of protection of this application.
[0036] In the various embodiments of this application, an optical waveguide can refer to a structure capable of confining light within itself and guiding light to propagate along a specific path. The working principle of an optical waveguide is based on the phenomenon of total internal reflection. When light enters the optical waveguide at a certain angle, due to the difference in refractive index between the optical waveguide and the surrounding medium, total internal reflection occurs at the boundary of the optical waveguide, thereby confining the light within the optical waveguide for propagation.
[0037] In the embodiments of this application, an augmented reality display device can refer to a device that combines virtual digital information with a real scene and presents the fused content to the user. It senses the environment through sensors such as cameras and gyroscopes, and displays the information using optical or video perspective methods. During operation, it matches virtual and real information based on sensor data. This type of device has wide applications, allowing users to see virtual elements in real-world scenes and enhancing their perception of the world.
[0038] Diffractive optical waveguide AR (Augmented Reality) glasses are favored by many manufacturers due to their lightness, thinness, ease of mass production and other advantages. There are many diffractive optical waveguide AR glasses on the market. These AR glasses can meet certain imaging, viewing and gaming needs, but they all have a common problem, that is, the imaging quality is not high (imaging quality can be characterized by MTF), that is, the MTF (Modulation Transfer Function) is poor, resulting in poor user experience, which to some extent hinders the development of AR glasses.
[0039] MTF is used to describe the response of an optical system to an input signal (usually an image). It measures the transfer ability of an optical system to image contrast at different spatial frequencies. Spatial frequency refers to the density of details in an image, low spatial frequency corresponds to large-scale features in the image, and high spatial frequency corresponds to small-scale details in the image. The value of MTF ranges from 0 to 1, where 1 represents perfect transfer, that is, the contrast of the input signal is completely preserved in the output; 0 represents no transfer at all.
[0040] In some embodiments of the present application, a method for improving the MTF of a diffractive optical waveguide is proposed to overcome the problem of low imaging quality of the diffractive optical waveguide, and a diffractive optical waveguide with high imaging quality is designed based on this method.
[0041] In some embodiments of the present application, a high-quality augmented reality diffractive optical waveguide is provided, which includes a grating area and a blank area. The grating area can include a coupling-in grating area, a turning grating area, a coupling-out grating area, a uniform light area, an energy recycling area, etc. The blank area refers to other areas (mainly refers to non-grating areas through which light propagates) other than the grating area. The propagation of light in the optical waveguide involves complex geometrical optics and physical optics. The phase jump in the propagation of light plays a decisive role in the imaging quality of the optical waveguide. By controlling the optical path difference between the grating area and the blank area, the phase jump at the junction of the grating area and the blank area can be solved, thereby greatly improving the MTF of the diffractive optical waveguide. By controlling the optical path difference (phase jump amount) of light in the grating area and the blank area, the imaging quality of the diffractive optical waveguide can be improved.
[0042] In some embodiments of the present application, the optical path difference of light when passing through the grating area and the blank area is 0 or an integer multiple of the wavelength of light. When the optical path of light in the grating area and the blank area is equal or the optical path difference is an integer multiple of the wavelength of light, there is no phase jump, and the imaging quality of the diffractive optical waveguide is best.
[0043] In some embodiments of the present application, the grating structure of the grating region can include one-dimensional grating, two-dimensional grating, double-sided one-dimensional grating, etc. The distribution of the grating region can include two-partition, three-partition, four-partition, etc. The optical path of the grating region can be calculated by using the equivalent refractive index. The method of using the equivalent refractive index to calculate the optical path of the grating region can greatly reduce the amount of calculation.
[0044] In some embodiments of the present application, the optical path of the blank region is calculated using the product of the medium refractive index and the optical path length, and is compared with the optical path of the grating region. By accurately calculating the optical path of the grating region and the blank region, the difference in optical path between the grating region and the blank region is provided for the adjustment of the diffractive optical waveguide.
[0045] In some embodiments of the present application, by controlling the thickness of the residual medium layer of the grating region, the difference in optical path between the grating region and the blank region is achieved. This method is simple and easy to implement, and the MTF improvement effect is obvious.
[0046] In some embodiments of the present application, by controlling the optical path of the light passing through the blank region, the difference in optical path between the grating region and the blank region is achieved. This method does not change the existing grating and architecture of the diffractive optical waveguide, and has excellent effect on improving the imaging quality of existing or previous products.
[0047] In some embodiments of the present application, the optical path of the blank region is achieved by reducing or increasing the thickness of the substrate of the blank region or increasing or reducing the thickness of the medium on the substrate of the blank region, so as to control the difference in optical path between the grating region and the blank region.
[0048] In some embodiments of the present application, the optical path of the blank region is achieved by increasing the sub-nanometer structure or the gradient material, so as to control the difference in optical path between the grating region and the blank region.
[0049] In some embodiments of the present application, the imaging quality of the diffractive optical waveguide can be verified by calculating the Strehl ratio of the diffractive optical waveguide, or the imaging quality of the diffractive optical waveguide can be verified by calculating the MTF of the diffractive optical waveguide.
[0050] Figure 1 A structure schematic diagram of an optical waveguide according to an embodiment of the present application is shown.
[0051] As Figure 1As shown, the optical waveguide 100 comprises: an optical waveguide substrate 110, the optical waveguide substrate 110 comprising a grating region 111 and a blank region 112; and a grating 120, the grating 120 being located in the grating region 111. Wherein, the light has a first optical path when passing through the grating region 111, and has a second optical path when passing through the blank region 112, the optical path difference between the first optical path and the second optical path being between 0.8 and 1.2 times of a target optical path difference, the target optical path difference being zero or an integer multiple of the wavelength of the light. The optical path difference of the light when passing through the grating region and the blank region is zero or close to zero, or is an integer multiple of the wavelength of the light. By controlling the optical path difference between the first optical path and the second optical path in this way, the phase jump of the light when passing through the grating region and the blank region is greatly weakened or eliminated, thereby significantly improving the imaging quality of the optical waveguide, and facilitating the further widespread use of near-eye display devices using optical waveguide technology.
[0052] As an example, the optical path difference is equal to the target optical path difference. The present inventors have found that when the optical path difference between the first optical path and the second optical path is between 0.8 and 1.2 times of the target optical path difference, the imaging quality can be improved to a certain extent; when the optical path difference is equal to the target optical path difference, the imaging quality can be further improved to achieve the optimal effect under the current conditions.
[0053] As an example, the second optical path is determined according to the refractive index of the optical waveguide substrate 110 and the height H112 of the blank region 112. When calculating the optical path of the blank region, the height of the blank region can be taken as the actual path of the light, and the refractive index of the optical waveguide substrate can be taken as the refractive index of the blank region, because the blank region is entirely composed of the material of the optical waveguide substrate. In this way, the calculation of the second optical path of the blank region can be greatly simplified, thereby facilitating the determination of the manufacturing method and related dimensions of the optical waveguide to achieve the corresponding imaging effect.
[0054] As an example, the optical path difference is adjusted by adjusting the height H112 of the blank region 112. Since the blank region does not have a grating and does not produce a diffraction effect, the optical path difference can be adjusted by adjusting the height of the blank region, while avoiding affecting the normal performance of the optical waveguide. The height of the blank region can be adjusted in various ways, and the height of the blank region can be controlled by mature and low-cost methods (such as etching, inkjet printing, etc.), so that the adjustment and setting of the optical path difference are greatly simplified, and the applicability of the technical solution of the present application is improved.
[0055] Figure 2 A structural schematic diagram of an optical waveguide according to an embodiment of the present application is shown.
[0056] As Figure 2As shown, the optical waveguide 200 includes an optical waveguide substrate 210 and a grating 220, the optical waveguide substrate 210 includes a grating region 211 and a blank region 212, and the grating 220 is located in the grating region 211. In this embodiment, the optical waveguide 200 further includes a medium layer 230, which is located in the grating region 211 and below the grating 220. By providing a medium layer in the grating region of the optical waveguide, it is convenient to manufacture the grating. When manufacturing the grating, for example, by a method of embossing or etching, a layer of medium is usually left in the grating region, which can be residual glue or etched material. By reserving the medium layer, it is more convenient to adjust the first optical path of the grating region, thereby more conveniently adjusting the optical path difference to improve the imaging quality.
[0057] As an example, the first optical path is the sum of a first sub-optical path when the light passes through the medium layer 230 and a second sub-optical path when the light passes through the grating 220, the first sub-optical path is determined according to the height H230 of the medium layer 230 and the refractive index of the medium layer 230, and the second sub-optical path is determined according to the height H220 of the grating 220 and the equivalent refractive index of the grating 220. The equivalent refractive index refers to a virtual refractive index value introduced for the convenience of analysis and calculation when a complex optical system or a non-uniform medium is equivalent to a uniform medium with a single refractive index. It is an equivalent description of the optical properties of the actual optical system or medium, so that similar methods for handling uniform media can be used when dealing with some complex optical problems. By determining the optical path of the medium layer (the first sub-optical path) through the height and refractive index of the medium layer, it is convenient to simplify the calculation of the optical path of the medium layer. The optical path of the grating (the second sub-optical path) is calculated by the height of the grating and the equivalent refractive index of the grating, which simplifies the calculation of the optical path of the grating. In these two calculation methods, the height of the corresponding structure is taken as the actual path of the light, and the optical path is calculated according to the corresponding refractive index, which can make the optical path value easy to determine, thereby facilitating the adjustment of the corresponding optical structure, so as to adjust the optical path difference as needed to achieve the purpose of improving the imaging quality.
[0058] As an example, the optical path difference is adjusted by adjusting the height H230 of the medium layer 230, or by adjusting the height H230 of the medium layer 230 and the height H212 of the blank region 212 at the same time. Since the medium layer and the grating are both provided in the grating region, the optical path of the grating is difficult to adjust due to its diffractive structure, so the height of the medium layer can be adjusted to adjust the optical path of the grating region. By adjusting the height of the medium layer alone or adjusting the height of the medium layer and the blank region at the same time, the adjustment of the optical path difference can be realized in a relatively simple way, thereby achieving a higher imaging quality at a lower cost.
[0059] As an example, the equivalent refractive index of the grating 220 includes a second-order equivalent refractive index of the grating 220. It has been proved through a large number of researches and practices of the inventor of the present application that the second-order equivalent refractive index of the grating can well simulate or represent the real refractive index of the grating, so that a relatively accurate optical path value can be calculated. Therefore, by using the second-order equivalent refractive index of the grating to calculate the optical path of the grating, a relatively accurate first optical path of the grating region can be obtained, so that a relatively accurate optical path difference can be obtained, and then the optical path difference can be accurately adjusted to obtain good imaging quality.
[0060] As an example, the second-order equivalent refractive index of the grating 220 includes a second-order equivalent refractive index of a TE wave (Transverse Electric Field) and / or a second-order equivalent refractive index of a TM wave (Transverse Magnetic Field). Since the grating size of the optical waveguide is close to the wavelength of light, in some cases the grating is a subwavelength structure (a structure with a feature size equal to or less than the wavelength), so the different performances and influences of the TE wave and the TM wave need to be considered when calculating the equivalent refractive index. The second-order equivalent refractive indices calculated according to the calculation methods of the TE wave and the TM wave are different in value, and different results will be obtained when calculating the optical path difference. In order to determine the final adjustment size, the performance improvement effects brought by the calculation results of the TE wave and the TM wave can be compared, and the size of the corresponding structure of the optical waveguide is adjusted according to the light wave with a larger imaging performance improvement amplitude, so as to obtain the optimal imaging effect.
[0061] Figure 3 A top view structural schematic diagram of an optical waveguide according to an embodiment of the present application is shown.
[0062] As shown in Figure 3 , the optical waveguide 300 includes a turning grating region 310, a coupling-out grating region 320, and a blank region 330. Although in the present embodiment, the optical waveguide adopts a three-part form, in other embodiments, the optical waveguide can adopt other forms of two-part, four-part, etc., and the optical waveguide can also include a coupling-in grating region, a uniform light region, an energy recycling region, etc.
[0063] Figure 4 A side view structural schematic diagram of an optical waveguide according to Figure 3 an embodiment of the present application is shown.
[0064] As shown in Figure 4 , in the turning grating region 310, the grating has a height H1, and the dielectric layer has a height h1. In the coupling-out grating region 320, the grating has a height H2, and the dielectric layer has a height h2.
[0065] In the present embodiment, it can be assumed that the relevant parameters take the following values. Of course, those skilled in the art should know that these values are only examples and are used only to illustrate the calculation process, and cannot be regarded as a limitation on the technical solutions of the present application.
[0066] The grating parameters of the turning grating region 310 are as follows: turning period P1 = 362.01 nm, height H1 = 30 nm, residual glue (dielectric layer) h1 = 100 nm, duty cycle f1 = 70%, and refractive index n1 = 1.9355.
[0067] The grating parameters of the coupling-out grating region 320 are as follows: coupling-out period P2 = 375 nm, height H2 = 48.7 nm, residual glue (dielectric layer) h2 = 100 nm, duty cycle f2 = 45.699%, and refractive index n2 = 1.9355. The wavelength of the light is λ = 528 nm. The duty cycle refers to the ratio of the width of the light-transmitting (or light-reflecting) part to the entire period width in one period of the diffraction grating. It is usually expressed by a percentage or a decimal, and its value is between 0 and 1. For example, if the duty cycle of a diffraction grating is 0.5, it means that the width of the light-transmitting (or light-reflecting) part accounts for half of the entire period width in one complete period of the diffraction grating; if the duty cycle is 0.3, it means that the width of the light-transmitting (or light-reflecting) part accounts for 30% of the period width, and the remaining 70% is the non-light-transmitting (or non-light-reflecting) part. The duty cycle is an important parameter of the diffraction grating and has an important influence on the intensity distribution of the diffracted light and the diffraction efficiency. For example, in the design of a diffraction grating for spectral analysis, a suitable duty cycle can make the light of a specific wavelength have a higher diffraction efficiency, thereby improving the spectral resolution and measurement accuracy; in an integrated optical device such as an optical waveguide, the duty cycle determines the coupling efficiency and transmission characteristics of the light in the grating structure, and affects the performance of the device.
[0068] Based on the above parameters, the Strehl ratio and the MTF of the diffractive optical waveguide before the imaging quality is improved can be calculated. The calculation results of the Strehl ratio in the X direction and the Y direction are X: 0.38 and Y: 0.51, respectively, and the specific results are shown in Figure 5A and Figure 5B The calculation results of the MTF (MTF = 50%) in the X direction and the Y direction are X: 14.01 cycles / mm and Y: 16.02 cycles / mm, respectively, and the specific results are shown in Figure 6A and Figure 6B
[0069] In the embodiment, the Strehl ratio can refer to a key index for measuring the imaging quality of an optical system in the optical field, which is defined as the ratio of the maximum light intensity of the actual optical system at the image point to the maximum light intensity of the ideal aberration-free optical system at the corresponding image point with the same aperture and wavelength. In a physical sense, the Strehl ratio intuitively reflects the degree to which the actual optical system approaches the ideal state. When the Strehl ratio is 1, it means that the actual optical system has no aberration, and the imaging quality reaches the theoretical best state, and the light can be perfectly focused on the ideal image point; and as the Strehl ratio value gradually decreases, it means that the aberration of the actual optical system gradually increases, and the imaging quality decreases, and the light cannot be accurately converged on the ideal image point, but is diffused to the surrounding area, resulting in a blurred image and reduced contrast.
[0070] In the embodiment, based on Figure 4 The grating equivalent refractive index of the grating region can be calculated in the following manner according to the specific numerical values given in the description.
[0071] The zero-order equivalent approximate refractive index of the grating structure can be calculated according to the following two formulas:
[0072]
[0073] wherein, and are the zero-order equivalent refractive indices of TE and TM waves respectively, n i and n s are the refractive indices of the two media (i.e. the grating material and air), and f is the duty cycle of the grating region. The zero-order equivalent approximate refractive index can refer to the equivalent refractive index of the zero-order diffracted light passing through the grating region.
[0074] The second-order equivalent approximate refractive index of the grating structure can be derived from the zero-order equivalent approximate refractive index of the grating structure, and the second-order equivalent refractive index can be calculated according to the following two formulas:
[0075]
[0076] wherein d is the grating period, and are the second-order equivalent refractive indices of TE and TM waves respectively. The second-order equivalent refractive index can refer to the equivalent refractive index of the second-order diffracted light passing through the grating region.
[0077] According to the above parameters and formulas, the equivalent refractive index of the turning grating region can be calculated as follows: n TE: 1.8538 (second-order equivalent refractive index of TE wave), n TM: 1.7269 (second-order equivalent refractive index of TM wave).
[0078] Therefore, the optical path of the turning grating region is: s1 TE = H1 * n TE = 55.615 nm, s1 TM = H1 * n TM = 51.806 nm.
[0079] The optical path of the turning grating region containing residual glue (a medium layer) is: s1 t TE = s1 TE + h1 * n1 = 249.16 nm, s1 t TM = s1 TM + h1 * n1 = 245.36 nm.
[0080] According to the above parameters and formulas, the equivalent refractive index of the out-coupling grating region can be obtained: n2 TE: 1.7394, n2 TM: 1.3874.
[0081] The optical path of the out-coupling grating region is: s2 TE = H2 * n2 TE = 84.71 nm, s2 TM = H2 * n2 TM = 67.566 nm.
[0082] The optical path of the out-coupling grating region containing residual glue (a medium layer) is: s2 t TE = s2 TE + h2 * n2 = 278.26 nm, s2 t TM = s2 TM + h2 * n2 = 261.12 nm.
[0083] Figure 7 A side view cross-sectional structure schematic diagram of an optical waveguide according to an embodiment of the present application is shown.
[0084] In this embodiment, the relevant parameters are as follows: Figure 3 The numerical values of the embodiments are used to illustrate the calculation process. Those skilled in the art should know that these numerical values are only examples and cannot be regarded as a limitation on the technical solutions of the present application. In order to simplify the understanding of the technical solutions of the present application, this embodiment will only give the calculation method of TE wave with single wavelength and single angle. Those skilled in the art should know that the calculation method of TM wave is the same as or similar to that of TE wave. In order to obtain the best imaging quality, the height of the medium layer of the turning grating region and the out-coupling grating region can be calculated first in the case of TE wave according to the following method; and then the height of the medium layer of the turning grating region and the out-coupling grating region can be calculated in the case of TM wave according to a method similar to the following. For the two calculation results, simulation experiments can be performed to determine which calculation result has better imaging quality. For example, the experimental results show that the Strehl ratio and MTF have larger values when the calculation result of TE wave is used, so the height of the medium layer can be finally adjusted according to the calculation result of TE wave, without using the calculation result of TM wave. The corresponding calculation method can also be selected according to whether the light source actually used is TE wave or TM wave.
[0085] In this embodiment, the adjustment of the optical path difference is realized by adjusting the height of the dielectric layer of the grating region only. In this embodiment, the optical path difference between the first optical path of the grating region (turning grating region 710 or coupling-out grating region 720) and the second optical path of the blank region 730 is set to one wavelength (wavelength = 528 nm), and at this time the height of the blank region is 0 (thus the optical path is 0), so as to eliminate the phase jump of the light passing through the grating region and the blank region 730.
[0086] The height of the dielectric layer of the turning grating region 710 is calculated according to the following formula:
[0087] L1 = (λ - s1 TE) / n1 = (528 nm - 55.615 nm) / 1.9355 = 244.06 nm
[0088] The height of the dielectric layer of the coupling-out grating region 720 is calculated according to the following formula:
[0089] L2 = (λ - s2 TE) / n2 = (528 nm - 84.71 nm) / 1.9355 = 229.03 nm
[0090] After adjusting the height of the dielectric layer according to the above calculation results, the calculation results of the Strehl ratio of the optical waveguide 700 in the X direction and the Y direction are X: 0.57, Y: 0.6, and the specific results are shown in Figure 8A and Figure 8B The calculation results of the MTF (MTF = 50%) in the X direction and the Y direction are X: 20.02 cycles / mm, Y: 20.02 cycles / mm, and the specific results are shown in Figure 9A and Figure 9B
[0091] Figure 10 A side view schematic diagram of the optical waveguide according to an embodiment of the present application is shown.
[0092] In this embodiment, the numerical values of the parameters used in Figure 3 the embodiment of the present application are used to illustrate the calculation process. Those skilled in the art should know that these numerical values are only examples and cannot be regarded as a limitation on the technical solutions of the present application.
[0093] In this embodiment, the adjustment of the optical path difference is realized by adjusting the height of the dielectric layer of the grating region and the height of the blank region 1030. In this embodiment, the turning grating region 1010 and the coupling-out grating region 1020 and the blank region 1030 through which the light passes are set to have equal optical paths (the optical path can also be improved), so that the optical path difference between the first optical path of the grating region and the second optical path of the blank region 1030 is 0.
[0094] The optical path of the coupling-out grating region 1020 is larger than that of the turning grating region 1010 by L1, and L1 is calculated according to the following formula:
[0095] L1 = s2 TE - s1 TE = 84.71 nm - 55.615 nm = 29.095 nm
[0096] If the coupling-out grating region 1020 and the turning grating region 1010 have the same optical path, the residual glue thickness (height of the medium layer) of the coupling-out grating region 1020 needs to be reduced by L2, which is calculated as follows:
[0097] L2 = L1 / n1 = 29.095 nm / 1.9355 = 15.03 nm
[0098] When the light passes through the blank region 1030, if the same optical path as the turning grating region 1010 is to be maintained, that is, the increased optical path (the initial height and optical path of the blank region 1030 are 0) is s1 t TE = 249.16 nm, since the refractive index of the optical waveguide substrate is n3 = 2.0149, the blank region 1030 needs to increase the thickness L3, which is calculated as follows:
[0099] L3 = s1 t TE / n3 = 123.66 nm
[0100] In this embodiment, after adjusting the height of the grating region and the height of the blank region according to the above calculation results, the calculation results of the Strehl ratio of the optical waveguide 1000 in the X direction and the Y direction are X: 0.63, Y: 0.65, and the specific results are shown in Figure 11A and Figure 11B The calculation results of the MTF (MTF = 50%) in the X direction and the Y direction are X: 32.03 cycles / mm, Y: 38.04 cycles / mm, and the specific results are shown in Figure 12A and Figure 12B
[0101] As can be seen from this embodiment, the difference in optical path between the grating region and the blank region in the diffractive optical waveguide has a huge impact on the imaging quality, and the scheme of adjusting the optical path difference proposed in the present application greatly improves the MTF of the diffractive optical waveguide, which will be of great benefit to the promotion of the diffractive optical waveguide to the consumer market in the future.
[0102] The concepts, principles and ideas of the present application are described in detail above in combination with specific embodiments (including examples and instances). Those skilled in the art should understand that the embodiments of the present application are not limited to the above forms, and those skilled in the art can make any possible improvements, replacements and equivalents to the steps, methods, devices and components in the above embodiments after reading the present application file. These improvements, replacements and equivalents should be considered to fall within the scope of the present application. The protection scope of the present application is only subject to the claims.
Claims
1. An optical waveguide, characterized by, The optical waveguide comprises: an optical waveguide substrate (110) comprising a grating region (111) and a blank region (112); a grating (120) located in the grating region (111); wherein the light has a first optical path when passing through the grating region (111), and has a second optical path when passing through the blank region (112), the optical path difference between the first optical path and the second optical path is between 0.8 and 1.2 times a target optical path difference, the target optical path difference is zero or an integer multiple of the wavelength of the light.
2. The optical waveguide of claim 1, wherein, The optical path difference is equal to the target optical path difference.
3. The optical waveguide of claim 1, wherein, The second optical path is determined according to the refractive index of the optical waveguide substrate (110) and the height of the blank region (112).
4. The optical waveguide of claim 3, wherein, The optical path difference is adjusted by adjusting the height of the blank region (112).
5. The optical waveguide of claim 1, wherein, The optical waveguide further comprises a medium layer (230) located in the grating region (111) and below the grating (120).
6. The optical waveguide of claim 5, wherein, The first optical path is the sum of a first sub-optical path of the light passing through the medium layer (230) and a second sub-optical path of the light passing through the grating (120), the first sub-optical path is determined according to the height of the medium layer (230) and the refractive index of the medium layer (230), and the second sub-optical path is determined according to the height of the grating (120) and the equivalent refractive index of the grating (120).
7. The optical waveguide of claim 6, wherein, The optical path difference is adjusted by adjusting the height of the medium layer (230), or by adjusting the height of the medium layer (230) and the height of the blank region (112) at the same time.
8. The optical waveguide of claim 6, wherein, The equivalent refractive index of the grating (120) comprises a second-order equivalent refractive index of the grating (120).
9. The optical waveguide of claim 8, wherein, The second-order equivalent refractive index of the grating (120) comprises a second-order equivalent refractive index of TE wave and / or a second-order equivalent refractive index of TM wave.
10. An augmented reality display device, characterized by The optical waveguide according to any one of claims 1 to 9. The optical waveguide according to any one of claims 1 to 9.