An optical waveguide and augmented reality display device

Abstract

The application provides an optical waveguide and an augmented reality display device. The optical waveguide comprises: an optical waveguide substrate, the optical waveguide substrate comprising a grating area and a blank area; and 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 the light 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. According to the application, the phase jump problem of the light passing through the grating area and the blank area can be solved, and the imaging quality is improved.

Description

Technical Field

[0001] This application relates to the field of display technology, and in particular to an optical waveguide and an augmented reality display device. Background Technology

[0002] Augmented reality display devices employing optical waveguide technology already exist in this field. In existing optical waveguides, a phase abrupt change occurs when light passes from the grating region to the blank region, resulting in poor image quality. Current technologies lack effective methods to address this phase abrupt change, causing existing optical waveguides to fail to meet user needs and hindering their wider application. Therefore, there is an urgent need in this field for an optical waveguide that can resolve the phase abrupt change problem when light passes through the grating region and the blank region, thereby improving image quality. Summary of the Invention

[0003] Therefore, this application aims to provide an optical waveguide and augmented reality display device that can solve the problem of phase abrupt change when light passes through the grating area and blank area, thereby improving the imaging quality.

[0004] In one aspect, this application provides an optical waveguide, comprising: an optical waveguide substrate, the optical waveguide substrate including a grating region and a blank region; a grating, the grating being located in the grating region; wherein, light has a first optical path when passing through the grating region, and a second optical path when passing through the blank region, 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 being zero or an integer multiple of the wavelength of the light.

[0005] In one possible implementation of this application, the optical path difference is equal to the target optical path difference.

[0006] In one possible implementation of this application, the second optical path is determined based on the refractive index of the optical waveguide substrate and the height of the blanking area.

[0007] In one possible implementation of this application, the optical path difference is adjusted by adjusting the height of the blank area.

[0008] In one possible implementation of this application, the optical waveguide further includes a dielectric layer located in the grating region and below the grating.

[0009] In one possible implementation of this application, the first optical path is the sum of the first sub-optical path when the light passes through the dielectric layer and the second sub-optical path when the light passes through the grating. The first sub-optical path is determined based on the height of the dielectric layer and the refractive index of the dielectric layer, and the second sub-optical path is determined based on the height of the grating and the equivalent refractive index of the grating.

[0010] In one possible implementation of this application, the optical path difference is adjusted by adjusting the height of the dielectric layer, or by simultaneously adjusting the height of the dielectric layer and the height of the blank area.

[0011] In one possible implementation of this application, the equivalent refractive index of the grating includes the second-order equivalent refractive index of the grating.

[0012] In one possible implementation of this application, the second-order equivalent refractive index of the grating includes the second-order equivalent refractive index of the TE wave and / or the second-order equivalent refractive index of the TM wave.

[0013] On the other hand, this application provides an augmented reality display device, including the aforementioned optical waveguide. Attached Figure Description

[0014] The specific embodiments of this application are described in detail below with reference to the accompanying drawings, wherein:

[0015] Figure 1 A schematic diagram of an optical waveguide according to an embodiment of this application is shown;

[0016] Figure 2 A schematic diagram of an optical waveguide according to an embodiment of this application is shown;

[0017] Figure 3 A top view of an optical waveguide according to an embodiment of this application is shown.

[0018] Figure 4 Showing according to Figure 3 A side view cross-sectional structural diagram of the optical waveguide in the embodiment;

[0019] Figure 5A Showing according to Figure 3 A schematic diagram of the Strell ratio of the optical waveguide in the X direction in the embodiment;

[0020] Figure 5B Showing according to Figure 3 A schematic diagram of the Y-direction result of the Strell ratio of the optical waveguide in the embodiment;

[0021] Figure 6A Showing according to Figure 3 A schematic diagram of the MTF results in the X direction of the optical waveguide in the embodiment;

[0022] Figure 6B Showing according to Figure 3 A schematic diagram of the MTF results in the Y direction of the optical waveguide in the embodiment;

[0023] Figure 7 A schematic diagram of an optical waveguide according to an embodiment of this application is shown;

[0024] Figure 8A Showing according to Figure 7 A schematic diagram of the Strell ratio of the optical waveguide in the X direction in the embodiment;

[0025] Figure 8B Showing according to Figure 7 A schematic diagram of the Y-direction result of the Strell ratio of the optical waveguide in the embodiment;

[0026] Figure 9A Showing according to Figure 7 A schematic diagram of the MTF results in the X direction of the optical waveguide in the embodiment;

[0027] Figure 9B Showing according to Figure 7 A schematic diagram of the MTF results in the Y direction of the optical waveguide in the embodiment;

[0028] Figure 10 A schematic diagram of an optical waveguide according to an embodiment of this application is shown;

[0029] Figure 11A Showing according to Figure 10 A schematic diagram of the Strell ratio of the optical waveguide in the X direction in the embodiment;

[0030] Figure 11B Showing according to Figure 10 A schematic diagram of the Y-direction result of the Strell ratio of the optical waveguide in the embodiment;

[0031] Figure 12A Showing according to Figure 10 A schematic diagram of the MTF results in the X direction of the optical waveguide in the embodiment;

[0032] Figure 12B Showing according to Figure 10 A schematic diagram of the MTF in the Y direction of the optical waveguide in the embodiment. Detailed Implementation

[0033] To enable those skilled in the art to more clearly understand the concepts and ideas of this application, the application is described in detail below with reference to specific embodiments. It should be understood that the embodiments given herein are only a part of all possible embodiments of this application. After reading the specification of this application, those skilled in the art are capable of making improvements, modifications, or substitutions to parts or the entirety of the following embodiments, and such improvements, modifications, or substitutions are also included within the scope of protection claimed in this 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 waveguide AR (Augmented Reality) glasses are favored by many manufacturers due to their advantages such as being lightweight, thin, and easy to mass-produce. Currently, there are several Diffractive waveguide AR glasses on the market. These glasses can meet certain needs for imaging, watching movies, and playing games, but they generally suffer from low image quality (image quality can be characterized by MTF), specifically a poor MTF (Modulation Transfer Function), leading to a subpar user experience. This, to some extent, hinders the development of AR glasses.

[0039] MTF (Mean Transmission Scale) describes the response of an optical system to an input signal (usually an image). It measures the ability of an optical system to transmit image contrast at different spatial frequencies. Spatial frequency refers to the density of details in an image; low spatial frequencies correspond to large-scale features in the image, while high spatial frequencies correspond to small-scale details. The value of MTF ranges from 0 to 1, where 1 represents perfect transmission, meaning the contrast of the input signal is completely preserved in the output; 0 represents no transmission at all.

[0040] In some embodiments of this application, a method for improving the MTF of diffractive waveguides is proposed to address the drawback of low imaging quality, and a diffractive waveguide with high imaging quality is designed based on this method.

[0041] In some embodiments of this application, a high-quality augmented reality diffractive waveguide is provided, comprising a grating region and a blank region. The grating region may include an input grating region, a transition grating region, an output grating region, a homogenizing region, an energy recovery region, etc. The blank region refers to other regions outside the grating region (specifically, the non-grating region through which light propagates). Light propagation in the waveguide involves complex geometric and physical optics, and the phase abrupt change during propagation plays a decisive role in the waveguide's imaging quality. By controlling the optical path difference between the grating region and the blank region, the phase abrupt change at the boundary between them can be resolved, thereby significantly improving the MTF of the diffractive waveguide. Controlling the optical path difference (phase abrupt change) between the grating region and the blank region enhances the imaging quality of the diffractive waveguide.

[0042] In some embodiments of this application, the optical path difference between the light rays passing through the grating region and the blank region is 0, or is an integer multiple of the light wavelength. When the optical path of the light rays in the grating region and the blank region is equal, or the optical path difference is an integer multiple of the light wavelength, there is no phase abrupt change, and the imaging quality of the diffracted waveguide is optimal.

[0043] In some embodiments of this application, the grating structure of the grating region may include a one-dimensional grating, a two-dimensional grating, a double-sided one-dimensional grating, etc. The distribution of the grating region may include two-section, three-section, four-section, etc. The optical path of the grating region can be calculated using the equivalent refractive index. Calculating the optical path of the grating region using the equivalent refractive index method can greatly reduce the computational load.

[0044] In some embodiments of this application, the optical path of the blank area is calculated using the product of the refractive index of the medium and the path length of the light ray, and compared with the optical path of the grating area. Accurate calculation of the optical path between the grating area and the blank area provides a theoretical basis for adjusting the optical path difference between the grating area and the blank area in the diffractive waveguide.

[0045] In some embodiments of this application, the optical path difference between the grating region and the blank region is controlled by controlling the thickness of the residual dielectric layer in the grating region. This method is simple to implement and significantly improves the MTF (Mean Transmission Flow Rate).

[0046] In some embodiments of this application, the optical path difference between the grating region and the blank region is controlled by controlling the optical path length of light passing through the blank region. This method does not change the existing grating and architecture of the diffractive waveguide and is highly effective in improving the imaging quality of existing or previous products.

[0047] In some embodiments of this application, the optical path difference between the grating area and the blank area is controlled by reducing or increasing the substrate thickness of the blank area or increasing or decreasing the thickness of the medium on the substrate of the blank area.

[0048] In some embodiments of this application, the optical path difference between the grating region and the blank region is controlled by adding sub-nanometer structures or gradient materials to the blank region.

[0049] In some embodiments of this application, the imaging quality of the diffracted waveguide can be verified by calculating its Strehl Ratio or its MTF.

[0050] Figure 1 A schematic diagram of an optical waveguide according to an embodiment of this application is shown.

[0051] like Figure 1As shown, the optical waveguide 100 includes: an optical waveguide substrate 110, which includes a grating region 111 and a blank region 112; and a grating 120 located within the grating region 111. Light rays have a first optical path when passing through the grating region 111 and a second optical path when passing through the blank region 112. The optical path difference between the first and second optical paths is between 0.8 and 1.2 times the target optical path difference, which is zero or an integer multiple of the wavelength of the light. The optical path difference between the light rays passing through the grating region and the blank region is either close to zero or an integer multiple of the wavelength of the light. By controlling the optical path difference between the first and second optical paths in this way, the phase abrupt change when the light rays pass through the grating region and the blank region is significantly reduced or eliminated, thereby significantly improving the imaging quality of the optical waveguide and facilitating the further widespread use of near-eye display devices employing optical waveguide technology.

[0052] As an example, the optical path difference is equal to the target optical path difference. The inventors of this application have discovered that when the optical path difference between the first optical path and the second optical path is 0.8 to 1.2 times 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, achieving the optimal effect under the current conditions.

[0053] As an example, the second optical path is determined based on the refractive index of the optical waveguide substrate 110 and the height H112 of the blanking region 112. When calculating the optical path of the blanking region, the height of the blanking region can be used as an approximation of the actual path of the light ray, and the refractive index of the optical waveguide substrate can be used as the refractive index of the blanking region, since the blanking region is entirely composed of the material of the optical waveguide substrate. This significantly simplifies the calculation of the second optical path of the blanking region, thereby facilitating the determination of the manufacturing method and relevant dimensions of the optical waveguide to obtain the corresponding imaging effect.

[0054] As an example, the optical path difference is adjusted by adjusting the height H112 of the blank area 112. Since the blank area 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 area, while avoiding affecting the normal performance of the optical waveguide. There are various ways to adjust the height of the blank area, and the height of the blank area can be controlled by mature and low-cost methods (such as back etching, inkjet printing, etc.), which greatly simplifies the adjustment and setting of the optical path difference and improves the applicability of the technical solution of this application.

[0055] Figure 2 A schematic diagram of an optical waveguide according to an embodiment of this application is shown.

[0056] like 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 also includes a dielectric layer 230, which is located in the grating region 211 and below the grating 220. By setting a dielectric layer in the grating region of the optical waveguide, it is beneficial to facilitate the fabrication of the grating. When fabricating a grating, for example, by imprinting or etching, a dielectric layer is usually left in the grating region. This dielectric layer can be residual glue or etched material. By reserving this dielectric layer, the adjustment of the first optical path of the grating region is more convenient, thereby making it easier to adjust the optical path difference and improve the imaging quality.

[0057] As an example, the first optical path is the sum of the first sub-optical path of the light ray passing through the dielectric layer 230 and the second sub-optical path of the light ray passing through the grating 220. The first sub-optical path is determined based on the height H230 and refractive index of the dielectric layer 230, and the second sub-optical path is determined based on the height H220 and equivalent refractive index of the grating 220. The equivalent refractive index is a virtual refractive index value introduced in a specific optical structure or medium to facilitate analysis and calculation when a complex optical system or non-homogeneous medium is equivalent to a homogeneous medium with a single refractive index. It is an equivalent description of the optical properties of an actual optical system or medium, allowing for the use of methods similar to those used for homogeneous media when dealing with complex optical problems. Determining the optical path of the dielectric layer (the first sub-optical path) using its height and refractive index simplifies the calculation of the optical path of the dielectric layer. Similarly, calculating the optical path of the grating (the second sub-optical path) using its height and equivalent refractive index simplifies the calculation of the grating's optical path. In both calculation methods, the height of the corresponding structure is taken as the actual path traveled by the light, and the optical path is calculated based on the corresponding refractive index. This makes it easy to determine the optical path value, thereby facilitating the adjustment of the corresponding optical structure and adjusting the optical path difference as needed to improve the imaging quality.

[0058] As an example, the optical path difference can be adjusted by adjusting the height H230 of the dielectric layer 230, or by simultaneously adjusting the height H230 of the dielectric layer 230 and the height H212 of the blank area 212. Since both the dielectric layer and the grating are located within the grating region, and the grating's optical path is difficult to adjust due to its diffraction structure, the height of the dielectric layer can be adjusted to adjust the optical path of the grating region. By adjusting the height of the dielectric layer alone or simultaneously adjusting the heights of the dielectric layer and the blank area, the optical path difference can be adjusted in a relatively simple way, thereby achieving high imaging quality at a lower cost.

[0059] As an example, the equivalent refractive index of grating 220 includes its second-order equivalent refractive index. Extensive research and practical experience by the inventors of this application have demonstrated that the second-order equivalent refractive index of the grating can accurately simulate or represent its true refractive index, thus enabling the calculation of a relatively accurate optical path value. Therefore, by using the second-order equivalent refractive index of the grating to calculate its optical path, a more accurate first optical path of the grating region can be obtained, leading to a more accurate optical path difference. This allows for precise adjustment of the optical path difference to achieve good imaging quality.

[0060] As an example, the second-order equivalent refractive index of grating 220 includes the second-order equivalent refractive index of TE wave (Transverse Electric Field) and / or 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 subwavelength structure is a structure whose characteristic size is equivalent to or smaller than the wavelength). Therefore, when calculating its equivalent refractive index, the different behaviors and effects of TE and TM waves need to be considered. Calculating the second-order equivalent refractive index separately according to the calculation methods for TE and TM waves will yield different values, resulting in different results when calculating the optical path difference. To determine the final adjustment size, the performance improvement brought by the calculation results of TE and TM waves can be compared. For the light waves with a larger improvement in imaging performance, the size of the corresponding structure of the optical waveguide can be adjusted to obtain the optimal imaging effect.

[0061] Figure 3 A top view of an optical waveguide according to an embodiment of this application is shown.

[0062] like Figure 3 As shown, the optical waveguide 300 includes a transition grating region 310, a coupling grating region 320, and a blanking region 330. Although the optical waveguide adopts a three-partition form in this embodiment, in other embodiments, the optical waveguide can adopt other partition forms such as two-partition or four-partition. The optical waveguide may also include a coupling grating region, a homogenizing region, an energy recovery region, etc.

[0063] Figure 4 Showing according to Figure 3 A side view cross-sectional structural diagram of the optical waveguide in the embodiment.

[0064] like Figure 4 As shown, in the transition grating region 310, the grating has a height H1, and the dielectric layer has a height h1. In the coupling grating region 320, the grating has a height H2, and the dielectric layer has a height h2.

[0065] In this embodiment, it can be assumed that the relevant parameters adopt the following values. Of course, those skilled in the art should know that these values ​​are merely examples, used only to illustrate the calculation process, and should not be regarded as a limitation on the technical solution of this application.

[0066] The grating parameters of the transition grating region 310 are as follows: transition period P1 = 362.01 nm, height H1 = 30 nm, residual adhesive (dielectric layer) h1 = 100 nm, duty cycle f1 = 70%, and refractive index n1 = 1.9355.

[0067] The grating parameters for the coupling grating region 320 are as follows: coupling period P2 = 375 nm, height H2 = 48.7 nm, residual adhesive (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 transparent (or reflective) portion to the width of the entire period within one period of the diffraction grating. It is usually expressed as a percentage or decimal, with a value between 0 and 1. For example, a duty cycle of 0.5 for a diffraction grating means that in one complete period, the width of the transparent (or reflective) portion occupies half of the entire period width; if the duty cycle is 0.3, it means that the width of the transparent (or reflective) portion only occupies 30% of the period width, with the remaining 70% being opaque (or non-reflective). Duty cycle is a crucial parameter of diffraction gratings, significantly influencing the intensity distribution and diffraction efficiency of diffracted light. For instance, in designing diffraction gratings for spectral analysis, a suitable duty cycle can ensure high diffraction efficiency for specific wavelengths, thereby improving spectral resolution and measurement accuracy. In integrated optical devices such as optical waveguides, the duty cycle determines the coupling efficiency and transmission characteristics of light within the grating structure, thus affecting the device's performance.

[0068] Based on the above parameters, the Strell ratio and MTF of the diffracted waveguide before image quality improvement can be calculated. The Strell ratio calculation results in the X and Y directions are X: 0.38 and Y: 0.51, respectively. Specific results are as follows: Figure 5A and Figure 5B As shown. The calculated MTF (MTF = 50%) in the X and Y directions are X: 14.01 cycles / mm and Y: 16.02 cycles / mm, respectively. Specific results are as follows: Figure 6A and Figure 6B As shown.

[0069] In this embodiment, the Strell ratio refers to a key indicator in optics used to measure the imaging quality of an optical system. It is defined as the ratio of the maximum light intensity of an actual optical system at the image point to the maximum light intensity of an ideal, aberration-free optical system with the same aperture and wavelength at the corresponding image point. Physically, the Strell ratio intuitively reflects how close the actual optical system is to an ideal state. When the Strell ratio is 1, it means that the actual optical system has no aberrations, the imaging quality has reached its theoretical optimal state, and the light can be perfectly focused on the ideal image point. As the Strell ratio gradually decreases, it indicates that the aberrations of the actual optical system gradually increase, the imaging quality decreases, the light cannot be precisely focused on the ideal image point, but diffuses into the surrounding area, resulting in a blurred image and reduced contrast.

[0070] In this embodiment, based on Figure 4 Regarding the specific values ​​given in the description, the equivalent refractive index of the grating region can be calculated as follows.

[0071] The zeroth-order equivalent approximate refractive index of the grating structure can be calculated using the following two formulas:

[0072]

[0073] in, and These are the zero-order equivalent refractive indices of TE and TM waves, respectively, n i and n s These 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 zeroth-order equivalent approximate refractive index can refer to the equivalent refractive index when the zeroth-order diffracted light passes 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. The second-order equivalent refractive index can be calculated using the following two formulas:

[0075]

[0076] Where d is the grating period. and These are the second-order equivalent refractive indices for TE and TM waves, respectively. The second-order equivalent refractive index can refer to the equivalent refractive index when second-order diffracted light passes through the grating region.

[0077] Based on the above parameters and formulas, the equivalent refractive index of the transition 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 length of the transition grating region is: s1_TE=H1*n_TE=55.615nm, s1_TM=H1*n_TM=51.806nm.

[0079] The optical path length when the transition grating region contains residual adhesive (dielectric layer) is: s1_t_TE=s1_TE+h1*n1=249.16nm, s1_t_TM=s1_TM+h1*n1=245.36nm.

[0080] Based on the above parameters and formulas, the equivalent refractive index of the coupled grating region can be calculated as: n2_TE: 1.7394, n2_TM: 1.3874.

[0081] The optical path length of the coupled grating region is: s2_TE=H2*n2_TE=84.71nm, s2_TM=H2*n2_TM=67.566nm.

[0082] The optical path length when the coupled grating region contains residual adhesive (dielectric layer) is: s2_t_TE=s2_TE+h2*n2=278.26nm, s2_t_TM=s2_TM+h2*n2=261.12nm.

[0083] Figure 7 This diagram shows a side view cross-sectional structure of an optical waveguide according to an embodiment of the present application.

[0084] In this embodiment, the relevant parameters are adopted. Figure 3 The numerical values ​​in the embodiments are used to illustrate the calculation process. Those skilled in the art should understand that these values ​​are merely examples and should not be considered as limitations on the technical solutions of this application. To simplify the understanding of the technical solutions of this application, this embodiment will only provide the calculation method for a single wavelength and single angle TE wave. Those skilled in the art should understand that the calculation method for TM waves is the same as or similar to that for TE. To obtain the best imaging quality, the dielectric layer heights of the transition grating region and the coupling grating region can be calculated first in the case of TE waves; then, the dielectric layer heights of the transition grating region and the coupling grating region can be calculated in a similar manner to that described below. Simulation experiments can be conducted for both calculation results to determine which calculation result yields better imaging quality. For example, experimental results show that when using the calculation results for TE waves, the Strell ratio and MTF have larger values, so the dielectric layer height can be ultimately adjusted based on the calculation results for TE waves, instead of using the calculation results for TM waves. Alternatively, the appropriate calculation method can be selected based on whether the actual light source used is a TE wave or a TM wave.

[0085] In this embodiment, the optical path difference is adjusted only by adjusting the height of the dielectric layer in the grating region. In this embodiment, the optical path difference between the first optical path of the grating region (turning grating region 710 or coupling grating region 720) and the second optical path of the blank region 730 is set to one wavelength (wavelength = 528nm), and at this time the height of the blank region is 0 (therefore the optical path is 0), thereby eliminating the phase abrupt change when the light passes through the grating region and the blank region 730.

[0086] The dielectric layer height of the transition grating region 710 is calculated according to the following formula:

[0087] L1=(λ-s1_TE) / n1=(528nm-55.615nm) / 1.9355=244.06nm

[0088] The dielectric layer height of the coupling grating region 720 is calculated according to the following formula:

[0089] L2=(λ-s2_TE) / n2=(528nm-84.71nm) / 1.9355=229.03nm

[0090] After adjusting the height of the dielectric layer based on the above calculation results, the Strell ratio of the optical waveguide 700 in the X and Y directions is calculated to be X: 0.57 and Y: 0.6, respectively. Specific results are as follows: Figure 8A and Figure 8B As shown. The calculated MTF (MTF = 50%) in the X and Y directions are X: 20.02 cycles / mm and Y: 20.02 cycles / mm, respectively. Specific results are as follows: Figure 9A and Figure 9B As shown.

[0091] Figure 10 This diagram shows a side view cross-sectional structure of an optical waveguide according to an embodiment of the present application.

[0092] In this embodiment, the relevant parameters are adopted. Figure 3 The numerical values ​​in the examples are used to illustrate the calculation process. Those skilled in the art should understand that these numerical values ​​are merely examples and should not be considered as limiting the technical solutions of this application.

[0093] In this embodiment, the optical path difference is adjusted by simultaneously adjusting the height of the dielectric layer in the grating region and the height of the blank region 1030. In this embodiment, the turning grating region 1010, the coupling grating region 1020, and the blank region 1030 through which the light passes are set to have equal optical paths (closer optical paths can also improve the situation), so 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 length of the coupling grating region 1020 is L1 greater than that of the transition grating region 1010, where L1 is calculated according to the following formula:

[0095] L1=s2_TE-s1_TE=84.71nm-55.615nm=29.095nm

[0096] To ensure that the coupled grating region 1020 and the transition grating region 1010 have the same optical path, the residual adhesive thickness (dielectric layer height) of the coupled grating region 1020 needs to be reduced by L2, which is calculated according to the following formula:

[0097] L2=L1 / n1=29.095nm / 1.9355=15.03nm

[0098] When light passes through the blank area 1030, to maintain the same optical path as the transition grating area 1010, the required increase in optical path (assuming the initial height and optical path of the blank area 1030 are 0) is s1_t_TE = 249.16 nm. Since the refractive index of the optical waveguide substrate is n3 = 2.0149, the required increase in thickness of the blank area 1030 through which the light passes is L3, calculated according to the following formula:

[0099] L3 = s1_t_TE / n3 = 123.66nm

[0100] In this embodiment, after adjusting the height of the grating area and the height of the blank area simultaneously according to the above calculation results, the calculated Strell ratio of the optical waveguide 1000 in the X and Y directions is X: 0.63 and Y: 0.65, respectively. The specific results are as follows: Figure 11A and Figure 11B As shown. The calculated MTF (MTF = 50%) in the X and Y directions are X: 32.03 cycles / mm and Y: 38.04 cycles / mm, respectively. Specific results are as follows: Figure 12A and Figure 12B As shown.

[0101] As can be seen from this embodiment, the optical path difference between the grating region and the blank region in a diffractive waveguide has a significant impact on the imaging quality. The proposed method for adjusting the optical path difference in this application greatly improves the MTF of the diffractive waveguide, which will be of great benefit to the future promotion of diffractive waveguides to the consumer market.

[0102] The concepts, principles, and ideas of this application have been described in detail above with reference to specific embodiments (including examples and instances). Those skilled in the art should understand that the embodiments of this application are not limited to those given above. After reading this application, those skilled in the art can make any possible improvements, substitutions, and equivalents to the steps, methods, apparatus, and components in the above embodiments, and such improvements, substitutions, and equivalents should be considered to fall within the scope of this application. The scope of protection of this application is limited to the claims.

Claims

1. An optical waveguide, characterized in that, include: An optical waveguide substrate (110) includes a grating region (111) and a blank region (112); A grating (120) is located in the grating region (111); The light has a first optical path when it passes through the grating area (111), and a second optical path when it passes through the blank area (112). The optical path difference between the first optical path and the second optical path is between 0.8 and 1.2 times the target optical path difference, and the target optical path difference is zero or an integer multiple of the wavelength of the light.

2. The optical waveguide according to claim 1, characterized in that, The optical path difference is equal to the target optical path difference.

3. The optical waveguide according to claim 1, characterized in that, The second optical path is determined based on the refractive index of the optical waveguide substrate (110) and the height of the blank area (112).

4. The optical waveguide according to claim 3, characterized in that, The optical path difference is adjusted by adjusting the height of the blank area (112).

5. The optical waveguide according to claim 1, characterized in that, The optical waveguide also includes a dielectric layer (230), which is located in the grating region (111) and below the grating (120).

6. The optical waveguide according to claim 5, characterized in that, The first optical path is the sum of the first sub-optical path when the light passes through the dielectric layer (230) and the second sub-optical path when the light passes through the grating (120). The first sub-optical path is determined based on the height of the dielectric layer (230) and the refractive index of the dielectric layer (230), and the second sub-optical path is determined based on the height of the grating (120) and the equivalent refractive index of the grating (120).

7. The optical waveguide according to claim 6, characterized in that, The optical path difference can be adjusted by adjusting the height of the dielectric layer (230), or by simultaneously adjusting the height of the dielectric layer (230) and the height of the blank area (112).

8. The optical waveguide according to claim 6, characterized in that, The equivalent refractive index of the grating (120) includes the second-order equivalent refractive index of the grating (120).

9. The optical waveguide according to claim 8, characterized in that, The second-order equivalent refractive index of the grating (120) includes the second-order equivalent refractive index of TE waves and / or the second-order equivalent refractive index of TM waves.

10. An augmented reality display device, characterized in that, The optical waveguide includes any one of claims 1 to 9.

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