Optical waveguide and near-eye display module

Abstract

An optical waveguide (100) and a near-eye display module. The optical waveguide (100) comprises a waveguide substrate (101), and the waveguide substrate (101) is provided with two or more grating regions (102, 103, 104) having specific optical functions; grating structures (20) each composed of periodically distributed grating units (200) are provided in the grating regions (102, 103, 104); some or all of the grating units (200) comprise a first grating portion (201) and a second grating portion (202); the first grating portion (201) and the second grating portion (202) each comprise at least one grating layer (201i, 201j); and the first grating portion (201) and the second grating portion (202) have different equivalent refractive indexes.

Description

Optical waveguide and near-eye display module

[0001] The present application claims priority to the invention application with the application date of April 29, 2024, the application number of "202410527054.7", and the patent name of "Optical waveguide and near-eye display module", and priority to the utility model application with the application date of April 29, 2024, the application number of "202420925251.X", and the patent name of "Optical waveguide and near-eye display module", the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of display, in particular to an optical waveguide and a near-eye display module. BACKGROUND

[0003] At present, AR glasses develop towards light weight and color display, and usually adopt a scheme of using a light engine with three colors (RGB, i.e., red, green, and blue) of light to cooperate with a single optical waveguide (for monocular) to make the three colors of light transmit in a single optical waveguide.

[0004] However, for this scheme, as shown in FIG. 1, due to the inconsistent wavelengths of the three colors of light, the diffraction angles (such as the three angles of a, b, and g shown in FIG. 1) and diffraction efficiencies of the RGB light are different due to the influence of the grating structure in the optical waveguide, which will affect the display brightness uniformity, color uniformity, and other display effects, thereby seriously affecting the user's viewing experience. SUMMARY

[0005] Based on the above, the present application provides an optical waveguide and a near-eye display module to solve the problems existing in the existing optical waveguide.

[0006] Based on one aspect of the present application, an optical waveguide is provided, which comprises a waveguide substrate, and two or more grating regions with specific optical functions are arranged on the waveguide substrate.

[0007] The grating regions are provided with a grating structure composed of periodically distributed grating units, and part or all of the grating units comprise a first grating part and a second grating part, and the first grating part and the second grating part each include at least one grating layer.

[0008] The first grating part and the second grating part have different equivalent refractive indices.

[0009] Optionally, when the grating layer in the first grating part or the second grating part is more than one layer, the refractive indices of each grating layer are different.

[0010] Optionally, the material, refractive index and depth of the grating layers in the first grating section and the grating layers in the second grating section are the same.

[0011] Optionally, the grating layers with the same material, refractive index and depth are located at the same level between the first grating section and the second grating section.

[0012] Optionally, the grating layers with the same material, refractive index and depth are one, two or more layers in contact with and / or close to the waveguide substrate.

[0013] Optionally, the material of the grating layers in the first grating section and the second grating section includes one or more fluorides with a refractive index in the range of 1.4-1.6.

[0014] Optionally, the material of the grating layers in the first grating section and the second grating section includes one or more oxides with a refractive index in the range of 1.5-2.5.

[0015] Optionally, the material of the grating layers in the first grating section and the second grating section includes one or more compounds with a refractive index greater than 2.

[0016] Optionally, the material of the grating layers in the first grating section and the second grating section includes a composite material obtained by doping or the like based on the aforementioned compound.

[0017] Optionally, the material of a specific grating layer in the first grating section or the second grating section includes an exit space medium.

[0018] Optionally, the depth of the first grating section in the third direction is greater than or equal to the depth of the second grating section in the third direction.

[0019] Optionally, the topography of the grating layers in the first grating section is the same as the topography of the grating layers in the second grating section.

[0020] Optionally, the topography formed by the stacking of the grating layers in the first grating section is the same as the topography formed by the stacking of the grating layers in the second grating section.

[0021] Optionally, the depth of the grating layers in the first grating section is the same; the depth of the grating layers in the second grating section is the same.

[0022] Based on another aspect of the present application, the embodiment of the present application provides a near-eye display module, comprising an image projection device and the aforementioned optical waveguide, the image projection device is used to generate image light and project the image light to a corresponding grating area of the optical waveguide, and the image light is output through the corresponding grating area after being transmitted through the optical waveguide.

[0023] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be achieved and obtained by means of the structures and / or processes particularly pointed out in the description, claims and accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0024] Other features, objects and advantages of the present application will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0025] Fig. 1 is a schematic diagram of RGB light propagating in a waveguide;

[0026] Fig. 2a is a schematic diagram of a waveguide structure provided by an embodiment of the present application;

[0027] Fig. 2b is a schematic diagram of a grating structure provided by an embodiment of the present application;

[0028] Fig. 2c is a schematic diagram of a grating unit structure provided by an embodiment of the present application;

[0029] Fig. 3a is a schematic diagram of a grating unit 300 provided by an embodiment of the present application;

[0030] Fig. 3b is a schematic diagram of data curves related to diffraction efficiency of the grating unit 300 in Fig. 3a;

[0031] Fig. 3c is a schematic diagram of propagation of TE and TM polarized light provided by an embodiment of the present application;

[0032] Fig. 4a is a schematic diagram of a grating unit 400 provided by an embodiment of the present application;

[0033] Fig. 4b is a schematic diagram of data curves related to diffraction efficiency of the grating unit 400 in Fig. 4a;

[0034] Fig. 5a is a schematic diagram of a grating unit 500 provided by an embodiment of the present application;

[0035] Fig. 5b is a schematic diagram of data curves related to diffraction efficiency of the grating unit 500 in Fig. 5a;

[0036] Fig. 6a is a schematic diagram of a grating unit 600 provided by an embodiment of the present application;

[0037] FIG. 6b is a data curve diagram related to diffraction efficiency of the grating unit 600 in FIG. 6a;

[0038] FIG. 7a is a structural diagram of a grating unit 700 according to an embodiment of the present application;

[0039] FIG. 7b is a diagram of a variant of the grating unit 700;

[0040] FIG. 8a is a structural diagram of a grating unit 800 according to an embodiment of the present application;

[0041] FIG. 8b is a diagram of a variant of the grating unit 800;

[0042] FIG. 9a is a structural diagram of a grating unit 900 according to an embodiment of the present application;

[0043] FIG. 9b is a diagram of a variant of the grating unit 900. DETAILED DESCRIPTION

[0044] The present application will be further described below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and are not a limitation on the application. In addition, it should be noted that, for the convenience of description, only the parts related to the application are shown in the drawings.

[0045] In the embodiments of the present application, the light engine (also referred to as an image projection device in the present application) can be composed of at least one display technology, device suitable for the field of AR glasses, such as LCOS, MicroLED, MicroOLED, Micro-Electro-Mechanical Systems (MEMS) scanning mirror, Fiber Scanner, etc., and can generally emit light of RGB three colors (i.e., corresponding to three wavelengths). Since the diffraction angles and diffraction efficiencies of light of RGB three wavelengths after the grating are different, in order to maximize the uniformity of brightness and color of the image formed by light of three wavelengths after the grating, the present application provides a light waveguide with a corresponding grating structure.

[0046] Referring to FIG. 2a, a light waveguide 100 according to an embodiment of the present application includes a waveguide substrate 101 and a grating region with specific optical functions disposed on the waveguide substrate 101. The grating region further includes a coupling-in region 102, a relay region 103 and a coupling-out region 104.

[0047] The grating structure is arranged in the coupling-in region 102, the relay region 103 and the coupling-out region 104, and can be implemented by processes such as embossing, coating, etching, etc., which are not limited herein. In the subsequent description of the present application, the grating structure arranged in the coupling-in region 102 can be referred to as a coupling-in grating; the grating structure arranged in the relay region 103 can be referred to as a relay grating; and the grating structure arranged in the coupling-out region 104 can be referred to as a coupling-out grating.

[0048] The light rays can be coupled into the waveguide substrate 101 through the coupling-in region 102 and transmitted therein, the relay region 103 receives the light rays transmitted by the coupling-in region 102, expands and deflects the light rays to the coupling-out region 104; and the coupling-out region 104 receives the light rays deflected by the relay region 103 and couples the light rays out of the waveguide substrate 101.

[0049] Of course, the profiles, relative positions of the coupling-in region 102, the relay region 103 and the coupling-out region 104 shown in FIG. 2a are exemplary, and can be changed in actual applications, for example, the coupling-in region 102 can not be a square profile as shown in FIG. 2a, but can be a circular profile, a trapezoidal profile, etc.; and the relay region 103 can be located below the coupling-out region 104. Therefore, the structure of the waveguide 100 shown in FIG. 2a should not be understood as a limitation of the present application.

[0050] It should be noted that in the drawings of the present application, an xyz coordinate system is shown, and for the convenience of description, in the embodiments of the present application, the direction parallel to the y-axis can also be referred to as a first direction, a vertical direction or a longitudinal direction; the direction parallel to the x-axis can also be referred to as a second direction, a horizontal direction or a transverse direction; the direction perpendicular to the xy plane can be considered as the z-axis direction; and the direction parallel to the z-axis can also be referred to as a third direction or a depth direction. The coordinate system is also used in other views or embodiments of the present application, and the corresponding direction names are also applicable throughout the description.

[0051] Referring to FIGS. 2b-2c, a grating structure 20 in an embodiment of the present application has a cross-section in the xz plane as shown in FIG. 2b, and includes a plurality of periodically distributed grating units 200. The specific structure of the grating unit 200 is shown in FIG. 2c, which includes a first grating portion 201 and a second grating portion 202. The first grating portion 201 further includes rectangular grating layers 201i (i = 1, 2,...), where i is at least equal to 1, i.e., the first grating portion 201 has at least one grating layer; the second grating portion 202 further includes rectangular grating layers 202j (j = 1, 2,...), where j is at least equal to 1, i.e., the second grating portion 202 has at least one grating layer. In some embodiments, the grating layers 201i can be respectively composed of different materials and have different refractive indexes. The grating layers 202j can also be composed of different materials and have different refractive indexes. In other embodiments, for the first grating portion 201, some or all of the grating layers 201i are composed of the same material; for the second grating portion 202, some or all of the grating layers 202j are composed of the same material.

[0052] In addition, in some embodiments, some of the grating layers 201i in the first grating portion 201 and some of the grating layers 202j in the second grating portion 202 are composed of the same material and have the same refractive index, and the depths (i.e., the thicknesses of the grating layers in the z-axis direction) of these grating layers which have the same material and the same refractive index are also the same. It should be noted that the grating layers which have the same material, the same refractive index and the same depth in the first grating portion 201 and the second grating portion 202 are located at the same level between the first grating portion 201 and the second grating portion 202, and are usually one, two or more layers in contact with and / or close to the waveguide substrate 101.

[0053] In some embodiments, the refractive indexes of the grating layers 201i can be partially the same or all the same. Similarly, the refractive indexes of the grating layers 202j can also be partially the same or all the same. It should be noted that in the embodiments of the present application, the equivalent refractive index of the first grating portion 201 and the equivalent refractive index of the second grating portion 202 are different, regardless of whether the refractive indexes of the grating layers of the first grating portion 201 and the second grating portion 202 are the same or different.

[0054] By configuring the grating layer structure and the refractive indexes corresponding to the grating layers, the grating structure in the embodiments of the present application can flexibly control the modulation characteristics of the grating for different wavelengths of incident light.

[0055] In the embodiments of the present application, the material of part or all of the grating layers 201i in the first grating part 201 and part or all of the grating layers 202j in the second grating part 202 can include one or more fluorides with a refractive index in the range of 1.4-1.6, such as cerium fluoride (CeF3), ytterbium fluoride (YbF3), yttrium fluoride (YF3), aluminum fluoride (AlF3), barium fluoride (BaF2), calcium fluoride (CaF2), magnesium fluoride (MgF2), etc.

[0056] Optionally, the material of part or all of the grating layers 201i and the grating layers 202j can also include one or more oxides with a refractive index in the range of 1.5-2.5, such as niobium oxide (Nb2O5), titanium oxide (TiO, TiO2, Ti2O3, Ti3O5), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), cerium oxide (CeO2), yttrium oxide (Y2O3), hafnium oxide (HfO2), magnesium oxide (MgO), aluminum oxide (Al2O3), indium tin oxide (ITO), silicon dioxide (SiO2), zinc oxide (ZnO), etc.

[0057] Optionally, the material of part or all of the grating layers 201i and the grating layers 202j can also include one or more compound classes with a refractive index greater than 2, such as silicon carbide (SiC), strontium titanate (STO), zinc sulfide (ZnS), silicon nitride (Si3N4), lithium niobate (LiNbO3), etc.

[0058] Optionally, the material of part or all of the grating layers 201i and the grating layers 202j can also include composite materials obtained based on the aforementioned compounds through processes such as doping, etc.

[0059] Optionally, the material of a specific grating layer among the grating layers 201i or 202j can also include an exit space medium, such as air or the material used by the waveguide substrate 101, etc.

[0060] In addition to the differences between the aforementioned materials and refractive indices, in the embodiments of the present application, the first grating part 201 and the second grating part 202 can also have differences in structure, topography, etc. Specifically, the depth of the first grating part 201 in the Z-axis direction is greater than or equal to the depth of the second grating part 202 in the Z-axis direction.

[0061] Optionally, in the embodiments of the present application, the topography of the grating layers of the first grating part 201 is different from the topography of the grating layers of the second grating part 202.

[0062] Based on the material, refractive index, structure, etc. of the grating layers, the degree of freedom of grating regulation can be increased, which is more conducive to the modulation of light rays of different wavelengths.

[0063] Further, the first grating part 201 and the second grating part 202 can be used to balance the diffraction efficiency of light of different wavelengths. Different materials have different characteristics in the visible light range, and the refractive index of the material for the wavelengths of RGB light is respectively n R , n G , n B . For some materials, such as magnesium fluoride (MgF2), aluminum oxide (Al2O3), the corresponding n R , n G , n B difference is small; and for some materials, such as indium tin oxide (ITO), zinc sulfide (ZnS), the corresponding n R , n G , n B difference is large. By using the difference of n R , n G , n B , the difference in diffraction efficiency of RGB light can be adjusted to some extent, so as to adjust the color uniformity of the system. The inventors of the present application found that when the refractive index difference of n R , n G , n B corresponding to the material used by the grating structure is less than 0.5, the modulation difference of light of different wavelengths can be maximized. Taking red (R) light with the largest diffraction angle and blue (B) light with the smallest diffraction angle as an example, a material group with a red light equivalent refractive index difference greater than a blue light equivalent refractive index difference is selected, that is, n eff1 (R)-n eff2 (R) neff1 (B)-n eff2 (B), wherein n eff1 (R) represents the equivalent refractive index of the first grating part 201 under red light; n eff2 (R) represents the equivalent refractive index of the second grating part 202 under red light; neff1 (B) represents the equivalent refractive index of the first grating part 201 under blue light; n eff2 (B) represents the equivalent refractive index of the second grating part 202 under blue light. Thus, the grating structure has stronger regulation on the efficiency of red light. Due to the limitations of materials and processes, it is difficult to achieve this in actual production, and therefore, the layered structure of the first grating part 201 and the second grating part 202 in the present application can make up for this defect, so that the equivalent refractive index of the first grating part 201 and the second grating part 202 is close.

[0064] To further clearly illustrate the scheme of the present application, the following will be described with a plurality of specific examples.

[0065] Referring to FIG. 3a, a grating unit 300 is shown, which includes a first grating part 301 and a second grating part 302. In this example, the first grating part 301 includes three grating layers 3011-3013; and the second grating part 302 includes three grating layers 3021-3023.

[0066] The grating layers 3011-3013 are respectively made of different materials, and the refractive indexes are respectively denoted as n 311 , n 312 and n 313 . The depths of the grating layers 3011-3013 are respectively denoted as t 311 , t 312 and t 313 . The ranges of t 311 , t 312 and t 313 may be 20-400nm.

[0067] The grating layers 3021-3023 are also respectively made of different materials, and the refractive indexes are respectively denoted as n 321 , n 322 and n 323 . The depths of the grating layers 3021-3023 are respectively denoted as t 321 , t 322 and t 323 . The ranges of t 321 , t 322 and t 323 may be 20-400nm.

[0068] The period P of the grating unit 300 ranges from 200nm to 500nm. The range of the refractive index boundary coefficient r n is from 0 to 1.

[0069] In this example, the grating layer 3013 in the first grating part 301 and the grating layer 3023 in the second grating part 302 are made of the same material, have the same refractive index (i.e., n 313 =n 323 ), are located at the lowermost layers of the grating parts and have the same depth (i.e., t 313 =t 323 ). Such a structure can balance the diffraction efficiency of different propagation angles.

[0070] According to the above parameters, the objective function f m can be parameter-optimized, and the objective function f m includes multiple objectives such as grating out-coupling diffraction efficiency and RGB three-color ratio, and the local optimal solution of the parameters corresponding to each objective of the grating structure can be obtained.

[0071] Further, referring to Table 1 and FIG. 3b, Table 1 shows the parameter setting values of the grating pattern.

[0072] Table 1

[0073] FIG. 3b respectively shows the RGB coupling-out diffraction efficiency of the two types of grating structures under multi-view field and the corresponding B / R ratio and B / G ratio Based on FIG. 3b, it can be seen that the grating design of the present scheme reduces the B / R ratio and B / G ratio, thereby effectively improving the color uniformity.

[0074] Referring to FIG. 3c, in the propagation process of the light, the oblique incident light has two polarization states of TE and TM, and only the TM polarized light will be affected by the equivalent refractive index n z perpendicular to the grating layer when obliquely incident, and therefore, the diffraction efficiency of each propagation angle light can be controlled by adjusting the material and thickness of the same grating layer between the first grating part 301 and the second grating part 302.

[0075] It should be noted here that the equivalent refractive index of the structure parallel to the grating layer and the structure perpendicular to the grating layer can be respectively represented as:

[0076] and

[0077] wherein n x is the equivalent refractive index parallel to the x-axis direction of the grating layer;

[0078] n y is the equivalent refractive index parallel to the y-axis direction of the grating layer;

[0079] n z is the equivalent refractive index perpendicular to the grating layer;

[0080] N is the total number of grating layers;

[0081] t is the total depth of the grating layer;

[0082] t i is the depth of the i-th grating layer (i = 1, 2, …);

[0083] f i is the ratio of the depth of the i-th grating layer to the total depth t (i = 1, 2, …);

[0084] n i is the refractive index of the i-th grating layer (i = 1, 2, …).

[0085] If there are two or more grating layers between the first grating part 301 and the second grating part 302, in the embodiment, the refractive index difference of the grating layers is preferably less than 0.8.

[0086] Referring to FIG. 4a, a grating unit 400 is shown, which includes a first grating part 401 and a second grating part 402. In this example, the first grating part 401 includes two grating layers 4011 and 4012; and the second grating part 402 includes two grating layers 4021 and 4022.

[0087] The grating layers 4011 and 4012 are respectively made of different materials, and the refractive indexes are respectively denoted as n 411 and n 412 . The depths of the grating layers 4011 and 4012 are respectively denoted as t 411 and t 412 .

[0088] The grating layers 4021 and 4022 are respectively made of different materials, and the refractive indexes are respectively denoted as n 421 and n 422 . The depths of the grating layers 4021 and 4022 are respectively denoted as t 421 and t 422 . It should be noted that in this example, the material of the grating layer 4021 is an exit space medium (e.g., air), and thus is represented by a dashed line in FIG. 4a. This representation is also applicable to subsequent embodiments, which will not be described in detail hereinafter.

[0089] In this example, the depths of the grating layers 4011, 4012 and 4022 are respectively denoted as t 411 , t 412 and t 422 , which can range from 20 to 400 nm. The refractive index boundary coefficient r n between the first grating part 401 and the second grating part 402 can range from 0 to 1. The period P of the grating unit 400 can range from 200 to 500 nm.

[0090] According to the above parameters, the objective function f m can be optimized, and the objective function f m includes multiple objectives such as grating coupling-out diffraction efficiency and RGB color ratio, and the local optimal solution of the parameters corresponding to each objective of the grating structure can be obtained.

[0091] Further, referring to Table 2 and FIG. 4b, a basic rectangular grating is used for comparison, and Table 2 shows the parameter setting values of the grating pattern.

[0092] Table 2

[0093] Figure 4b shows the RGB coupling-out diffraction efficiency of the two types of optimized grating structures under multi-viewing angles, respectively and the corresponding B / R ratio and the B / G ratio Based on Figure 4b, it can be seen that the grating design of the present scheme reduces the B / R ratio by improving the red light efficiency, thereby improving the color uniformity.

[0094] It should be noted that when the material of a specific grating layer (e.g., grating layer 4021) in the grating portion is the exit medium, the difference in refractive index between the material and other materials can be large, which can cause the difference between the equivalent refractive index n z and n x to be large, and when the grating portion does not contain the grating layer of the exit medium material, the difference between the equivalent refractive index n z and n x is small, which makes the difference in diffraction efficiency of the high-order light of TE and TM large. To ensure good imaging effect, the equivalent refractive index n z and n x of the second grating portion satisfy the following relationship:

[0095] In addition, n′ x = kn o , and calculation can obtain

[0096] where n′ x is the equivalent refractive index in the x-axis direction parallel to other grating layers when the exit medium is not contained;

[0097] n′ y is the equivalent refractive index in the y-axis direction parallel to other grating layers when the exit medium is not contained;

[0098] n′ z is the equivalent refractive index perpendicular to other grating layers when the exit medium is not contained;

[0099] n x is the equivalent refractive index in the x-axis direction parallel to the grating layer when the exit medium is contained;

[0100] n y is the equivalent refractive index in the y-axis direction parallel to the grating layer when the exit medium is contained;

[0101] n z is the equivalent refractive index perpendicular to the grating layer when the exit medium is contained;

[0102] N is the total number of grating layers;

[0103] t is the total depth of the grating layers;

[0104] f1 is the ratio of the depth of the exit medium layer to the total depth t;

[0105] n1、n o The refractive index of the exit medium layer;

[0106] f i It is the ratio of the depth of the i-th layer to the total depth t (i = 1, 2, ...);

[0107] n i Let be the refractive index of the i-th layer (i = 1, 2, ...);

[0108] k is the equivalent refractive index n′ x With air layer refractive index n o ratio

[0109] In Figure 4b, the equivalent refractive index n of the second grating section z 'and n x The ratio of ' is approximately 0.82, which meets the above conditions.

[0110] Referring to FIG5a, a grating unit 500 is shown, including a first grating portion 501 and a second grating portion 502. In this example, the first grating portion 501 includes two grating layers 5011 and 5012; the second grating portion 502 includes three grating layers 5021 to 5023.

[0111] Grating layers 5011 and 5012 are made of different materials, with refractive indices denoted as n. 511 and n 512 The depths of grating layers 5011 and 5012 are denoted as t, respectively. 511 and t 512 . t 511 and t 512 The range can be 20-400nm.

[0112] Grating layers 5021 to 5023 are made of different materials, and their refractive indices are denoted as n. 521 n 522 and n 523 The depths of grating layers 5011 to 5013 are denoted as t. 511 t 522 and t 523 . t 511 t 522 and t 523 The range can be 20-400nm.

[0113] The period P of the grating unit 500 ranges from 200 to 500 nm. The refractive index boundary coefficient ranges from r to r. n It is 0-1.

[0114] In this example, the grating layer 5012 in the first grating section 501 and the grating layer 5023 in the second grating section 502 are made of the same material and have the same refractive index (i.e., n). 512 =n 523 All of them are located at the bottom layer of the grating section and have the same depth (i.e., t). 512 =t 523 Furthermore, the material of the grating layer 5021 is the outgoing space medium (e.g., air).

[0115] Based on the above parameters, the objective function f can be... m Perform parameter optimization, objective function f m By considering multiple targets, such as grating coupling diffraction efficiency and RGB three-color ratio, local optimal solutions for the parameters corresponding to each target of the grating structure can be obtained.

[0116] Furthermore, referring to Table 3 and Figure 5b, a comparison is made using a basic rectangular grating. Table 3 shows the parameter settings for each grating pattern.

[0117] Table 3

[0118] Figure 5b shows the RGB coupling diffraction efficiencies of the two optimized grating structures under multi-field conditions. and the corresponding B / R ratio B / G ratio As shown in Figure 5b, the grating design in this scheme reduces the B / R ratio and B / G ratio by improving the efficiency of green and red light, thereby significantly improving color uniformity.

[0119] Referring to FIG6a, a grating unit 600 is shown, including a first grating portion 601 and a second grating portion 602. In this example, the first grating portion 601 includes three grating layers 6011 to 6013; the second grating portion 602 includes three grating layers 6021 to 6023.

[0120] Grating layers 6011 to 6013 are composed of different materials, and their refractive indices are denoted as n. 611 n 612 and n 613 The depths of grating layers 6011 to 6013 are denoted as t. 611 t 612 and t 613 . t 611 ~t 613 The range can be 20-400nm.

[0121] Grating layers 6021 to 6023 are composed of different materials, and their refractive indices are denoted as n. 621 n 622 and n623 The depths of the grating layers 6021-6023 are respectively denoted as t 621 , t 622 , and t 623 . The ranges of t 621 , t 622 , and t 623 may be 20-400 nm.

[0122] In the present example, the grating layer 6013 in the first grating part 601 and the grating layer 6023 in the second grating part 602 adopt the same material, have the same refractive index (i.e., n 613 = n 623 ), are located at the lowermost layers of the grating parts, and have the same depth (i.e., t 613 = t 623 ). Moreover, the material of the grating layer 6021 is an exit space medium (e.g., air).

[0123] According to the above parameters, the objective function f m may be parameter-optimized, and the objective function f m includes multiple objectives such as grating out-coupling diffraction efficiency and RGB three-color ratio, and a local optimal solution of the parameters corresponding to each objective of the grating structure can be obtained.

[0124] Further, referring to Table 4 and FIG. 6b, the parameter setting values of the grating pattern are shown in Table 4.

[0125] Table 4

[0126] FIG. 6b respectively shows the RGB out-coupling diffraction efficiency , the corresponding B / R ratio , and the B / G ratio Based on FIG. 5b, it can be seen that the grating design of the present scheme reduces the B / R ratio and the B / G ratio by improving the green light and red light efficiency, thereby greatly improving the color uniformity.

[0127] In addition, in other embodiments of the present application, the grating layers in the grating unit may also have different forms.

[0128] Referring to FIG. 7a, a grating unit 700 is shown, which includes a first grating part 701 and a second grating part 702. The first grating part 701 includes four grating layers 7011-7014. The sizes of the grating layers 7011-7013 in the first direction gradually increase, forming a “triangular” stacking morphology. The morphology of the grating layer 7014 is rectangular.

[0129] The second grating part 702 includes 3 grating layers 7021-7023, and is divided into two parts, so that the grating layers 7021-7023 are distributed on both sides of the "triangular" stack topography formed by the grating layers 7011-7013, that is, the grating layers 7021-7023 form two "inverted triangular" shapes on both sides of the grating layers 7011-7013 of the "triangle", so that the grating unit 700 as a whole presents a rectangular shape.

[0130] Other deformation structures of the grating unit 700 are shown in FIG. 7b, which will not be described here.

[0131] Referring to FIG. 8a, a grating unit 800 is shown, which includes a first grating part 801 and a second grating part 802. The first grating part 801 includes 4 grating layers 8011-8014. The grating layers 8011-8013 gradually increase in size in the first direction, forming a "trapezoidal" stack topography. The grating layer 8014 has a rectangular shape.

[0132] The second grating part 802 includes 3 grating layers 8021-8023, and is also divided into two parts, so that the grating layers 8021-8023 are distributed on both sides of the "trapezoidal" stack topography formed by the grating layers 8011-8013, that is, the grating layers 8021-8023 form two "inverted triangular" shapes on both sides of the grating layers 8011-8013 of the "trapezoid", so that the grating unit 800 as a whole presents a rectangular shape.

[0133] Other deformation structures of the grating unit 800 are shown in FIG. 8b, which will not be described here.

[0134] Referring to FIG. 9a, a grating unit 900 is shown, which includes a first grating part 901 and a second grating part 902. The first grating part 901 includes 4 grating layers 9011-9014. The grating layers 9011-9013 gradually increase in size in the first direction, forming a "parallelogram" stack topography. The grating layer 9014 has a rectangular shape.

[0135] The second grating part 902 includes 3 grating layers 9021-9023, and is also divided into two parts, so that the grating layers 9021-9023 are distributed on both sides of the "parallelogram" stack topography formed by the grating layers 9011-9013, that is, the grating layers 9021-9023 form an "inverted triangular" shape and a "trapezoidal" shape on both sides of the grating layers 9011-9013 of the "parallelogram", so that the grating unit 900 as a whole presents a rectangular shape.

[0136] Other deformation structures of the grating unit 900 are shown in FIG. 9b, which will not be described here.

[0137] In some embodiments, the partial grating structures can be located in different planes, for example, in the grating region, the protruding degree of the grating structures along the positive direction of the X axis gradually increases from left to right, so that the grating structures are located in different planes. Of course, this should not be understood as a limitation of the present application.

[0138] For the optical waveguide in the foregoing embodiments, the grating structures are arranged on the surface of the grating region of the waveguide; and in another implementation, the grating region is located in the optical waveguide instead of on the surface, and accordingly, the foregoing grating structures are arranged in the optical waveguide.

[0139] Optionally, the topography of some or all of the grating layers 201i in the first grating part 201 is the same as the topography of some or all of the grating layers 201j in the second grating part 202. Of course, in some other embodiments of the present application, the topography of some grating layers in the first grating part 201 can be different from the topography of some grating layers in the second grating part 202.

[0140] Optionally, the topography formed by the stacking of some or all of the grating layers 201i in the first grating part 201 can be the same as the topography formed by the stacking of some or all of the grating layers 201j in the second grating part 202. Of course, in some other embodiments of the present application, the topography formed by the stacking of some or all of the grating layers 201i in the first grating part 201 can be different from the topography formed by the stacking of some or all of the grating layers 201j in the second grating part 202 (for example, refer to FIGS. 7a-9b).

[0141] Further, the layered structure adopted by the first grating part 201 and the second grating part 202 can be used to balance the diffraction efficiency of light of different wavelengths, thereby facilitating the adjustment of the color uniformity of the system.

[0142] Based on the optical waveguide described above, the present application further provides a near-eye display module, which can be applied to AR glasses. The near-eye display module comprises an image projection device and the foregoing optical waveguide. The image projection device is used to generate image light and project the image light onto the corresponding grating region (for example, the coupling-in region) of the optical waveguide, so that the image light can be transmitted in the waveguide and coupled out through the corresponding grating region (for example, the coupling-out region).

[0143] The expressions “first”, “second”, “the first” or “the second” used in various embodiments of the present disclosure can modify various components regardless of order and / or importance, but these expressions do not limit the corresponding components. The above expressions are only configured for the purpose of distinguishing elements from other elements.

[0144] The above description is only the preferred embodiment of the present application and the explanation of the technical principles. It should be understood by those skilled in the art that the scope of the protection of the present application is not limited to the technical solutions formed by the specific combinations of the above technical features. It should also cover other technical solutions formed by the combinations of the above technical features or their equivalent features without departing from the concept of the present application. For example, the technical solutions formed by the mutual replacement of the above features and the technical features with similar functions disclosed (but not limited to) in the present application.

Claims

1. An optical waveguide, characterized by, The optical waveguide comprises a waveguide substrate, and two or more grating regions with specific optical functions are arranged on the waveguide substrate; The grating regions are provided with a grating structure composed of periodically distributed grating units; part or all of the grating units comprise a first grating part and a second grating part, and the first grating part and the second grating part each include at least one grating layer; The first grating part and the second grating part have different equivalent refractive indices.

2. The optical waveguide of claim 1, wherein, When the grating layer included in the first grating part or the second grating part is more than one layer, the refractive indices of the grating layers are different.

3. The optical waveguide of claim 1, wherein, The materials, refractive indices and depths of part of the grating layers in the first grating part and part of the grating layers in the second grating part are the same.

4. The optical waveguide of claim 3, wherein, The grating layers with the same materials, refractive indices and depths are located at the same level between the first grating part and the second grating part.

5. The optical waveguide of claim 3, wherein, The materials of part or all of the grating layers in the first grating part and the second grating part include one or more fluorides with refractive indices in the range of 1.4-1.

6.

6. The optical waveguide of claim 1, wherein, The materials of part or all of the grating layers in the first grating part and the second grating part include one or more oxides with refractive indices in the range of 1.5-2.

5.

7. The optical waveguide of claim 1, wherein, The materials of part or all of the grating layers in the first grating part and the second grating part include one or more compounds with refractive indices greater than 2.

8. The optical waveguide of any one of claims 5-7, wherein, The materials of part or all of the grating layers in the first grating part and the second grating part include composite materials obtained based on the compounds in claims 5-7.

9. The optical waveguide of claim 1, wherein, The material of a specific grating layer in the first grating part or the second grating part includes an exit space medium.

10. The optical waveguide of claim 3, wherein, The grating layers with the same materials, refractive indices and depths are one, two or more layers in contact with and / or close to the waveguide substrate.

11. The optical waveguide of claim 1, wherein, The depth of the first grating part in the third direction is greater than or equal to the depth of the second grating part in the third direction.

12. The optical waveguide of claim 1, wherein, The topography of part or all of the grating layers in the first grating part is the same as the topography of part or all of the grating layers in the second grating part.

13. The optical waveguide of claim 12, wherein, The topography formed by the stacking of part or all of the grating layers in the first grating part is the same as the topography formed by the stacking of part or all of the grating layers in the second grating part.

14. The optical waveguide of claim 1, wherein, The depths of part or all of the grating layers in the first grating part are the same. The depths of part or all of the grating layers in the second grating part are the same.

15. A near-eye display module, comprising: The image projection device is used to generate image light and project it onto the corresponding grating region of the optical waveguide, and the image light is output through the corresponding grating region after being transmitted through the optical waveguide.

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