Optical waveguide and near-to-eye display module

Abstract

The utility model discloses an optical waveguide and a near-to-eye display module, and the optical waveguide comprises a plurality of grating units which are arranged in the light propagation direction and are distributed periodically, a grating wire groove is formed between every two adjacent grating units, and each grating unit at least comprises a first grating part and a second grating part which are sequentially arranged in the light propagation direction. The refractive index of the first grating part is not larger than that of the second grating part.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of display, in particular to a light waveguide and a near-eye display module. BACKGROUND

[0002] In the augmented reality (AR) technology, a surface relief grating (SRG) can be used to adjust the diffraction angle and diffraction efficiency of light. Generally, one-dimensional gratings include rectangular gratings, blazed gratings, tilted gratings, trapezoidal gratings, and stepped gratings. The diffraction efficiency of the gratings can be adjusted by adjusting parameters such as the duty cycle, the tilt angle, and the side length.

[0003] AR glasses face problems such as light leakage, rainbow, and grating appearance. The light leakage phenomenon refers to the fact that when light in the light waveguide is coupled out to the eye observation side through the grating, part of the diffracted light is also coupled out to the external environment side, and the image content can be seen from the external environment side, which may cause privacy leakage and other problems. The rainbow phenomenon refers to the fact that when ambient light from the external environment side (relative to the eye observation side) passes through the grating region of the light waveguide, the exit diffraction angles of different wavelengths of ambient light are different, resulting in the phenomenon that the colors are independent and connected like a rainbow when observed by the human eye. The rainbow phenomenon causes a layer of rainbow stripes to be superimposed on part of the user's field of view, affecting the final display effect of the AR device. The grating appearance refers to the fact that the grating region is displayed prominently relative to the entire light waveguide, affecting the appearance of the product. CONTENT OF THE UTILITY MODEL

[0004] Based on the above, the purpose of the present application is to provide a light waveguide and a near-eye display module to adjust the adjustable degrees of freedom of the grating structure, reduce the light leakage ratio, and improve the rainbow.

[0005] The present application provides a light waveguide, which is provided with a plurality of periodically distributed grating units along the light propagation direction, and has a grating line groove between adjacent two grating units. Each grating unit comprises a first grating part and a second grating part arranged in sequence along the light propagation direction, and the refractive index of the first grating part is not greater than that of the second grating part.

[0006] Further, in the preferred embodiment of the present application, the ratio of the refractive index of the second grating part to the refractive index of the first grating part is in the range of 1-3.

[0007] Further, in the preferred embodiment of the present application, the ratio of the refractive index of the second grating part to the refractive index of the first grating part is in the range of 1.4-3.

[0008] Further, in the preferred embodiment of the present application, each of the grating units comprises a first grating part, a second grating part and a third grating part arranged in sequence along the light propagation direction, and the refractive index of the second grating part is not greater than the refractive index of the third grating part.

[0009] Further, in the preferred embodiment of the present application, the ratio of the refractive index of the third grating part to the refractive index of the second grating part is in the range of 1-3.

[0010] Further, in the preferred embodiment of the present application, the ratio of the refractive index of the third grating part to the refractive index of the second grating part is in the range of 1.4-3.

[0011] Further, in the preferred embodiment of the present application, the grating structure further comprises a film structure, and the film structure is distributed on the groove surface of the grating structure.

[0012] Further, in the preferred embodiment of the present application, the ratio of the refractive index of the film structure to the equivalent refractive index of the grating structure is in the range of 1.5-2.4.

[0013] Further, in the preferred embodiment of the present application, a substrate layer is further included, and the substrate layer is located between the grating structure and a waveguide substrate, and the waveguide substrate is used to carry the plurality of grating structures.

[0014] Another aspect of the embodiments of the present application provides a near-eye display module, which comprises an image projection device and the above-mentioned optical waveguide, and the image projection device is used to generate image light and project the image light to the optical waveguide, and then output the image light via the optical waveguide.

[0015] The technical solutions in the embodiments of the present application can achieve the following technical effects: the optical waveguide provided by the embodiments of the present application can improve the adjustable degree of freedom of the grating structure by arranging different grating parts, such as a first grating part and a second grating part, in each grating unit, and the refractive index of the first grating part is not greater than the refractive index of the second grating part. When the incident light passes through the grating parts with different refractive indexes, the refractive index changes differently along the light propagation direction. The change of the refractive index along the light propagation direction is affected by the grating pattern and the different refractive indexes, and this change is non-uniform, thereby greatly changing the reflection function and the transmission function of the grating, and further changing the diffraction efficiency of different diffraction orders of the grating to reduce the light leakage ratio. In addition, by arranging the film structure on the surface of the grating unit, the reflection efficiency of the light can be improved to further reduce the light leakage ratio, and the problem of rainbow stripes can also be improved.

[0016] 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 application. The objects and other advantages of the present application will be realized and attained by means of the instrumentalities and combinations particularly pointed out in the description and appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0017] Other features, objects, and advantages of the present application will become more apparent from the following detailed description when read in connection with the following drawings:

[0018] Figure 1 is a structural schematic diagram of a waveguide structure provided by an embodiment of the present application;

[0019] Figure 2 is a structural schematic diagram of a grating structure provided by an embodiment of the present application;

[0020] Figure 3 is a structural schematic diagram of another grating structure provided by an embodiment of the present application;

[0021] Figure 4 is a structural schematic diagram of still another grating structure provided by an embodiment of the present application;

[0022] Figure 5 is a structural schematic diagram of yet another grating structure provided by an embodiment of the present application;

[0023] Figure 6 is a structural schematic diagram of a basic blazed grating;

[0024] Figure 7a is Figure 6 RGB coupling-out diffraction efficiency of the basic blazed grating in the multi-view field in the embodiment of the present application;

[0025] Figure 7b is Figure 6 light leakage ratio of the grating structure in the multi-view field in the embodiment of the present application;

[0026] Figure 8a is a structural schematic diagram of a grating structure provided by an embodiment of the present application; Figure 2 RGB coupling-out diffraction efficiency of the grating structure in the multi-view field in the embodiment of the present application;

[0027] Figure 8b is a structural schematic diagram of a grating structure provided by an embodiment of the present application; Figure 2 light leakage ratio of the grating structure in the multi-view field in the embodiment of the present application;

[0028] Figure 9 is a structural schematic diagram of a grating structure with a film structure provided by an embodiment of the present application;

[0029] Figure 10a is a structural schematic diagram of a grating structure provided by an embodiment of the present application; Figure 9RGB coupling-out diffraction efficiency of a grating structure with a film structure under multi-view field

[0030] Figure 10b is a structure diagram of a grating structure with a film structure provided by an embodiment of the present application Figure 9 Light leakage ratio of a grating structure with a film structure under multi-view field

[0031] Figure 11 is a structure diagram of a basic blazed grating with a film structure

[0032] Figure 12a is a structure diagram of a grating structure provided by an embodiment of the present application Figure 11 RGB coupling-out diffraction efficiency of a grating structure under multi-view field

[0033] Figure 12b is a structure diagram of a grating structure provided by an embodiment of the present application Figure 11 Light leakage ratio of a grating structure under multi-view field

[0034] Figure 13 is a structure diagram of a grating structure provided by an embodiment of the present application

[0035] Figure 14 is a structure diagram of a grating structure provided by an embodiment of the present application

[0036] Figure 15a is a structure diagram of a grating structure provided by an embodiment of the present application Figure 14 RGB coupling-out diffraction efficiency of a grating structure under multi-view field

[0037] Figure 15b is a structure diagram of a grating structure provided by an embodiment of the present application Figure 14 Light leakage ratio of a grating structure under multi-view field

[0038] Figure 16 is a structure diagram of a grating structure provided by an embodiment of the present application

[0039] Figure 17a is a structure diagram of a grating structure provided by an embodiment of the present application Figure 16 RGB coupling-out diffraction efficiency of a grating structure under multi-view field

[0040] Figure 17b is a structure diagram of a grating structure provided by an embodiment of the present application Figure 16 Light leakage ratio of a grating structure under multi-view field

[0041] Figure 18 is a structure diagram of a grating structure provided by an embodiment of the present application DETAILED DESCRIPTION

[0042] The application will be described in further detail below with reference to the 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 of the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for ease of description.

[0043] 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 light of three wavelengths after imaging through the grating, the present application provides a light waveguide with a corresponding grating structure.

[0044] Reference Figure 1 A light waveguide 100 provided in the embodiments of the present application includes a waveguide substrate 101 and a grating region with a specific optical function disposed on the waveguide substrate 101. The optical region further includes a coupling-in region 102, a relay region 103 and a coupling-out region 104.

[0045] The grating structure is disposed in the coupling-in region 102, the relay region 103 and the coupling-out region 104, and the grating structure can be realized by processes such as embossing, coating, etching, etc., which are not limited here. In the subsequent description of the present application, the grating structure disposed in the coupling-in region 102 can be referred to as a coupling-in grating; the grating structure disposed in the relay region 103 can be referred to as a relay grating; and the grating structure disposed in the coupling-out region 104 can be referred to as a coupling-out grating.

[0046] Light can be coupled into the waveguide substrate 101 through the coupling-in region 102 and transmitted therein, the relay region 103 receives the light transmitted by the coupling-in region 101 and deflects the light after expansion to the coupling-out region 104; the coupling-out region 104 receives the light deflected by the relay region 103 and couples the light out of the waveguide substrate 101.

[0047] Of course, Figure 1 The profiles, relative positions of the coupling-in region 102, the relay region 103 and the coupling-out region 104 shown in the drawings are exemplary and can change in actual application, for example, the coupling-in region 102 can not be Figure 1 square profile shown in the drawings, but can be circular, trapezoidal, etc.; the relay region 103 can be located below the coupling-out region 104. Therefore,Figure 1 The structure of waveguide 100 shown should not be construed as limiting this application.

[0048] It should be noted that the accompanying drawings of this application show an xyz coordinate system. For ease of description, in the embodiments of this application, the direction parallel to the y-axis can also be referred to as: the first direction, the vertical direction, or the longitudinal direction; the direction parallel to the x-axis can also be referred to as: the second direction, the horizontal direction, or the 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: the third direction or the depth direction. This coordinate system is used in other views or embodiments of this application, and the descriptions of the corresponding direction names are also applicable throughout.

[0049] refer to Figure 2 In one embodiment of this application, a grating structure 20 has a cross-section in the xz plane as shown below. Figure 2 As shown, the grating structure 20 includes a plurality of periodically distributed grating units 200, wherein there is a grating groove 210 between two adjacent grating units, and the light beam propagates in the grating units and the grating groove 210. Figure 2 The diagram illustrates the specific structure of a grating unit 200, including a first grating portion 201 and a second grating portion 202 arranged sequentially along the light propagation direction. In some embodiments, to reduce the light leakage ratio of the grating unit, the refractive index of the first grating portion 201 is not greater than the refractive index of the second grating portion 202. For example, the refractive index of the first grating portion 201 can be the same as the refractive index of the second grating portion 202. Alternatively, the refractive index of the first grating portion 201 can be less than the refractive index of the second grating portion 202. In some embodiments, the ratio of the refractive index of the second grating portion 202 to the refractive index of the first grating portion 201 is in the range of 1 to 3. Preferably, the ratio of the refractive index of the second grating portion 202 to the refractive index of the first grating portion 201 is in the range of 1.4 to 3. In the grating unit provided in the embodiments of this specification, when incident light passes through the first grating section 201 and the second grating section 202 with different refractive indices, the refractive index changes differently along the direction of light propagation. Since the refractive index change along the direction of light propagation is affected by the shape and refractive index of the grating structure, this change is non-uniform, which causes the reflection function and transmission function of the grating structure to be significantly different, thereby changing the diffraction efficiency of different diffraction orders of the grating structure, and thus reducing the light leakage ratio of the grating structure 20.

[0050] In some embodiments of the present application, the material of the grating structure in part or all of the first grating part 201 and in part or all of the second grating part 202 can include one or more fluorinated materials, such as cerium fluoride (CeF3), ytterbium fluoride (YbF3), yttrium fluoride (YF3), aluminum fluoride (AlF3), barium fluoride (BaF2), calcium fluoride (CaF2), magnesium fluoride (MgF2), and the like. It should be noted that the materials of the first grating part 201 and the second grating part 202 can be the same or different. Further preferably, when the first grating part 201 and the second grating part 202 are selected from the above fluorinated materials, the refractive index ratio of the second grating part 202 to the first grating part 201 can be in the range of 1.2-2.5. Preferably, the refractive index ratio of the second grating part 202 to the first grating part 201 can be in the range of 1.4-1.6. In addition, under the premise that the refractive index of the first grating part 201 is not greater than that of the second grating part 202, the refractive index ratio of the second grating part 202 to the first grating part 201 is not limited to the above ratio range, but can also be less than 1.2 or greater than 2.5.

[0051] Alternatively, the material of the grating structure in part or all can include one or more oxide materials, such as niobium oxide (Nb2O5), titanium oxide (TiO, TiO2, Ti2O3, Ti3O5), zirconium oxide (ZrO2), tantalum pentoxide (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), and the like. It should be noted that the materials of the first grating part 201 and the second grating part 202 can be the same or different. Further preferably, when the first grating part 201 and the second grating part 202 are selected from the above oxide materials, the refractive index ratio of the second grating part 202 to the first grating part 201 can be in the range of 1.2-2.8. Preferably, the refractive index ratio of the second grating part 202 to the first grating part 201 can be in the range of 1.5-2.5. In addition, under the premise that the refractive index of the first grating part 201 is not greater than that of the second grating part 202, the refractive index ratio of the second grating part 202 to the first grating part 201 is not limited to the above ratio range, but can also be less than 1.2 or greater than 2.8.

[0052] Optionally, the material of the grating structure can be one or more compound materials, such as silicon carbide (SiC), strontium titanate (STO), zinc sulfide (ZnS), silicon nitride (Si3N4), lithium niobate (LiNbO3), etc. It should be noted that the materials of the first grating part 201 and the second grating part 202 can be the same or different. Further preferably, when the first grating part 201 and the second grating part 202 are selected from the above compound materials, the refractive index ratio of the second grating part 202 to the first grating part 201 can be greater than 1.4. Preferably, the refractive index ratio of the second grating part 202 to the first grating part 201 can be in the range of 1.4-2.5. In addition, under the premise that the refractive index of the first grating part 201 is not greater than that of the second grating part 202, the refractive index ratio of the second grating part 202 to the first grating part 201 is not limited to the above ratio range, but can also be less than 1.4 or greater than 2.5.

[0053] Optionally, the material of the grating structure can also include a composite material obtained based on the aforementioned compound through a process such as doping.

[0054] It should be noted that the grating structure is not limited to the above Figure 2 structure, but can also use another side grating inclination angle, two-side grating inclination angle, etc. parameter group, which can construct the same type of grating pattern. For example, Figure 3 other blazed grating structure of the grating unit is also shown in FIG. 6, i.e., the cross-sectional shape of the first grating part 201 and the second grating part 202 is a triangle, which will not be described here. As shown in FIG. 7, Figure 4 in some embodiments, the cross-sectional shape of the first grating part 201 can be a triangle, and the cross-sectional shape of the second grating part 202 can be a quadrilateral (e.g., parallelogram, rectangle, trapezoid, etc.). As shown in FIG. 8, Figure 5 in some embodiments, the cross-sectional shape of the first grating part 201 can be a quadrilateral (e.g., parallelogram, rectangle, trapezoid, etc.), and the cross-sectional shape of the second grating part 202 can also be a quadrilateral (e.g., parallelogram, rectangle, trapezoid, etc.).

[0055] In some embodiments, the optical waveguide further includes a waveguide substrate for carrying the grating structure and a substrate layer, wherein the substrate layer is located between the waveguide substrate and the grating structure. Specifically, as shown in FIG. 9, Figure 2 the waveguide substrate is located at the bottom of the grating unit 200, one side of the substrate layer is connected with the bottom side of the grating unit 200, and the other side of the substrate layer is connected with the upper surface of the waveguide substrate (the surface of the waveguide substrate opposite to the bottom side of the grating unit 200). It should be noted that the substrate layer and the waveguide substrate are not limited to the above Figure 2The rainbow stripe region is not shown. In the embodiments of this specification, a substrate layer is disposed between the grating structure and the waveguide substrate to reduce the rainbow stripe region. The material of the substrate layer can be the same as or different from the material of the first grating portion or the second grating portion. The number of substrate layers can be one or more, and the materials of the multiple substrate layers can be the same or different. For information on the material of the substrate layer, please refer to the description of the material of the first grating portion or the second grating portion. It should be noted that the refractive index of the substrate layer can be greater than or less than the refractive index of the grating structure.

[0056] To more clearly illustrate the effect of the grating structure provided in the embodiments of this specification in reducing the light leakage ratio, a blazed grating is used as an example for explanation. Figure 6 This is a schematic diagram of a basic blazed grating structure using a single refractive index material. Figure 2 The grating unit shown has a period of P, a grating depth of h, and a grating tilt angle of θ. The refractive indices of the first grating portion 201 and the second grating portion 202 of the grating unit 200 are n1 and n2, respectively, and the refractive index boundary length is r. n *P. Further, the period P of the grating unit 200 ranges from 200 to 500 nm, the grating depth h ranges from 20 to 400 nm, the grating tilt angle θ ranges from 0° to 90°, and the refractive index boundary coefficient r... n The range is 0-1. The above parameters are only one of the parameter sets for constructing raster graphics.

[0057] Based on the above parameters, the objective function f can be... m (h,θ,n1,n2,r n ) Perform parameter optimization, objective function f m By considering multiple targets, including grating coupling diffraction efficiency and light leakage ratio, the local optimal solution for each target of the grating structure can be obtained.

[0058] Further, refer to Table 1. Figure 2 and Figure 6 Taking basic blazed gratings and combined blazed gratings as examples, Table 1 shows the parameter settings for each grating structure.

[0059] Table 1

[0060]

[0061] Under the condition that the grating period is the same and the coupling diffraction efficiency is similar... Figure 7a , Figure 7b as well as Figure 8a , Figure 8b The basic blazed grating and Figure 2 RGB coupling diffraction efficiency of grating structure in multiple fields of view And the corresponding light leakage ratio. represents the diffraction efficiency of the light in the waveguide coupling out of the waveguide with +1 order at the corresponding wavelength. T avg represents the transmittance, R avg represents the reflectance, T avg represents the diffraction efficiency of the light in the waveguide coupling out of the waveguide with +1 order to the outside environment side, i.e. the light leakage; R avg represents the diffraction efficiency of the light in the waveguide coupling out of the waveguide with +1 order to the human eye observation side. In the embodiments of the present specification, the ratio T avg / R avg represents the light leakage ratio, and the smaller the value is, the better. In the figure, the horizontal coordinate is the incident light angle, i.e. the multi-view field, and the vertical coordinates are the coupling-out diffraction efficiency and the ratio respectively.

[0062] As can be seen from the data shown in Figures 8a to 8b , compared with the results of the basic blazed grating structure in FIG. 8 and Figure 2 the grating structure provided in the embodiments of the present application has a lower light leakage ratio than the basic blazed grating structure. Figure 2 Figure 6

[0063] Figure 9 is a structural schematic diagram of the grating structure provided in some embodiments of the present application. As shown in Figure 9 , in some embodiments, the grating structure can further include a film structure distributed on the groove surface of the grating structure to further reduce the light leakage ratio. In the embodiments of the present specification, the groove surface of the grating structure refers to the side surface of each grating unit for incident and emergent light. The material of the film structure can refer to the material of the grating part described above. Further, the relative value of the refractive index of the film structure and the equivalent refractive index of the grating unit will affect the light leakage ratio of the grating structure. Considering that the refractive index of the film structure is too small to affect the reflection efficiency of light, in order to effectively further reduce the light leakage ratio and improve the reflection efficiency, in some embodiments, the ratio of the refractive index of the film structure to the equivalent refractive index of the grating unit is in the range of 1.5-2.4.

[0064] In order to more clearly illustrate the effect of the grating structure provided in the embodiments of the present application and provided with a film structure to reduce the light leakage ratio, an exemplary description is made in combination with Figures 7a-12b . Figure 10a , Figure 10b is Figure 9 the RGB coupling-out diffraction efficiency of the grating structure under the multi-view field and the corresponding light leakage ratio, Figure 11 is a schematic diagram of the basic blazed grating provided with a film structure, Figure 12a , Figure 12b is Figure 11 the RGB coupling-out diffraction efficiency of the basic blazed grating provided with a film structure in the multi-view field ​​and the corresponding light leakage ratio. Regarding Figure 11 the base blaze grating and Figure 9 The parameter setting values of the grating structure are shown in Table 2.

[0065] Table 2

[0066]

[0067] n in Table 2 f represents the refractive index of the film structure, and t represents the thickness of the film structure.

[0068] Based on Figure 7a , Figure 7b , Figure 8a , Figure 8b , Figure 10a , Figure 10b , Figure 12a and Figure 12b It can be seen that Figure 9 the light leakage ratio of the grating structure provided with the film structure in the embodiment is the lowest. In addition, Figure 11 the light leakage ratio of the base blaze grating provided with the film structure in the embodiment is relatively Figure 6 the light leakage ratio of the base blaze grating without the film structure does not change significantly. Therefore, the grating structure with the film structure provided in the embodiment of the present application has the effect of improving the degree of freedom more obviously. Figure 9 the grating structure with the film structure shown in the embodiment has the effect of improving the degree of freedom more obviously.

[0069] Further, the grating structure with the grating part having different refractive indexes provided in the embodiment of the present application can also improve the rainbow stripe phenomenon, which will be described in detail with reference to Figure 13 and the related description.

[0070] According to the formation reason of the rainbow stripe phenomenon, the grating structure is simulated and analyzed when the ambient light is incident on the grating structure in the waveguide from the outside environment at various angles and directions. The diffraction order of the ambient light coupled out of the optical waveguide and observed by the human eye is selected, that is, the diffraction order whose diffraction angle is less than the total reflection angle of the optical waveguide. Figure 13 the diffraction angle and the diffraction efficiency of the diffraction order corresponding to the wavelength of different grating structures. Among them, Figure 13 column (a) in the table is the diffraction angle of the grating diffraction order coupled out of the optical waveguide into the air, column (b) is Figure 6 the diffraction efficiency corresponding to the grating diffraction order of the base blaze grating, column (c) is Figure 2 the diffraction efficiency corresponding to the grating diffraction order of the grating structure, column (d) is Figure 11 the diffraction efficiency corresponding to the grating diffraction order of the base blaze grating with the film structure, and column (e) is Figure 9The diffraction efficiency corresponding to the diffraction order of a grating structure with a film structure. Under normal circumstances, assuming the distance from the human eye to the optical waveguide (Eye Relief) is d, and the width of the grating region producing diffraction is l, then the maximum diffraction angle of the light rays entering the human eye is... Let d = 25mm and l = 40mm, then the maximum diffraction angle of light entering the human eye is 38.7°. According to... Figure 13 As shown in the attached figure (a), when the theta angle is large and the phi angle is close to the edge of the outer frame, the diffraction order diffraction angles in this region meet the conditions. (Comparison) Figure 13 Columns (b) and (c), Figure 2 Grating structure compared to Figure 6 The efficiency of the basic blazed grating decreases significantly in the aforementioned region (i.e. Figure 13 (The bright areas shown are lighter in color). (Comparison) Figure 13 Columns (d) and (e), Figure 9 Grating structures with membrane structures compared to Figure 11 The efficiency of the basic blazed grating with a film structure decreases significantly in the aforementioned region. Therefore, the grating structure with different refractive indices provided in the embodiments of this specification can improve rainbow fringes.

[0071] Furthermore, comparing the data in Table 3, the difference between the grating region and the non-grating region of the optical waveguide provided in this application embodiment is not significant. Therefore, it can be seen that the optical waveguide provided in this application embodiment does not affect the overall appearance of the optical waveguide.

[0072] Table 3

[0073]

[0074] Table 3 shows the reflection and diffraction efficiencies of the grating structure (light incident normally on the substrate material) and the four grating structures when the light is normally incident on the grating structure from the ambient side at wavelengths of 450nm (blue light), 520nm (green light), and 638nm (red light). Specifically, compared to the grating structure, the higher the diffraction efficiency of the grating structure, the greater the difference between the grating region and the grating-free region observed from the ambient side. By comparing the diffraction efficiency data in Table 3, it can be seen that... Figure 9 Although the grating structure with a film structure slightly increases the diffraction efficiency of normal incidence reflection, it is still comparable to... Figure 6 The differences in the grating structures using a single refractive index material shown are not significant. Therefore, it can be seen that the grating structure design provided in the embodiments of this application does not cause a significant change in the appearance of the grating.

[0075] It should be noted that the grating unit provided in the embodiments of this specification is not limited to the first grating portion 201 and the second grating portion 202 described above. The grating unit may also include grating portions having two or more different refractive indices. For example Figure 14As shown in some embodiments, the grating unit 1400 can also include three grating sections with different refractive indexes, i.e., the grating unit 1400 can include a first grating section 1410, a second grating section 1420 and a third grating section 1430 arranged in sequence along the light propagation direction, wherein the refractive index of the first grating section 1410 is not greater than the refractive index of the second grating section 1420, and the refractive index of the second grating section 1420 is not greater than the refractive index of the third grating section 1430. Preferably, the ratio of the refractive index of the second grating section 1420 to the refractive index of the first grating section 1410 is within the range of 1-3, and the ratio of the refractive index of the third grating section 1430 to the refractive index of the second grating section 1420 is within the range of 1-3. For specific contents of the material and shape of the grating unit 1400, please refer to the description of the grating unit 1000. Figures 2 to 5 and the related description, which will not be further elaborated here.

[0076] In some embodiments, the optical waveguide further includes a waveguide substrate for carrying the grating structure and a substrate layer, wherein the substrate layer is located between the waveguide substrate and the grating structure. Specifically, as shown in Figure 14 , the waveguide substrate is located at the bottom of the grating unit 1400, one side of the substrate layer is connected with the bottom side of the grating unit 1400, and the other side of the substrate layer is connected with the upper surface of the waveguide substrate (the surface of the waveguide substrate opposite to the bottom side of the grating unit 1400). It should be noted that the substrate layer and the waveguide substrate are not shown in Figure 14 . In the embodiments of the present specification, the substrate layer is arranged between the grating structure and the waveguide substrate to reduce the rainbow stripe area. The material of the substrate layer can be the same as or different from the material of the first grating section or the second grating section. The number of layers of the substrate layer can be one or more, and the materials of the multiple layers of the substrate layer can be the same or different. For the material of the substrate layer, please refer to the description of the material of the first grating section or the second grating section. It should be noted that the refractive index of the substrate layer can be greater than or less than the refractive index of the grating structure.

[0077] In order to more clearly illustrate the effect of reducing the light leakage ratio of the grating structure provided by the embodiments of the present specification, the blazed grating is taken as an example for illustration. As shown in Figure 14 , the blazed grating is composed of three different refractive indexes. Define the grating pattern period as P, the grating depth as h, the grating inclination angle as θ, the refractive indexes of the pattern as n1, n2, n3, and the refractive index boundary length as r n1 *P, r n2 (1-r n1 )P. The period P ranges from 200-500nm, the grating depth h ranges from 20-400nm, the grating inclination angle θ ranges from 0°-90°, and the refractive index boundary coefficient r n1 , r n2 ranges from 0-1. The above parameters are only one of the parameter groups for constructing the grating pattern.

[0078] Based on each parameter, the objective function f m (h,θ,n1,n2,n3,r n1 ,r n2 ) Perform parameter optimization, objective function f m By considering multiple targets, including grating coupling diffraction efficiency and light leakage ratio, the local optimal solution for each target of the grating structure can be obtained.

[0079] Further, refer to Table 4. Figure 6 and Figure 14 Taking a basic blazed grating and a combined blazed grating with three different refractive indexes as examples, Table 4 shows the parameter settings for each grating structure.

[0080] Table 4

[0081]

[0082] Under the condition that the grating period is the same and the coupling diffraction efficiency is similar... Figure 15a and Figure 15b Give each Figure 14 RGB coupling diffraction efficiency of grating structure in multiple fields of view And the corresponding light leakage ratio. Combined with... Figure 7a , Figure 7b and Figure 15a , Figure 15b ,contrast Figure 6 Basic blazed grating and Figure 14 The result of the grating structure is visible Figure 14 The light leakage ratio of the grating structure is relatively Figure 6 The basic blazed grating has a lower light leakage ratio.

[0083] It should be noted that the grating section of the grating unit is not limited to that described in this specification. Figure 2 The two shown are Figure 14 The number of grating sections shown is three or more, such as four, five, or more, which will not be described further here.

[0084] Figure 16 These are schematic diagrams of the grating structures provided in some embodiments of this application. For example... Figure 16As shown, in some embodiments, the grating structure can further comprise a film structure distributed on the groove surface of the grating structure to further reduce the light leakage ratio. In the embodiments of the present application, the groove surface of the grating structure refers to the side surface of each grating unit for incident and emergent light. The material of the film structure can refer to the material of the grating part described above. Further, the relative value of the refractive index of the film structure and the equivalent refractive index of the grating unit will affect the light leakage ratio of the grating structure. Considering that the refractive index of the film structure is too small to affect the reflection efficiency of light, in order to effectively further reduce the light leakage ratio and improve the reflection efficiency, in some embodiments, the ratio of the refractive index of the film structure to the equivalent refractive index of the grating unit is in the range of 1.5-2.4.

[0085] In order to more clearly illustrate the effect of the grating structure provided by the embodiments of the present application and provided with a film structure to reduce the light leakage ratio, exemplary descriptions are made herein in combination with Figure 12a 、 Figure 12b and 17a 、 Figure 17b . Figure 17a 、 Figure 17b For Figure 16 the RGB coupling-out diffraction efficiency of the grating structure under multi-view field and the corresponding light leakage ratio. As for Figure 11 the basic blazed grating and Figure 16 the parameter setting values of each grating structure can be seen from Table 5.

[0086] Table 5

[0087]

[0088] Based on Figure 12a 、 Figure 12b 、 Figure 17a and Figure 17b it can be seen that Figure 16 the light leakage ratio of the grating structure provided with the film structure and having a grating part with three refractive indexes is relatively Figure 11 the light leakage ratio of the blazed grating provided with the film structure and having a single refractive index is greatly reduced. Thus, it can be seen that the grating structure provided by the embodiments of the present application and provided with the film structure has a higher degree of freedom. Figure 16 The effect of the grating structure provided with the film structure shown in the above-mentioned embodiments is more obvious.

[0089] Further, the grating structure provided by the embodiments of the present application and having a grating part with three identical refractive indexes can also improve the rainbow stripe phenomenon, which can be seen from Figure 18 and the related description thereof.

[0090] Figure 18 is the diffraction angle and the diffraction efficiency under the wavelength corresponding to the diffraction order. Among them, Figure 18(a) column in Table 4 lists the diffraction angles of the grating diffraction orders of the base blazed grating, (b) column lists the diffraction angles of the grating diffraction orders of the grating structure, (c) column lists the diffraction efficiencies of the grating diffraction orders of the base blazed grating, and (d) column lists the diffraction efficiencies of the grating diffraction orders of the grating structure. Figure 6 (a) column in Table 4 lists the diffraction angles of the grating diffraction orders of the base blazed grating, (b) column lists the diffraction angles of the grating diffraction orders of the grating structure, (c) column lists the diffraction efficiencies of the grating diffraction orders of the base blazed grating, and (d) column lists the diffraction efficiencies of the grating diffraction orders of the grating structure. Figure 14 (a) column in Table 4 lists the diffraction angles of the grating diffraction orders of the base blazed grating, (b) column lists the diffraction angles of the grating diffraction orders of the grating structure, (c) column lists the diffraction efficiencies of the grating diffraction orders of the base blazed grating, and (d) column lists the diffraction efficiencies of the grating diffraction orders of the grating structure. Figure 11 (a) column in Table 4 lists the diffraction angles of the grating diffraction orders of the base blazed grating, (b) column lists the diffraction angles of the grating diffraction orders of the grating structure, (c) column lists the diffraction efficiencies of the grating diffraction orders of the base blazed grating, and (d) column lists the diffraction efficiencies of the grating diffraction orders of the grating structure. Figure 16 (a) column in Table 4 lists the diffraction angles of the grating diffraction orders of the base blazed grating, (b) column lists the diffraction angles of the grating diffraction orders of the grating structure, (c) column lists the diffraction efficiencies of the grating diffraction orders of the base blazed grating, and (d) column lists the diffraction efficiencies of the grating diffraction orders of the grating structure. Figure 18 (b) column and (c) column in Table 4, Figure 14 the grating structure with the film structure is compared with the base blazed grating with the film structure, Figure 11 the grating structure with the film structure is compared with the base blazed grating with the film structure, Figure 18 (d) column and (e) column in Table 6, Figure 16 the grating structure with the film structure is compared with the base blazed grating with the film structure, Figure 11 the grating structure with the film structure is compared with the base blazed grating with the film structure. It can be seen that the grating structure with the grating part having different refractive indexes provided in the embodiments of the present application can improve the rainbow stripes.

[0091] Further, compared with the data in Table 6, the difference between the grating region and the non-grating region of the optical waveguide provided in the embodiments of the present application is not obvious. It can be seen that the optical waveguide provided in the embodiments of the present application does not affect the overall appearance of the optical waveguide.

[0092] Table 6

[0093]

[0094] As shown in Table 6, the reflection diffraction efficiencies of the grating structure and the non-grating structure (light is normally incident on the substrate material) and four grating structures are obtained when the grating structure is normally incident from the environment side at wavelengths of 450 nm (blue light), 520 nm (green light) and 638 nm (red light). Specifically, compared with the non-grating structure, the higher the diffraction efficiency of the grating structure, the greater the difference between the grating region and the non-grating region observed from the environment side. By comparing the diffraction efficiency data in Table 6, it can be seen that Figure 16 the grating structure with the film structure in Table 6 slightly increases the normal incidence reflection diffraction efficiency, but the difference with the grating structure using a single refractive index material shown in Table 4 is not large, and thus it can be seen that the grating structure design provided in the embodiments of the present application does not cause a large change in the appearance of the grating. Figure 6 the grating structure with the film structure is compared with the base blazed grating with the film structure,

[0095] For the optical waveguide in the foregoing embodiments, the grating structure is 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 correspondingly, the foregoing grating structure is arranged in the optical waveguide.

[0096] Of course, the specific structure to be adopted will depend on the needs of the actual application, and this does not constitute a limitation on the present application.

[0097] The light waveguide provided by the embodiments of the present specification can be prepared by a method such as imprinting, etching or deposition to obtain a basic light waveguide structure of a layered structure. And on the prepared basic light waveguide structure, through methods such as resist, directional etching, overlay or control of substrate inclination deposition, the required grating pattern is finally prepared.

[0098] Based on the light waveguide described above, the embodiments of the present application also provide a near-eye display module, which can be applied to AR glasses. The near-eye display module comprises an image projection device and the aforementioned light waveguide. The image projection device is used to generate image light and project it onto the corresponding grating area (such as the coupling-in area) of the light waveguide, so that the image light can be transmitted in the waveguide and coupled out through the corresponding grating area (such as the coupling-out area).

[0099] Each of the embodiments in the present application is described in a progressive manner, and the same or similar parts between each embodiment can be referred to each other. Each embodiment focuses on the difference from other embodiments.

[0100] 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 the elements from other elements.

Claims

1. An optical waveguide, characterized in that, The optical waveguide is provided with a plurality of periodically distributed grating units along the light propagation direction, and there are grating grooves between two adjacent grating units. Each grating unit includes at least a first grating part and a second grating part arranged sequentially along the light propagation direction, and the refractive index of the first grating part is not greater than the refractive index of the second grating part.

2. The optical waveguide according to claim 1, characterized in that, The ratio of the refractive index of the second grating portion to the refractive index of the first grating portion is in the range of 1 to 3.

3. The optical waveguide according to claim 2, characterized in that, The ratio of the refractive index of the second grating portion to the refractive index of the first grating portion is in the range of 1.4 to 3.

4. The optical waveguide according to claim 1, characterized in that, Each grating unit includes a first grating portion, a second grating portion, and a third grating portion arranged sequentially along the light propagation direction, wherein the refractive index of the second grating portion is not greater than the refractive index of the third grating portion.

5. The optical waveguide according to claim 4, characterized in that, The ratio of the refractive index of the third grating section to the refractive index of the second grating section is in the range of 1 to 3.

6. The optical waveguide according to claim 5, characterized in that, The ratio of the refractive index of the third grating portion to the refractive index of the second grating portion is in the range of 1.4 to 3.

7. The optical waveguide according to any one of claims 1-6, characterized in that, The grating unit further includes a membrane structure distributed on the groove surface of the grating unit.

8. The optical waveguide according to claim 7, characterized in that, The ratio of the refractive index of the film structure to the equivalent refractive index of the grating unit is in the range of 1.5 to 2.

4.

9. The optical waveguide according to any one of claims 1-6, characterized in that, It also includes a substrate layer located between the grating units and the waveguide substrate, the waveguide substrate being used to support the plurality of grating units.

10. A near-eye display module, characterized in that, The invention includes an image projection device and an optical waveguide as described in any one of claims 1-9, wherein the image projection device is used to generate image light rays and project them onto the optical waveguide, and then output them after transmission through the optical waveguide.

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