Grating structure, preparation method of grating structure and diffraction optical waveguide

Abstract

The invention discloses a grating structure, a preparation method of the grating structure and a diffraction optical waveguide, the grating structure comprises a plurality of structural units which are arranged on the surface of a waveguide substrate and are periodically arranged, each structural unit comprises a main body structure and an additional structure, and the main body structure and the additional structure are adjacently arranged and have the same height; the period of the structural unit is the sum of the width of the main body structure and the width of the additional structure; wherein the additional structure comprises at least two material layers, the refractive index of each material layer is gradually reduced along with the distance from the surface of the waveguide substrate, and the refractive index of each material layer is smaller than the refractive index of the main body structure; according to the grating structure provided by the invention, the unexpected rainbow effect can be improved, so that the display effect of the diffraction optical waveguide is improved.

Description

Technical Field

[0001] The present application relates to the field of augmented reality, and in particular to a grating structure, a method for preparing the grating structure, and a diffraction optical waveguide. Background Art

[0002] Augmented reality is a technology that integrates the real world and virtual information. The augmented reality display system usually includes a micro projector and an optical display screen. The micro projector provides virtual display content for the augmented reality display system and projects it into the human eye through the optical display screen. The optical display screen is usually a transparent optical component, so that users can also see the real world through the optical display screen.

[0003] Diffraction waveguide is a way to realize optical display screen. Grating structure is usually used to expand the exit pupil. However, the grating structure can also act on ambient light. It has different diffraction angles for light of different wavelengths, which causes different colors of light to have different angle deviations when passing through the diffraction grating, thus forming a rainbow phenomenon with uneven color distribution in the eyes of the observer, which greatly affects the display effect. Summary of the invention

[0004] The embodiments of the present application provide a grating structure, a method for preparing the grating structure, and a diffraction light waveguide, which can improve the undesired rainbow effect, thereby enhancing the display effect of the diffraction light waveguide.

[0005] On the one hand, the present application provides a grating structure, which includes a plurality of periodically arranged structural units disposed on the surface of a waveguide substrate, the structural units including a main structure and an additional structure, the main structure and the additional structure are adjacently disposed and have the same height, and the period of the structural unit is the sum of the widths of the main structure and the additional structure; wherein the additional structure includes at least two material layers, the refractive index of each of the material layers gradually decreases as it moves away from the surface of the waveguide substrate, and the refractive index of each of the material layers is smaller than the refractive index of the main structure.

[0006] Practically, the main structure and the additional structure are both helical tooth structures and have the same inclination angle.

[0007] In practice, the height of each of the material layers gradually decreases as it moves away from the surface of the waveguide substrate.

[0008] Practically, the height of the main structure ranges from 100nm to 250nm.

[0009] Practically, along the direction away from the surface of the waveguide substrate, the additional structure includes a first material layer and a second material layer, the refractive index difference between the first material layer and the main structure ranges from 0.1 to 0.3, and the refractive index difference between the second material layer and the main structure ranges from 0.2 to 0.4.

[0010] In practice, the grating structure further includes a functional layer, which is located on a surface of the structural unit that is away from the surface of the waveguide substrate; and the refractive index of the functional layer is smaller than the refractive index of each part of the structural unit.

[0011] On the other hand, the present application provides a method for preparing a grating structure, which is used to prepare the grating structure described in any of the above items, and the preparation method comprises: providing a waveguide substrate; Forming multiple material layers on the waveguide substrate in sequence, wherein the refractive index of each material layer gradually decreases as it moves away from the surface of the waveguide substrate; Forming a plurality of periodically arranged grooves in the multi-layer material layer by means of embossing or etching to obtain a plurality of periodically arranged additional structures; The grooves between the additional structures are filled with grating material to form the main structure.

[0012] In practice, the step of sequentially forming multiple material layers on the waveguide substrate comprises: Spin coating different materials sequentially on the waveguide substrate to form multiple material layers; The method of forming a plurality of periodically arranged grooves in the multi-layer material layer by means of embossing or etching to obtain a plurality of periodically arranged additional structures includes: forming a patterned mask layer on the outer surface of the multi-layer material layer; The multi-layer material layer is etched using the mask layer as a mask to form a plurality of periodically arranged grooves, thereby obtaining a plurality of periodically arranged additional structures.

[0013] In practice, the step of sequentially forming multiple material layers on the waveguide substrate comprises: Spraying materials on the waveguide substrate in sequence to form multiple material layers; The method of forming a plurality of periodically arranged grooves in the multi-layer material layer by means of embossing or etching to obtain a plurality of periodically arranged additional structures includes: Directing the side of the imprint template with the microstructure toward the multi-layer material layer; Applying pressure to the imprint template to transfer the microstructure of the imprint template to the multi-layer material layer, and forming the additional structure after curing and demoulding.

[0014] On the other hand, the present application provides a diffraction optical waveguide, which includes a coupling-in grating and a coupling-out grating, or a coupling-in grating, a turning grating and a coupling-out grating, and the turning grating and / or the coupling-out grating are implemented as the grating structure described in any one of the above items.

[0015] The present application provides a grating structure, a method for preparing the grating structure, and a diffractive optical waveguide. The grating structure includes a plurality of periodically arranged structural units disposed on the surface of a waveguide substrate, each structural unit includes a main structure and an additional structure. Compared with the existing grating structure, the additional structure is cleverly added, and the additional structure includes at least two material layers, the refractive index of each material layer gradually decreases as it moves away from the surface of the waveguide substrate, and the refractive index of each material layer is smaller than the refractive index of the main structure. The design of this multi-layer asymmetric structure enables the refractive index of the grating structure to form a process of smoothly changing from the main structure to the additional structure, which can reduce the efficiency of the grating structure to a large extent, thereby reducing the brightness of the rainbow stripes; and the efficiency will not be reduced too much to affect the overall performance of the diffractive optical waveguide including the grating structure.

[0016] Especially for the grating structure with oblique teeth, due to the excessively high efficiency of the grating structure with oblique teeth, it will also bring problems of poor uniformity and strong visibility. The grating structure provided by itself, including the main structure and the additional structure, can not only improve the undesirable rainbow effect, but also optimize the uniformity and visibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 A schematic diagram of a grating structure provided in an embodiment of the present application; Figure 2 A schematic diagram of another grating structure provided in an embodiment of the present application; Figure 3 A schematic diagram of another grating structure provided in an embodiment of the present application; Figure 4 A schematic diagram of a process for preparing a grating structure provided in an embodiment of the present application; Figure 5 A schematic flow chart of another method for preparing a grating structure provided in an embodiment of the present application; Figure ID: 100: grating structure; 110: Main structure; 120: additional structure; 121: first material layer; 122: second material layer; 200: waveguide substrate; 130: functional layer; 300: mask layer; 400: Embossing template. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0020] The technical solution of the present application is described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0021] The present application provides a grating structure, which includes a plurality of periodically arranged structural units arranged on the surface of a waveguide substrate, wherein the structural units include a main structure and an additional structure, wherein the main structure and the additional structure are adjacently arranged and have the same height, and the period of the structural unit is the sum of the widths of the main structure and the additional structure; wherein the additional structure includes at least two material layers, wherein the refractive index of each material layer gradually decreases as it moves away from the surface of the waveguide substrate, and the refractive index of each material layer is less than the refractive index of the main structure.

[0022] Specifically, refer to Figure 1 and Figure 2 The grating structure 100 includes a plurality of periodically arranged structural units disposed on the surface of a waveguide substrate 200. The structural units include a main structure 110 and an additional structure 120. The main structure 110 and the additional structure 120 are adjacently disposed and have the same height. The period of the structural unit is the sum of the widths of the main structure 110 and the additional structure 120. The additional structure 120 includes at least two material layers.

[0023] The heights of the main structure 110 and the additional structure 120 are dimensions along the normal direction of the surface of the waveguide substrate 200 , and the heights of the main structure 110 and the additional structure 120 are dimensions along the periodic arrangement direction.

[0024] It can be understood that the rainbow effect will become more obvious as the diffraction efficiency of the grating structure increases. Conventional grating structures are more likely to produce more obvious rainbows due to the large difference between the refractive index of the grating structure and the refractive index of air. In the present application, the grating structure includes an additional structure, and the additional structure includes at least two material layers. The refractive index of each material layer gradually decreases as it moves away from the surface of the waveguide substrate, and the refractive index of each material layer is smaller than the refractive index of the main structure. In this way, the refractive index of the grating structure forms a process of gently changing the refractive index from the main structure to the additional structure, which can improve or even eliminate the undesirable rainbow effect.

[0025] In optical principles, the more material layers the additional structure has, the larger the parameter space is, and better diffraction performance can be achieved. However, in actual preparation, the more material layers the additional structure has, the more difficult the process is.

[0026] In the grating structure provided by the present application, each structural unit includes a main structure and an additional structure, and the additional structure includes at least two material layers, and the refractive index of each material layer gradually decreases as it moves away from the surface of the waveguide substrate, and the refractive index of each material layer is smaller than the refractive index of the main structure. The grating efficiency modulation range of this multi-layer asymmetric structure is very wide. Through parameter optimization, it can achieve a very high diffraction efficiency and a lower diffraction efficiency. Therefore, it can reduce the efficiency of the grating structure to a large extent and reduce the brightness of the rainbow stripes without reducing the efficiency too much to affect the overall performance of the diffraction optical waveguide.

[0027] Further practicably, along the direction away from the surface of the waveguide substrate, the refractive index difference between two adjacent material layers gradually increases.

[0028] In the embodiment of the present application, the main structure of the grating structure can be a straight tooth structure or a helical tooth structure, etc. In practice, the width of the main structure is kept consistent in the direction away from the waveguide substrate. In practice, the main structure and the additional structure are both helical tooth structures and have the same inclination angle.

[0029] Specifically, when the grating period, grating height and inclination angle of the slanted teeth of the slanted grating structure meet certain conditions, the rainbow effect can be reduced to a certain extent. However, if the efficiency of the slanted grating is too high, the uniformity of the image will deteriorate, and if the efficiency is too high, the reflectivity of the grating area will be too high and the transmittance will be too low, which will seriously affect the appearance of the diffraction optical waveguide. The main structure of the grating structure provided in the present application can also be a slanted tooth structure. In this way, the advantage of the slanted tooth grating in reducing the rainbow effect can be utilized, and the diffraction efficiency of the grating structure as a whole can be reduced by means of an additional structure, thereby alleviating or even eliminating other problems caused by the high efficiency of the slanted tooth grating.

[0030] Practically, the height of each material layer gradually decreases as it moves away from the surface of the waveguide substrate.

[0031] In the present application, the height of each material layer gradually decreases as it moves away from the surface of the waveguide substrate, and the height of each material layer is also set to gradually decrease as it moves away from the surface of the waveguide substrate, that is, the closer the refractive index of the material layer is to the refractive index of the main structure, the higher the height. This can ensure that the diffraction efficiency of the overall grating structure is not too high, and the part with a lower refractive index in the additional structure plays a role in locally fine-tuning the diffraction efficiency of light of different wavelengths.

[0032] The height of the main structure can be 100 nm to 250 nm. The height of the main structure is the height of the grating structure. Setting the height of the grating structure within this range can ensure that the grating structure has a good diffraction effect.

[0033] Practically, in a direction away from the surface of the waveguide substrate, the additional structure includes a first material layer and a second material layer, the refractive index difference between the first material layer and the main structure ranges from 0.1 to 0.3, and the refractive index difference between the second material layer and the main structure ranges from 0.2 to 0.4.

[0034] refer to Figure 2 The grating structure 100 includes a plurality of periodically arranged structural units disposed on the surface of a waveguide substrate 200 . The structural units include a main structure 110 and an additional structure 120 . In a direction away from the surface of the waveguide substrate 200 , the additional structure 120 includes a first material layer 121 and a second material layer 122 .

[0035] Among them, the refractive index n0 of the main structure 110 is greater than the refractive index n1 of the first material layer 121, and the refractive index n1 of the first material layer 121 is greater than the refractive index n2 of the second material layer 122. The refractive index difference between the first material layer and the main structure is less than the refractive index difference between the second material layer and the main structure. The refractive index difference between the first material layer and the main structure is less than the refractive index difference between the first material layer and the second material layer. The material of the main structure 110 can be an inorganic material with a high refractive index such as titanium oxide and niobium oxide.

[0036] Exemplarily, in a specific embodiment, the refractive index n0 of the main structure 110 is 2.4, the refractive index n1 of the first material layer 121 is 2.3, and the refractive index n2 of the second material layer 122 is 2.0. The refractive index of the grating structure forms a process in which the refractive index decreases smoothly from the main structure to the additional structure, which can reduce the diffraction efficiency to a certain extent, thereby reducing rainbow and reflectivity.

[0037] Further practicably, the grating structure further includes a functional layer, which is located on a surface of the structural unit facing away from the surface of the waveguide substrate; and the refractive index of the functional layer is smaller than the refractive index of each part in the structural unit.

[0038] refer to Figure 3The grating structure 100 includes a plurality of periodically arranged structural units disposed on the surface of a waveguide substrate 200 , and also includes a functional layer 130 located on a surface of the structural unit away from the surface of the waveguide substrate 200 .

[0039] Specifically, the refractive index of the functional layer should be smaller than the refractive index of each part in the structural unit, and the closer to the refractive index of air, the better, so as to avoid affecting the effect of the additional structure and the transmittance of the grating structure. The functional layer is mainly used to enhance the stability of the diffraction optical waveguide when the grating structure is used for the diffraction optical waveguide. Usually, the diffraction optical waveguide will have the overlap of the waveguide plate and the protective plate. After the overlap, the internal and external air pressure is unbalanced, which can easily cause the waveguide plate to bend. The waveguide plate is an optical device with very high requirements for flatness, and a slight bend will cause the image to be blurred. Therefore, the functional layer serves as the connecting part between the waveguide plate and the protective plate, and the physical part provides mechanical strength for the diffraction optical waveguide, extending the service life of the diffraction optical waveguide. At this time, if the refractive index of the functional layer is too high, the propagating light in the waveguide plate will enter the protective plate, but in general, based on cost and use considerations, the flatness and refractive index of the protective plate are different from those of the waveguide plate. The light entering the protective plate will cause image unevenness and MTF decrease, affecting the overall performance of the diffraction optical waveguide.

[0040] The grating structure provided in the present application includes a plurality of periodically arranged structural units disposed on the surface of a waveguide substrate, each structural unit includes a main structure and an additional structure. Compared with the existing grating structure, the additional structure is cleverly added, and the additional structure includes at least two material layers, the refractive index of each material layer gradually decreases as it moves away from the surface of the waveguide substrate, and the refractive index of each material layer is smaller than the refractive index of the main structure. The design of this multi-layer asymmetric structure enables the refractive index of the grating structure to form a process of smoothly changing from the main structure to the additional structure, which can reduce the efficiency of the grating structure to a large extent, thereby reducing the brightness of the rainbow stripes; and will not reduce the efficiency too much to affect the overall performance of the diffraction light waveguide including the grating structure.

[0041] Especially for the grating structure with oblique teeth, due to the excessively high efficiency of the grating structure with oblique teeth, it will also bring problems of poor uniformity and strong visibility. The grating structure provided in the present application, including the main structure and the additional structure, can not only improve the undesirable rainbow effect, but also be optimized in terms of uniformity and visibility.

[0042] On the other hand, the present application provides a method for preparing a grating structure, which is used to prepare any of the above grating structures, and the preparation method comprises: providing a waveguide substrate; A plurality of material layers are sequentially formed on the waveguide substrate, wherein the refractive index of each material layer gradually decreases as it moves away from the surface of the waveguide substrate; By means of embossing or etching, a plurality of periodically arranged grooves are formed in the multi-layer material layer to obtain a plurality of periodically arranged additional structures; The grooves between the additional structures are filled with grating materials to form a main structure.

[0043] Different from the conventional grating preparation method, the present application mainly uses etching or embossing of lower refractive index materials to first form an additional structure with a low refractive index; the main structure with a high refractive index is formed by filling after the preparation of the additional structure is completed, thus avoiding the process difficulty of etching high refractive index materials, and the etching depth accuracy is higher, and the verticality of the main structure is better.

[0044] In practice, multiple material layers are sequentially formed on the waveguide substrate, including: Spin coating different materials on the waveguide substrate in sequence to form multiple material layers; By means of embossing or etching, a plurality of periodically arranged grooves are formed in the multi-layer material layer to obtain a plurality of periodically arranged additional structures, including: forming a patterned mask layer on the outer surface of the multi-layer material layer; The multi-layer material layer is etched using the mask layer as a mask to form a plurality of periodically arranged grooves, thereby obtaining a plurality of periodically arranged additional structures.

[0045] Specifically, refer to Figure 4 After obtaining the waveguide substrate 200, a first material is spin-coated on the surface of the waveguide substrate 200 to form a first material layer 121, and then a second material is spin-coated on the surface of the first material layer 121 to form a second material layer 122, thereby forming a multi-layer material layer with a lower refractive index. Then, a patterned mask layer 300 is formed on the outer surface of the second material layer 122, and the multi-layer material layer is etched using the mask layer 300 as a mask to form a number of periodically arranged grooves, thereby obtaining a number of periodically arranged additional structures 120. Then, the grooves between the additional structures 120 are filled with grating materials, and the mask layer 300 and the excess grating materials are removed, so that the height of the grating material is consistent with the height of the additional structure 120, and the main structure 110 is formed.

[0046] In practice, multiple material layers are sequentially formed on the waveguide substrate, including: Spraying materials on the waveguide substrate in sequence to form multiple material layers; By means of embossing or etching, a plurality of periodically arranged grooves are formed in the multi-layer material layer to obtain a plurality of periodically arranged additional structures, including: The side of the imprint template with the microstructure is directed toward the multi-layer material layer; Pressure is applied to the imprint template to transfer the microstructure of the imprint template into the multi-layer material layer, and additional structures are formed after curing and demolding.

[0047] Specifically, refer to Figure 5 After obtaining the waveguide substrate 200, a first material is sprayed on the surface of the waveguide substrate 200 to form a first material layer 121, and then a second material is sprayed on the surface of the first material layer 121 to form a second material layer 122, thereby forming a multilayer material layer with a lower refractive index. Then, the side of the imprint template 400 with the microstructure faces the multilayer material layer, and pressure is applied to the imprint template 400 to transfer the microstructure of the imprint template 400 to the multilayer material layer, and demolding is performed after curing to form an additional structure 120. Then, the grooves between the additional structures 120 are filled with grating material, and the excess grating material is removed so that the height of the grating material is consistent with the height of the additional structure 120, thereby forming a main structure 110.

[0048] On the other hand, the present application provides a diffraction optical waveguide, which includes a coupling-in grating and a coupling-out grating, or a coupling-in grating, a turning grating and a coupling-out grating, and the turning grating and / or the coupling-out grating are implemented as any of the grating structures mentioned above.

[0049] Specifically, the rainbow effect usually appears at the turning grating and the coupling-out grating of the diffraction optical waveguide. The present application adopts the grating structure provided by the present application at the turning grating and / or the coupling-out grating of the diffraction optical waveguide. The undesired rainbow effect can be improved by designing a multi-layer asymmetric structure, and the uniformity and visibility can be optimized when the grating structure is a helical tooth structure.

[0050] Furthermore, when the turning grating and / or outcoupling grating on the waveguide plate in the diffraction optical waveguide adopts the grating structure provided in the present application, and the grating structure includes a functional layer, when the waveguide plate is superimposed on the protective plate, the functional layer is directly adhered to the protective plate, and there is no air gap between the waveguide plate and the protective plate.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A grating structure, comprising a plurality of periodically arranged structural units disposed on a surface of a waveguide substrate, characterized in that: The structural unit includes a main structure and an additional structure, the main structure and the additional structure are adjacently arranged and have the same height, and the period of the structural unit is the sum of the widths of the main structure and the additional structure; wherein the additional structure includes at least two material layers, the refractive index of each material layer gradually decreases as it moves away from the surface of the waveguide substrate, and the refractive index of each material layer is smaller than the refractive index of the main structure.

2. The grating structure according to claim 1, characterized in that The main structure and the additional structure are both helical tooth structures with the same inclination angle.

3. The grating structure according to claim 1, characterized in that The height of each material layer gradually decreases as it moves away from the surface of the waveguide substrate.

4. The grating structure according to claim 1, characterized in that The height of the main structure ranges from 100nm to 250nm.

5. The grating structure according to claim 1, characterized in that Along the direction away from the surface of the waveguide substrate, the additional structure includes a first material layer and a second material layer, the refractive index difference between the first material layer and the main structure ranges from 0.1 to 0.3, and the refractive index difference between the second material layer and the main structure ranges from 0.2 to 0.

4.

6. The grating structure according to claim 1, characterized in that The grating structure further comprises a functional layer, and the functional layer is located on a surface of the structural unit that is away from the surface of the waveguide substrate; the refractive index of the functional layer is smaller than the refractive index of each part in the structural unit.

7. A method for preparing a grating structure, for preparing the grating structure according to any one of claims 1 to 6, characterized in that: The preparation method comprises: providing a waveguide substrate; Forming multiple material layers on the waveguide substrate in sequence, wherein the refractive index of each material layer gradually decreases as it moves away from the surface of the waveguide substrate; Forming a plurality of periodically arranged grooves in the multi-layer material layer by means of embossing or etching to obtain a plurality of periodically arranged additional structures; The grooves between the additional structures are filled with grating material to form the main structure.

8. The preparation method according to claim 7, characterized in that: The step of sequentially forming multiple material layers on the waveguide substrate comprises: Spin coating different materials sequentially on the waveguide substrate to form multiple material layers; The method of forming a plurality of periodically arranged grooves in the multi-layer material layer by means of embossing or etching to obtain a plurality of periodically arranged additional structures includes: forming a patterned mask layer on the outer surface of the multi-layer material layer; The multi-layer material layer is etched using the mask layer as a mask to form a plurality of periodically arranged grooves, thereby obtaining a plurality of periodically arranged additional structures.

9. The preparation method according to claim 7, characterized in that: The step of sequentially forming multiple material layers on the waveguide substrate comprises: Spraying materials on the waveguide substrate in sequence to form multiple material layers; The method of forming a plurality of periodically arranged grooves in the multi-layer material layer by means of embossing or etching to obtain a plurality of periodically arranged additional structures includes: Directing the side of the imprint template with the microstructure toward the multi-layer material layer; Applying pressure to the imprint template to transfer the microstructure of the imprint template to the multi-layer material layer, and forming the additional structure after curing and demoulding.

10. A diffractive optical waveguide, comprising an in-coupling grating and an out-coupling grating, or an in-coupling grating, a turning grating and an out-coupling grating, characterized in that: The turning grating and / or the outcoupling grating is implemented as a grating structure according to any one of claims 1 to 6.

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