CN116194819A

CN116194819A - Optical waveguide assembly and display apparatus including the same

Info

Publication number: CN116194819A
Application number: CN202180055152.XA
Authority: CN
Inventors: 赵瑜; 马珂奇
Original assignee: Ningbo Sunny Opotech Co Ltd
Current assignee: Ningbo Sunny Opotech Co Ltd
Priority date: 2020-09-11
Filing date: 2021-09-08
Publication date: 2023-05-30
Also published as: WO2022052949A1; CN114167606A; CN114167606B

Abstract

An optical waveguide assembly comprising: the optical waveguide device comprises a waveguide sheet (1) and at least two diffraction units, wherein the first diffraction unit (2) comprises a first coupling-in liquid crystal grating (21) and a first coupling-out liquid crystal grating (22), the first coupling-in liquid crystal grating (21) is used for coupling first light into the waveguide sheet (1), and the first coupling-out liquid crystal grating (22) is used for coupling the first light out of the waveguide sheet (1); the second diffraction unit (3) comprises a second coupling-in liquid crystal grating (31) and a second coupling-out liquid crystal grating (32), the second coupling-in liquid crystal grating (31) is used for coupling second light into the waveguide sheet (1), and the second coupling-out liquid crystal grating (32) is used for coupling the second light out of the waveguide sheet (1); by alternately applying voltages to the diffraction units, the first coupling-in liquid crystal grating (21) and the first coupling-out liquid crystal grating (22) of the first diffraction unit (2) or the second coupling-in liquid crystal grating (31) and the second coupling-out liquid crystal grating (32) of the second diffraction unit (3) are in grating states in the first direction, so that light rays with different wavelengths can be diffracted respectively, and full-color display can be realized, and the full-color display device is simple in structure, light and thin and small.

Description

Optical waveguide assembly and display apparatus including the same

Technical Field

The application relates to the technical field of optical transmission, in particular to an optical waveguide assembly and display equipment comprising the same.

Background

The display device is mainly used for displaying pictures or videos into human eyes, and can be widely applied to the fields of virtual reality, augmented reality, mixed reality or military and the like.

The display device comprises a light waveguide sheet and an image source, wherein the image source inputs light into the light waveguide sheet, and the light enters human eyes after forming vision difference through diffraction, so that a 3D effect is formed. In order to give the user a better visual experience, the display device needs to be displayed in full color.

However, the transmission efficiency and diffraction angle of the single-layer waveguide sheet on light with different wavelengths are different, which generally causes imbalance of the proportion and the emergent angle after light with three colors of red, green and blue is transmitted, so that the problems of uneven color, color cast display, rainbow effect and the like are caused.

Currently, for full-color display, a structure in which a plurality of waveguide sheets are stacked is generally employed, and light of a specific wavelength range is modulated by each waveguide sheet. For example, a two-layer waveguide sheet stacked structure, one layer for processing light of a blue light field and a partial green light field, and the other layer for processing light of a partial green light field and a full red light field; also for example, a three-layer waveguide sheet stack structure is provided, and the three-layer waveguide sheets are respectively used for processing light rays of blue light, red light and green light fields.

However, such a stacked structure of waveguide sheets results in a large overall thickness of the display device, which is disadvantageous in downsizing and weight saving of the device.

Disclosure of Invention

The main object of the present application is to provide an optical waveguide assembly capable of full color display and having a simple structure, and a display apparatus including the optical waveguide assembly.

An embodiment of the present application provides an optical waveguide assembly, including:

a waveguide sheet including a first optical surface and a second optical surface opposite to the first optical surface, and configured to perform total reflection transmission of light therein; and

at least two diffraction units, wherein

The first diffraction unit comprises a first incoupling liquid crystal grating and a first incoupling liquid crystal grating arranged on the first optical surface, the first incoupling liquid crystal grating and the first incoupling liquid crystal grating being arranged in a grating state in a first direction when a voltage is applied or not, the first incoupling liquid crystal grating being used for coupling first light into the waveguide sheet in the case of the grating state in the first direction, the first incoupling liquid crystal grating being used for coupling first light out of the waveguide sheet into the viewable area in the case of the grating state in the first direction, and

-the second diffraction unit comprises a second incoupling liquid crystal grating and a second incoupling liquid crystal grating provided at the second optical surface, the second incoupling liquid crystal grating and the second incoupling liquid crystal grating being arranged in a grating state in a first direction when a voltage is applied or not applied, the second incoupling liquid crystal grating being arranged to couple a second light ray into the waveguide sheet in the case of a grating state in the first direction, the second incoupling liquid crystal grating being arranged to couple a second light ray out of the waveguide sheet into the viewing area in the case of a grating state in the first direction, the second light ray having a wavelength different from the wavelength of the first light ray;

the first coupling-in liquid crystal grating and the first coupling-out liquid crystal grating of the first diffraction unit or the second coupling-in liquid crystal grating and the second coupling-out liquid crystal grating of the second diffraction unit are in a grating state in the first direction by alternately applying voltages to the diffraction units, so that first light rays and second light rays with different wavelengths can be diffracted respectively.

In one embodiment, the periods of the first in-coupling liquid crystal grating and the first out-coupling liquid crystal grating are set to correspond to the wavelength of the first light;

The period of the second in-coupling liquid crystal grating and the period of the second out-coupling liquid crystal grating are set to correspond to the wavelength of the second light.

In one embodiment, the first light is blue light and a portion of green light having a wavelength close to that of the blue light, and the second light is red light and another portion of green light having a wavelength close to that of the red light.

In one embodiment, the first in-coupling liquid crystal grating, the first out-coupling liquid crystal grating, the second in-coupling liquid crystal grating, and the second out-coupling liquid crystal grating are configured to be in a grating state in a first direction when a voltage is applied and to be in a uniform medium state in the first direction when no voltage is applied.

In one embodiment, the first direction is parallel to the first optical surface or the second optical surface of the waveguide sheet, and the first incoupling liquid crystal grating, the second incoupling liquid crystal grating and the second incoupling liquid crystal grating are in a one-dimensional grating state in the first direction when a voltage is applied.

In one embodiment, the first in-coupling liquid crystal grating, the first out-coupling liquid crystal grating, the second in-coupling liquid crystal grating, and the second out-coupling liquid crystal grating each comprise:

A liquid crystal layer including a plurality of liquid crystals, the liquid crystals being cholesteric liquid crystals;

two alignment film layers disposed at opposite sides of the liquid crystal layer with a gap therebetween for giving the liquid crystal initial director;

a first electrode layer; and

and the first electrode layer and the second electrode layer are oppositely arranged at the outer sides of the two alignment film layers at intervals.

In one embodiment, the first incoupling liquid crystal grating and the first incoupling liquid crystal grating have a liquid crystal pitch of 340nm.

In one embodiment, the liquid crystal pitch of the second in-coupling liquid crystal grating and the second out-coupling liquid crystal grating is 440nm.

In one embodiment, the thickness of the liquid crystal layer is no more than 2.5 times the liquid crystal pitch.

In one embodiment, the square wave alternating current with the voltage of 1KHz is applied to the first coupling-in liquid crystal grating, the first coupling-out liquid crystal grating, the second coupling-in liquid crystal grating and the second coupling-out liquid crystal grating, and the voltage amplitude is 5V-22V.

In one embodiment, the first electrode layer and the second electrode layer are made of Indium Tin Oxide (ITO) material.

In one embodiment, the first in-coupling liquid crystal grating, the first out-coupling liquid crystal grating, the second in-coupling liquid crystal grating and the second out-coupling liquid crystal grating each further comprise a plurality of spacers, and the spacers are distributed between the two alignment layers to support the two alignment layers and maintain and determine the distance between the two alignment layers.

In one embodiment, the waveguide sheet forms a substrate of the liquid crystal grating, and the first in-coupling liquid crystal grating, the first out-coupling liquid crystal grating, the second in-coupling liquid crystal grating and the second out-coupling liquid crystal grating respectively further comprise a protective layer, and the substrate and the protective layer are arranged on the outer sides of the first electrode layer and the second electrode layer at intervals.

In one embodiment, the protective layer is made of a glass material and has a thickness of 0.1mm to 0.3mm.

In one embodiment, the thickness of the waveguide sheet is 0.3-2.5 mm and the refractive index is 1.4-2.2.

In one embodiment, the optical waveguide assembly further comprises a third diffraction unit, the third diffraction unit comprising a third in-coupling liquid crystal grating and a third out-coupling liquid crystal grating, the third in-coupling liquid crystal grating being provided on a surface of the first in-coupling liquid crystal grating opposite to the waveguide sheet or on a surface of the second in-coupling liquid crystal grating opposite to the waveguide sheet, the third out-coupling liquid crystal grating being provided on a surface of the first out-coupling liquid crystal grating opposite to the waveguide sheet or on a surface of the second out-coupling liquid crystal grating opposite to the waveguide sheet, the third in-coupling liquid crystal grating and the third out-coupling liquid crystal grating being arranged to be in a grating state in a first direction when a voltage is applied or not applied;

The third coupling-in liquid crystal grating is used for coupling third light into the waveguide plate under the condition that the first direction is in a grating state, the third coupling-in liquid crystal grating is used for coupling the third light out of the waveguide plate to a visible region under the condition that the first direction is in a grating state, the wavelength of the third light is different from the wavelengths of the first light and the second light,

the first coupling-in liquid crystal grating and the first coupling-out liquid crystal grating of the first diffraction unit or the second coupling-in liquid crystal grating and the second coupling-out liquid crystal grating of the second diffraction unit or the third coupling-in liquid crystal grating and the third coupling-out liquid crystal grating of the third diffraction unit are in grating states in the first direction by alternately applying voltages to the diffraction units, so that first light rays, second light rays and third light rays with different wavelengths can be diffracted respectively.

An embodiment of the present application further provides a display device, including:

the projection optical machine comprises a display chip and a projection lens, wherein the display chip is used for controlling at least first light and second light which are used for outputting display images at a certain frequency according to time sequence, and the projection lens is used for projecting the light output by the display core; and

An optical waveguide assembly according to any one of the above embodiments, wherein at least a first incoupling liquid crystal grating of a first diffraction unit and a second incoupling liquid crystal grating of a second diffraction unit of the optical waveguide assembly are used for coupling light projected by the projection lens into a waveguide plate of the optical waveguide assembly, at least a first incoupling liquid crystal grating of the first diffraction unit and a second incoupling liquid crystal grating of the second diffraction unit of the optical waveguide assembly are used for coupling light coupled into the waveguide plate out of the waveguide plate into a viewing area,

the optical waveguide assembly is controlled at the same frequency as the output first light and the second light by alternately applying a voltage to each diffraction cell, and the grating of the first diffraction cell or the second diffraction cell is brought into a grating state in the first direction, so as to diffract the first light and the second light having different wavelengths, respectively.

In one embodiment, corresponding periodic voltages are applied to the first coupling-in liquid crystal grating, the first coupling-out liquid crystal grating, and the second coupling-in liquid crystal grating of the second diffraction unit, respectively, so as to control the first coupling-in liquid crystal grating, the first coupling-out liquid crystal grating, and the second coupling-in liquid crystal grating of the second diffraction unit to be in grating states in a first direction.

In one embodiment, the frequency of the first light and the second light output by the display chip is 60Hz.

The beneficial effects are that:

According to the optical waveguide component, the diffraction units are respectively arranged on the two surfaces of the waveguide sheet, each diffraction unit comprises the coupling-in liquid crystal grating and the coupling-out liquid crystal grating, the coupling-in liquid crystal grating and the coupling-out liquid crystal grating are arranged to be in the grating state in the first direction when voltage is applied or not applied, and the grating states of the first diffraction unit and the second diffraction unit are made to be in the grating state in the first direction by applying voltage to the coupling-in liquid crystal grating and the coupling-out liquid crystal grating of the corresponding diffraction unit or not, so that light rays with different wavelengths (different colors and different wavelengths) are diffracted. In addition, under the condition that only a single-layer waveguide sheet is used for the optical waveguide assembly, light rays with different wavelengths are diffracted by different gratings, so that the certain diffraction angle of the light rays with different wavelengths can be ensured, the diffraction efficiency is improved, and the problems of color cast, chromatic dispersion, color unevenness, rainbow effect and the like are avoided. In addition, the first coupling-in liquid crystal grating, the first coupling-out liquid crystal grating, the second coupling-in liquid crystal grating and the second coupling-out liquid crystal grating of the optical waveguide assembly provided by the embodiment are equivalent to the common one-dimensional surface relief grating, so that the field angle range is mainly influenced by the refractive index of the waveguide sheet, and the optical waveguide assembly can have the field angle range which can be achieved by the waveguide sheet of the common surface relief grating, and the field angle is large.

drawings

The advantages of the foregoing and/or additional aspects of the present invention will become apparent and readily appreciated from the description of the embodiments, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic structural diagram of an optical waveguide assembly according to an embodiment of the present disclosure;

FIG. 2 is a schematic diagram of a liquid crystal grating of an optical waveguide assembly according to an embodiment of the present disclosure;

FIG. 3 is a schematic diagram illustrating an operation state of a liquid crystal grating of an optical waveguide assembly according to an embodiment of the present disclosure;

FIG. 4 is a schematic diagram illustrating another working state of a liquid crystal grating of an optical waveguide assembly according to an embodiment of the present disclosure;

fig. 5 is a schematic structural diagram of a display device according to an embodiment of the present application;

fig. 6 is a voltage/time (U/t) variation diagram when performing a power-up manipulation for a diffraction unit of an optical waveguide assembly according to an embodiment of the present application.

The correspondence between the reference numerals and the component names in fig. 1 to 6 is:

1. a waveguide sheet; 2. a first diffraction unit; 21. a first coupling-in liquid crystal grating; 22. a first coupling liquid crystal grating; 3. a second diffraction unit; 31. a second coupling-in liquid crystal grating; 32. a second coupling liquid crystal grating; 4. a liquid crystal layer; 41. a liquid crystal; 5. an alignment film layer; 6. a first electrode layer; 7. a second electrode layer; 8. a substrate; 9. a protective layer; 10. a projection light machine; 101. a display chip; 102. a projection lens; 11. a spacer.

Detailed Description

In order that the above-recited objects, features and advantages of the present invention will be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description. It should be noted that, in the case of no conflict, the embodiments of the present application and the features in the embodiments may be combined with each other.

The optical waveguide assembly and the display device are mainly applied to the technical fields of virtual reality, augmented reality and mixed reality, whether the optical waveguide assembly and the display device are virtual reality, augmented reality or mixed reality is achieved by converting a source image into two images which are respectively input into left and right eyes, visual difference is formed, and accordingly 3D effects are achieved for people.

Specifically, the display device comprises a projection optical machine and an optical waveguide assembly, wherein the optical waveguide assembly further comprises a waveguide sheet, and a coupling-in grating and a coupling-out grating arranged on the waveguide sheet.

The projection optical machine projects image light to the coupling-in grating, the coupling-in grating diffracts light into the waveguide plate, the light is transmitted in the waveguide plate in a total reflection mode, the light is transmitted to the coupling-out grating, and the coupling-out grating diffracts the light into a visible area outside the waveguide plate, so that the light is received by human eyes.

Since the light is to be observed by human eyes, the image light projected by the projection light machine is visible light, the visible light is divided into multiple colors of light, and the wavelengths of the different colors of light are different. The diffraction angle of the light is related to the wavelength of the light and the period of the grating, so that when the same grating diffracts light with different colors, the diffraction angle and diffraction efficiency are different, the proportion and the emergent angle of the light with different colors are out of balance after the light with different colors is transmitted, and the problems of uneven color, color cast display, rainbow effect and the like are caused.

The three colors of red, green and blue are basic colors, and other colors can be displayed by superposition combination of two or three colors of the three colors, so that the projection optical machine only needs to project the three colors of red, green and blue, and the coupling-in and coupling-out gratings only need to diffract the three colors of light.

The optical waveguide assembly and the display device provided in the present application will be described in detail below.

Example 1

Fig. 1 is a schematic structural diagram of an optical waveguide assembly according to an embodiment of the present disclosure.

As shown in fig. 1, the present embodiment provides an optical waveguide assembly including:

a waveguide sheet 1 including a first optical surface and a second optical surface opposite to the first optical surface, and the waveguide sheet 1 for total reflection transmission of light therein; and

at least two diffraction units, wherein

A first diffraction unit 2 comprising a first incoupling liquid crystal grating 21 and a first incoupling liquid crystal grating 22 provided on the first optical surface, the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 being arranged to be grating-like in a first direction when a voltage is applied or not applied, the first incoupling liquid crystal grating 21 being arranged to couple first light into the waveguide sheet 1 in case of grating-like in the first direction, the first incoupling liquid crystal grating 22 being arranged to couple first light out of the waveguide sheet 1 to the viewing area in case of grating-like in the first direction; and

A second diffraction unit 3 comprising a second incoupling liquid crystal grating 31 and a second incoupling liquid crystal grating 32 provided on the second optical surface, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 being arranged in a grating state in the first direction when a voltage is applied or not applied, the second incoupling liquid crystal grating 31 being arranged to couple a second light ray into the waveguide sheet 1 in the case of a grating state in the first direction, the second incoupling liquid crystal grating 32 being arranged to couple the second light ray out of the waveguide sheet 1 into the viewing area in the case of a grating state in the first direction, the wavelength of the second light ray being different from the wavelength of the first light ray,

by alternately applying voltages to the diffraction units, the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 of the first diffraction unit 2 or the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 of the second diffraction unit 3 are in a grating state in the first direction, so that the first light and the second light with different wavelengths can be diffracted respectively.

The specific working principle of the optical waveguide component provided in this embodiment is as follows:

when the first light is to be diffracted, the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 of the first diffraction unit 2 are in a grating state in the first direction, and the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 of the second diffraction unit 3 are not in a grating state in the first direction by applying or not applying a voltage, and at this time, the grating of the first diffraction unit 2 diffracts the first light, and the grating of the second diffraction unit 3 does not diffract the light.

When the second light is to be diffracted, the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 of the first diffraction unit 2 are not in a grating state in the first direction, and the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 of the second diffraction unit 3 are in a grating state in the first direction by applying or not applying a voltage, and at this time, the grating of the first diffraction unit 2 does not diffract the light, and the grating of the second diffraction unit 3 diffracts the second light.

The optical waveguide assembly provided in this embodiment is provided with a diffraction unit on two surfaces of the waveguide sheet 1, each diffraction unit includes a coupling liquid crystal grating and a coupling liquid crystal grating, the coupling liquid crystal grating and the coupling liquid crystal grating are set to be in a grating state in a first direction when a voltage is applied or no voltage is applied, and the grating of the first diffraction unit 2 and the grating of the second diffraction unit 3 are in a grating state in the first direction by applying a voltage to the coupling liquid crystal grating and the coupling liquid crystal grating of the corresponding diffraction unit or not, so that light rays with different wavelengths (light rays with different colors and different wavelengths) are diffracted. In addition, under the condition that only a single-layer waveguide sheet is used for the optical waveguide assembly, light rays with different wavelengths are diffracted by different gratings, so that the certain diffraction angle of the light rays with different wavelengths can be ensured, the diffraction efficiency is improved, and the problems of color cast, chromatic dispersion, color unevenness, rainbow effect and the like are avoided. The first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 of the optical waveguide assembly provided in this embodiment are equivalent to the common one-dimensional surface relief grating, so that the field angle range is mainly affected by the refractive index of the waveguide sheet 1 itself, and the field angle range which can be reached by the waveguide sheet of the common surface relief grating is about 40 ° to 60 °.

Specifically, the periods of the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 are set to correspond to the wavelength of the first light, that is, the periods of the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 are not greatly different from the wavelength of the first light, so as to ensure that the diffraction angle of the first light is certain and improve the diffraction efficiency. The period of the second in-coupling liquid crystal grating 31 and the second out-coupling liquid crystal grating 32 are set to correspond to the wavelength of the second light, that is, the period of the second in-coupling liquid crystal grating 31 and the second out-coupling liquid crystal grating 32 is not greatly different from the wavelength of the second light, so as to ensure that the diffraction angle of the second light is certain and improve the diffraction efficiency.

Further, in this embodiment, the first light is blue light and a portion of green light having a wavelength close to that of the blue light, and the second light is red light and another portion of green light having a wavelength close to that of the red light. Those skilled in the art will readily recognize that, in other embodiments, the first light or the second light is light of other colors, which is also within the scope of the present application.

In this embodiment, the first incoupling liquid crystal grating 21, the first incoupling liquid crystal grating 22, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 are set to be in a grating state in the first direction when voltage is applied and to be in a uniform medium state in the first direction when no voltage is applied, that is, the optical waveguide assembly provided in this embodiment switches the working states of the gratings of the diffraction units by controlling the voltage applied to the first incoupling liquid crystal grating 21, the first incoupling liquid crystal grating 22, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32. Further, the first direction is parallel to the first optical surface or the second optical surface of the waveguide plate 1, and the first incoupling liquid crystal grating 21, the first incoupling liquid crystal grating 22, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 are in a one-dimensional grating state in the first direction when a voltage is applied. The specific working principle of the optical waveguide component provided in this embodiment is as follows:

When the first light needs to be diffracted, a voltage is applied to the first coupling-in liquid crystal grating 21 and the first coupling-out liquid crystal grating 22 of the first diffraction unit 2, and no voltage is applied to the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 of the second diffraction unit 3, and at this time, the grating of the first diffraction unit 2 is in a one-dimensional grating state in the first direction, and diffracts the first light. The grating of the second diffraction element 3 is in a uniform medium state in the first direction and does not diffract light.

When the second light needs to be diffracted, no voltage is applied to the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 of the first diffraction unit 2, and no voltage is applied to the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 of the second diffraction unit 3, and at this time, the gratings of the first diffraction unit 2 are in a uniform medium state in the first direction, and do not diffract the light. The grating of the second diffraction element 3 is in a one-dimensional grating state in the first direction, and diffracts the second light.

In other embodiments, the first incoupling liquid crystal grating 21, the first incoupling liquid crystal grating 22, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 may be set to be in a uniform medium state in the first direction when voltage is applied and in a grating state in the first direction when no voltage is applied.

Fig. 2 is a schematic structural diagram of a liquid crystal grating of an optical waveguide assembly according to an embodiment of the present application, and fig. 3 is a schematic working state of the liquid crystal grating of the optical waveguide assembly according to an embodiment of the present application.

As shown in fig. 2 and 3, in the present embodiment, the first incoupling liquid crystal grating 21, the first incoupling liquid crystal grating 22, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 are respectively included as liquid crystal gratings:

a liquid crystal layer 4 including a plurality of liquid crystals 41, the liquid crystals 41 being cholesteric liquid crystals;

two alignment film layers 5, the two alignment film layers 5 are disposed on both sides of the liquid crystal layer 4 at intervals opposite to each other and are used for giving an initial director of the liquid crystal 41;

a first electrode layer 6; and

the second electrode layer 7, the first electrode layer 6 and the second electrode layer 7 are disposed on the outer sides of the two alignment layers 5 with a gap therebetween.

When a voltage is applied to the first electrode layer 6 and the second electrode layer 7, an electric field E is formed between the first electrode layer 6 and the second electrode layer 7, so that the liquid crystal 41 located in the electric field E deflects the director, and thus the operation state of the grating is switched. That is, the operation state of the grating is switched by controlling whether or not a voltage is applied to the first electrode layer 6 and the second electrode layer 7.

Fig. 4 is a schematic diagram illustrating another operation state of a liquid crystal grating of an optical waveguide assembly according to an embodiment of the present disclosure.

The working principle is more specifically as follows:

when the first light is to be diffracted, a voltage (the voltage value is not zero) is applied to the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 of the first diffraction unit 2, the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 are in a one-dimensional grating state in the first direction (i.e. the horizontal direction in the present embodiment), as shown in fig. 3, a diffraction effect is generated on the first light, and at the same time, no voltage (the voltage value is zero) is applied to the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 of the second diffraction unit 3, at this time, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 are in a uniform medium state in the first direction (i.e. the horizontal direction in the present embodiment), as shown in fig. 4, no diffraction effect is generated on the light, i.e. the second optical surface equivalent to the waveguide 1 does not exist.

When the second light is to be diffracted, no voltage (with a voltage value of zero) is applied to the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 of the first diffraction unit 2, the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 are in a uniform medium state in the first direction (i.e. the horizontal direction in the embodiment), as shown in fig. 4, no diffraction effect is generated on the light, that is, no grating is present on the first optical surface of the waveguide sheet 1 at the moment, while a voltage (with a voltage value of non-zero) is applied to the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 of the second diffraction unit 3, at this time, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 are in a one-dimensional grating state in the first direction (i.e. the horizontal direction in the embodiment), as shown in fig. 3, and the diffraction effect is generated on the second light.

The first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31 and the liquid crystal 41 of the second coupling-out liquid crystal grating 32 of the optical waveguide assembly provided by the embodiment are cholesteric liquid crystals, the cholesteric liquid crystals have a pitch, so that the first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 have grating periods, and further the first electrode layer 6 and the second electrode layer 7 do not need to be configured into periodic structures, and the process manufacturing is simple and convenient. The pitch of cholesteric liquid crystal is the grating period. The pitch of the cholesteric liquid crystal can be slightly changed by changing the magnitude of the applied voltage, i.e. the magnitude of the grating period can be fine-tuned by changing the magnitude of the applied voltage. However, the pitch of the liquid crystal is mainly determined by the liquid crystal material itself, and the applied voltage can only be finely tuned.

Further, in the present embodiment, the pitch of the liquid crystal of the first coupling-in liquid crystal grating 21 and the first coupling-out liquid crystal grating 22 is 340nm, that is, the grating period of the first coupling-in liquid crystal grating 21 and the first coupling-out liquid crystal grating 22 is 340nm, so as to better diffract blue light with all wavelengths and part of green light close to the wavelength of the blue light, and the color development effect is good and the diffraction efficiency is high.

The pitch of the liquid crystal of the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 is 440nm, that is, the grating period of the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 is 440nm, so that all red light with the wavelength and the other part of green light close to the wavelength of the red light can be better diffracted, the color development effect is good, and the diffraction efficiency is high.

Furthermore, the thickness of the liquid crystal layer 4 is not more than 2.5 times of the liquid crystal pitch, the color development effect is good, and the diffraction efficiency is high.

In this embodiment, the square wave ac power with the voltage of 1KHz is applied to the first incoupling liquid crystal grating 21, the first incoupling liquid crystal grating 22, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32, and the voltage amplitude is 5V-22V.

In the present embodiment, the first electrode layer 6 and the second electrode layer 7 are made of Indium Tin Oxide (ITO).

In this embodiment, the liquid crystal 41 material of the liquid crystal layer 4 may be composed of a main body of BL015 nematic liquid crystal 41 plus a chiral agent ZLI-811, and the pitch of the cholesteric liquid crystal may be adjusted by the concentration of the chiral agent.

The first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 provided in this embodiment further include a plurality of spacers 11 (not shown), and the plurality of spacers 11 are distributed between the two alignment layers 5 to support the two alignment layers 5 and maintain and determine the distance therebetween.

Further, the waveguide sheet 1 forms a substrate 8 of the liquid crystal grating, and the first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 provided in this embodiment further include a protective layer 9, where the substrate 8 and the protective layer 9 are disposed on the outer sides of the first electrode layer 6 and the second electrode layer 7 in a spaced and opposite manner.

Specifically, the protective layer 9 is made of a glass material and has a thickness of 0.1mm to 0.3mm.

In the present embodiment, the thickness of the protective layer 9 is smaller than the thickness of the waveguide sheet 1. Further, the thickness of the waveguide sheet 1 can be 0.3-2.5 mm, the refractive index is 1.4-2.2, and the light transmission effect is good. Within this range, the higher the refractive index of the waveguide sheet 1 is, the better.

In the present embodiment, the spacers 11 are spheres having diameters corresponding to the thickness of the liquid crystal layer 4 arranged in a certain pattern or cylinders having heights corresponding to the thickness of the liquid crystal layer 4 arranged in a certain pattern.

Further, the first incoupling liquid crystal grating 21, the first incoupling liquid crystal grating 22, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 may further comprise a blocking member, respectively, which is located between the two alignment film layers 5 and is disposed around the liquid crystal layer 4, so as to prevent the liquid crystal 41 from overflowing.

The manufacturing methods of the first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 provided in the present embodiment are as follows:

providing a waveguide sheet 1 as a substrate 8 of each liquid crystal grating, and cleaning the waveguide sheet 1;

providing a protective layer 9 and cleaning the protective layer 9;

a first electrode layer 6 and a second electrode layer 7 are respectively arranged on the waveguide sheet 1 and the protective layer 9;

spin-coating an alignment film layer 5 on the first electrode layer 6 and the second electrode layer 7 respectively, and aligning;

spin-coating a spacer 11 between the two alignment film layers 5;

bonding the protective layer 9 and the waveguide sheet 1, wherein the alignment film layer 5 on the side of the protective layer 9 and the alignment film layer 5 on the side of the waveguide sheet 1 are opposite in alignment direction;

and filling the liquid crystal 41 and sealing to finish the manufacture of the grating.

The pitch of the cholesteric liquid crystal of the first coupled-in liquid crystal grating 21, the first coupled-in liquid crystal grating 22, the second coupled-in liquid crystal grating 31 and the second coupled-out liquid crystal grating 32 manufactured by the manufacturing method provided by the embodiment is the grating period, and the pitch can be finely adjusted by changing the voltage values applied to the first coupled-in liquid crystal grating 21, the first coupled-out liquid crystal grating 22, the second coupled-in liquid crystal grating 31 and the second coupled-out liquid crystal grating 32, so that the fine adjustment of the size of the grating period is flexible and convenient to use. And because the cholesteric liquid crystal provides grating periods for the first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32, the first electrode layer 6 and the second electrode layer 7 do not need to be manufactured into periodic structures, the manufacturing process is simple and convenient, and the production and the manufacturing are convenient.

Specifically, at the time of cleaning the waveguide sheet 1, the waveguide sheet 1 was ultrasonically cleaned with acetone, methanol, and isopropanol, respectively, for 10 minutes. During alignment, a friction alignment method or an optical alignment method is adopted for alignment, and the manufactured grating has good optical performance.

Of course, regarding the construction and fabrication of the first incoupling liquid crystal grating 21, the first incoupling liquid crystal grating 22, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32, instead of directly using a waveguide sheet as the liquid crystal grating substrate according to the above-described embodiments, a separate substrate, such as a sheet made of glass material, may be used. Accordingly, the liquid crystal grating and the waveguide sheet can be assembled after being prepared independently. In this case, the thickness of the optical waveguide assembly is increased by the additional glass sheet (substrate), but this embodiment may be a suitable choice for certain specific process conditions and/or applications in practice.

Example 2

The optical waveguide assembly provided in this embodiment further includes a third diffraction unit (not shown in the figure), where the third diffraction unit includes a third in-coupling liquid crystal grating and a third out-coupling liquid crystal grating, the third in-coupling liquid crystal grating is disposed on a surface of the first in-coupling liquid crystal grating 21 opposite to the waveguide sheet 1 or on a surface of the second in-coupling liquid crystal grating 31 opposite to the waveguide sheet 1, the third out-coupling liquid crystal grating is disposed on a surface of the first out-coupling liquid crystal grating 22 opposite to the waveguide sheet 1 or on a surface of the second out-coupling liquid crystal grating 32 opposite to the waveguide sheet 1, and the third in-coupling liquid crystal grating and the third out-coupling liquid crystal grating are configured to be in a grating state in the first direction when a voltage is applied or not applied;

The third coupling-in liquid crystal grating is used for coupling third light into the waveguide plate 1 under the condition that the first direction is in a grating state, the third coupling-in liquid crystal grating is used for coupling the third light out of the waveguide plate 1 to a visible region under the condition that the first direction is in a grating state, the wavelength of the third light is different from the wavelength of the first light and the second light, and the third light is intersected with the waveguide plate 1.

By alternately applying voltages to the diffraction cells, the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 of the first diffraction cell 2, the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 of the second diffraction cell 3, or the third incoupling liquid crystal grating and the third incoupling liquid crystal grating of the third diffraction cell are in a grating state in the first direction, so that the first light, the second light, and the third light with different wavelengths can be diffracted respectively.

In this embodiment, the third in-coupling liquid crystal grating and the third out-coupling liquid crystal grating are set to be in a one-dimensional grating state in the first direction when a voltage is applied and in a uniform medium state in the first direction when no voltage is applied. The specific working principle of the optical waveguide component provided in this embodiment is as follows:

when the first light needs to be diffracted, a voltage is applied to the first coupling-in liquid crystal grating 21 and the first coupling-out liquid crystal grating 22 of the first diffraction unit 2, and no voltage is applied to the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 of the second diffraction unit 3 and the third coupling-in liquid crystal grating and the third coupling-out liquid crystal grating of the third diffraction unit, at this time, the grating of the first diffraction unit 2 is in a one-dimensional grating state in the first direction, and diffracts the first light. The gratings of the second diffraction element 3 and the third diffraction element are in a uniform medium state in the first direction, and do not diffract light.

When the second light needs to be diffracted, no voltage is applied to the first coupling-in liquid crystal grating 21 and the first coupling-out liquid crystal grating 22 of the first diffraction unit 2, no voltage is applied to the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 of the second diffraction unit 3, and no voltage is applied to the third coupling-in liquid crystal grating and the third coupling-out liquid crystal grating of the third diffraction unit, and at this time, the gratings of the first diffraction unit 2 and the third diffraction unit are in a uniform medium state in the first direction, and do not diffract the light. The grating of the second diffraction element 3 is in a one-dimensional grating state in the first direction, and diffracts the second light.

When the third light is to be diffracted, no voltage is applied to the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 of the first diffraction unit 2 and the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 of the second diffraction unit 3, and no voltage is applied to the third incoupling liquid crystal grating and the third incoupling liquid crystal grating of the third diffraction unit, at which time the gratings of the first diffraction unit 2 and the second diffraction unit 3 are in a uniform medium state in the first direction and do not diffract the light. The grating of the third diffraction unit is in a one-dimensional grating state in the first direction and has a diffraction effect on the third light.

The optical waveguide assembly provided in this embodiment sets three diffraction units on two surfaces of the waveguide sheet 1, where each diffraction unit includes a coupling-in liquid crystal grating and a coupling-out liquid crystal grating, and the coupling-in liquid crystal grating and the coupling-out liquid crystal grating are set to be in a grating state in a first direction when a voltage is applied or no voltage is applied, and by applying a voltage to the coupling-in liquid crystal grating and the coupling-out liquid crystal grating of the corresponding diffraction unit, the gratings of the first diffraction unit 2, the second diffraction unit 3, or the third diffraction unit are in a grating state in the first direction, so that light rays with different wavelengths (light rays with different colors, and different wavelengths) are diffracted, so that the optical waveguide assembly provided in this embodiment can realize full-color display only by using a single-layer waveguide sheet, and has a simple structure, a light weight, a small size, a simple control method, and easy production and manufacture. And the optical waveguide component provided by the embodiment diffracts light rays with different wavelengths by different gratings under the condition of using only a single-layer waveguide sheet, so that the diffraction angle of the light rays with different wavelengths is ensured to be certain, the diffraction efficiency is improved, and the problems of color cast, chromatic dispersion, color non-uniformity, rainbow effect and the like are avoided. The first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31, the second coupling-out liquid crystal grating 32, the third coupling-in liquid crystal grating and the third coupling-out liquid crystal grating of the optical waveguide assembly provided by the embodiment are equivalent to the common one-dimensional surface relief grating, so that the field angle range is mainly influenced by the refractive index of the waveguide sheet 1, and the field angle range which can be reached by the waveguide sheet of the common surface relief grating can be provided, and the field angle is about 40-60 degrees.

Further, the periods of the third in-coupling liquid crystal grating and the third out-coupling liquid crystal grating are set to correspond to the wavelength of the third light, that is, the periods of the third in-coupling liquid crystal grating and the third out-coupling liquid crystal grating are not greatly different from the wavelength of the third light, so that the diffraction angle of the third light is ensured to be certain, and the diffraction efficiency is improved.

In this embodiment, the first light is blue light, the second light is green light, and the third light is red light. Because each chromatic light has the grating with the corresponding period to diffract, the diffraction angle is better controlled, and the diffraction efficiency is higher. It will be apparent to those skilled in the art that, in other embodiments, the first light, the second light, and the third light are light of other colors, which is also within the scope of the present application.

Example 3

Fig. 5 is a schematic structural diagram of a display device according to an embodiment of the present application.

As shown in fig. 5, the present embodiment further provides a display device, including:

a projection light machine 10, the projection light machine 10 comprising a display chip 101 and a projection lens 102, the display chip 101 being used for controlling the first light and the second light which are output at a certain frequency according to time sequence, the projection lens 102 being used for projecting the light output by the display chip 101; and

An optical waveguide assembly, which is the optical waveguide assembly according to any one of the above embodiments, at least the first incoupling liquid crystal grating 21 of the first diffraction unit 2 and the second incoupling liquid crystal grating 31 of the second diffraction unit 3 of the optical waveguide assembly are used for coupling the light projected by the projection lens 102 into the waveguide sheet 1 of the optical waveguide assembly, at least the first incoupling liquid crystal grating 22 of the first diffraction unit 2 and the second incoupling liquid crystal grating 32 of the second diffraction unit 3 of the optical waveguide assembly are used for coupling the light coupled into the waveguide sheet 1 out of the waveguide sheet 1 into the visible region,

by alternately applying a voltage to each diffraction cell, the optical waveguide assembly is controlled at the same frequency as the first light and the second light are output, and the grating of the first diffraction cell 2 or the second diffraction cell 3 is brought into a grating state in the first direction, so that the first light and the second light having different wavelengths are diffracted, respectively.

The detailed working principle of the display device provided in this embodiment is as follows:

when the display chip 101 outputs the first light of the display image, a voltage is applied to the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 (i.e. the voltage value is not zero), and the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 are in a one-dimensional grating state in the first direction (i.e. the horizontal direction in the embodiment), as shown in fig. 3, and generate a diffraction effect on the light. Meanwhile, no voltage (with zero voltage value) is applied to the second in-coupling liquid crystal grating 31 and the second out-coupling liquid crystal grating 32, and the second in-coupling liquid crystal grating 31 and the second out-coupling liquid crystal grating 32 are in a uniform medium state in the first direction (i.e., in the horizontal direction in the present embodiment), as shown in fig. 4, no diffraction effect is generated on light, i.e., no grating exists on the second optical surface of the waveguide sheet 1 at this moment.

When the display chip 101 outputs the second light of the display image, no voltage is applied to the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 (i.e. the voltage value is zero), the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 are in a uniform medium state in the first direction (i.e. the horizontal direction in the embodiment), as shown in fig. 4, no diffraction effect is generated on the light, that is, no grating is present on the first optical surface of the waveguide sheet 1 at the moment, while a voltage (the voltage value is not zero) is applied to the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32, and the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 are in a one-dimensional grating working state in the first direction (i.e. the horizontal direction in the embodiment), as shown in fig. 3.

That is, the optical waveguide assembly outputs the first light and the second light of the display image at a certain frequency. When the frequency is equal to or higher than the refresh rate of human eyes, the human eyes observe a color image formed by combining two parts of light rays (when the first light ray is blue light and part of green light, and the second light ray is red light and the other part of green light, the human eyes observe a full-color image formed by combining two parts of light rays).

The projection optical machine 10 of the display device provided in this embodiment projects the first light and the second light with a certain frequency, the optical waveguide component correspondingly switches the grating states of the first diffraction unit 2 or the second diffraction unit 3 in the first direction with the same frequency so as to diffract the light with different wavelengths (different light wavelengths of different colors), so that the display device provided in this embodiment can realize full-color display only by using a single-layer waveguide sheet, and has a simple structure, a light weight, a small size, a simple control method, and easy production and manufacture. In addition, under the condition that only a single-layer waveguide sheet is used, the display device provided by the embodiment diffracts light rays with different wavelengths through different gratings, so that the certain diffraction angle of the light rays with different wavelengths can be ensured, the diffraction efficiency is improved, and the problems of color cast, chromatic dispersion, color non-uniformity, rainbow effect and the like are avoided. The first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 of the display device provided by the embodiment are equivalent to the common one-dimensional surface relief grating, so that the field angle range is mainly affected by the refractive index of the waveguide sheet 1, and the field angle range which can be reached by the waveguide sheet of the common surface relief grating is about 40-60 degrees.

Further, as shown in fig. 6, the first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, and the second coupling-in liquid crystal grating 31, 32 of the first diffraction unit 2 are in a grating state in the first direction by applying corresponding periodic voltages to the first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, and the second coupling-out liquid crystal grating 31, 32 of the second diffraction unit 3, respectively, which are simple and convenient. Specifically, the period of the voltage applied to the first incoupling liquid crystal grating 21 and the first incoupling liquid crystal grating 22 of the first diffraction unit 2 and the period of the voltage applied to the second incoupling liquid crystal grating 31 and the second incoupling liquid crystal grating 32 of the second diffraction unit 3 are staggered with each other. The applied voltage is preferably a square wave alternating current with the self frequency of 1KHz, as shown in fig. 6, wherein the voltage value determines the period of the formed diffraction grating and the pitch of the corresponding cholesteric liquid crystal, and the voltage amplitude is generally 5-22V, and can be selected according to actual requirements.

Alternatively, the frequency of the first light and the second light output by the display chip 101 is 60Hz, and the full-color display effect is good.

Example 4

In the present embodiment, the display chip 101 is configured to control the first light, the second light, and the third light, which are output to display images at a certain frequency in time sequence, and accordingly, the optical waveguide assembly further includes a third diffraction unit.

The optical waveguide assembly correspondingly switches the grating of the first diffraction unit 2, the second diffraction unit 3 or the third diffraction unit in the first direction at the same frequency as that of outputting the first light, the second light and the third light to diffract the light with different wavelengths (different light wavelengths of different colors), so that the display device provided by the embodiment can realize full-color display by using the single-layer waveguide sheet, and has the advantages of simple structure, light weight, compactness, simple control method and easiness in production and manufacture. In addition, under the condition that only a single-layer waveguide sheet is used, the display device provided by the embodiment diffracts light rays with different wavelengths through different gratings, so that the certain diffraction angle of the light rays with different wavelengths can be ensured, the diffraction efficiency is improved, and the problems of color cast, chromatic dispersion, color non-uniformity, rainbow effect and the like are avoided. The first coupling-in liquid crystal grating 21, the first coupling-out liquid crystal grating 22, the second coupling-in liquid crystal grating 31 and the second coupling-out liquid crystal grating 32 of the display device provided by the embodiment are equivalent to the common one-dimensional surface relief grating, so that the field angle range is mainly affected by the refractive index of the waveguide sheet 1, and the field angle range which can be reached by the waveguide sheet of the common surface relief grating is about 40-60 degrees.

Further, the first light is blue light, the second light is green light, and the third light is red light. Because each chromatic light has the grating with the corresponding period to diffract, the diffraction angle is better controlled, and the diffraction efficiency is higher. It will be apparent to those skilled in the art that, in other embodiments, the first light, the second light, and the third light are light of other colors, which is also within the scope of the present application.

In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the apparatus or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; the communication may be direct or indirect through an intermediate medium, or may be internal to two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art. Furthermore, in the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more.

The foregoing is only illustrative of the present invention and is not to be construed as limiting thereof, but rather as various modifications, equivalent arrangements, improvements, etc., within the spirit and principles of the present invention.

Claims

An optical waveguide assembly, comprising:

a waveguide sheet (1) comprising a first optical surface and a second optical surface opposite to the first optical surface, and the waveguide sheet (1) is for total reflection transmission of light therein; and

at least two diffraction units, wherein

-the first diffraction unit (2) comprises a first incoupling liquid crystal grating (21) and a first incoupling liquid crystal grating (22) provided at the first optical surface, the first incoupling liquid crystal grating (21) and the first incoupling liquid crystal grating (22) being arranged to be grating-like in a first direction when a voltage is applied or not applied, the first incoupling liquid crystal grating (21) being arranged to couple first light into the waveguide sheet (1) in the case of grating-like in the first direction, the first incoupling liquid crystal grating (22) being arranged to couple first light out of the waveguide sheet (1) into the viewing area in the case of grating-like in the first direction, and

-a second diffraction unit (3) comprising a second incoupling liquid crystal grating (31) and a second incoupling liquid crystal grating (32) provided at the second optical surface, the second incoupling liquid crystal grating (31) and the second incoupling liquid crystal grating (32) being arranged to be grating-like in a first direction when a voltage is applied or not applied, the second incoupling liquid crystal grating (31) being arranged to couple second light into the waveguide sheet (1) in the case of grating-like in the first direction, the second incoupling liquid crystal grating (32) being arranged to couple second light out of the waveguide sheet (1) into the viewing area in the case of grating-like in the first direction, the wavelength of the second light being different from the wavelength of the first light;

The first coupling-in liquid crystal grating (21) and the first coupling-out liquid crystal grating (22) of the first diffraction unit (2) or the second coupling-in liquid crystal grating (31) and the second coupling-out liquid crystal grating (32) of the second diffraction unit (3) are in grating states in the first direction by alternately applying voltages to the diffraction units, so that first light rays and second light rays with different wavelengths can be diffracted respectively.
The optical waveguide assembly according to claim 1, characterized in that the period of the first incoupling liquid crystal grating (21) and the first incoupling liquid crystal grating (22) is arranged to correspond to the wavelength of the first light;

the period of the second in-coupling liquid crystal grating (31) and the second out-coupling liquid crystal grating (32) is set to correspond to the wavelength of the second light.
The optical waveguide assembly of claim 2, wherein the first light is blue light and a portion of green light having a wavelength close to that of the blue light, and the second light is red light and another portion of green light having a wavelength close to that of the red light.
The optical waveguide assembly according to claim 1, characterized in that the first incoupling liquid crystal grating (21), the first incoupling liquid crystal grating (22), the second incoupling liquid crystal grating (31) and the second incoupling liquid crystal grating (32) are arranged in a grating state in a first direction when a voltage is applied and in a uniform medium state in a first direction when no voltage is applied.
The optical waveguide assembly according to claim 4, characterized in that the first direction is parallel to the first optical surface or the second optical surface of the waveguide sheet (1), the first incoupling liquid crystal grating (21), the first incoupling liquid crystal grating (22), the second incoupling liquid crystal grating (31) and the second incoupling liquid crystal grating (32) being one-dimensional grating states in the first direction upon application of a voltage.
The optical waveguide assembly according to any one of claims 1 to 5, wherein the first in-coupling liquid crystal grating (21), the first out-coupling liquid crystal grating (22), the second in-coupling liquid crystal grating (31) and the second out-coupling liquid crystal grating (32) each comprise:

a liquid crystal layer (4) comprising a plurality of liquid crystals (41) which are cholesteric liquid crystals;

two alignment film layers (5), the two alignment film layers (5) are oppositely arranged at intervals on two sides of the liquid crystal layer (4) and are used for giving an initial director of the liquid crystal (41);

a first electrode layer (6); and

and the second electrode layers (7), the first electrode layers (6) and the second electrode layers (7) are oppositely arranged at intervals on the outer sides of the two alignment film layers (5).
The optical waveguide assembly according to claim 6, characterized in that the liquid crystal pitch of the first incoupling liquid crystal grating (21) and the first incoupling liquid crystal grating (22) is 340nm.
The optical waveguide assembly according to claim 6, characterized in that the liquid crystal pitch of the second incoupling liquid crystal grating (31) and the second incoupling liquid crystal grating (32) is 440nm.
The optical waveguide assembly according to claim 6, characterized in that the thickness of the liquid crystal layer (4) does not exceed 2.5 times the liquid crystal pitch.
The optical waveguide assembly according to claim 6, wherein the first incoupling liquid crystal grating (21), the first incoupling liquid crystal grating (22), the second incoupling liquid crystal grating (31) and the second incoupling liquid crystal grating (32) are applied with square wave alternating current with a voltage of 1KHz and a voltage amplitude of 5-22V.
The optical waveguide assembly according to claim 6, characterized in that the first electrode layer (6) and the second electrode layer (7) are made of Indium Tin Oxide (ITO) material.
The optical waveguide assembly according to claim 6, wherein the first incoupling liquid crystal grating (21), the first incoupling liquid crystal grating (22), the second incoupling liquid crystal grating (31) and the second incoupling liquid crystal grating (32) each further comprise a plurality of spacers, which are distributed between two alignment film layers (5) to support the two alignment film layers (5) and to maintain and determine the distance between them.
The optical waveguide assembly according to claim 6, wherein the waveguide sheet (1) constitutes a substrate (8) of a liquid crystal grating, the first incoupling liquid crystal grating (21), the first incoupling liquid crystal grating (22), the second incoupling liquid crystal grating (31) and the second incoupling liquid crystal grating (32) further comprise a protective layer (9), respectively, the substrate (8) and the protective layer (9) being arranged outside the first electrode layer (6) and the second electrode layer (7) at opposite intervals.
Optical waveguide assembly according to claim 13, characterized in that the protective layer (9) is made of glass material and has a thickness of 0.1mm to 0.3mm.
The optical waveguide assembly according to claim 1, characterized in that the waveguide sheet (1) has a thickness of 0.3-2.5 mm and a refractive index of 1.4-2.2.
The optical waveguide assembly according to claim 1, further comprising a third diffraction unit comprising a third incoupling liquid crystal grating provided on a surface of the first incoupling liquid crystal grating (21) opposite the waveguide sheet (1) or on a surface of the second incoupling liquid crystal grating (31) opposite the waveguide sheet (1), the third incoupling liquid crystal grating being provided on a surface of the first incoupling liquid crystal grating (22) opposite the waveguide sheet (1) or on a surface of the second incoupling liquid crystal grating (32) opposite the waveguide sheet (1), the third incoupling liquid crystal grating and the third incoupling liquid crystal grating being arranged to be grating states in a first direction when a voltage is applied or not applied;

The third coupling-in liquid crystal grating is used for coupling third light into the waveguide sheet (1) under the condition that the first direction is in a grating state, the third coupling-in liquid crystal grating is used for coupling the third light out of the waveguide sheet (1) to a visible region under the condition that the first direction is in a grating state, the wavelength of the third light is different from the wavelengths of the first light and the second light,

the first coupling-in liquid crystal grating (21) and the first coupling-out liquid crystal grating (22) of the first diffraction unit (2) or the second coupling-in liquid crystal grating (31) and the second coupling-out liquid crystal grating (32) of the second diffraction unit (3) or the third coupling-in liquid crystal grating and the third coupling-out liquid crystal grating of the third diffraction unit are alternately applied with voltages, so that the first light, the second light and the third light with different wavelengths can be diffracted respectively.
A display device, characterized by comprising:

a projection optical machine (10), wherein the projection optical machine (10) comprises a display chip (101) and a projection lens (102), the display chip (101) is used for controlling at least a first light ray and a second light ray which are output by a certain frequency according to time sequence, and the projection lens (102) is used for projecting the light rays output by the display chip (101); and

An optical waveguide assembly, which is an optical waveguide assembly according to any one of claims 1 to 16, at least a first incoupling liquid crystal grating (21) of a first diffraction unit (2) and a second incoupling liquid crystal grating (31) of a second diffraction unit (3) of the optical waveguide assembly being used for coupling light projected by the projection lens (102) into a waveguide sheet (1) of the optical waveguide assembly, at least a first incoupling liquid crystal grating (22) of the first diffraction unit (2) and a second incoupling liquid crystal grating (32) of the second diffraction unit (3) of the optical waveguide assembly being used for coupling light coupled into the waveguide sheet (1) out of the waveguide sheet (1) into a viewable area,

the optical waveguide assembly is controlled at the same frequency as the output of the first light and the second light by alternately applying a voltage to each diffraction cell, and the grating of the first diffraction cell (2) or the second diffraction cell (3) is brought into a grating state in the first direction so as to diffract the first light and the second light having different wavelengths, respectively.
A display device according to claim 17, characterized in that the first incoupling liquid crystal grating (21), the first incoupling liquid crystal grating (22) and the second incoupling liquid crystal grating (31, 32) of the first diffraction unit (2) are respectively applied with corresponding periodic voltages to control switching of the first incoupling liquid crystal grating (21), the first incoupling liquid crystal grating (22) and the second incoupling liquid crystal grating (31, 32) of the first diffraction unit (2) in a grating state in a first direction.
The display device according to claim 17, wherein the frequency at which the display chip (101) outputs the first light and the second light is 60Hz.