WO2020088055A1 - 基于彩色偏振体光栅的全彩波导耦合近眼显示结构、制备方法及ar可穿戴设备 - Google Patents

基于彩色偏振体光栅的全彩波导耦合近眼显示结构、制备方法及ar可穿戴设备 Download PDF

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WO2020088055A1
WO2020088055A1 PCT/CN2019/101983 CN2019101983W WO2020088055A1 WO 2020088055 A1 WO2020088055 A1 WO 2020088055A1 CN 2019101983 W CN2019101983 W CN 2019101983W WO 2020088055 A1 WO2020088055 A1 WO 2020088055A1
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waveguide
color
green
blue
layer
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French (fr)
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张宇宁
翁一士
崔静怡
刘奡
沈忠文
李晓华
王保平
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东南大学
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells

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  • the invention relates to a full-color waveguide coupling near-eye display structure based on a color polarizer grating, a preparation method and an AR wearable device.
  • the near-eye display system designed based on the planar waveguide with coupling elements has been greatly developed in the past ten years and is widely used in military and commercial fields.
  • the above-mentioned waveguide structure must meet the characteristics of light weight, small size, high transparency, and wide exit pupil.
  • the coupling element can determine important parameters such as field of view (FOV), coupling efficiency, and color rendering.
  • optical diffraction elements In order to further lighten the waveguide structure, optical diffraction elements (DOEs) have been extensively studied and used as coupling elements in waveguide near-eye display systems. Among such multiple diffraction elements, optical diffraction gratings are the most common. When used in a waveguide-coupled near-eye display system, the diffraction grating can couple the incident light beam from the microdisplay into the waveguide. The diffraction grating has a large diffraction angle, as well as angular selectivity and wavelength selectivity, which ensures that the beam can efficiently propagate in the waveguide when the total internal reflection condition is satisfied.
  • HVG holographic volume gratings
  • General holographic volume gratings can be made by recording interference patterns on holographic recording materials (such as photopolymers, dichromate gelatin, etc.).
  • holographic recording materials such as photopolymers, dichromate gelatin, etc.
  • HVG has high transparency to ambient light.
  • the short angular bandwidth and wavelength bandwidth limit the FOV of the field of view and when used in a waveguide-coupled display system, it also limits the realization of full-color transmission.
  • the difference in birefringence can determine the angle and wavelength bandwidth of the volume grating.
  • the birefringence material of traditional dichromate gelatin material can reach 0.15.
  • the difference in birefringence of most photopolymers used as recording media today is only 0.035.
  • Such a small birefringence difference results in a narrow angular bandwidth and wavelength bandwidth, resulting in a small angle of view.
  • the present invention proposes a preparation method of a full-color waveguide-coupled near-eye display system based on a color polarizer grating (CPVG), which is used to solve the low diffraction efficiency and small angle of view of the existing methods , Not conducive to the realization of full-color transmission and other issues.
  • CPVG color polarizer grating
  • the deflection characteristics of the grating make at least 50% of the unpolarized ambient light directly transmit the grating without diffraction.
  • a full-color waveguide-coupled near-eye display structure based on a color polarizer grating which uses a double-layer waveguide structure with a color polarizer grating as a coupling device to achieve full-color near-eye display, where one layer is used to propagate the blue
  • the green waveguide structure uses blue and green polarizer gratings as coupling devices to realize the transmission of blue and green light beams in the waveguide; the other layer of red waveguide structures used to propagate red beams uses red polarizer gratings as The coupling device thus realizes the transmission of the red light beam in the waveguide.
  • the in-coupling device and the out-coupling device in the blue and green waveguide structures are both blue and green PVG, and the in-coupling device and the out-coupling device in the blue and green waveguide structures are located at the mirror symmetry position of the planar waveguide structure; accordingly, the red waveguide
  • the in-coupling device and the out-coupling device in the structure are both red PVG, and the second in-coupling device and the out-coupling device in the red waveguide structure are also located at the mirror symmetry position of the planar waveguide structure.
  • the blue and green waveguide structures include two layers, a blue waveguide layer and a green waveguide layer.
  • the horizontal period length of the blue waveguide layer is the same as the horizontal period length of the green waveguide layer, which satisfies the Bragg diffraction formula:
  • n eff represents the equivalent refractive index of the birefringent material used for the grating
  • ⁇ x represents the horizontal period length of the grating in the x direction
  • ⁇ B represents the Bragg wavelength in vacuum.
  • the invention further discloses a method for preparing the full-color waveguide coupled near-eye display structure based on the color polarizer grating, which includes the following steps:
  • Step 1 After dissolving the photo-alignment material in the corresponding solvent, spin-coat on the clean glass waveguide surface, and form a thin film after heating for a period of time;
  • Step 2 Two beams of polarized light are subjected to interference exposure on the photo-alignment material film formed in Step 1, and a photo-alignment layer is further formed;
  • Step 3 Place the solution containing liquid crystal polymer and chiral material on the alignment layer formed in Step 2, and then place the glass on the spin coater at a certain rotation speed for a certain period of time to stop;
  • Step 4 Use 5J / cm 2 ultraviolet light to perform ultraviolet curing in a nitrogen environment
  • Step 5 Repeat Step 3 and Step 4 until the film thickness reaches 100nm to 1 ⁇ m to ensure the formation of the grating.
  • the green PVG thickness is first spin coated and cured to reach 100nm to 1 ⁇ m, and then directly on the green PVG layer Spin-coat and fix the blue waveguide layer.
  • the exposure environment in step two needs to satisfy a temperature between 20 ° C and 30 ° C and a relative humidity below 38.
  • the energy of the laser used for exposure in step 2 is controlled at 6J / cm 2 to 10J / cm 2 .
  • the invention further discloses an AR wearable device, which adopts the full-color waveguide coupling near-eye display structure based on the color polarizer grating.
  • the color volume holographic grating in the present invention which plays a coupling role, can couple the light in the blue-green band and the red band into two waveguides to realize a display system based on a full-color coupling waveguide.
  • the present invention forms a Bragg grating structure and the liquid crystal material used has a large birefringence difference ⁇ n. Therefore, it can be known from the coupled wave theory that the present invention can achieve very high grating diffraction efficiency.
  • the liquid crystal material used in the present invention has a large birefringence difference.
  • the coupling wave theory it can be known that the coupling grating has a larger incident angle bandwidth. Using this point, AR with a large field of view (up to 35 °) can be prepared. Wearable device.
  • FIG. 1 is a schematic structural view of a CPVG as a coupling device in the present invention
  • Figure 1 (a) shows the blue-green volume grating structure used to diffract blue and green, where ⁇ bgx represents the horizontal period length values of the blue waveguide layer and the green waveguide layer; ⁇ by and ⁇ gy represents the vertical period length values of the blue waveguide layer and the green waveguide layer respectively; the vectors K b and K g represent the Bragg vectors of the volume gratings in the blue waveguide layer and the green waveguide layer, respectively; with Respectively represent the inclination angle of the periodic refractive index plane in the blue waveguide layer and the green waveguide layer.
  • Fig. 1 (b) shows a PVG structure capable of Bragg diffraction of red light, where ⁇ rx represents the horizontal period length value of the red waveguide layer; ⁇ ry represents the vertical period length value; vector K r represents the volume grating in the red waveguide layerstitution vector Represents the inclination angle of the periodic refractive index plane in the red waveguide layer; ⁇ represents the angle between the optical axis of the liquid crystal molecule and the z-axis.
  • FIG. 2 is a schematic diagram of the double-layer waveguide structure described in the present invention.
  • Microdisplay 2. Retina of observer; 3. Human eye lens; 4. Collimator ; 5. Air layer between blue-green waveguide layer and red waveguide layer; 6. Blue-green waveguide layer; 7 1. Red waveguide layer; 8. In-coupling device of green waveguide layer; 9. Out-coupling device of cyan waveguide layer; 10. In-coupling device of red waveguide layer; 11. Out-coupling device of red waveguide layer;
  • FIG. 3 is a schematic diagram of the three-layer waveguide structure described in the present invention.
  • FIG. 6 is a schematic diagram of the exposure optical path used in the present invention.
  • 100 linearly polarized laser; 200, half wave plate; 300, polarized beam splitter PBS; (400, 900), quarter wave plate; (500, 800), beam expander lens; (600, 700 ), Plane mirror; 1000, sample to be exposed; ⁇ represents the angle between two polarized lights.
  • FIG. 1 The structure of the CPVG used as the coupling device in the present invention is shown in FIG. 1. It can be seen from FIG. 1 that the volume holographic grating PVG has a two-dimensional periodic structure, where,
  • the angle ⁇ between the optical axis of the liquid crystal molecule and the z axis will periodically change in the x direction, that is, the horizontal direction, and its period length is recorded as ⁇ x .
  • the liquid crystal material (or more broadly, the birefringent material) exhibits a periodic spiral structure in the y direction, that is, the vertical direction, and its period is recorded as ⁇ y .
  • Such a two-dimensional periodic structure can produce a series of tilted periodic refractive index planes, whose tilt angle It can be calculated by formula (1):
  • ⁇ B represents the Bragg wavelength in vacuum
  • n eff represents the equivalent refractive index of the birefringent medium, which is calculated by formula (4):
  • the two CPVG structures shown in Figure 1 represent (a) blue and green volume gratings (cyan PVG) used to diffract blue and green, respectively. Cyan PVG can be divided into two layers, blue and green. The horizontal period of these two layers is the same. It is recorded as ⁇ bgx in Figure 1 (a), and its value is calculated by the above formula (3):
  • n eff represents the equivalent refractive index of the birefringent material used for the grating
  • ⁇ x represents the horizontal period length of the grating in the x direction
  • ⁇ B represents the Bragg wavelength in vacuum.
  • ⁇ x is the horizontal period length of the blue waveguide layer; when the wavelength value ⁇ B is 532 nm (green), When it is the tilt angle of the refractive index plane in the green waveguide layer, ⁇ x is the horizontal period length value of the green waveguide layer. Since the blue-green waveguide layer has the same horizontal period length value in the structure proposed by the present invention, it is written as ⁇ bgx .
  • the blue and green waveguide layers satisfy the same grating dispersion equation (5):
  • ⁇ 0 represents the diffraction angle (beam propagation angle in the waveguide)
  • n glass represents the refractive index value of the glass waveguide
  • ⁇ represents the wavelength of the beam
  • ⁇ i represents the angle of incidence in the air
  • m represents the diffraction
  • the order (m 1 for volume gratings)
  • ⁇ x represents the horizontal period length of the grating in the x direction.
  • ⁇ x is ⁇ bgx .
  • CPVG In the preparation process, CPVG only needs one polarization interference exposure to produce the required horizontal period length ⁇ x on the photo-alignment material, and then spin-coat the chiral spiral materials with different ⁇ y in sequence.
  • Figure 1 (b) shows a PVG structure that can cause Bragg diffraction of red light, which has a different horizontal period length from blue and green CPVG, that is, ⁇ rx is not equal to ⁇ bgx .
  • Table 1 lists a set of example parameters. As an example in a specific implementation, Table 1 lists a set of relevant parameters of CPVG corresponding to different center wavelengths (457 nm, 532 nm, and 630 nm). The actual parameter values need to be changed according to the required design.
  • Fig. 2 shows the overall structure of the present invention.
  • the system includes a blue-green waveguide layer 6 (Waveguide (B + G)) that propagates blue and green and a red waveguide layer 7 (Waveguide (R)) that propagates red.
  • B + G blue-green waveguide layer 6
  • R red waveguide layer 7
  • the in-coupling device 8 of the green waveguide layer in the cyan waveguide layer 6 and the out-coupling device 9 of the cyan waveguide layer are both cyan PVG, and the in-coupling device 8 of the green waveguide layer and the out-coupling device 9 of the cyan waveguide layer It is located at the mirror symmetry position of the planar waveguide structure. Accordingly, the in-coupling device 10 of the red waveguide layer and the out-coupling device 11 of the red waveguide layer in the red waveguide layer 7 are both red PVG, and the in-coupling device 10 of the red waveguide layer and the out-coupling device 11 of the red waveguide layer are also It is located at the mirror symmetry position of the planar waveguide structure.
  • FIG. 2 shows the propagation of the light beam from the center wavelength band of the microdisplay 1 in the double-layer waveguide structure.
  • the white light emitted from the microdisplay 1 including the three wavelength bands of red, green and blue will pass through the in-coupling device 8 of the green waveguide layer of the blue-green waveguide layer and the in-coupling device 10 of the red waveguide layer vertically.
  • the in-coupling device 8 of the green waveguide layer of the blue-green waveguide layer the in-coupling device 10 of the red waveguide layer vertically.
  • the in-coupling device will diffract the incident light into the waveguide at different angles greater than the total internal reflection angle.
  • the two waveguides capable of propagating light beams of different wavelength bands have different PVGs.
  • the CPVGs of the blue and green waveguides at the top act on blue and green, and their diffraction angles can be obtained using equation (5).
  • the PVG of the red waveguide located at the bottom end only affects the red color. Similarly, its diffraction angle can also be obtained using equation (5).
  • the out-coupling PVG When the propagating light beam reaches the PVG as an out-coupling, the out-coupling PVG will diffract the light beam out of the waveguide at an angle when it reaches the in-coupling with the incident wave.
  • the observer's retina 2 After collimating the lens 3 of the human eye, the observer's retina 2 can receive a color pixel image at a suitable position. In fact, pixels are imaged at infinity and received by the human eye.
  • the dispersion phenomenon can be cancelled.
  • the color ghost image can be eliminated internally, which is an important feature for full-color display to ensure image quality.
  • the propagation of light beams propagating in different waveguides is irrelevant, and since the air layer 5 exists between the two waveguide layers, the crosstalk between the gratings of the different waveguides is negligible.
  • the continuity of the exit pupil is also a key issue for waveguide-based display systems, which affects the uniformity of color and brightness when viewing images at different locations. We have studied and recorded relevant facts in previous work. This problem can be solved efficiently by selecting the waveguide of appropriate thickness, propagation step size, and adjusting the size of the entrance pupil.
  • a high-refractive-index glass with a thickness of 1 mm is used as the waveguide, and the center wavelengths of the propagating beams of the three colors (red, green, and blue) are 630 nm, 532 nm, and 457 nm, respectively.
  • the minimum diffraction angle is calculated by formula (6):
  • n the refractive index value of the used waveguide material.
  • W represents the collimator empty diameter (10 mm in the present invention)
  • t represents the thickness of the waveguide (the thickness of the waveguide in each layer of the present invention is 1 mm).
  • Figure 4 shows the diffraction angle distribution curves with different incident angles under different wavelength conditions.
  • the FOV that can be realized is about 35.7 ° (-13.3 ° -22.4 °), and the field angle of this size meets the requirements of the current mainstream waveguide-based near-eye display system.
  • azo dyes such as SD1, BY, etc. can be selected as the photo-alignment material, and DMF as the solvent.
  • the spin coater rotates at a certain speed for a period of time and then stops, and then the waveguide is heated on a hot table at 120 ° C for 30 minutes to form a thin film.
  • Step 2 Two beams of polarized light are subjected to interference exposure on the photo-alignment material film formed in Step 1, and a photo-alignment layer is further formed.
  • the exposure device is shown in Figure 6:
  • the light beam emitted by the linear polarization laser 100 passes through the half-wave plate 200 and is split into two mutually orthogonal polarized light beams by a polarizing beam splitter (PBS) 300.
  • PBS polarizing beam splitter
  • QWP quarter-wave plates
  • the half-wave plate 200 is used to adjust the light intensity of the two channels to ensure that the two channels have the same intensity.
  • the two coherent lights After passing through the spatial filtering and beam expanding lens, the two coherent lights are respectively reflected by a plane mirror at a certain angle. Finally, the two circularly polarized lights with opposite circular polarization characteristics will be superimposed at an angle of ⁇ and formed on the photo-alignment layer of sample 1000 Interference pattern.
  • the horizontal period length As an example of the present invention, for blue, green, and red PVGs, if the exposure angles are set to 76 ° and 60 °, respectively, this will cause the horizontal period length to be 371.5 nm and 457 nm, respectively.
  • the exposure environment must meet certain temperature and humidity conditions.
  • the laser energy used in the exposure process must also meet certain conditions.
  • the laser energy used in the present invention is around 8 J / cm 2 .
  • Step 3 In the present invention, a liquid crystal polymer and a chiral material are used to generate a spiral structure in the y direction in FIG. 1, and a photoinitiator and corresponding solvent are used.
  • Irgacure 651 can be used as a photoinitiator and toluene as a solvent.
  • the mass liquid ratio of the solution containing the liquid crystal polymer and the chiral material mentioned in step three used in the present invention is in the range of about 15% to 20%.
  • the spin coater stops at a certain rotation speed for a certain period of time, and the vertical period length ⁇ y can reach the required value.
  • the horizontal period length value ⁇ x and vertical period of the three-color waveguide layer of red (center wavelength 457 nm), green (center wavelength 532 nm), blue (center wavelength 630 nm) as given in Table 1 can be selected.
  • the length value ⁇ y is prepared.
  • the birefringent material molecules can form a helical structure.
  • Step 4 Use ultraviolet light to perform ultraviolet curing in a nitrogen environment.
  • the specific power value of ultraviolet light needs to be determined according to factors such as the type of material used.
  • the ultraviolet light energy used in the present invention satisfies 1J / cm 2 ⁇ 10J / cm 2
  • Step 5 Repeat steps 3 and 4 until the film thickness is greater than a certain value (as an example, this value is about 4.5 ⁇ m in the present invention).
  • a certain value as an example, this value is about 4.5 ⁇ m in the present invention.
  • the green PVG is first spin-coated and cured to the required thickness, and then the blue solution is directly spin-coated and fixed on the green PVG layer.
  • a waveguide can be produced, and then repeat the above five steps to prepare another color waveguide. If two waveguides are superimposed together, a full-color coupling waveguide based on a color polarizer grating is produced.
  • the bottom surface of the glass substrate used in the present invention is a rectangle of 25 mm ⁇ 75 mm, the thickness is 0.05 mm, and the birefringence value is 0.18.
  • spin coating and grating preparation another identical clean glass was adhered to the surface of the formed grating using a transparent ultraviolet curing agent, and the final layer of waveguide was 1 mm thick.
  • the invention also includes a three-layer waveguide structure.
  • the single-layer blue and green waveguides are divided into two layers: blue waveguide layer 60 and green waveguide layer 70.
  • the fabrication of each layer of waveguide is also carried out according to the steps described in FIG. 5. Then, the blue waveguide layer 60 with a center wavelength of 457 nm, the green red waveguide layer 70 with a center wavelength of 532 nm, and the red waveguide layer 7 with a center wavelength of 630 nm are superposed to form the three-layer waveguide structure described in FIG.
  • the white light beam from the microdisplay 1 containing three wavelength bands of red, green and blue is collimated by the collimator 4 and then passes through the coupling device 20 of the blue waveguide layer and the inlet of the green waveguide layer
  • the coupling device 30 and the red waveguide layer enter the coupling device 10 and then perpendicularly enter the waveguide. Then, the in-coupling PVG will diffract the incident light into the waveguide at different angles greater than the total internal reflection angle.
  • the out-coupling PVG will turn the light beam at an angle to the incident wave when reaching the in-coupling Diffraction out of the waveguide.
  • 40 represents the out-coupling device of the blue waveguide layer
  • 50 represents the out-coupling device in the green waveguide layer
  • 11 represents the out-coupling device in the red waveguide layer
  • 5 represents the air layer between different waveguide layers.
  • the light beam exits the waveguide After the light beam exits the waveguide, it is collimated by the lens 3 of the human eye, and the observer's retina 2 can receive a color pixel image at a suitable position.
  • pixels are imaged at infinity and received by the human eye.

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Abstract

提供了一种基于彩色偏振体光栅的全彩波导耦合近眼显示结构和制备方法，及AR可穿戴设备。使用彩色偏振体全息光栅作为波导（6,7,60,70）的耦合装置（8,10,20,30），这种光栅利用液晶的自组装效应和各向异性，具有高衍射效率，大衍射角度，同时可工作在较宽的波长与角度带宽，结合多层波导结构（6,7,60,70），应用于近眼显示装置，可实现大视场角、高透明度、高效率的彩色图像传输。

Description

基于彩色偏振体光栅的全彩波导耦合近眼显示结构、制备方法及AR可穿戴设备 技术领域
本发明涉及一种基于彩色偏振体光栅的全彩波导耦合近眼显示结构、制备方法及AR可穿戴设备。
背景技术
基于具有耦合元件的平面波导而设计的近眼显示系统在过去的十几年有了很大的发展，被广泛应用到军事和商业领域。在AR设备上，上述的波导结构必须满足重量轻、体积小、高透明度以及出瞳广阔的特点。作为耦合波导近眼显示系统的基本组件之一，耦合元件能够决定视场角(FOV)、耦合效率、显色性等重要参数。
为了更进一步轻化波导结构，光学衍射元件(DOEs)已经被广泛研究并在波导近眼显示系统中被用作耦合元件。这种多衍射元件中，光学衍射光栅是最普遍的。当被应用在波导耦合式近眼显示系统中时，衍射光栅可以将来自微显示器的入射光束耦合到波导内。衍射光栅在具有大的衍射角的同时还具有角度选择性和波长选择性，这就保证了在满足全内反射条件时光束能够在波导中高效率地传播。
考虑到光衍射元件的多样性，全息体光栅(HVG)具有独特的优点，因此被广泛用作波导中的耦合装置。一般的全息体光栅可以通过在全息记录材料(如光致聚合物、重铬酸盐明胶等)记录干涉图样制成。当满足布拉格条件的光束照射到HVG上时，能够发生高衍射效率的单级衍射，并且衍射角度很大，这是HVG的重要特点。同时，由于其具有窄带宽和严格的角度选择性，HVG对环境光具有高透过性。但是，角度带宽和波长带宽很短会限制视场角FOV的大小并且当被用到波导耦合显示系统中时，也会限制全彩传输的实现。
双折射率的差值能够决定体光栅的角度和波长带宽。传统的重铬酸盐明胶材料的双折射率材料能够达到0.15。但是其对环境的高度敏感性以及其复杂的制备过程导致如今大多数被用作记录介质的光致聚合物的双折射率差值仅有0.035。如此小的双折射率差值导致角度带宽和波长带宽均很窄，从而导致视场 角很小。
发明内容
针对现有技术的不足，本发明提出一种基于彩色偏振体光栅(CPVG)的全彩波导耦合近眼显示系统的制备方法，用于解决现有的方法中存在的衍射效率低、视场角小、不利于实现全彩传输等问题。并且光栅的偏折特性使得至少50％的非偏振环境光直接透过光栅而不发生衍射。
技术方案：为解决上述问题，本发明采用以下技术方案：
一种基于彩色偏振体光栅的全彩波导耦合近眼显示结构，采用以彩色偏振体光栅作为耦合装置的双层波导结构来实现全彩近眼显示，其中一层被用来传播蓝、绿色光束的蓝、绿色波导结构中使用了蓝、绿色的偏振体光栅作为耦合装置从而实现在波导中传输蓝色和绿色光束；另一层被用来传播红色光束的红色波导结构中使用了红色偏振体光栅作为耦合装置从而实现在波导中传输红色光束。
蓝、绿色波导结构中的入耦合装置和出耦合装置均为蓝、绿色PVG，并且蓝、绿色波导结构中的入耦合装置和出耦合装置位于平面波导结构的镜面对称位置；相应地，红色波导结构中的入耦合装置和出耦合装置均为红色PVG，并且红色波导结构中第二入耦合装置和出耦合装置也位于平面波导结构的镜面对称位置。
所述蓝、绿色波导结构包括蓝色波导层和绿色波导层两层。
每两个波导层叠加在一起后在两个波导层之间存在着空气层。
蓝色波导层的水平周期长度值和绿色波导层水平周期长度值相同，其满足布拉格衍射公式：
Figure PCTCN2019101983-appb-000001
式(3)中，n eff代表光栅所用的双折射材料的等效折射率；Λ x代表光栅在x方向上的的水平周期长度；
Figure PCTCN2019101983-appb-000002
代表波导层中具有周期性的折射率平面的倾斜角；λ B代表真空中的布拉格波长。
本发明还进一步公开了一种所述的基于彩色偏振体光栅的全彩波导耦合近眼显示结构的制备方法，包括以下几个步骤：
步骤一、将光取向材料溶于相应的溶剂后在干净的玻璃波导表面进行旋涂，加热一段时间后形成薄膜；
步骤二、两束偏振光在步骤一中形成的光取向材料薄膜上进行干涉曝光，并进一步形成光取向层；
步骤三、将含有液晶聚合物和手性材料的溶液地在步骤二中形成的取向层上，再将玻璃放在旋涂机上以一定的旋转速度旋转一定时间后停止；
步骤四、使用5J/cm 2的紫外光在氮环境中进行紫外固化；
步骤五、重复步骤三和步骤四直到薄膜厚度达到100nm到1μm以保证形成光栅，此外，对于蓝、绿色波导结构首先旋涂和固化绿色的PVG厚度达到100nm～1μm，之后在绿色PVG层上直接旋涂和固定蓝色的波导层。
步骤二中的曝光环境需要满足温度为20℃～30℃之间、相对湿度保持在38以下。
步骤二中曝光所使用的激光器能量控制在6J/cm 2～10J/cm 2。
本发明还进一步的公开了一种AR可穿戴设备，采用所述基于彩色偏振体光栅的全彩波导耦合近眼显示结构。
有益效果：
第一、本发明中起到耦合作用的彩色体全息光栅能够将蓝绿波段和红色波段的光分别耦合到两个波导中来实现基于全彩耦合波导的显示系统。
第二、本发明形成了布拉格光栅的结构并且所使用的液晶材料具有大的双折射率差值Δn，因此根据耦合波理论可知本发明能够实现很高的光栅衍射效率。
第三、本发明采用的液晶材料具有较大的双折射率差值，根据耦合波理论可知耦合光栅入射角带宽变大，利用这一点可以制备具有大视场角(可以达到35°)的AR可穿戴设备。
附图说明
图1为本发明中作为耦合装置的CPVG结构示意图；
其中，图1(a)展示了被用来衍射蓝色和绿色的蓝绿色体光栅结构，其中，Λ bgx代表蓝色波导层和绿色波导层这两层的水平周期长度值；Λ by和Λ gy分别代表蓝色波导层和绿色波导层的垂直周期长度值；向量K b和K g分别代表蓝色波导 层和绿色波导层中体光栅的布拉格矢量；
Figure PCTCN2019101983-appb-000003
和
Figure PCTCN2019101983-appb-000004
分别代表蓝色波导层和绿色波导层中具有周期性的折射率平面的倾斜角。
图1(b)展示了能够使红光发生布拉格衍射的PVG结构，其中，Λ rx代表红色波导层的水平周期长度值；Λ ry代表垂直周期长度值；向量K r代表红色波导层中体光栅的布拉格矢量；
Figure PCTCN2019101983-appb-000005
代表红色波导层中具有周期性折射率平面的倾斜角；α代表液晶分子光轴与z轴之间的夹角。
图2为本发明所阐述的双层波导结构的示意图；
其中，1、微显示器；2、观察者的视网膜；3、人眼晶状体；4、 准直器；5、蓝绿色波导层和红色波导层之间的空气层；6、蓝绿色波导层；7、红色波导层；8、绿色波导层的入耦合装置；9、蓝绿色波导层的出耦合装置；10、红色波导层的入耦合装置；11、红色波导层的出耦合装置；
图3为本发明所阐述的三层波导结构的示意图；
其中，20、蓝色波导层的入耦合装置；30、绿色波导层的入耦合装置；40、蓝色波导层的出耦合装置；50、绿色波导层的出耦合装置；60、蓝色波导层；70、绿色波导层；
图4为本发明的衍射角随入射角变化而变化的曲线图；
图5为本发明的流程图；
图6为本发明所用到的曝光光路示意图；
其中，100、线偏振激光器；200、半波片；300、偏振光分束器PBS；(400，900)、四分之一波片；(500，800)、扩束透镜；(600，700)、平面镜；1000、待曝光的样片；α代表两束偏振光之间的夹角。
具体实施方式
下面结合附图对本发明作更进一步的说明。
本发明中所用到的作为耦合装置的CPVG的结构如图1所示。由图1可知体全息光栅PVG具有二维周期结构，其中，
在x-z平面(水平面)，液晶分子光轴与z轴之间的夹角α会沿x方向，既水平方向发生周期性变化，其周期长度记作Λ x。
在y-z平面上，液晶材料(或者更广泛地，双折射材料)在y方向，既垂直 方向上呈现出周期螺旋结构，其周期记作Λ y。
这样的二维周期结构能够产生一系列倾斜的具有周期性的折射率平面，其倾斜角
Figure PCTCN2019101983-appb-000006
可由式(1)计算：
Figure PCTCN2019101983-appb-000007
为了简化分析而不失一般性，假设反射式PVG的倾斜角满足
Figure PCTCN2019101983-appb-000008
并且α可由式(2)计算：
Figure PCTCN2019101983-appb-000009
如果双折射率材料层足够厚，则布拉格衍射能够被建立。事实上，垂直入射光的衍射光具有高衍射效率，布拉格衍射由式(3)所表示：
Figure PCTCN2019101983-appb-000010
式(3)中λ B代表真空中的布拉格波长，n eff代表双折射介质的等效折射率，由式(4)计算：
Figure PCTCN2019101983-appb-000011
图1中所展示的两种CPVG结构分别代表(a)被用来衍射蓝色和绿色的蓝、绿色体光栅(cyan PVG)。Cyan PVG可以被分为蓝色和绿色两层，这两层的水平周期长度相同，在图1(a)中被记作Λ bgx，其值由上述式(3)计算：
Figure PCTCN2019101983-appb-000012
式(3)中，n eff代表光栅所用的双折射材料的等效折射率；Λ x代表光栅在x方向上的的水平周期长度；
Figure PCTCN2019101983-appb-000013
代表波导层中具有周期性的折射率平面的倾斜角；λ B代表真空中的布拉格波长。
当波长值λ B为457nm(蓝色)，
Figure PCTCN2019101983-appb-000014
为蓝色波导层中的折射率平面倾斜角时，Λ x为蓝色波导层水平周期长度值；当波长值λ B为532nm(绿色)，
Figure PCTCN2019101983-appb-000015
为绿色波导层中的折射率平面倾斜角时，Λ x为绿色波导层水平周期长度值。由于在本发明所提的结构中蓝绿色波导层的水平周期长度数值相同，因此记为将其记Λ bgx。
由于蓝绿两层具有相同的水平周期长度值，所以蓝、绿两层波导层满足相同的光栅色散方程(5)：
Figure PCTCN2019101983-appb-000016
式(5)中，θ 0代表衍射角(光束在波导中的传播角)，n glass代表玻璃波导的折射率值，λ代表光束的波长，θ i代表在空气中的入射角，m代表衍射级次(对于体光栅而言m＝1)，Λ x代表光栅在x方向上的的水平周期长度。对于蓝、绿色波导层而言，Λ x即为Λ bgx。
蓝、绿两层的不同之处在于y方向上的周期长度不同，即图1(a)中的Λ by和Λ gy不同，由式(1)和(3)可知，这决定了垂直入射时的布拉格中心波长的不同。
在制备过程中CPVG仅需要一次偏振干涉曝光即可在光取向材料上产生所需要的水平周期长度Λ x，之后依次旋涂具有不同Λ y的手性螺旋材料即可。
图1(b)展示了能够使红光发生布拉格衍射的PVG结构，它具有和蓝、绿色CPVG不同的水平周期长度，即Λ rx不等于Λ bgx。
表1列出了一组示例参数。作为具体实施中的举例，表1列出了一组对应不同中心波长(457nm,532nm,630nm)的CPVG的相关参数。实际情况下的具体参数值需要按照所需设计改变。
图2展示了本发明的整体结构，系统包含一个传播蓝、绿色的蓝绿色波导层6(Waveguide(B+G))和一个传播红色的红色波导层7(Waveguide(R))。
蓝绿色波导层6中的绿色波导层的入耦合装置8和蓝绿色波导层的出耦合装置9均为蓝绿色PVG，并且绿色波导层的入耦合装置8和蓝绿色波导层的出耦合装置9位于平面波导结构的镜面对称位置。相应地，红色波导层7中的红色波导层的入耦合装置10和红色波导层的出耦合装置11均为红色PVG，并且红色波导层的入耦合装置10和红色波导层的出耦合装置11也位于平面波导结构的镜面对称位置。
更清楚地，图2展示了来自微显示器1的中心波长段的光束在双层波导结构 中的传播。经过准直器4准直后，由微显示器1发出的包含红绿蓝三种波段的白光将通过蓝绿色波导层的绿色波导层的入耦合装置8和红色波导层的入耦合装置10垂直射入波导中。
然后，入耦合装置将会以大于全内反射角的不同角度将入射光衍射到波导中。这两个能够传播不同波段光束的波导具有不同的PVG。
位于顶端的蓝、绿色波导的CPVG对蓝色和绿色起作用，其衍射角可以利用式(5)得到。
位于底端的红色波导的PVG仅对红色起作用，同样地，其衍射角也可以利用式(5)得到。
当传播的光束到达作为出耦合的PVG时，出耦合PVG会以与入射波到达入耦合时的角度将光束衍射出波导。
经过人眼晶状体3的准直，观察者的视网膜2在合适的位置可以接受到一个彩色的像素图像。事实上，像素在无穷远处成像并被人眼所接收。
另外，由于入耦合和出耦合PVG在水平方向上的对称性，色散现象可以被抵消。也就是说，彩色鬼影图像可以在内部被消除，这对保证图像质量的全彩显示而言是一个重要的特点。而且，在不同波导内传播的光束的传播是不相关的，并且由于两个波导层之间存在着空气层5，因此在不同波导的光栅之间的串扰是可以忽略不计的。在另一方面，出瞳的连续性对于基于波导的显示系统而言也是一个关键问题，它会影响在不同位置观察图像时的颜色和亮度的统一性。我们已经在以前的工作中研究并记录了相关的事实。通过选择合适厚度的波导、传播步长和调整入瞳大小的方法，该问题可以被高效解决。
采用厚度为1mm的高折射率玻璃作为波导，并且三种颜色(红、绿、蓝)的传播光束的中心波长分别为630nm、532nm、457nm。
为了使光束能够沿着波导传播，最小的衍射角由公式(6)计算得到：
θ min＝arcsin(1/n),      (6)
式(6)中n代表所用波导材料的折射率值。
最大衍射角度由公式(7)计算得到：
θ max＝arctan(W/2t),    (7)
式(7)中W代表准直器空径(本发明中为10mm)，t代表波导的厚度(本发明中每层的波导厚度为1mm)。
图4展示了在不同波长条件下具有不同入射角的衍射角度分布曲线。
由图4可知所能够实现的FOV大约为35.7°(-13.3°～22.4°)，这种大小的视场角满足了当前主流的基于波导的近眼显示系统的需求。
图5为具体制备流程图：
步骤一、将光取向材料溶于相应的溶剂后在干净的玻璃波导(n＝1.85)表面进行旋涂。
作为示例可选择偶氮染料类如SD1、BY等作为光取向材料，DMF作为溶剂。旋涂机以一定转速旋转一段时间后停止，之后将波导在120℃的热台上加热30分钟形成薄膜。
步骤二、两束偏振光在步骤一中形成的光取向材料薄膜上进行干涉曝光，并进一步形成光取向层，曝光装置如图6所示：
由线偏振激光器100发出的光束在经过半波片200后被偏振光分束器(PBS)300分成两束相互正交的偏振光束。两个四分之一波片(QWP)再将两束偏振光分别转变为右旋圆偏光和左旋圆偏光。
半波片200被用来调整两路光的光强以保证两路光强相同。
两路相干光在经过空间滤波和扩束透镜之后，分别被平面镜一定角度反射，最后这两束圆偏特性相反的圆偏光将会以α的夹角叠加并在样品1000的光取向层上形成干涉图样。
作为本发明的示例，对于蓝、绿色和红色的PVG，如果曝光角度分别被设置为76°和60°，这将会使其水平方向的的周期长度分别为371.5nm和457nm。
曝光环境必须满足一定温度和湿度的条件。此外曝光过程中所使用的激光器能量也必须满足一定条件。作为示例，本发明所使用的激光器能量在8J/cm 2左右。
步骤三、本发明中采用液晶聚合物和手性材料来产生图1中y方向上的螺旋结构，并使用光引发剂和相应溶剂。作为示例可采用Irgacure651作为光引发剂，采用甲苯作为溶剂。
作为示例，本发明所用到的步骤三中所提的含有液晶聚合物和手性材料的溶液的质液比例大约在15％～20％的范围内。
旋涂机以一定的旋转速度旋转一定时间后停止，垂直周期长度Λ y能够达到 所需要的值。
作为示例，可以选择如表1中所给出的红(中心波长为457nm)、绿(中心波长为532nm)、蓝(中心波长为630nm)三色波导层的水平周期长度值Λ x和垂直周期长度值Λ y进行制备。
Figure PCTCN2019101983-appb-000017
表1
事实上，由于光取向层的锚定能和手性材料的螺旋扭曲能产生的二维周期结构，双折射材料分子能够形成螺旋结构。
步骤四、使用紫外光在氮环境中进行紫外固化，紫外光的具体功率值需要根据所使用的材料种类等因素确定。作为示例，本发明中所使用的紫外光能量满足1J/cm 2～10J/cm 2的
步骤五、重复步骤三四直到薄膜厚度大于一定值(作为示例，本发明中该值约为4.5μm)。此外对于蓝、绿色的PVG首先旋涂和固化绿色的PVG到所需要的厚度，之后在绿色PVG层上直接旋涂和固定蓝色的溶液。
经过以上五个步骤能够制得一个波导，之后重复以上五步再制备出另一种颜色的波导，讲两个波导就叠加在一起就制得了基于彩色偏振体光栅的全彩耦合波导。
作为示例，本发明这里所使用的玻璃基底的底面为25mm×75mm的长方形，厚度为0.05mm,双折射率值为0.18。在旋涂和光栅制备之后，利用透明紫外光固化剂将另一个相同的干净的玻璃粘合在所形成的光栅表面，最终制得的一层波导厚度为1mm。
基于同样的工作原理，作为本发明还包含三层波导结构。
如图3所示，即将单层的蓝、绿色波导分为蓝色波导层60、绿色波导层70两层。每层波导的制作同样按照图5中所述的步骤进行。之后将中心波长为457nm 的蓝色波导层60和中心波长为532nm的绿色红色波导层70以及中心波长为630nm的红色波导层7叠加在一起即组成了图3中所描述的三层波导结构。
和双层波导结构类似地，来自微显示器1的包含红绿蓝三种波段的白光光束在经过准直器4准直后，依次通过蓝色波导层的入耦合装置20、绿色波导层的入耦合装置30以及红色波导层的入耦合装置10后垂直射入波导中。然后，入耦合PVG将会以大于全内反射角的不同角度将入射光衍射到波导中。由于入耦合装置和出耦合装置关于于波导具有镜面对称性，因此当在不同波导层中传播的光束到达作为出耦合的PVG时，出耦合PVG会以与入射波到达入耦合时的角度将光束衍射出波导。
图3中40代表蓝色波导层的出耦合装置，50代表绿色波导层中的出耦合装置，11代表红色波导层中的出耦合装置，5代表不同波导层之间的空气层。
光束从波导射出后经过人眼晶状体3的准直，观察者的视网膜2在合适的位置可以接受到一个彩色的像素图像。
事实上，像素在无穷远处成像并被人眼所接收。
以上所述仅是本发明的优选实施方式，应当指出：对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也应视为本发明的保护范围。

Claims (9)

  1. 一种基于彩色偏振体光栅的全彩波导耦合近眼显示结构，其特征在于：采用以彩色偏振体光栅作为耦合装置的双层波导结构来实现全彩近眼显示，其中一层被用来传播蓝、绿色光束的蓝、绿色波导结构中使用了蓝、绿色的偏振体光栅作为耦合装置从而实现在波导中传输蓝色和绿色光束；另一层被用来传播红色光束的红色波导结构中使用了红色偏振体光栅作为耦合装置从而实现在波导中传输红色光束。
  2. 根据权利要求1所述的基于彩色偏振体光栅的全彩波导耦合近眼显示结构，其特征在于：蓝、绿色波导结构中的入耦合装置和出耦合装置均为蓝、绿色PVG，并且蓝、绿色波导结构中的入耦合装置和出耦合装置位于平面波导结构的镜面对称位置；相应地，红色波导结构中的入耦合装置和出耦合装置均为红色PVG，并且红色波导结构中第二入耦合装置和出耦合装置也位于平面波导结构的镜面对称位置。
  3. 根据权利要求1所述的基于彩色偏振体光栅的全彩波导耦合近眼显示结构，其特征在于：所述蓝、绿色波导结构包括蓝色波导层和绿色波导层两层。
  4. 根据权利要求3所述的基于彩色偏振体光栅的全彩波导耦合近眼显示结构，其特征在于：每两个波导层叠加在一起后在两个波导层之间存在着空气层。
  5. 根据权利要求3所述的基于彩色偏振体光栅的全彩波导耦合近眼显示结构，其特征在于：蓝色波导层的水平周期长度值和绿色波导层水平周期长度值相同，其满足布拉格衍射公式：
    Figure PCTCN2019101983-appb-100001
    式(3)中，n eff代表光栅所用的双折射材料的等效折射率；Λ x代表光栅在x方向上的的水平周期长度；
    Figure PCTCN2019101983-appb-100002
    代表波导层中具有周期性的折射率平面的倾斜角；λ B代表真空中的布拉格波长。
  6. 根据权利要求1所述的基于彩色偏振体光栅的全彩波导耦合近眼显示结构的制备方法，其特征在于：包括以下几个步骤：
    步骤一、将光取向材料溶于相应的溶剂后在干净的玻璃波导表面进行旋涂，加热一段时间后形成薄膜；
    步骤二、两束偏振光在步骤一中形成的光取向材料薄膜上进行干涉曝光，并 进一步形成光取向层；
    步骤三、将含有液晶聚合物和手性材料的溶液地在步骤二中形成的取向层上，再将玻璃放在旋涂机上以一定的旋转速度旋转一定时间后停止；
    步骤四、使用5J/cm 2的紫外光在氮环境中进行紫外固化；
    步骤五、重复步骤三和步骤四直到薄膜厚度达到100nm到1μm以保证形成光栅，此外，对于蓝、绿色波导结构首先旋涂和固化绿色的PVG厚度达到100nm～1μm，之后在绿色PVG层上直接旋涂和固定蓝色的波导层。
  7. 根据权利要求6所述的基于彩色偏振体光栅的全彩波导耦合近眼显示结构的制备方法，其特征在于：步骤二中的曝光环境需要满足温度为20℃～30℃之间、相对湿度保持在38以下。
  8. 根据权利要求6所述的基于彩色偏振体光栅的全彩波导耦合近眼显示结构的制备方法，其特征在于：步骤二中曝光所使用的激光器能量控制在6J/cm 2～10J/cm 2。
  9. 一种AR可穿戴设备，其特征在于，采用如权利要求1～5中任一所述基于彩色偏振体光栅的全彩波导耦合近眼显示结构。
PCT/CN2019/101983 2018-10-31 2019-08-22 基于彩色偏振体光栅的全彩波导耦合近眼显示结构、制备方法及ar可穿戴设备 WO2020088055A1 (zh)

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