A liquid crystal two-dimensional polarization grating, its fabrication method, and a beam array generation system.

Abstract

This invention discloses a liquid crystal two-dimensional polarization grating, its fabrication method, and a beam array generation system. The liquid crystal two-dimensional polarization grating includes a first substrate and a second substrate disposed opposite to each other, and a liquid crystal layer located between the first and second substrates. Spacer particles are disposed between the first and second substrates to support them. A photo-alignment film is disposed on one side of the first and second substrates adjacent to the liquid crystal layer. The molecular pointing vectors of the photo-alignment film are arranged according to the phase control pattern of the two-dimensional polarization grating. The photo-alignment film controls the pointing vectors of the liquid crystal molecules in the liquid crystal layer to be arranged according to the phase control pattern of the two-dimensional polarization grating, so that the incident beam illuminating the liquid crystal two-dimensional polarization grating is converted into a polarization-controllable beam array with a preset spatial distribution of diffraction orders. Compared with the prior art, the technical solution provided by this invention significantly improves diffraction efficiency and provides a richer configuration of diffraction order lattice distribution.

Description

Technical Field

[0001] This invention relates to the field of design and orientation control technology of liquid crystal two-dimensional polarization gratings, and particularly to a liquid crystal two-dimensional polarization grating, its fabrication method, and a beam array generation system. Background Technology

[0002] Gratings, as a traditional diffractive optical element, have been widely used in fields such as spectral analysis, precision measurement, integrated optics, and optical communication. Polarization gratings, as a special type of grating, can concentrate all incident light energy at the ±1st order, and the energy distribution of these two orders can be adjusted by changing the polarization state of the incident light.

[0003] With the continuous advancement of technology, in some scenarios, such as multi-channel parallel processing in optical communication and point / line / area array lidar scanning in the security field, one-dimensional polarization gratings are no longer sufficient to meet people's needs for efficient generation and control of multiple beams. Summary of the Invention

[0004] This invention provides a liquid crystal two-dimensional polarization grating, its fabrication method, and a beam array generation system. This liquid crystal two-dimensional polarization grating can divide a beam of signal light into a two-dimensional beam array with controllable polarization according to a certain spatial distribution. It has broad application prospects in the measurement of light field Stokes parameters, beam deflection control, augmented reality / virtual reality display, and other fields.

[0005] According to one aspect of the present invention, a liquid crystal two-dimensional polarization grating is provided, comprising a first substrate and a second substrate disposed opposite to each other, and a liquid crystal layer located between the first substrate and the second substrate; wherein, spacer particles are disposed between the first substrate and the second substrate to support the first substrate and the second substrate;

[0006] A photo-alignment film is disposed on one side of the first substrate and the second substrate adjacent to the liquid crystal layer. The molecular pointing vectors of the photo-alignment film are arranged according to the phase control pattern of a two-dimensional polarization grating. The photo-alignment film controls the pointing vectors of the liquid crystal molecules in the liquid crystal layer to be arranged according to the phase control pattern of the two-dimensional polarization grating, so that the incident light beam illuminating the two-dimensional polarization grating of the liquid crystal is converted into a polarization controllable beam array with a preset spatial distribution of diffraction orders.

[0007] Optionally, the phase control pattern of the two-dimensional polarization grating is obtained by multi-beam interference calculation based on polarization holography, and the molecular orientation vector of the optically controlled alignment film satisfies:

[0008]

[0009] Where χ is defined as:

[0010]

[0011] Among them, A x and A y Let δ represent the amplitude components of the electric field vector E in the x and y directions, respectively. x and δ y Let x and y represent the phase components of the electric field vector E in the x and y directions, respectively. E is the field distribution obtained by multi-beam interference, which can be expressed as:

[0012]

[0013] E i (x, y) is the electric field vector for each interference beam, which can be expressed as:

[0014] E i =A i P i exp(ik i ·r+δ);

[0015] Among them, A i P represents amplitude. i Represents the polarization vector; the left-hand circular polarization vector is represented as... The right-hand circular polarization vector is represented as k i denoted by r, r represents the position vector, and δ represents the initial phase.

[0016] Optionally, by adjusting the transmission vector k i and polarization vector P i The phase control patterns of different types of two-dimensional polarization gratings are generated by calculation so that the incident beam illuminating the liquid crystal two-dimensional polarization grating is transformed into a polarization-controllable beam array with different diffraction orders in spatial distribution.

[0017] Optionally, the material of the liquid crystal layer includes any one of nematic liquid crystal, dual-frequency liquid crystal, ferroelectric liquid crystal, liquid crystal polymer or cholesteric liquid crystal;

[0018] The two-dimensional polarization grating phase control pattern formed by the optically controlled alignment film is erasable and rewritable, and the material of the optically controlled alignment film includes azo dyes.

[0019] Optionally, the phase difference between ordinary and extraordinary light in the liquid crystal layer satisfies:

[0020]

[0021] Where Δn represents the birefringence difference of the liquid crystal molecules, d represents the thickness of the liquid crystal layer, λ represents the wavelength of the incident Gaussian light, and k is a natural number.

[0022] According to another aspect of the present invention, a polarization-controllable beam array generation system is provided, comprising:

[0023] The aforementioned liquid crystal two-dimensional polarization grating;

[0024] A light source located on the incident light side of the liquid crystal two-dimensional polarization grating generates an incident Gaussian beam;

[0025] A polarizer and a quarter-wave plate are located between the light source and the liquid crystal two-dimensional polarization grating;

[0026] The lens and imaging device are located on the light-emitting side of the liquid crystal two-dimensional polarization grating.

[0027] Optionally, the optical axes of the light source, the polarizer, the quarter-wave plate, the liquid crystal two-dimensional polarization grating, the lens, and the imaging device are located on the same straight line;

[0028] The intensity and polarization state of the incident Gaussian beam are controlled by adjusting the angle between the fast axis direction of the quarter-wave plate and the polarization direction of the polarizer.

[0029] Optionally, when the incident Gaussian beam is a linearly polarized Gaussian beam, the liquid crystal two-dimensional polarization grating converts the linearly polarized Gaussian beam into an array of left- and right-hand circularly polarized beams with orthogonal diffraction orders in circular polarization states.

[0030] When the incident Gaussian beam is a left-handed circularly polarized Gaussian beam, the liquid crystal two-dimensional polarization grating converts the left-handed circularly polarized Gaussian beam into a right-handed circularly polarized beam array with one side diffraction order.

[0031] When the incident Gaussian beam is a right-hand circularly polarized Gaussian beam, the liquid crystal two-dimensional polarization grating converts the right-hand circularly polarized Gaussian beam into a left-hand circularly polarized beam array of the other diffraction order.

[0032] According to another aspect of the present invention, a method for fabricating a liquid crystal two-dimensional polarization grating is provided, comprising:

[0033] Provide a first substrate and a second substrate;

[0034] A light-controlled alignment film is formed on one side of the first substrate and the second substrate;

[0035] Spacer particles are disposed on one side of the first substrate and encapsulated with the second substrate, wherein the photo-alignment film side of the first substrate is disposed opposite to the photo-alignment film side of the second substrate;

[0036] The photo-aligned film is subjected to multi-step overlapping exposure so that the molecular orientation vector of the photo-aligned film is arranged according to the phase control pattern of a two-dimensional polarization grating.

[0037] A liquid crystal layer is injected between the first substrate and the second substrate, and the photo-alignment film controls the alignment of the liquid crystal molecules in the liquid crystal layer according to the phase control pattern of the two-dimensional polarization grating.

[0038] Optionally, the photo-alignment film undergoes multi-step overlapping exposure to align the molecular orientation vectors of the photo-alignment film according to a two-dimensional polarization grating phase control pattern, including:

[0039] A micro-projection exposure system based on a digital micromirror array is used. According to the exposure sequence, the exposure pattern with the corresponding phase value and the corresponding polarization direction of the induced light are selected and exposed sequentially.

[0040] In this process, the exposure areas of the exposure patterns in adjacent steps partially overlap, and the polarization direction of the induced light changes uniformly with the exposure sequence to form a preset two-dimensional polarization grating phase control pattern.

[0041] The liquid crystal two-dimensional polarization grating provided in this embodiment of the invention includes a first substrate and a second substrate disposed opposite to each other, and a liquid crystal layer located between the first substrate and the second substrate; wherein, spacer particles are disposed between the first substrate and the second substrate to support the first substrate and the second substrate; a photo-alignment film is disposed on one side of the first substrate and the second substrate adjacent to the liquid crystal layer, the molecular pointing vectors of the photo-alignment film are arranged according to the phase control pattern of the two-dimensional polarization grating, and the photo-alignment film controls the pointing vectors of liquid crystal molecules in the liquid crystal layer to be arranged according to the phase control pattern of the two-dimensional polarization grating, so that the incident light beam irradiating the liquid crystal two-dimensional polarization grating is converted into a polarization controllable beam array with a preset spatial distribution of diffraction order. By setting a photo-aligned film on a first substrate and a second substrate arranged opposite to each other, and arranging the molecular directores of the photo-aligned film according to the phase control pattern of a two-dimensional polarization grating, the control pattern of the photo-aligned film controls the liquid crystal molecules in the liquid crystal layer to gradually distribute from 0° to 180° according to the phase control pattern of the two-dimensional polarization grating. This allows the Gaussian beam illuminating the two-dimensional polarization grating of the liquid crystal to be converted into a polarization-controllable beam array with a preset spatial distribution of diffraction orders. This method has broad application prospects in the measurement of Stokes parameters of the light field, beam deflection control, and augmented reality / virtual reality displays.

[0042] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of a liquid crystal two-dimensional polarization grating provided in an embodiment of the present invention;

[0045] Figure 2 A schematic diagram of a two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention;

[0046] Figure 3 For corresponding Figure 2 A top view of the liquid crystal director distribution in the structure;

[0047] Figure 4 A schematic diagram of the microstructure of a liquid crystal two-dimensional polarization grating sample when the phase difference between ordinary and extraordinary light is an odd multiple of π;

[0048] Figure 5 A schematic diagram of a polarization-controllable beam array generation system provided in an embodiment of the present invention;

[0049] Figures 6-8 They are respectively Figure 4 The diagram shows a polarization-controllable beam array in which the diffraction orders of a liquid crystal two-dimensional polarization grating are spatially distributed under different polarization states of the incident light.

[0050] Figure 9 A schematic diagram of another two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention;

[0051] Figure 10 for Figure 9 A schematic diagram of the polarization microstructure of the corresponding liquid crystal two-dimensional polarization grating sample;

[0052] Figure 11 for Figure 10 A schematic diagram of the order distribution of a two-dimensional polarization grating in a liquid crystal under different incident lights;

[0053] Figure 12 A schematic diagram of another two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention;

[0054] Figure 13 for Figure 12 A schematic diagram of the polarization microstructure of the corresponding liquid crystal two-dimensional polarization grating sample;

[0055] Figure 14 for Figure 13 The diagram shows the order distribution of a two-dimensional polarization grating for liquid crystal under different incident lights.

[0056] Figure 15 A schematic diagram of another two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention;

[0057] Figure 16 for Figure 15 A schematic diagram of the polarization microstructure of the corresponding liquid crystal two-dimensional polarization grating sample;

[0058] Figure 17 for Figure 16 A schematic diagram of the order distribution of a two-dimensional polarization grating in a liquid crystal under different incident lights;

[0059] Figure 18 A schematic diagram of another two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention;

[0060] Figure 19 for Figure 18 A schematic diagram of the polarization microstructure of the corresponding liquid crystal two-dimensional polarization grating sample;

[0061] Figure 20 for Figure 19 The diagram shows the order distribution of a two-dimensional polarization grating for liquid crystal under different incident lights.

[0062] Figure 21 A schematic flowchart illustrating a method for fabricating a two-dimensional polarization grating of liquid crystal provided for the implementation of this invention;

[0063] Figure 22 This is a schematic diagram of a process for multi-step overlapping exposure of a photo-aligned film, provided as an embodiment of the present invention. Detailed Implementation

[0064] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0065] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0066] Figure 1 This is a schematic diagram of a liquid crystal two-dimensional polarization grating provided in an embodiment of the present invention, with reference to... Figure 1 The liquid crystal two-dimensional polarization grating includes a first substrate 11 and a second substrate 12 disposed opposite to each other, and a liquid crystal layer 13 located between the first substrate 11 and the second substrate 12; wherein, spacer particles 14 are disposed between the first substrate 11 and the second substrate 12 to support the first substrate 11 and the second substrate 12; photo-alignment films 15 and 16 are respectively disposed on the side of the first substrate 11 and the second substrate 12 adjacent to the liquid crystal layer, the molecular pointing vectors of the photo-alignment films 15 and 16 are arranged according to the phase control pattern of the two-dimensional polarization grating, and the photo-alignment films 15 and 16 control the pointing vectors of the liquid crystal molecules in the liquid crystal layer 13 to be arranged according to the phase control pattern of the two-dimensional polarization grating, so that the incident light beam irradiating the liquid crystal two-dimensional polarization grating is converted into a polarization controllable beam array with a preset spatial distribution of diffraction order.

[0067] For example, Figure 2 This is a schematic diagram of a two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention. (Reference) Figure 2 The phase control pattern of the two-dimensional polarization grating is obtained by interference of three circularly polarized beams. The gray-scale gradient in the figure can be regarded as a simulation diagram of the liquid crystal pointing direction being spatially gradually distributed from 0° to 180°. The transition from dark to bright in the figure indicates that the liquid crystal pointing direction gradually changes from 0° to 180°.

[0068] Figure 3 For corresponding Figure 2 A top view schematic diagram of the liquid crystal director distribution in the structure. (Reference) Figure 3 Under the anchoring effect of the photo-aligned film, since the molecular orientation direction of the photo-aligned film is arranged according to the phase control pattern of the two-dimensional polarization grating, that is, according to the gray value of 0-255 gradually changing from 0° to 180°, the photo-aligned film makes the orientation of the liquid crystal molecules in the liquid crystal layer also arranged in a corresponding manner from 0° to 180°.

[0069] The technical solution of this invention involves setting a photo-controlled alignment film on a first substrate and a second substrate arranged opposite to each other, and arranging the molecular pointing vectors of the photo-controlled alignment film according to the phase control pattern of a two-dimensional polarization grating. The control pattern of the photo-controlled alignment film controls the pointing vectors of liquid crystal molecules in the liquid crystal layer to be distributed in a gradual range of 0°-180° according to the phase control pattern of the two-dimensional polarization grating, so that the Gaussian beam illuminating the two-dimensional polarization grating of the liquid crystal is converted into a polarization-controllable beam array with a preset spatial distribution of diffraction orders. This solution has broad application prospects in the measurement of Stokes parameters of the light field, beam deflection control, augmented reality / virtual reality display, etc.

[0070] In the above-mentioned optional technical solutions, the phase control pattern of the two-dimensional polarization grating is obtained by multi-beam interference calculation based on polarization holography, and the molecular orientation vector of the optically controlled alignment film satisfies:

[0071]

[0072] Where χ is defined as:

[0073]

[0074] Among them, A x and A y Let δ represent the amplitude components of the electric field vector E in the x and y directions, respectively. x and δ y Let x and y represent the phase components of the electric field vector E in the x and y directions, respectively. E is the field distribution obtained by multi-beam interference, which can be expressed as:

[0075]

[0076] E i (x, y) is the electric field vector for each interference beam, which can be expressed as:

[0077] E i =A i P i exp(ik i ·r+δ);

[0078] Among them, A i P represents amplitude. i Represents the polarization vector; the left-hand circular polarization vector is represented as... The right-hand circular polarization vector is represented as k i denoted by r, r represents the position vector, and δ represents the initial phase.

[0079] Optionally, by adjusting the transmission vector k i and polarization vector P iThe phase control patterns of different types of two-dimensional polarization gratings are generated by calculation so that the incident beam illuminating the liquid crystal two-dimensional polarization grating is transformed into a polarization-controllable beam array with different diffraction orders in spatial distribution.

[0080] Among them, by adjusting the transmission vector k i and polarization vector P i The changes in the two-dimensional polarization grating phase control pattern can be designed according to the requirements, thereby producing different types of liquid crystal two-dimensional polarization gratings. This can meet the application needs of many fields such as the measurement of light field Stokes parameters, new displays such as augmented reality / virtual reality, multi-channel parallel processing in the field of optical communication, and point / line / area array lidar scanning in the security field.

[0081] Continue to refer to Figure 2 The phase control pattern of this two-dimensional polarization grating is obtained by the interference of two right-handed circularly polarized beams and one left-handed circularly polarized beam. The expression for the polarization vector satisfies:

[0082]

[0083]

[0084] The transmission vectors corresponding to the respective beams are as follows:

[0085] k1 = 2π / λ[sinθ, 0];

[0086] k2 = 2π / λ[-sinθ, 0];

[0087] k3 = 2π / λ[0, sinθ];

[0088] Where θ is the polar angle (k) of the interference beam propagation vector. i (The angle between the z-axis and the z-axis).

[0089] Optionally, the material of the liquid crystal layer includes any one of nematic liquid crystal, dual-frequency liquid crystal, ferroelectric liquid crystal, liquid crystal polymer, or cholesteric liquid crystal, which can be selected according to the actual situation during specific implementation; the phase control pattern of the two-dimensional polarization grating formed by the photo-alignment film is erasable and rewritable, and the material of the photo-alignment film includes azo dye, so that the liquid crystal two-dimensional polarization grating can be reused. By erasing and rewriting the phase control pattern of the two-dimensional polarization grating on the photo-alignment film, the structure of the liquid crystal two-dimensional polarization grating can be changed in real time, so as to generate a polarization controllable beam array with a certain spatial distribution of diffraction orders.

[0090] Optionally, the phase difference between ordinary and unusual light in the liquid crystal layer satisfies:

[0091]

[0092] Where Δn represents the birefringence difference of the liquid crystal molecules, d represents the thickness of the liquid crystal layer, λ represents the wavelength of the incident Gaussian light, and k is a natural number.

[0093] It is understandable that by adjusting the size of the spacer particles and thus the distance between the first and second substrates, the thickness of the liquid crystal layer can be controlled, so that the phase difference between the ordinary and extraordinary rays of incident light in the liquid crystal two-dimensional polarization grating is equal to an odd multiple of π. Figure 4 This is a schematic diagram of the microstructure of a liquid crystal two-dimensional polarization grating sample when the phase difference between the ordinary and extraordinary rays is an odd multiple of π. The scale bar in the figure is 100 μm. The advantage of this setting is that when the phase difference between the ordinary and extraordinary rays of the incident light in the liquid crystal two-dimensional polarization grating is an odd multiple of π, the principal diffraction order energy of the incident light after irradiating the liquid crystal two-dimensional polarization grating is the highest, and the diffraction efficiency is the highest, thus avoiding the use of electrodes.

[0094] Figure 5 This is a schematic diagram of a polarization-controllable beam array generation system provided in an embodiment of the present invention, with reference to... Figure 5 The polarization-controllable beam array generation system includes: a liquid crystal two-dimensional polarization grating 21 provided in the above embodiment; a light source 22 located on the light-incident side of the liquid crystal two-dimensional polarization grating 21, the light source 22 generating an incident Gaussian beam; a polarizer 25 and a quarter-wave plate 26 located between the light source 22 and the liquid crystal two-dimensional polarization grating 21; and a lens 21 and an imaging device 24 located on the light-outceasing side of the liquid crystal two-dimensional polarization grating 21.

[0095] The light source 22 can be a laser source, which has good collimation and produces a high-quality beam array with a spatially distributed diffraction order after conversion by the liquid crystal two-dimensional polarization grating 21. Furthermore, the wavelength range of the light source 22 is not limited. For example, a wavelength greater than 500 nm can be set to avoid the influence of the incident light emitted by the light source 22 on the phase control pattern of the two-dimensional polarization grating in the liquid crystal two-dimensional polarization grating 21. For instance, irradiating the liquid crystal two-dimensional polarization grating 21 with a 633 nm laser and focusing it onto the imaging device 24 through a lens 23 with a focal length of 125 mm can obtain a beam array with a spatially distributed diffraction order. In this embodiment of the invention, the focal length of the lens 23 is not limited. The imaging device 24 can be a charge-coupled device (CCD), etc.

[0096] The present invention provides a beam array generation system with a spatially distributed diffraction order and controllable polarization. It generates an incident Gaussian beam from a light source, wherein the incident Gaussian beam is pre-polarized. A two-dimensional polarization grating in a liquid crystal converts the incident beam into a beam array with a spatially distributed diffraction order and controllable polarization. The beam array generated by this invention features equal energy distribution and a mutually orthogonal left- and right-handed circularly polarized distribution of positive and negative diffraction orders. Furthermore, the array structure can be customized by altering the phase control pattern of the two-dimensional polarization grating as needed.

[0097] Continue to refer to Figure 5 Optionally, the optical axes of the light source 22, polarizer 25, quarter-wave plate 26, liquid crystal two-dimensional polarization grating 21, lens 23 and imaging device 24 are located on the same straight line; the intensity and polarization state of the incident Gaussian beam are controlled by adjusting the angle between the fast axis direction of the quarter-wave plate 26 and the polarization direction of the polarizer 25.

[0098] Optionally, when the incident Gaussian beam is a linearly polarized Gaussian beam, the liquid crystal two-dimensional polarization grating 21 converts the linearly polarized Gaussian beam into an array of left- and right-hand circularly polarized beams with orthogonal diffraction orders; when the incident Gaussian beam is a left-hand circularly polarized Gaussian beam, the liquid crystal two-dimensional polarization grating 21 converts the left-hand circularly polarized Gaussian beam into an array of right-hand circularly polarized beams with diffraction orders on one side; when the incident Gaussian beam is a right-hand circularly polarized Gaussian beam, the liquid crystal two-dimensional polarization grating 21 converts the right-hand circularly polarized Gaussian beam into an array of left-hand circularly polarized beams with diffraction orders on the other side.

[0099] Figures 6-8 They are respectively Figure 4 The diagram shows a controllable polarization beam array where the diffraction orders of a two-dimensional polarization grating produced by the incident light under different polarization states exhibit a certain spatial distribution. (Reference) Figure 6 When the incident light from the light source is linearly polarized, it is converted into a square-shaped beam array with diffraction orders by a liquid crystal two-dimensional polarization grating. Each beam has the same intensity, and measurements show that the diffraction efficiency of these four first-order diffracted beams reaches 66.6%. (Reference) Figure 7 When the incident light from the light source is left-handed circularly polarized, the incident light is converted into a right-handed circularly polarized beam array of the -1st order diffraction order by a liquid crystal two-dimensional polarization grating. (Reference) Figure 8When the incident light generated by the light source is right-handed circularly polarized, the incident light is converted into a left-handed circularly polarized beam array with a right-hand +1st order diffraction order by a liquid crystal two-dimensional polarization grating. The liquid crystal two-dimensional polarization grating provided in this embodiment of the invention has polarization selectivity. By selecting different incident light polarization characteristics, different circularly polarized states and different numbers of beam arrays can be obtained, which can meet its application in the measurement of light field Stokes parameters, beam deflection control, high-transmittance polarizers, new displays such as augmented reality / virtual reality, and even the measurement of minute optical forces.

[0100] Optionally, by erasing and rewriting the phase control pattern of the two-dimensional polarization grating on the optically controlled alignment film, the structure of the liquid crystal two-dimensional polarization grating can be changed in real time, thereby generating a polarization-controllable beam array with a certain spatial distribution of diffraction orders.

[0101] Optionally, the transmission vector k in the multi-beam interferometry calculation can be changed. i and polarization vector P i The settings generate different two-dimensional polarization grating structures. Figure 9 This is a schematic diagram of another two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention. This two-dimensional polarization grating phase control pattern is obtained by introducing linear polarization light interference calculations based on the interference of three circularly polarized beams. Figure 10 for Figure 9 A schematic diagram of the polarization microstructure of the corresponding liquid crystal two-dimensional polarization grating sample. (Reference) Figure 9 The phase control pattern of the two-dimensional polarization grating is obtained by interference calculation of three circularly polarized beams and one linearly polarized beam with an intensity of 1 / 5 that of the circularly polarized beams (a total of four beams). The advantage of this design is that, compared to... Figure 2 The phase control pattern shown was prepared Figure 4 The liquid crystal two-dimensional polarization grating structure shown can reduce the occurrence of liquid crystal alignment misalignment lines caused by the phase abrupt change from 0 to π / 2.

[0102] Optional, continue to refer to Figure 9 The phase control pattern of this two-dimensional polarization grating is obtained by interference of two right-handed circularly polarized beams, one left-handed circularly polarized beam, and one weakly linearly polarized beam. The expression for the polarization vector satisfies:

[0103]

[0104]

[0105] P = [1, 0] T ;

[0106] The transmission vectors of the corresponding beams are as follows:

[0107] k1 = 2π / λ[sinθ, 0];

[0108] k2 = 2π / λ[-sinθ, 0];

[0109] k3 = 2π / λ[0, sinθ];

[0110] k4 = 2π / λ[0, -sinθ];

[0111] The effect of this setup is that when incident light illuminates the liquid crystal two-dimensional polarization grating, the resulting diffraction order is a beam array with a square distribution. Figure 11 for Figure 10 The diagram illustrates the diffraction order distribution of a liquid crystal two-dimensional polarization grating under different incident lights. From left to right, the incident light is linearly polarized, left-handed circularly polarized, and right-handed circularly polarized, resulting in a square-shaped beam array with right-handed and left-handed diffraction orders under polarization control. After linear polarization correction, the phase control pattern of the two-dimensional polarization grating obtained through interferometry shows a more continuous change in phase value, thus increasing the diffraction efficiency of the prepared liquid crystal two-dimensional polarization grating to 75.3%.

[0112] Figure 12 This is a schematic diagram of another two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention. This two-dimensional polarization grating phase control pattern is obtained based on the interference calculation of four circularly polarized beams. Figure 13 for Figure 12 A schematic diagram of the polarization microstructure of the corresponding liquid crystal two-dimensional polarization grating sample.

[0113] Optional, see reference Figure 12 The phase control pattern of this two-dimensional polarization grating is obtained by interference of three right-handed circularly polarized beams and one left-handed circularly polarized beam. The expression for the polarization vector satisfies:

[0114]

[0115]

[0116] The transmission vectors of the corresponding beams are as follows:

[0117] k1 = 2π / λ[sinθ, 0];

[0118] k2 = 2π / λ[-sinθ, 0];

[0119] k3 = 2π / λ[0, sinθ];

[0120] k4 = 2π / λ[0, -sinθ];

[0121] The effect of this setup is that when incident light illuminates the liquid crystal two-dimensional polarization grating, the resulting diffraction order is a beam array distributed in a hexagonal pattern. Figure 14 for Figure 13The diagram shows the diffraction order distribution of a two-dimensional polarization grating of liquid crystal under different incident lights. From left to right, the incident light is linearly polarized, left-handed circularly polarized, and right-handed circularly polarized, resulting in a hexagonal beam array with varying diffraction orders, and the right-handed and left-handed diffraction orders under polarization modulation. Experiments show that the diffraction efficiency of this two-dimensional polarization grating of liquid crystal can reach 80.7%.

[0122] In order to generate a polarization-controllable beam array with a richer spatial distribution of diffraction orders, embodiments of the present invention have explored the interference of more beams. Figure 15 This is a schematic diagram of another two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention. This two-dimensional polarization grating phase control pattern is obtained based on the interference calculation of six circularly polarized beams. Figure 16 for Figure 15 A schematic diagram of the polarization microstructure of the corresponding liquid crystal two-dimensional polarization grating sample.

[0123] Optional, see reference Figure 15 The phase control pattern of this two-dimensional polarization grating is obtained by interference calculation of one right-handed circularly polarized beam and five left-handed circularly polarized beams. The expression for the polarization vector satisfies:

[0124]

[0125]

[0126] The polarization vector of the corresponding beam is set as follows:

[0127] {P L P L P R P L P L P L};

[0128] To output diffracted beams of the same intensity, the amplitude A of the interference beam is calculated. i The value is set to:

[0129] {1.05, 1.12, 1, 1.12, 1.05, 1.063};

[0130] The transmission vectors of the corresponding beams are as follows:

[0131]

[0132]

[0133] k3 = 2π / λ[-sinθ, 0];

[0134]

[0135]

[0136] k6 = 2π / λ[sinθ, 0];

[0137] The effect of this setting is that after the incident light shines on the liquid crystal two-dimensional polarization grating, the resulting diffraction order is a beam array distributed in the shape of the number "0". Figure 17 for Figure 16 The diagram shows the diffraction order distribution of a two-dimensional polarization grating of liquid crystal under different incident lights. The incident lights from left to right are linearly polarized, left-handed circularly polarized, and right-handed circularly polarized, respectively. The resulting beam array has a diffraction order distribution in the shape of the number "0", and the right-handed and left-handed diffraction orders are controlled by polarization.

[0138] Figure 18 This is a schematic diagram of another two-dimensional polarization grating phase control pattern provided in an embodiment of the present invention. This two-dimensional polarization grating phase control pattern is obtained based on the interference calculation of six circularly polarized beams. Figure 19 for Figure 18 A schematic diagram of the polarization microstructure of the corresponding liquid crystal two-dimensional polarization grating sample.

[0139] Optional, see reference Figure 18 The phase control pattern of this two-dimensional polarization grating is obtained by interference of three right-handed circularly polarized beams and three left-handed circularly polarized beams, and the expression for the polarization vector satisfies:

[0140]

[0141]

[0142] The polarization vector of the corresponding beam is set as follows:

[0143] {P R P L P L P L P R P R};

[0144] The transmission vectors of the corresponding beams are as follows:

[0145]

[0146]

[0147] k3 = 2π / λ[-sinθ, 0];

[0148]

[0149]

[0150] k6 = 2π / λ[sinθ, 0];

[0151] The effect of this setup is that when incident light illuminates the liquid crystal two-dimensional polarization grating, the resulting diffraction order is a beam array distributed in the shape of butterfly wings. Figure 20 for Figure 19 The diagram shows the diffraction order distribution of a two-dimensional polarization grating of liquid crystal under different incident lights. The incident lights from left to right are linearly polarized, left-handed circularly polarized, and right-handed circularly polarized, respectively. The resulting beam array has a butterfly wing-shaped distribution of diffraction orders, and the right-handed and left-handed diffraction orders are controlled by polarization.

[0152] Figure 21 A schematic flowchart illustrating a method for fabricating a liquid crystal two-dimensional polarization grating according to an embodiment of the present invention is provided. This method is used to fabricate the liquid crystal two-dimensional polarization grating provided in the above embodiment. (Refer to...) Figure 21 The preparation method includes:

[0153] S110, providing a first substrate and a second substrate.

[0154] Both the first and second substrates can be glass substrates. Before forming the photo-alignment film, to increase the wettability and adhesion between the photo-alignment film and the first and second substrates, the glass substrates are ultrasonically cleaned for 30 minutes with a cleaning solution (a mixture of acetone, alcohol, etc.), and then ultrasonically cleaned twice with ultrapure water for 10 minutes each time. After drying in a 120°C oven for 40 minutes, they are then UVO (ultraviolet ozone) cleaned for 30 minutes.

[0155] S120, a photo-alignment film is formed on one side of the first substrate and the second substrate.

[0156] The optically controlled alignment film can be formed in the following ways:

[0157] The photo-alignment material was spin-coated on one side of the first and second substrates. The spin-coating parameters were: low-speed spin-coating for 5 seconds at a speed of 800 rpm, and high-speed spin-coating for 40 seconds at a speed of 3000 rpm.

[0158] The first and second substrates, which are spin-coated with photo-alignment material, are annealed for 10 minutes at a temperature of 100°C to form a photo-alignment film.

[0159] S130. Spacer particles are disposed on one side of the first substrate and encapsulated with the second substrate, wherein the photo-alignment film side of the first substrate is disposed opposite to the photo-alignment film side of the second substrate.

[0160] The size of the spacer particles can be selected according to specific needs. By selecting spacer particles of different sizes, the distance between the first substrate and the second substrate can be adjusted so that the phase difference between the ordinary and extraordinary rays of the incident light in the liquid crystal two-dimensional polarization grating is equal to an odd multiple of π. The advantage of this setting is that when the phase difference between the ordinary and extraordinary rays of the incident light in the liquid crystal two-dimensional polarization grating is equal to an odd multiple of π, the beam emitted after the incident light irradiates the liquid crystal two-dimensional polarization grating is a polarization-controllable beam array with a certain spatial distribution of the set diffraction order.

[0161] S140. Perform multi-step overlapping exposure on the photo-aligned film so that the molecular orientation vector of the photo-aligned film is arranged according to the phase control pattern of the two-dimensional polarization grating.

[0162] The phase control pattern of the two-dimensional polarization grating is obtained by multi-beam interference calculation using polarization holography. The molecular director in the photo-controlled alignment film can be set by the polarization direction of the induced light. Specifically, multiple partially overlapping exposures from 0° to 180° can be used to form a two-dimensional polarization grating phase control pattern on the photo-controlled alignment film with a spatially gradually varying molecular director direction.

[0163] Optionally, the photo-alignment film undergoes multi-step overlapping exposure to align the molecular orientation vectors of the photo-alignment film according to the phase control pattern of a two-dimensional polarization grating, including:

[0164] A miniature projection exposure system based on a digital micromirror array is used. According to the exposure sequence, the exposure pattern with the corresponding phase value and the corresponding polarization direction of the induced light are selected and exposed sequentially.

[0165] In this process, the exposure areas of the exposure patterns in adjacent steps partially overlap, and the polarization direction of the induced light changes uniformly with the exposure sequence to form a preset two-dimensional polarization grating phase control pattern.

[0166] Figure 22 This is a schematic diagram illustrating a multi-step overlapping exposure process for a photo-aligned film, provided as an embodiment of the present invention. (Reference) Figure 22, Exemplarily, there are three exposures in sequence: the first exposure, the second exposure, and the third exposure. The exposure patterns of the three exposures have the same period. Exemplarily, each exposure pattern is set to have 3 periods T1, T2, T3, and the width of each period gradually decreases from the central region of the exposure pattern to both sides. Exemplarily, T1 = T3 < T2. During the first exposure, a digital micromirror device (DMD) exposure system is used to select the first exposure pattern. The polarization direction of the induced light corresponding to the first exposure is 0°. Each period is divided into 3 equal parts Tn1, Tn2, and Tn3, where n = 1, 2, 3. The exposure regions of the first exposure pattern are T11 and T12 of T1, T21 and T22 of T2, and T31 and T32 of T3. After the first exposure is completed, the second exposure pattern is replaced, and the corresponding polarization direction of the induced light is selected to be 60°. Each period is divided into 3 equal parts. The exposure regions of the second exposure pattern are T12 and T13 of T1, T22 and T23 of T2, and T32 and T33 of T3. After the second exposure is completed, the third exposure image is replaced, and the corresponding polarization direction of the induced light is selected to be 120°. Each period is divided into 3 equal parts. The exposure regions of the third exposure pattern are T11 and T13 of T1, T21 and T23 of T2, and T31 and T33 of T3. Therefore, the exposure region of the first exposure pattern partially overlaps with the exposure region of the second exposure pattern, and the overlapping parts are T12, T22, T32; the exposure region of the second exposure pattern partially overlaps with the exposure region of the third exposure pattern, and the overlapping parts are T13, T23, T33. T11, T12, T13, T21, T22, T23, T31, T32, and T33 are all exposed twice, and the polarization direction of the induced light for each exposure is different. Since the dose for each exposure is not sufficient to make the molecular director arrangement of the photo-alignment film reach a stable arrangement (for example, when the exposure dose is 5 J / cm 2 , it can make the molecular director arrangement of the photo-alignment film reach a stable arrangement. When performing step-by-step overlapping exposure, the exposure dose can be selected to be 1 J / cm 2 ), the sum of the multiple exposure doses makes it in a stable state, and the molecular director direction of the photo-alignment film is between the intermediate states of the polarization angles experienced in the multiple exposures. For example, for T12, the polarization angle is 0° during the first exposure, and the polarization angle is 60° during the second exposure. Then, the molecular director direction of the photo-alignment film in the T12 region is between 0° - 60°. Therefore, after multi-step overlapping exposure, a control pattern with a spatially gradual change in the molecular director direction will be generated on the photo-alignment film. <> <>

[0167] It should be noted that Figure 22The exemplary selection of three-step overlapping exposure is not a limitation of the embodiments of the present invention. Generally speaking, the more exposures (i.e., the more polarization angles are evenly divided from 0° to 180°), the more evenly the number of periods in the exposure pattern, the finer the spatial gradient distribution of the liquid crystal pointing direction, and the better the quality of the final obtained polarization-controllable beam array with a certain spatial distribution of diffraction orders. In other embodiments, the number of exposures and the number of evenly divided periods can be selected according to actual needs.

[0168] S150, A liquid crystal layer is injected between the first substrate and the second substrate, and a photo-alignment film controls the alignment of the liquid crystal molecules in the liquid crystal layer according to the phase control pattern of a two-dimensional polarization grating.

[0169] Among them, the light-controlled alignment film has an anchoring function. Under the control of the two-dimensional polarization grating phase control pattern formed by S140, the liquid crystal molecules in the liquid crystal layer are distributed in a spatially gradual manner from 0° to 180°. The incident light irradiating the phase plate of the liquid crystal two-dimensional polarization grating is converted into a polarization controllable beam array with a certain spatial distribution of diffraction order.

[0170] The liquid crystal two-dimensional polarization grating provided in this invention can split a beam of signal light into multiple beams of signal light in a two-dimensional lattice with controllable polarization according to a certain spatial distribution. Particularly for liquid crystal two-dimensional polarization gratings fabricated based on optical alignment technology and a DMD-based miniaturized projection exposure system, on the one hand, the calculated phase structure of the two-dimensional polarization grating can be accurately transferred to the liquid crystal microstructure through the DMD system, thereby improving diffraction efficiency; on the other hand, by flexibly adjusting the parameters of the interference beam in holographic calculation, different phase structures of the two-dimensional polarization gratings can be obtained, achieving a more complex and richer spatial lattice arrangement of diffraction orders. Furthermore, the energy conversion between the beam array and the central single order can be adjusted by changing the voltage applied to the liquid crystal sample, and the energy distribution between positive and negative diffraction orders can be adjusted by regulating the polarization state of the incident light. These characteristics give the liquid crystal two-dimensional polarization grating proposed in this invention broad application prospects in the measurement of light field Stokes parameters, beam deflection control, and augmented reality / virtual reality displays.

[0171] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A liquid crystal two-dimensional polarization grating, characterized in that, It includes a first substrate and a second substrate disposed opposite to each other, and a liquid crystal layer located between the first substrate and the second substrate; wherein, spacer particles are disposed between the first substrate and the second substrate to support the first substrate and the second substrate; A photo-alignment film is provided on one side of the first substrate and the second substrate adjacent to the liquid crystal layer. The molecular pointing vectors of the photo-alignment film are arranged according to the phase control pattern of the two-dimensional polarization grating. The photo-alignment film controls the pointing vectors of the liquid crystal molecules in the liquid crystal layer to be arranged according to the phase control pattern of the two-dimensional polarization grating, so that the incident light beam irradiating the two-dimensional polarization grating of the liquid crystal is converted into a polarization controllable light beam array with a preset spatial distribution of diffraction order. The phase control pattern of the two-dimensional polarization grating is obtained by multi-beam interference calculation based on polarization holography, and the molecular orientation vector of the optically controlled alignment film satisfies: ； Where χ is defined as: ； Among them, A x and A y Let δ represent the amplitude components of the electric field vector E in the x and y directions, respectively. x and δ y Let x and y represent the phase components of the electric field vector E in the x and y directions, respectively. E is the field distribution obtained by multi-beam interference, which can be expressed as: ； E i (x, y) is the electric field vector for each interference beam, which can be expressed as: ； Among them, A i P represents amplitude. i The polarization vector is represented by P, where P is the left-hand circular polarization vector. L = [1, +i] T The right-hand circularly polarized vector is represented as P R = [1, -i] T k i denoted by r, r represents the position vector, and δ represents the initial phase.

2. The liquid crystal two-dimensional polarization grating according to claim 1, characterized in that, By adjusting the transmission vector k i and polarization vector P i The phase control patterns of different types of two-dimensional polarization gratings are generated by calculation so that the incident beam illuminating the liquid crystal two-dimensional polarization grating is transformed into a polarization-controllable beam array with different diffraction orders in spatial distribution.

3. The liquid crystal two-dimensional polarization grating according to claim 1, characterized in that, The material of the liquid crystal layer includes any one of nematic liquid crystal, dual-frequency liquid crystal, ferroelectric liquid crystal, liquid crystal polymer or cholesteric liquid crystal. The two-dimensional polarization grating phase control pattern formed by the optically controlled alignment film is erasable and rewritable, and the material of the optically controlled alignment film includes azo dyes.

4. The liquid crystal two-dimensional polarization grating according to claim 1, characterized in that, The phase difference between ordinary and extraordinary light in the liquid crystal layer satisfies: ； in, λ represents the birefringence difference of the liquid crystal molecules, d represents the thickness of the liquid crystal layer, λ represents the wavelength of the incident Gaussian light, and k is a natural number.

5. A polarization-controllable beam array generation system, characterized in that, include: The liquid crystal two-dimensional polarization grating according to any one of claims 1-4; A light source located on the incident light side of the liquid crystal two-dimensional polarization grating generates an incident Gaussian beam; A polarizer and a quarter-wave plate are located between the light source and the liquid crystal two-dimensional polarization grating; The lens and imaging device are located on the light-emitting side of the liquid crystal two-dimensional polarization grating.

6. The polarization-controllable beam array generation system according to claim 5, characterized in that, The optical axes of the light source, the polarizer, the quarter-wave plate, the liquid crystal two-dimensional polarization grating, the lens, and the imaging device are located on the same straight line; The intensity and polarization state of the incident Gaussian beam are controlled by adjusting the angle between the fast axis direction of the quarter-wave plate and the polarization direction of the polarizer.

7. The polarization-controllable beam array generation system according to claim 6, characterized in that, When the incident Gaussian beam is a linearly polarized Gaussian beam, the liquid crystal two-dimensional polarization grating converts the linearly polarized Gaussian beam into an array of left and right circularly polarized beams with orthogonal diffraction orders in circular polarization states. When the incident Gaussian beam is a left-handed circularly polarized Gaussian beam, the liquid crystal two-dimensional polarization grating converts the left-handed circularly polarized Gaussian beam into a right-handed circularly polarized beam array with one side diffraction order. When the incident Gaussian beam is a right-hand circularly polarized Gaussian beam, the liquid crystal two-dimensional polarization grating converts the right-hand circularly polarized Gaussian beam into a left-hand circularly polarized beam array of the other diffraction order.

8. A method for fabricating a liquid crystal two-dimensional polarization grating, characterized in that, The method for preparing the liquid crystal two-dimensional polarization grating according to any one of claims 1-4 includes: Provide a first substrate and a second substrate; A light-controlled alignment film is formed on one side of the first substrate and the second substrate; Spacer particles are disposed on one side of the first substrate and encapsulated with the second substrate, wherein the photo-alignment film side of the first substrate is disposed opposite to the photo-alignment film side of the second substrate; The photo-aligned film is subjected to multi-step overlapping exposure so that the molecular orientation vector of the photo-aligned film is arranged according to the phase control pattern of a two-dimensional polarization grating. A liquid crystal layer is injected between the first substrate and the second substrate, and the photo-alignment film controls the orientation vectors of the liquid crystal molecules in the liquid crystal layer to be arranged according to the phase control pattern of the two-dimensional polarization grating. The phase control pattern of the two-dimensional polarization grating is obtained by multi-beam interference calculation based on polarization holography, and the molecular orientation vector of the optically controlled alignment film satisfies: ； Where χ is defined as: ； Among them, A x and A y Let δ represent the amplitude components of the electric field vector E in the x and y directions, respectively. x and δ y Let x and y represent the phase components of the electric field vector E in the x and y directions, respectively. E is the field distribution obtained by multi-beam interference, which can be expressed as: ； E i (x, y) is the electric field vector for each interference beam, which can be expressed as: ； Among them, A i P represents amplitude. i The polarization vector is represented by P, where P is the left-hand circular polarization vector. L = [1, +i] T The right-hand circularly polarized vector is represented as P R = [1, -i] T k i denoted by r, r represents the position vector, and δ represents the initial phase.

9. The preparation method according to claim 8, characterized in that, The photo-aligned film undergoes multi-step overlapping exposure to align the molecular orientation vectors of the photo-aligned film according to a two-dimensional polarization grating phase control pattern, including: A micro-projection exposure system based on a digital micromirror array is used. According to the exposure sequence, the exposure pattern with the corresponding phase value and the corresponding polarization direction of the induced light are selected and exposed sequentially. In this process, the exposure areas of the exposure patterns in adjacent steps partially overlap, and the polarization direction of the induced light changes uniformly with the exposure sequence to form a preset two-dimensional polarization grating phase control pattern.

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