Nonlinear perfect vector beam generation element, preparation method and application thereof

Abstract

The application belongs to the technical field of nonlinear optics, and particularly relates to a nonlinear perfect vector beam generating element, a preparation method and application. The element comprises a first glass substrate, a first light-controlled orientation layer, a ferroelectric nematic liquid crystal layer, a second light-controlled orientation layer and a second glass substrate. The first glass substrate and the second glass substrate are oppositely arranged. The first glass substrate and the second glass substrate are further respectively provided with the first light-controlled orientation layer and the second light-controlled orientation layer. The first light-controlled orientation layer and the second light-controlled orientation layer are provided with a nonlinear perfect vector beam control pattern. The nonlinear perfect vector beam control pattern controls liquid crystal molecules in the ferroelectric nematic liquid crystal layer to be periodically distributed in concentric circular rings. The application realizes the integration and miniaturization of the nonlinear perfect vector beam device and the one-step direct generation of the nonlinear perfect vector beam through the direct orientation of the liquid crystal electric dipole.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nonlinear optics, and particularly relates to a nonlinear perfect vector beam generating element, a preparation method and application. BACKGROUND

[0002] Vector beams are a kind of structured light field with programmable vector distribution characteristics, which have shown important application value in optical communication, high-resolution imaging, micro-manipulation and other fields. Recently, the concept of perfect vector beams has been proposed. The annular intensity distribution of this beam has no direct correlation with its topological charge, and the topological charge can be arbitrarily coded. It is worth noting that perfect vector beams with different topological charge numbers constitute a series of orthogonal bases, ensuring that the mutual crosstalk between them is extremely low. Based on this characteristic, perfect vector beams can theoretically carry an unlimited number of topological charges during transmission, thereby providing new possibilities for significantly improving the communication capacity in the field of optical communication, and also making high-density optical information storage and transmission more efficient and reliable.

[0003] At present, different methods such as combined linear diffraction elements, using spatial light modulators, etc. have been proposed to generate such perfect vector beams. Current researches mainly focus on the generation and control of linear perfect vector beams, and there are few studies on encoding perfect vector beams during nonlinear frequency conversion. The main reason is that it is difficult to freely orient and manipulate electric dipoles. The study of encoding perfect vector beams during nonlinear frequency conversion has important theoretical and application significance. Not only can it efficiently utilize the degrees of freedom of light frequency, improve the transmission capacity and flexibility of the communication system, but also can reduce the crosstalk between signals through its orthogonal base characteristics, improve the robustness and stability of the system. In addition, this technology also provides new tools and methods for designing new photonic devices and conducting basic scientific research on light-matter interaction, promoting the technological innovation and development in the fields of optical communication, quantum information processing and super-resolution imaging. For the currently widely used uniaxial ferroelectric crystal element, due to the sensitivity of the phase matching condition to the polarization direction of the electric vector, the vector characteristics will be erased when directly performing nonlinear frequency conversion. And generally, a complex optical system with multiple element superposition is needed to achieve it.

[0004] Therefore, it is of great significance to develop a new nonlinear perfect vector beam generating element. SUMMARY

[0005] The present application aims to solve the problems of the current nonlinear perfect vector beam generation process requiring a complex optical system with multiple element superposition and the difficulty of orienting and manipulating electric dipoles, and proposes a nonlinear perfect vector beam generating element prepared by using the structured orientation of liquid crystals, which can realize the integration and miniaturization of nonlinear perfect vector beam devices and the direct generation of nonlinear perfect vector beams.

[0006] The application also aims to solve the preparation method of the above-mentioned nonlinear perfect vector beam generating element.

[0007] In order to solve the above-mentioned technical problems, the application discloses a nonlinear perfect vector beam generating element, which comprises a first glass substrate, a first photo-controlled orientation layer, a ferroelectric nematic liquid crystal layer, a second photo-controlled orientation layer and a second glass substrate; the first glass substrate and the second glass substrate are oppositely arranged; the inner sides of the first glass substrate and the second glass substrate are respectively provided with the first photo-controlled orientation layer and the second photo-controlled orientation layer; and the first photo-controlled orientation layer and the second photo-controlled orientation layer are provided with interval particles.

[0008] The first photo-controlled orientation layer and the second photo-controlled orientation layer are provided with a nonlinear perfect vector beam control pattern; and the nonlinear perfect vector beam control pattern controls the liquid crystal molecules in the ferroelectric nematic liquid crystal layer to be arranged in a number of periodic concentric circular ring orientation distributions.

[0009] Specifically, the interval particles are used to control the distance between the first photo-controlled orientation layer and the second photo-controlled orientation layer.

[0010] Specifically, the first photo-controlled orientation layer, the second photo-controlled orientation layer and the interval particles form a liquid crystal cell after being encapsulated; and the liquid crystal cell forms the ferroelectric nematic liquid crystal layer after being injected with ferroelectric nematic liquid crystal material.

[0011] The nonlinear perfect vector beam control pattern provided on the first and second photo-controlled orientation layers can correspond to nonlinear perfect vector beams with different topological charges, but is not limited to these topological charges, and includes nonlinear perfect vector beams corresponding to any topological charge.

[0012] Preferably, the nonlinear perfect vector beam control pattern controls the diameter of the nonlinear perfect vector beam by controlling the size of the circular ring period.

[0013] Preferably, the nonlinear perfect vector beam control pattern is composed of two concentric circular ring orientation distributions in a single period, and the orientation angle difference between adjacent circular rings is 90 degrees; and the nonlinear perfect vector beam control pattern controls the intensity of the nonlinear perfect vector beam by controlling the width ratio of the two concentric circular rings in a single period.

[0014] Preferably, the orientation rotation angle of a single circular ring in a single period of the nonlinear perfect vector beam control pattern is any angle; and the nonlinear perfect vector beam control pattern controls the topological charge of the nonlinear perfect vector beam by controlling the orientation rotation angle of the single circular ring.

[0015] Specifically, in some embodiments of the present application, by controlling the single circular ring molecule orientation rotation angle in the nonlinear perfect vector beam control pattern to be 360°, 540°, 720° and 1080° respectively, nonlinear perfect vector beams with topological charges of 2, 3, 4 and 6 are respectively realized.

[0016] The present application also provides a preparation method of the above-mentioned nonlinear perfect vector beam generating element, and the specific steps are as follows:

[0017] S1. ultrasonic cleaning and drying the first glass substrate and the second glass substrate, and then ultraviolet ozone cleaning;

[0018] S2. spin coating a photo-alignment agent on the first glass substrate and the second glass substrate after S1 cleaning, and forming a first photo-controlled orientation layer and a second photo-controlled orientation layer after solidification;

[0019] S3. smearing spacer particles on both sides of the first photo-controlled orientation layer, and then placing the second photo-controlled orientation layer to encapsulate, forming a liquid crystal cell;

[0020] S4. polarized ultraviolet exposure orientation of the first photo-controlled orientation layer and the second photo-controlled orientation layer to form a nonlinear perfect vector beam control pattern;

[0021] S5. injecting a ferroelectric nematic liquid crystal material into the liquid crystal cell to form a ferroelectric nematic liquid crystal layer, thereby obtaining the nonlinear perfect vector beam generating element.

[0022] Specifically, the photo-alignment agent is an azo photo-controlled orientation material SD1.

[0023] Specifically, the ferroelectric nematic liquid crystal material is a ferroelectric nematic phase containing intermediate polar phase liquid crystal material;

[0024] Preferably, the ferroelectric nematic liquid crystal material is 4-((4-nitrophenoxy)carbonyl)-3-(trifluoromethyl)phenyl 2-fluoro-4-methoxybenzoate.

[0025] Specifically, in S1, the ultrasonic cleaning includes ultrasonic cleaning with ethanol alcohol cleaning solution and ultrasonic cleaning with ultrapure water.

[0026] Preferably, the ultrasonic cleaning time with the ethanol alcohol cleaning solution is 20 minutes; and the ultrasonic cleaning with ultrapure water is divided into two times, each time for 10 minutes.

[0027] Specifically, in S1, the drying is performed at a temperature of 140℃ for 40 minutes.

[0028] Specifically, in S1, the ultraviolet ozone cleaning is performed for 30 minutes.

[0029] Specifically, in S2, the spin coating has the following parameters: the rotation speed of the first step of spin coating is 3000 rpm, and the spin coating time is 40 seconds; the rotation speed of the second step of spin coating is 300 rpm, and the spin coating time is 10 seconds.

[0030] Specifically, in S2, the solidification has the following conditions: 100 degrees Celsius for 10 minutes.

[0031] Specifically, in S3, the spacer particles are silica microspheres.

[0032] Further, the application of the above-mentioned nonlinear perfect vector beam generating element in generating a nonlinear perfect vector beam is also within the protection scope of the present application.

[0033] Specifically, in the embodiments of the present application, the nonlinear perfect vector beam generating element can simultaneously realize the frequency doubling process and the simultaneous conversion of the vector field of the incident fundamental frequency Gaussian light. In the process of nonlinear frequency conversion, the original fundamental frequency Gaussian mode is converted into a perfect vector beam, and different nonlinear perfect vector beam control patterns are set to realize the generation of nonlinear perfect vector beams with topological charges of 2, 3, 4 and 6, respectively.

[0034] Beneficial effects: The present application can realize the integration and miniaturization of the nonlinear perfect vector beam device and the one-step direct generation of the nonlinear perfect vector beam through the direct orientation of the liquid crystal electric dipole. BRIEF DESCRIPTION OF DRAWINGS

[0035] The above and / or other aspects of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the accompanying drawings, in which:

[0036] Figure 1 Structure diagram of the nonlinear perfect vector beam generating element prepared by the present application;

[0037] Figure 2 Molecular orientation diagram of the nonlinear perfect vector beam generating element prepared by the present application;

[0038] Figure 3 Texture diagram of the nonlinear perfect vector beam generating element prepared by the present application under a polarizing microscope;

[0039] Figure 4 Process diagram of the nonlinear perfect vector beam generation prepared by the present application;

[0040] Figure 5 Analysis of the nonlinear perfect vector beam prepared by the present application under a topological charge equal to 2;

[0041] Figure 6A schematic diagram of molecular orientation of a nonlinear perfect vector beam generating element corresponding to the nonlinear perfect vector beam with topological charge equal to 3, 4, 6 prepared in the present application;

[0042] Figure 7 The nonlinear perfect vector beam with topological charge equal to 3, 4, 6 prepared in the present application. DETAILED DESCRIPTION

[0043] The present application will be further described below in conjunction with the accompanying drawings and examples. It can be understood that the specific examples described herein are only used to explain the present application, but not to limit the present application. In addition, it should be noted that, for the convenience of description, only the parts related to the present application are shown in the drawings, but not all the structures.

[0044] In the following examples, the synthesis route of the ferroelectric nematic liquid crystal material 4-((4-nitrophenoxy)carbonyl)-3-(trifluoromethyl)phenyl 2-fluoro-4-methoxybenzoate (NJU001) is as follows:

[0045]

[0046] The specific steps are as follows:

[0047] Synthesis of A1: 250ml three-necked flask was added 8.5g (50mmol) of 2-fluoro-4-methoxybenzoic acid, 15g (50mmol) of 2-trifluoromethyl-4-hydroxybenzyl benzoate, 0.2g of DMAP, 100ml of dichloromethane, and the temperature was stirred and lowered to 5℃, then a solution of DCC (12.5g (60mmol) dissolved in 30ml of dichloromethane) was added dropwise at a temperature of 5-10℃, and after the dropwise addition was completed, the reaction was incubated for 12h, the filtrate was washed with 1% hydrochloric acid 50ml, the dichloromethane layer was collected, dried over anhydrous magnesium sulfate, and the dichloromethane was removed by concentration, 50ml of ethanol was added to crystallize to obtain 18.4g (41mmol) of A1, with a yield of 82.14%;

[0048] Synthesis of A2: 100ml hydrogenation kettle was added 15g (33mmol) of A1, 50ml of tetrahydrofuran, then 1g of 5% palladium-carbon was added, after hydrogen replacement (0.1Mpa), hydrogenation reaction was carried out for 12h, the hydrogenation kettle was replaced with nitrogen, the palladium-carbon was filtered off, the tetrahydrofuran was removed by concentration, 50ml of ethanol was added to crystallize to obtain 10.4g (28.1mmol) of A2, with a yield of 85.11%;

[0049] Synthesis of NJU001: 250ml three-necked flask was added 8g (22mmol) of A2, 3.4g (24.5mmol) of p-nitrophenol, 0.1g of DMAP, 100ml of dichloromethane, and the temperature was lowered to 5℃, and a solution of DCC in dichloromethane (5.53g in 20ml DCM) was added dropwise, and after the addition was completed, the reaction was incubated for 12h, filtered, the filtrate was washed with 1% hydrochloric acid 50ml, dried over anhydrous magnesium sulfate, concentrated to remove dichloromethane, and then column chromatography was performed using a flash column, and ethanol was crystallized to obtain NJU001 4.8g (10mmol). The content was 99.3%, and the yield was 44.8%.

[0050] Example 1

[0051] The embodiment of the present application provides a nonlinear perfect vector beam generating element, Figure 1 The liquid crystal element structure provided by the present application specifically comprises a first glass substrate and a second glass substrate which are oppositely arranged; the inner sides of the first glass substrate and the second glass substrate are further respectively provided with a first photo-controlled alignment layer and a second photo-controlled alignment layer which are formed by spin coating a photo-alignment agent and then curing; interval particles are arranged on both sides of the first photo-controlled alignment layer and the second photo-controlled alignment layer; after curing, a liquid crystal cell is formed in the first photo-controlled alignment layer, the second photo-controlled alignment layer and the interval particles arranged on both sides, and a ferroelectric nematic liquid crystal layer is formed after liquid crystal material is filled.

[0052] The embodiment of the present application further provides a preparation method of a nonlinear perfect vector beam generating element, and the specific steps are as follows:

[0053] Firstly, the first glass substrate and the second glass substrate are ultrasonically cleaned with anhydrous ethanol solution, and the cleaning time is 20 minutes. Then, the first glass substrate and the second glass substrate are ultrasonically cleaned with ultrapure water repeatedly twice, and the cleaning time of each time is 10 minutes. The cleaned substrates are placed in a drying oven, the temperature of the drying oven is adjusted to 140℃, and the drying time is 40 minutes. Finally, the first glass substrate and the second glass substrate are ultraviolet ozone cleaned for 30 minutes.

[0054] Then, a photo-alignment agent SD1 is spin coated on the first glass substrate and the second glass substrate. The spin coating mode is as follows: the rotation speed of the first step of spin coating is 3000r / min, and the spin coating time is 40 seconds. The rotation speed of the second step of spin coating is 300r / min, and the spin coating time is 10 seconds. After the photo-controlled alignment layer prepared from the selected SD1 material is spin coated on the first glass substrate and the second glass substrate, the first glass substrate and the second glass substrate are placed on a hot stage with a temperature of 100℃ to cure the photo-controlled alignment layer, and the curing time is 10 minutes. After curing, the first photo-controlled alignment layer is formed on one side of the first glass substrate, and the second photo-controlled alignment layer is formed on one side of the second glass substrate.

[0055] Silica microspheres and UV sealing adhesive were selected as spacers. After uniform mixing, the mixture was applied to both sides of the first photocontrol alignment layer. Then, the side of the second glass substrate with the second photocontrol alignment layer formed was placed on top of the spacers for encapsulation. The first and second glass substrates were then bonded together with a staggered alignment. Figure 1 The silica microspheres were then placed under ultraviolet light until the sealant cured, forming a liquid crystal cell. The cell thickness was controlled by changing the diameter of the silica microspheres, and the cell thickness of the liquid crystal cell in this embodiment was measured by interferometry.

[0056] The first and second photo-aligned layers are oriented by polarized ultraviolet exposure. An azo-based photo-aligned material SD1 is selected as the alignment agent for the first and second photo-aligned layers. Under the irradiation of linearly polarized light, the molecules of the photo-aligned material align in a direction perpendicular to the direction of the linearly polarized light. Through the interaction with the liquid crystal molecules, the liquid crystal molecules form a specially designed ordered arrangement. Liquid crystal material is injected between the first and second glass substrates. The novel ferroelectric nematic liquid crystal material NJU001 is heated to 150 degrees Celsius and injected into the liquid crystal cell through a capillary glass tube to obtain the nonlinear perfect vector beam generating element.

[0057] Figure 2 This is a schematic diagram of the liquid crystal molecule orientation of the nonlinear perfect vector beam generating element prepared in this invention. The diagram shows the orientation distribution of liquid crystal molecules in the first period of the nonlinear perfect vector beam control pattern. Each period consists of two concentric rings of equal width with an orientation distribution of 90 degrees between adjacent rings. Figure 3 The texture of the nonlinear perfect vector beam generating element prepared in this invention is shown under a polarizing microscope.

[0058] Optionally, the annular period of the nonlinear perfect vector beam control pattern is not limited to the distribution shown in the figure. Nonlinear perfect vector beam control patterns with arbitrary period sizes will determine the diameter of the nonlinear perfect vector beam.

[0059] Optionally, the rotation angle of the orientation of individual ring molecules in the nonlinear perfect vector beam control pattern is not limited to the 360 ​​degrees shown in the figure, but includes nonlinear perfect vector beams with different topological charges corresponding to arbitrary rotation angles.

[0060] Optionally, each period of the nonlinear perfect vector beam control pattern consists of, but is not limited to, two concentric ring orientation distributions of equal width, including any two concentric ring orientation distributions of unequal width, which determine the intensity of the nonlinear perfect vector beam.

[0061] Figure 4The process schematic diagram of the nonlinear perfect vector beam generating element prepared by the application generates the beam, in the cooling process, the novel ferroelectric nematic liquid crystal NJU001 experiences the following phase state transition: isotropic state when the temperature is higher than 132 DEG C; nematic phase when the temperature is 132-76 DEG C; intermediate polar phase when the temperature is 76-58 DEG C; and ferroelectric nematic phase when the temperature is less than 58 DEG C; in general, the ferroelectric nematic phase is difficult to be oriented and controlled by the electric dipole, the intermediate polar phase of NJU001 is selected in the application, the electric dipole can be well controlled by the light control orientation, and different nonlinear perfect vector beam control patterns are set; after the temperature is cooled to the intermediate polar phase, the temperature is kept unchanged, the lens imaging is added behind the nonlinear perfect vector beam generating element, and the nonlinear perfect vector beam is obtained.

[0062] Optionally, the novel ferroelectric nematic material NJU001 (4-((4-nitrophenoxy)carbonyl)-3-(trifluoromethyl)phenyl 2-fluoro-4-methoxybenzoate) but is not limited to this material, and all materials of this type containing the intermediate polar phase of the ferroelectric nematic phase, the materials of this type can have good light control orientation characteristics while keeping the stable frequency doubling signal.

[0063] Figure 5 The nonlinear perfect vector beam prepared by the application is analyzed in the light beam with the topological charge equal to 2; the nonlinear perfect vector beam control pattern with the topological charge equal to 2 is set; the frequency doubling perfect vector beam is imaged at the lens focal point position; when the nonlinear perfect vector beam with the topological charge equal to 2 is emitted, a polarizer is placed behind the light beam, and the nonlinear perfect vector beam will become 4-petal light spots.

[0064] Figure 6 The orientation schematic diagram of the nonlinear perfect vector beam generating element corresponding to the nonlinear perfect vector beam with the topological charge equal to 3, 4 and 6 prepared by the application; the rotation angle of the single ring molecule orientation is 540 DEG, 720 DEG and 1080 DEG respectively.

[0065] Figure 7 The nonlinear perfect vector beams with different topological charge numbers prepared by the application; the nonlinear perfect vector beam control patterns with the topological charge equal to 3, 4 and 6 are set; the frequency doubling perfect vector beam is imaged at the lens focal point position; when the nonlinear perfect vector beam with the topological charge equal to 3, 4 and 6 is emitted, a polarizer is placed behind the light beam, and the nonlinear perfect vector beam will become 6-petal, 8-petal and 12-petal light spots.

[0066] Optionally, the present application provides nonlinear perfect vector beams with topological charges of 2, 3, 4, 6, but is not limited to these topological charge numbers, and includes nonlinear perfect vector beams corresponding to larger or smaller topological charge numbers.

[0067] The present application provides a nonlinear perfect vector beam generating element, a preparation method and an application idea. There are many methods and approaches to realize the technical scheme, and the above description is only the preferred embodiment of the present application. It should be pointed out that for ordinary skilled persons in the art, some improvements and refinements can be made without departing from the principle of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application. The components not explicitly described in the embodiments can be realized by using existing technology.

Claims

1. A nonlinear perfect vector beam generating element, characterized in that, The element comprises a first glass substrate, a first photo-controllable orientation layer, a ferroelectric nematic liquid crystal layer, a second photo-controllable orientation layer and a second glass substrate; the first glass substrate and the second glass substrate are oppositely arranged; the inner sides of the first glass substrate and the second glass substrate are respectively provided with the first photo-controllable orientation layer and the second photo-controllable orientation layer; the first photo-controllable orientation layer and the second photo-controllable orientation layer are provided with interval particles therebetween. The first photo-controllable orientation layer and the second photo-controllable orientation layer are provided with a nonlinear perfect vector beam control pattern; the nonlinear perfect vector beam control pattern controls the liquid crystal molecules in the ferroelectric nematic liquid crystal layer to be arranged in a number of periodic concentric circular ring orientation distributions; the ferroelectric nematic liquid crystal material is a ferroelectric nematic phase liquid crystal material containing an intermediate polar phase.

2. The element according to claim 1, characterized in that The nonlinear perfect vector beam control pattern is composed of two concentric circular ring orientation distributions in a single period, and the orientation angle difference between adjacent circular rings is 90 degrees.

3. The element according to claim 1, characterized in that The nonlinear perfect vector beam control pattern has a single circular ring molecular orientation rotation angle of any angle in a single period.

4. The method of producing a non-linear perfect vector beam generating element according to any one of claims 1 to 3, characterized in that, The specific steps are as follows: S1. ultrasonic cleaning and drying the first glass substrate and the second glass substrate, and then performing ultraviolet ozone cleaning; S2. spin coating a photo-alignment agent on the first glass substrate and the second glass substrate after S1, and forming a first photo-controllable orientation layer and a second photo-controllable orientation layer after solidification; S3. applying interval particles on both sides of the first photo-controllable orientation layer, and then placing the second photo-controllable orientation layer to encapsulate, forming a liquid crystal cell; S4. performing polarization ultraviolet exposure orientation on the first photo-controllable orientation layer and the second photo-controllable orientation layer to form a nonlinear perfect vector beam control pattern; S5. injecting a ferroelectric nematic liquid crystal material into the liquid crystal cell to form a ferroelectric nematic liquid crystal layer, thereby obtaining the nonlinear perfect vector beam generating element.

5. The preparation method according to claim 4, characterized in that, The photo-alignment agent is an azo photo-controllable orientation material SD1.

6. The preparation method according to claim 4, characterized in that, The ferroelectric nematic liquid crystal material is 4-((4-nitrophenoxy)carbonyl)-3-(trifluoromethyl)phenyl 2-fluoro-4-methoxybenzoate.

7. The preparation method according to claim 4, characterized in that, In S2, the spin coating has the following parameters: the first step of spin coating has a rotation speed of 3000 rpm and a spin coating time of 40 seconds; the second step of spin coating has a rotation speed of 300 rpm and a spin coating time of 10 seconds.

8. The preparation method according to claim 4, characterized in that, In S2, the solidification has the following conditions: solidification at 100 degrees Celsius for 10 minutes.

9. The nonlinear perfect vector beam generating element according to any one of claims 1-3, applied to generating a nonlinear perfect vector beam.

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