阅读说明：本技术 柔性液晶微透镜阵列、制备方法和三维光学防伪测试方法 (Flexible liquid crystal micro-lens array, preparation method and three-dimensional optical anti-counterfeiting test method ) 是由 李晖 陈伟灵 于 2020-11-19 设计创作，主要内容包括：本发明提供了柔性液晶微透镜阵列、制备方法和三维光学防伪测试方法,通过在外加电场作用下,使液晶分子在液晶层内形成阵列型梯度折射率分布；在单个单元处,液晶分子形成的梯度折射率分布对平行入射光产生相位延迟,形成汇聚式球面波输出,使柔性液晶微透镜阵列表现为正透镜效果；将液晶微透镜阵列对准实际目标物体,该目标物体经过液晶微透镜阵列重建获得三维图像,实现了防伪的功能。本发明通过柔性液晶微透镜阵列的光学性能及成像能力,为其应用于面向透明视窗的光学防伪领域提供了典型实验数据和规律。本发明在塑料钞票中透明视窗的防伪领域,以及在外表不规则需要发生形变的高附加值产品、重要法律证件的防伪等领域具有应用推广价值。(The invention provides a flexible liquid crystal micro-lens array, a preparation method and a three-dimensional optical anti-counterfeiting test method, wherein liquid crystal molecules form array type gradient refractive index distribution in a liquid crystal layer under the action of an external electric field; at a single unit, the gradient refractive index distribution formed by liquid crystal molecules generates phase delay on parallel incident light to form convergent spherical wave output, so that the flexible liquid crystal micro-lens array shows a positive lens effect; the liquid crystal micro-lens array is aligned to an actual target object, and the target object is reconstructed by the liquid crystal micro-lens array to obtain a three-dimensional image, so that the anti-counterfeiting function is realized. The invention provides typical experimental data and rules for the application of the flexible liquid crystal micro-lens array in the field of optical anti-counterfeiting facing transparent windows through the optical performance and imaging capability of the flexible liquid crystal micro-lens array. The invention has application and popularization value in the anti-counterfeiting field of transparent windows in plastic banknotes, and the anti-counterfeiting field of high-added-value products and important legal documents with irregular outer surfaces and the like which need to deform.)

1. The flexible liquid crystal micro-lens array is characterized in that: the device comprises a layered structure which is sequentially provided with a lower substrate, a Teflon flexible film, a first IPS (in-plane switching) type ITO electrode, an insulating layer, a second IPS type ITO electrode and a polymer liquid crystal layer from bottom to top; the electrode pattern of the first IPS-type ITO electrode is in a central circular shape, the electrode pattern of the second IPS-type ITO electrode is in a peripheral circular ring shape, and when the flexible liquid crystal device is seen from the upper side in a plan view, the second IPS-type ITO electrode and the first IPS-type ITO electrode form structural distribution of the central circular shape and the peripheral circular ring shape to form an IPS-type electrode structure of the flexible liquid crystal device.

2. The flexible liquid crystal microlens array of claim 1, wherein: the polymer liquid crystal layer has electric field induced phase separation and forms gradient refractive index distribution and polymer wall shape after ultraviolet light photopolymerization curing.

3. The method for preparing a flexible liquid crystal microlens array according to any one of claims 1 to 2, wherein: the method comprises the following steps:

s1: testing parameters in the processes of phase separation of the liquid crystal and the monomer and photopolymerization induced by the electric field;

s2: preparing a flexible liquid crystal micro-lens array;

s3: testing the optical performance of the flexible liquid crystal micro-lens array;

s4: carrying out imaging test through the flexible liquid crystal micro-lens array;

s5: and (4) carrying out optical anti-counterfeiting characteristic evaluation on the flexible liquid crystal micro-lens array.

4. The production method according to claim 3, characterized in that: in the step S1, the specific steps are as follows:

s11: preparing a sample:

coating a polytetrafluoroethylene solution on a glass substrate by adopting a rotary coating method to form a flexible film;

plating an ITO conductive layer on the flexible film by adopting a magnetron sputtering method;

obtaining an IPS type electrode pattern by adopting ultraviolet lithography and wet etching, and preparing a lower substrate of the flexible liquid crystal device;

adopting an ultrasonic oscillation method to prepare mixed liquid with different liquid crystal and monomer solubility ratios at room temperature;

smearing the mixed liquid on a lower substrate of the flexible device by adopting a rotary smearing method;

continuously acting on the IPS type electrode through an electric field to induce the liquid crystal and the monomer to separate;

adopting continuous ultraviolet irradiation to make the monomer photocure;

peeling the glass substrate of the flexible liquid crystal device;

s12: test data:

observing and comparing the bright and dark states of the sample under different voltage conditions through POM to obtain the influence degree of the solubility ratio of the liquid crystal and the monomer, the IPS type electrode pattern, the ultraviolet light intensity and the irradiation duration on the induced liquid crystal and monomer phase separation;

and observing the gradient refractive index distribution formed by the flexible liquid crystal device after photopolymerization and the form of the polymer wall through SEM, and comparing the test results of the sample to obtain the data formed by the gradient refractive index distribution and the polymer wall.

5. The method of claim 4, wherein: in the step S2, the specific steps are as follows:

s21: preparing a Teflon flexible film on a glass substrate by adopting a rotary smearing method;

s22: plating an ITO conductive layer on the Teflon flexible film by adopting magnetron sputtering;

s23: preparing a first IPS type ITO electrode with an electrode pattern in a central circle shape by adopting ultraviolet lithography and wet etching;

s24: plating silicon nitride on the first IPS type ITO electrode as an insulating layer;

s25: plating an ITO conductive layer on the insulating layer by adopting magnetron sputtering;

s26: preparing an electrode pattern in a peripheral ring shape by adopting ultraviolet lithography and wet etching, and forming central circular and peripheral ring structural distribution between the second layer of IPS-type ITO electrode and the first layer of IPS-type ITO electrode when the flexible liquid crystal device is viewed from above, so as to form an IPS-type electrode structure of the flexible liquid crystal device;

s27: preparing a lower substrate of a flexible liquid crystal device with two layers of IPS type electrode structures;

s28: mixing mixed liquid with different liquid crystal and monomer solubility ratios by adopting an ultrasonic oscillation method at room temperature, and smearing the mixed liquid on a lower substrate of the flexible device by adopting a rotary smearing method;

s29: the flexible liquid crystal micro-lens array which is suitable for a transparent window, is easy to integrate with other anti-counterfeiting technologies and materials and has different parameters and an IPS type double-layer electrode array structure is obtained.

6. The method of claim 5, wherein: in the step S3, the specific steps are as follows:

s31: establishing a performance test system, and sequentially placing a monochromatic laser, a beam expander, a diaphragm, a polaroid, a flexible liquid crystal device and test equipment on a light path;

s32: adopting a photodiode to test and obtain the threshold voltage, the transmittance and the response time of the flexible liquid crystal micro-lens array;

s33: testing by adopting a CCD camera to obtain a monochromatic laser interference pattern of the flexible liquid crystal micro-lens array, and analyzing test data to obtain the relation between voltage and focal length;

s34: when the central circle and the peripheral ring are respectively grounded, correspondingly measuring interference patterns of the flexible liquid crystal device, and verifying the working characteristics of the flexible liquid crystal micro-lens array switched between focusing and diverging;

s35: and comparing the test results of the sample to obtain the influence of the solubility ratio of the liquid crystal and the monomer, the IPS type double-layer electrode array structure, the ultraviolet light intensity and the irradiation duration on the optical performance of the flexible liquid crystal micro-lens array.

7. The method of claim 6, wherein: in the step S4, the specific steps are as follows:

s41: establishing an imaging test system, and sequentially placing monochromatic laser, a polaroid, a diaphragm, a flexible liquid crystal device, a lens and a CCD camera on an optical path;

s42: keeping the distance between the flexible liquid crystal micro-lens array and the CCD camera unchanged, and measuring the imaging condition of the monochromatic laser serving as the point light source under different voltages;

s43: calculating by Fourier transform to obtain an MTF curve of the flexible liquid crystal micro-lens array;

s44: and comparing the test result of the sample to obtain the influence of the solubility ratio of the liquid crystal and the monomer, the IPS type double-layer electrode array structure, the ultraviolet light intensity and the irradiation duration on the imaging capacity of the flexible liquid crystal micro-lens array.

8. The method of claim 7, wherein: in the step S5, the specific steps are as follows:

s51: establishing an electric control tuning imaging test system, and sequentially placing a target object, a flexible liquid crystal device, a lens and a CCD camera on an optical path;

s52: keeping the distance between the flexible liquid crystal micro-lens array and the CCD camera unchanged, and obtaining two-dimensional optical images with different depths of field through the flexible liquid crystal micro-lens array under different voltage-frequency conditions;

s53: and reconstructing a three-dimensional optical image of the target object by adopting a back projection algorithm and adopting two-dimensional optical images under different depth of field conditions.

9. The method of claim 8, wherein: in the step S52, the specific steps are as follows:

an electric field applied to the flexible liquid crystal micro-lens array adopts a square wave driving signal, the voltage range of the signal is 0-20 Vrms, and the frequency is 1 kHz;

the signal is loaded at two layers of electrodes of a lower substrate of the designed liquid crystal micro-lens array, a positive electrode signal is loaded at the first layer of electrodes, and a negative electrode signal is loaded at the second layer of electrodes.

10. The three-dimensional optical anti-counterfeiting test method based on the flexible liquid crystal micro-lens array of any one of claims 1 to 2 is characterized in that: the method comprises the following steps:

s1: preparing a flexible liquid crystal micro-lens array;

s2: forming an imaging system by the flexible liquid crystal micro-lens array and the CCD camera to image a target object;

s3: applying an external electric field to the flexible liquid crystal micro-lens array to tune the focal length, electrically controlling and adjusting to a clear imaging state, and recording a driving voltage V1;

s4: gradually loading voltage by taking the voltage Va as a step length, and obtaining two-dimensional optical images under the voltages of V2, V3 and … … Vn at the CCD camera;

s5: and processing the two-dimensional optical images V1, V2 and … Vn by adopting a back projection algorithm to obtain a three-dimensional optical image with the depth of field characteristic, thereby realizing a three-dimensional image of the target object.

Technical Field

The invention belongs to the technical field of optical anti-counterfeiting, and particularly relates to a flexible liquid crystal micro-lens array, a preparation method and a three-dimensional optical anti-counterfeiting test method.

Background

Optical anti-counterfeiting refers to various anti-counterfeiting technologies developed by using the basic principles of light waves, such as light reflection, transmission, refraction, interference, diffraction, polarization, birefringence, micro/nano optics and the like. According to the principle of using different optical imaging, common optical anti-counterfeiting technologies, such as watermarks, holograms, diffraction light variation images, interference light variation images, zero-order diffraction light variation images and the like, have been successfully applied to the aspects of well-known product trademarks, high value-added products, important legal documents (passports, identity cards, driving licenses and the like), credit cards, currency, securities and the like. In recent years, with the gradual expansion of the application field of the optical anti-counterfeiting technology, new application requirements in the optical anti-counterfeiting field, such as the anti-counterfeiting of a transparent window in a plastic banknote, are continuously emerging. However, the problem that the traditional optical anti-counterfeiting method cannot meet the application requirement of the transparent window exists. Therefore, the flexible optical imaging element which meets the application requirement of the transparent window and has the characteristics of multi-dimension, dynamic sense, three-dimensional imaging, easy identification and difficult counterfeiting is designed, and the flexible optical imaging element has important theoretical and practical significance for the development and application of the next generation of advanced optical anti-counterfeiting technology.

The existing optical anti-counterfeiting method is difficult to prepare a flexible optical imaging element which meets the characteristics of multi-dimensional, dynamic and three-dimensional imaging and is easy to integrate with other anti-counterfeiting technologies/materials.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the flexible liquid crystal micro-lens array, the preparation method and the three-dimensional optical anti-counterfeiting test method are provided and used for reconstructing a three-dimensional image of a target object.

The technical scheme adopted by the invention for solving the technical problems is as follows: the flexible liquid crystal micro-lens array comprises a layered structure which is sequentially provided with a lower substrate, a Teflon flexible film, a first IPS (in-plane switching) type ITO (indium tin oxide) electrode, an insulating layer, a second IPS type ITO electrode and a polymer liquid crystal layer from bottom to top; the electrode pattern of the first IPS-type ITO electrode is in a central circular shape, the electrode pattern of the second IPS-type ITO electrode is in a peripheral circular ring shape, and when the flexible liquid crystal device is seen from the upper side in a plan view, the second IPS-type ITO electrode and the first IPS-type ITO electrode form structural distribution of the central circular shape and the peripheral circular ring shape to form an IPS-type electrode structure of the flexible liquid crystal device.

According to the scheme, the polymer liquid crystal layer has the forms of gradient refractive index distribution and polymer walls after electric field induced phase separation and ultraviolet light photopolymerization curing.

The preparation method of the flexible liquid crystal micro-lens array comprises the following steps:

s1: testing parameters in the processes of phase separation of the liquid crystal and the monomer and photopolymerization induced by the electric field;

s2: preparing a flexible liquid crystal micro-lens array;

s3: testing the optical performance of the flexible liquid crystal micro-lens array;

s4: carrying out imaging test through the flexible liquid crystal micro-lens array;

s5: and (4) carrying out optical anti-counterfeiting characteristic evaluation on the flexible liquid crystal micro-lens array.

Further, in step S1, the specific steps include:

s11: preparing a sample:

coating a polytetrafluoroethylene solution on a glass substrate by adopting a rotary coating method to form a flexible film;

plating an ITO conductive layer on the flexible film by adopting a magnetron sputtering method;

obtaining an IPS type electrode pattern by adopting ultraviolet lithography and wet etching, and preparing a lower substrate of the flexible liquid crystal device;

adopting an ultrasonic oscillation method to prepare mixed liquid with different liquid crystal and monomer solubility ratios at room temperature;

smearing the mixed liquid on a lower substrate of the flexible device by adopting a rotary smearing method;

continuously acting on the IPS type electrode through an electric field to induce the liquid crystal and the monomer to separate;

adopting continuous ultraviolet irradiation to make the monomer photocure;

peeling the glass substrate of the flexible liquid crystal device;

s12: test data:

observing and comparing the bright and dark states of the sample under different voltage conditions through POM to obtain the influence degree of the solubility ratio of the liquid crystal and the monomer, the IPS type electrode pattern, the ultraviolet light intensity and the irradiation duration on the induced liquid crystal and monomer phase separation;

and observing the gradient refractive index distribution formed by the flexible liquid crystal device after photopolymerization and the form of the polymer wall through SEM, and comparing the test results of the sample to obtain the data formed by the gradient refractive index distribution and the polymer wall.

Further, in step S2, the specific steps include:

s21: preparing a Teflon flexible film on a glass substrate by adopting a rotary smearing method;

s22: plating an ITO conductive layer on the Teflon flexible film by adopting magnetron sputtering;

s23: preparing a first IPS type ITO electrode with an electrode pattern in a central circle shape by adopting ultraviolet lithography and wet etching;

s24: plating silicon nitride on the first IPS type ITO electrode as an insulating layer;

s25: plating an ITO conductive layer on the insulating layer by adopting magnetron sputtering;

s26: preparing an electrode pattern in a peripheral ring shape by adopting ultraviolet lithography and wet etching, and forming central circular and peripheral ring structural distribution between the second layer of IPS-type ITO electrode and the first layer of IPS-type ITO electrode when the flexible liquid crystal device is viewed from above, so as to form an IPS-type electrode structure of the flexible liquid crystal device;

s27: preparing a lower substrate of a flexible liquid crystal device with two layers of IPS type electrode structures;

s28: mixing mixed liquid with different liquid crystal and monomer solubility ratios by adopting an ultrasonic oscillation method at room temperature, and smearing the mixed liquid on a lower substrate of the flexible device by adopting a rotary smearing method;

s29: the flexible liquid crystal micro-lens array which is suitable for a transparent window, is easy to integrate with other anti-counterfeiting technologies and materials and has different parameters and an IPS type double-layer electrode array structure is obtained.

Further, in step S3, the specific steps include:

s31: establishing a performance test system, and sequentially placing a monochromatic laser, a beam expander, a diaphragm, a polaroid, a flexible liquid crystal device and test equipment on a light path;

s32: adopting a photodiode to test and obtain the threshold voltage, the transmittance and the response time of the flexible liquid crystal micro-lens array;

s33: testing by adopting a CCD camera to obtain a monochromatic laser interference pattern of the flexible liquid crystal micro-lens array, and analyzing test data to obtain the relation between voltage and focal length;

s34: when the central circle and the peripheral ring are respectively grounded, correspondingly measuring interference patterns of the flexible liquid crystal device, and verifying the working characteristics of the flexible liquid crystal micro-lens array switched between focusing and diverging;

s35: and comparing the test results of the sample to obtain the influence of the solubility ratio of the liquid crystal and the monomer, the IPS type double-layer electrode array structure, the ultraviolet light intensity and the irradiation duration on the optical performance of the flexible liquid crystal micro-lens array.

Further, in step S4, the specific steps include:

s41: establishing an imaging test system, and sequentially placing monochromatic laser, a polaroid, a diaphragm, a flexible liquid crystal device, a lens and a CCD camera on an optical path;

s42: keeping the distance between the flexible liquid crystal micro-lens array and the CCD camera unchanged, and measuring the imaging condition of the monochromatic laser serving as the point light source under different voltages;

s43: calculating by Fourier transform to obtain an MTF curve of the flexible liquid crystal micro-lens array;

s44: and comparing the test result of the sample to obtain the influence of the solubility ratio of the liquid crystal and the monomer, the IPS type double-layer electrode array structure, the ultraviolet light intensity and the irradiation duration on the imaging capacity of the flexible liquid crystal micro-lens array.

Further, in step S5, the specific steps include:

s51: establishing an electric control tuning imaging test system, and sequentially placing a target object, a flexible liquid crystal device, a lens and a CCD camera on an optical path;

s52: keeping the distance between the flexible liquid crystal micro-lens array and the CCD camera unchanged, and obtaining two-dimensional optical images with different depths of field through the flexible liquid crystal micro-lens array under different voltage-frequency conditions;

s53: and reconstructing a three-dimensional optical image of the target object by adopting a back projection algorithm and adopting two-dimensional optical images under different depth of field conditions.

Further, in step S52, the specific steps include:

an electric field applied to the flexible liquid crystal micro-lens array adopts a square wave driving signal, the voltage range of the signal is 0-20 Vrms, and the frequency is 1 kHz;

the signal is loaded at two layers of electrodes of a lower substrate of the designed liquid crystal micro-lens array, a positive electrode signal is loaded at the first layer of electrodes, and a negative electrode signal is loaded at the second layer of electrodes.

The three-dimensional optical anti-counterfeiting test method of the flexible liquid crystal micro-lens array comprises the following steps:

s1: preparing a flexible liquid crystal micro-lens array;

s2: forming an imaging system by the flexible liquid crystal micro-lens array and the CCD camera to image a target object;

s3: applying an external electric field to the flexible liquid crystal micro-lens array to tune the focal length, electrically controlling and adjusting to a clear imaging state, and recording a driving voltage V1;

s4: gradually loading voltage by taking the voltage Va as a step length, and obtaining two-dimensional optical images under the voltages of V2, V3 and … … Vn at the CCD camera;

s5: and processing the two-dimensional optical images V1, V2 and … Vn by adopting a back projection algorithm to obtain a three-dimensional optical image with the depth of field characteristic, thereby realizing a three-dimensional image of the target object.

The invention has the beneficial effects that:

1. according to the flexible liquid crystal micro-lens array, the preparation method and the three-dimensional optical anti-counterfeiting test method, liquid crystal molecules form array type gradient refractive index distribution in a liquid crystal layer under the action of an external electric field; at a single unit, the gradient refractive index distribution formed by liquid crystal molecules generates phase delay on parallel incident light to form convergent spherical wave output, so that the flexible liquid crystal micro-lens array shows a positive lens effect; the liquid crystal micro-lens array is aligned to an actual target object, and the target object is reconstructed by the liquid crystal micro-lens array to obtain a three-dimensional image, so that the anti-counterfeiting function is realized.

2. The invention provides typical experimental data and rules for the application of the flexible liquid crystal micro-lens array in the field of optical anti-counterfeiting facing transparent windows through the optical performance and imaging capability of the flexible liquid crystal micro-lens array.

3. The invention has application and popularization value in the anti-counterfeiting field of transparent windows in plastic banknotes, and the anti-counterfeiting field of high-added-value products and important legal documents with irregular outer surfaces and the like which need to deform.

Drawings

FIG. 1 is a schematic representation of a spin-on process used to form a Teflon film in accordance with an embodiment of the present invention.

FIG. 2 is a schematic diagram of an ITO conductive layer prepared by magnetron sputtering, ultraviolet lithography and wet etching in an embodiment of the invention.

FIG. 3 is a schematic diagram of a spin-on process for forming a polymer and monomer hybrid film according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of the IPS-type electrode loaded with an electric field to induce phase separation of liquid crystal and monomer according to an embodiment of the present invention;

FIG. 5 is a schematic view of an embodiment of the present invention;

FIG. 6 is a schematic view of a peel-off of an embodiment of the present invention;

FIG. 7 is a schematic diagram of a two-layer IPS type electrode array structure (2 × 2 cell) according to an embodiment of the present invention;

FIG. 8 is a schematic structural diagram of a flexible liquid crystal microlens array according to an embodiment of the present invention;

FIG. 9 is a schematic diagram of a performance testing system of an embodiment of the present invention;

FIG. 10 is a schematic view of a monochromatic laser point light source imaging test system according to an embodiment of the present invention;

FIG. 11 is a schematic diagram of an electronically controlled tuned imaging test system according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

A flexible liquid crystal device having an IPS (In-Plane Switching) type electrode structure was prepared using a polymer/liquid crystal composite material:

1. preparing a first layer structure of an electrode array with a circular center on a Teflon (polytetrafluoroethylene thin) film by ITO (indium tin oxide) film plating, ultraviolet lithography and wet etching; then growing silicon nitride on the electrode layer as an insulating layer; preparing a second layer structure of the electrode array with a circular periphery on the insulating layer by ITO film plating, ultraviolet lithography and wet etching; the IPS type electrode structure of the flexible liquid crystal device is formed by the two layers of electrode structures;

2. inducing liquid crystal and monomer phase separation by an electric field acting on an IPS (in-plane switching) type electrode, and forming gradient refractive index distribution and a polymer wall shape in a polymer/liquid crystal layer after ultraviolet light is used for curing the monomer to obtain a flexible micro-lens array which is suitable for a transparent window and is easy to integrate with other anti-counterfeiting technologies/materials; the liquid crystal micro-lens array can tune the focal length along with an external electric field to obtain scene two-dimensional images under different voltages;

3. and processing the obtained two-dimensional scene images under different voltages through a backward projection algorithm to finally obtain a three-dimensional optical image with the depth of field characteristic so as to realize three-dimensional imaging.

The preparation and test process of the flexible liquid crystal micro-lens array is as follows:

1) the electric field induces phase separation of the liquid crystal and the monomer and photopolymerization.

Coating a polytetrafluoroethylene solution (Teflon) on a glass substrate by a rotary coating method to form a flexible film, as shown in FIG. 1; plating an ITO conductive layer on the flexible film by adopting a magnetron sputtering method; and obtaining a required IPS type electrode pattern by adopting ultraviolet lithography and wet etching, and preparing a lower substrate of the flexible liquid crystal device, as shown in FIG. 2.

Mixing liquid crystal (E7) and monomer (NOA65) at room temperature by ultrasonic oscillation method to obtain mixed liquid with different solubility ratios; applying the mixed liquid to the lower substrate of the flexible device by using a rotary application method, as shown in fig. 3; continuously acting on the IPS type electrode through an electric field to induce the liquid crystal and the monomer to separate, as shown in FIG. 4; the monomer is photocured using continuous uv irradiation, as shown in fig. 5. The completed flexible liquid crystal device was peeled off the glass substrate as shown in fig. 6. The light and dark states of the sample under different voltage conditions are observed and compared through a polarization Microscope (POM), and the influence of the solubility ratio of the liquid crystal and the monomer, the IPS type electrode pattern, the ultraviolet light intensity and the irradiation time on the induced liquid crystal and monomer phase separation is obtained.

Then, a Scanning Electron Microscope (SEM) is used to observe the gradient refractive index distribution and the morphology of the polymer wall formed by the flexible liquid crystal device after photopolymerization, and the test results of the sample are compared to obtain the gradient refractive index distribution and the polymer wall forming mechanism.

2) Preparation and performance evaluation of flexible liquid crystal micro-lens array

Preparing a Teflon flexible film by adopting a rotary smearing method; plating an ITO conductive layer by magnetron sputtering; and preparing a first IPS type ITO electrode by adopting ultraviolet lithography and wet etching, wherein the electrode pattern is a circular array.

Plating silicon nitride (SiNx) on the first layer of electrode to serve as an insulating layer between the two layers of electrodes; plating an ITO conductive layer by magnetron sputtering; and preparing a second layer of IPS type ITO electrode by adopting an ultraviolet photoetching and hydrochloric acid corrosion method, wherein the electrode pattern is a circular ring array, and the circular ring array and the first layer of electrode form structural distribution of a central circular ring and a peripheral circular ring in a overlooking mode, and preparing a lower substrate of the flexible liquid crystal device with a two-layer IPS type electrode structure as shown in FIG. 7.

An electric field induced phase separation and photopolymerization method is adopted, and a polymer/liquid crystal composite material is used for preparing a plurality of flexible liquid crystal micro-lens arrays with different parameters and IPS type double-layer electrode array structures (central circular and peripheral circular rings), wherein the structure is schematically shown in FIG. 8.

Establishing a performance test system as shown in fig. 9, and obtaining the threshold voltage, transmittance, response time and the like of the flexible liquid crystal micro-lens array when adopting a photodiode test; when a Charge Coupled Device (CCD) camera is used for testing, a single-color laser interference pattern of the flexible liquid crystal micro-lens array is obtained, and the relation between voltage and focal length and the like are obtained by analyzing test data; and measuring the interference pattern of the flexible liquid crystal device when the central circle is grounded, and measuring the interference pattern of the flexible liquid crystal device when the peripheral circle is grounded, and verifying the focusing/diverging switchable working characteristics of the flexible liquid crystal micro-lens array. Comparing the test results of the samples, the influence of the solubility ratio of the liquid crystal and the monomer, the IPS type double-layer electrode array structure (central circular and peripheral circular rings), the ultraviolet light intensity and the irradiation time on the optical performance is obtained.

An imaging test system as shown in fig. 10 is established, the distance between the flexible liquid crystal micro-lens array and the CCD camera is kept unchanged, the imaging condition of the point light source under different voltages is measured, and the flexible liquid crystal micro-lens array MTF curve is obtained by fourier transform calculation. Comparing the test results of the samples, the influence of the solubility ratio of the liquid crystal and the monomer, the IPS type double-layer electrode array structure (central circular and peripheral circular rings), the ultraviolet light intensity and the irradiation time on the imaging capability of the IPS type double-layer electrode array structure is obtained.

3) Evaluation of optical anti-counterfeiting characteristics of flexible liquid crystal micro-lens array

An electrically controlled tuned imaging test system as shown in fig. 11 was set up to keep the distance between the flexible liquid crystal microlens array and the CCD camera unchanged and obtain two-dimensional optical images generated by the system under different voltage-frequency conditions.

And a back projection algorithm is adopted, and the flexible liquid crystal micro-lens array is used for obtaining two-dimensional optical images under different depth of field conditions to reconstruct three-dimensional optical images of the target object. The optical performance and imaging capability of the flexible liquid crystal micro-lens array are utilized to provide typical experimental data and rules for the application of the flexible liquid crystal micro-lens array in the field of optical anti-counterfeiting facing transparent windows.

Fig. 11 is a schematic view of optical imaging according to an embodiment of the present invention.

The liquid crystal micro lens array adopts square wave driving signals, the voltage control range of the signals is 0-20 Vrms, and the frequency is 1 KHz. In the specific implementation process, the signal is loaded at two layers of electrodes of a lower substrate of the designed liquid crystal micro-lens array, the first layer of electrodes are loaded with positive signals, and the second layer of electrodes are loaded with negative signals.

Under the action of an external electric field, liquid crystal molecules are subjected to the action of the electric field, and array type gradient refractive index distribution is formed in the liquid crystal layer. Taking a single unit as an example for explanation, at the single unit, liquid crystal molecules form gradient refractive index distribution, and can generate phase delay on parallel incident light to form convergent spherical wave output, that is, the liquid crystal micro lens array shows a positive (convex) lens effect.

The general idea to produce optical anti-counterfeiting applications is: the liquid crystal micro-lens array is aligned to an actual target object, and when the target object is reconstructed by a designed method to obtain a three-dimensional image, the anti-counterfeiting purpose can be determined to be achieved.

The specific operating method for producing optical anti-counterfeiting applications is as follows: firstly, forming an imaging system by a liquid crystal micro lens array and a CCD camera, imaging a target object, electrically controlling and adjusting the liquid crystal micro lens array to a clear imaging state, and recording a driving voltage V1; subsequently, a voltage is gradually applied in steps of a Va voltage, and two-dimensional optical images at V2, V3, … … Vn voltages are obtained at the CCD camera; and then, a back projection algorithm is adopted, and the flexible liquid crystal micro-lens array is used for obtaining two-dimensional optical images under different depth of field conditions to reconstruct three-dimensional optical images of the target object.

The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes and modifications made in accordance with the principles and concepts disclosed herein are intended to be included within the scope of the present invention.