CN114895457A - Design method of optical anti-counterfeiting liquid crystal element - Google Patents
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- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 4
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
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Abstract
The invention discloses a design method of an optical anti-counterfeiting liquid crystal element, wherein the liquid crystal element designed by the method is composed of a substrate and a liquid crystal array on the substrate, a plurality of units with the same period size are divided on the substrate, liquid crystal molecules with the same rotation angle are coated on each unit in a spinning mode, so that the liquid crystal array is formed, the liquid crystal element is provided with two display channels which are a channel 1 and a channel2 respectively, and the light intensity of the channel 1 and the channel2 regularly changes along with the change of the rotation angle of the liquid crystal molecules. The invention integrates multiple functions into one element by utilizing the excellent light field regulation and control capability of the liquid crystal, thereby expanding the application of the liquid crystal and enhancing the anti-counterfeiting effect. Compared with the prior design method, the method realizes more functions, enables the optical regulation and control capability of the element to be greatly improved, and has more excellent performance in the aspects of information capacity and optical anti-counterfeiting safety. Therefore, the design method has wide application prospect.
Description
Technical Field
The invention belongs to the field of optical anti-counterfeiting technology and polarization optics, and relates to a liquid crystal element design method for multi-channel image display.
Background
The optical anti-counterfeiting technology is a very important direction in the optical field, and can protect the safety of information and reduce the economic loss caused by counterfeit commodities. With the development of optical theory and processing means, the anti-counterfeiting technology is continuously updated, however, the current anti-counterfeiting technology has the problems of complex design method, high processing difficulty and the like, and part of anti-counterfeiting means is easy to crack and is not suitable for image encryption and anti-counterfeiting. How to construct an element with low cost, simple design and high anti-counterfeiting performance is a problem which needs to be solved urgently. The liquid crystal is a low-cost material which can be applied to batch production, has liquid fluidity and crystal anisotropy, and can realize free regulation and control of parameters such as amplitude, polarization, phase and the like of light waves through a relatively simple design and processing method. In recent years, liquid crystal has been used to realize specific anti-counterfeiting functions, such as color invisible patterns, optically variable films, etc., but such liquid crystal devices have a single function, can only display information in a specific channel, and the corresponding anti-counterfeiting information is easy to crack, and the anti-counterfeiting effect is poor.
Disclosure of Invention
The invention aims to provide a design method of an optical anti-counterfeiting liquid crystal element, and the liquid crystal element designed by the method can realize independent switching of two binary gray level images. The invention integrates multiple functions into one element by utilizing the excellent light field regulation and control capability of the liquid crystal, thereby expanding the application of the liquid crystal and enhancing the anti-counterfeiting effect. Compared with the prior design method, the method realizes more functions, enables the optical regulation and control capability of the element to be greatly improved, and has more excellent performance in the aspects of information capacity and optical anti-counterfeiting safety. Therefore, the design method has wide application prospect.
The purpose of the invention is realized by the following technical scheme:
a design method of an optical anti-counterfeiting liquid crystal element comprises the following steps:
step one, constructing a liquid crystal array:
dividing a plurality of units with the same period size on a substrate, wherein liquid crystal molecules with the same rotation angle are coated on each unit in a spinning mode, so that a liquid crystal array is formed, the substrate and the liquid crystal array on the substrate form a liquid crystal element, the liquid crystal element is provided with two display channels which are a channel 1 and a channel2 respectively, and the light intensity of the channel 1 and the channel2 regularly changes along with the change of the rotation angle of the liquid crystal molecules;
step two, when linearly polarized light vertically enters and passes through the liquid crystal molecules and the analyzer, the emergent light field can be expressed as:
wherein alpha is 1 Is the angle of polarization, α 2 For the angle of polarization detection, l and s are the major and minor axes of the liquid crystal molecules, t l And t s The transmission coefficients of the long axis and the short axis of the liquid crystal molecules are shown, and theta is an included angle between the long axis and the x axis of the liquid crystal molecules in the x-y plane;
thirdly, carrying out gray level design on the light intensity of the channel 1 in the liquid crystal element:
when the linearly polarized incident light passes through the liquid crystal molecules and the analyzer, the emergent light intensity is as follows:
wherein, I 0 Is the intensity of incident light, I 1 The light intensity of emergent light of the channel 1;
fourthly, gray level design is carried out on the light intensity of the channel2 in the liquid crystal element:
rotating the liquid crystal element around the optical axis by a counterclockwise rotation angle beta, wherein the emergent light intensity is as follows:
wherein, I 2 The light intensity of emergent light of the channel 2;
step five, designing the rotation angle of the liquid crystal molecules of the binary gray image 1 in the channel 1:
when alpha is 1 And alpha 2 Satisfies | α 1 -α 2 When | ═ pi/2 and the rotation angle of the liquid crystal element is 0, the intensity of the emergent light is normalizedDistribution of degrees satisfies sin 2 (2 theta), defining the value of the pixel with smaller light intensity in the binary image as 0, and defining the candidate rotation angle corresponding to the liquid crystal molecules as theta 1 And theta 4 (ii) a The value of the pixel with the higher light intensity is defined as 1, and the candidate rotation angle corresponding to the liquid crystal molecules is theta 2 And theta 3 ；
Sixthly, designing the rotation angle of the liquid crystal molecules of the binary gray level image 2 in the channel 2:
when alpha is 1 And alpha 2 Satisfies | α 1 -α 2 When | ═ pi/2 and the rotation angle of the liquid crystal element is beta, the normalized intensity distribution of the intensity of the emergent light satisfies sin 2 (2 theta-2 beta), the value of the pixel with smaller light intensity in the binary image is defined as 0, and the candidate rotation angle corresponding to the liquid crystal molecules is theta 1 And theta 2 (ii) a The value of the pixel with the higher light intensity is defined as 1, and the candidate rotation angle corresponding to the liquid crystal molecules is theta 3 And theta 4 ；
Step seven, combining the step five and the step six, coding the binary gray level images of the channel 1 and the channel2 into 4 2-system codes: "00", "10", "11", "01", each code corresponds to the distribution of the light intensity of the same pixel point of the channel 1 and the channel2, and 4 codes correspond to the liquid crystal molecules of 4 different rotation angles one by one, wherein: the rotation angle of the liquid crystal molecules is theta 1 When theta is greater than theta 1 Corresponding to "00" in binary coding; the rotation angle of the liquid crystal molecules is theta 2 When theta is greater than theta 2 Corresponding to "10" in binary coding; the rotation angle of the liquid crystal molecules is theta 3 When theta is greater than theta 3 Corresponding to "11" in binary coding; the rotation angle of the liquid crystal molecules is theta 4 When θ 4 Corresponding to "01" in binary coding;
step eight, regarding each unit of the liquid crystal element as a pixel, modulating the rotation angle of liquid crystal molecules on each pixel point one by one according to the method of the step five to the step seven, when linearly polarized light enters the liquid crystal element, modulating the polarization and the light intensity of the incident light, after transmission, collecting the binary gray image of the channel 1 through an analyzer with the difference of the polarization angle and the polarization angle of the incident light being pi/2, and collecting the binary gray image of the channel2 after the element rotates anticlockwise around the optical axis by beta;
and step nine, obtaining the rotation angle of the liquid crystal molecules in each pixel according to the step eight, and manufacturing the liquid crystal element through a digital micro-mirror device system.
Compared with the prior art, the invention has the following advantages:
1. the invention does not need complex algorithm, and is easier to carry out personalized design of the anti-counterfeiting pattern. The invention has the capability of switching two unrelated images, can realize double anti-counterfeiting and has good concealment. In addition, the image can be displayed only under the specified polarized light, element rotation angle and polarization detection angle, and is not easy to imitate and tamper, so that the anti-counterfeiting effect is very strong.
2. The invention utilizes the liquid crystal material, the material is simple in processing and manufacturing, and low in cost, and can meet the requirement of large-scale batch production.
3. The liquid crystal element designed by the invention can independently regulate and control the two channels without influencing each other. The binary gray level images of the two channels are clear, the contrast is good, and the two channels are very convenient to switch.
4. Because the liquid crystal element designed by the invention can independently regulate and control the two channels, no association exists between two images, and the image of one channel cannot be deduced into the image of the other channel, so that the technology can provide a brand new design idea for security and secrecy.
5. The invention can realize the independent design of double channels only by utilizing the rotation of the angle of the liquid crystal molecules, and the method does not increase the processing and manufacturing difficulty of elements and does not influence the information density and the imaging quality of two patterns.
Drawings
Fig. 1 is a working principle diagram of the present invention.
Fig. 2 is an effect diagram of an optical anti-counterfeiting liquid crystal element in the embodiment of the invention.
FIG. 3 is a graph showing the polarization conversion efficiency of liquid crystal molecules of the present invention without considering the dispersion of materials.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings, but not limited thereto, and any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection scope of the present invention.
The invention provides a design method of an optical anti-counterfeiting liquid crystal element, which comprises the following steps:
(1) the liquid crystal array is constructed, and the proposed element comprises liquid crystal molecules and a substrate (glass), wherein the size, the geometric shape and the substrate of each liquid crystal molecule are the same, and the only difference is that the rotation angle theta of each liquid crystal molecule is the included angle between the long axis of each liquid crystal molecule and the x axis in the x-y plane.
(2) Linearly polarized light (polarization angle alpha) 1 ) Vertically incident through the liquid crystal molecules and the analyzer (the analyzer angle is alpha) 2 ) Then, the emergent light field of the liquid crystal molecules can be expressed as:
wherein l and s are respectively the major and minor axes of the liquid crystal molecules, t l And t s The transmission coefficients of the major and minor axes of the liquid crystal molecules are shown.
(3) According to (2), the gray level design is carried out on the light intensity of the channel 1 in the liquid crystal element, and after linearly polarized incident light passes through liquid crystal molecules and an analyzer, the emergent light intensity is as follows:
wherein, I 0 Is the intensity of incident light, I 1 The intensity of the emergent light of the channel 1.
(4) The gray level design is carried out on the light intensity of the channel2 in the liquid crystal element, the liquid crystal element rotates anticlockwise around the optical axis by the angle beta, and the emergent light intensity changes to be as follows:
wherein, I 2 The intensity of the emergent light of the channel 2. From the formulas (2) and (3), the polarization angle α of incident polarized light can be obtained 1 Angle of analysis alpha 2 And the rotation angle beta of the liquid crystal element is determined, the light intensity change of the channel 1 and the channel2 is only related to the rotation angle theta of the liquid crystal molecules.
(5) The liquid crystal molecule rotation angle (normalized intensity distribution satisfies sin) of the binary gray image 1 in the design channel 1 2 (2 θ)): when alpha is 1 And alpha 2 Satisfies | α 1 -α 2 When | ═ π/2 and the rotation angle of the liquid crystal element is 0, the normalized intensity distribution of the light intensity of the outgoing light satisfies sin 2 (2. theta.) of the composition. Wherein, the value of the light intensity is defined as 0, and the candidate rotation angle corresponding to the liquid crystal molecule is theta 1 And theta 4 (ii) a Defining the value of the larger light intensity as 1, and the candidate rotation angle corresponding to the liquid crystal molecules is theta 2 And theta 3 。
(6) The liquid crystal molecule rotation angle (normalized intensity distribution satisfies sin) of the binary gray scale image 2 in the design channel2 2 (2. theta. -2. beta.)): when alpha is 1 And alpha 2 Satisfies | α 1 -α 2 When | ═ pi/2 and the rotation angle of the liquid crystal element is beta, the normalized intensity distribution of the intensity of the emergent light satisfies sin 2 (2. theta. -2. beta.). Defining the value with smaller light intensity in the binary image as 0, wherein the candidate rotation angle corresponding to the liquid crystal molecules is theta 1 And theta 2 (ii) a Defining the value of the larger light intensity as 1, and the candidate rotation angle corresponding to the liquid crystal molecules is theta 3 And theta 4 。
(7) Combining (5) and (6), the light intensities of the two channels can be encoded into 4 2-ary codes: the codes are 00, 10, 11 and 01, each code corresponds to the light intensity distribution of the same pixel point of the channel 1 and the channel2, and 4 codes correspond to liquid crystal molecules with 4 different rotation angles one by one. Wherein: the rotation angle of the liquid crystal molecules is theta 1 When theta is greater than theta 1 Corresponding to "00" in binary coding; the rotation angle of the liquid crystal molecules is theta 2 When theta is greater than theta 2 Corresponding to "10" in binary encoding; the rotation angle of the liquid crystal molecules is θ 3 When theta is greater than theta 3 Corresponding to "11" in binary coding; the rotation angle of the liquid crystal molecules is theta 4 When theta is greater than theta 4 Corresponding to "01" in binary encoding.
(8) The rotation angles of the liquid crystal molecules are arranged pixel by pixel according to (5), (6), and (7). When linearly polarized light is incident on the designed liquid crystal cell, both the polarization and the intensity of the incident light are modulated. After transmission, the binary gray scale image of the channel 1 can be collected through an analyzer with the difference between the polarization angle and the polarization angle of the incident light being pi/2. After rotating the liquid crystal element counterclockwise by β around the optical axis at this time, a binary gray scale image of the channel2 can be collected. Due to the fact that imaging of each channel is only related to the rotation angle theta, and under the condition that material dispersion is not considered, the liquid crystal molecules have high polarization conversion rate in a visible light wave band.
(9) The rotation angle of the liquid crystal molecules in each pixel is obtained according to (8), and a liquid crystal element is manufactured by a Digital Micro-mirror Device (DMD) system.
According to the scheme, two mutually independent channels can be freely switched, so that the anti-counterfeiting function is realized. In addition, because the liquid crystal molecules have high polarization conversion rate in a visible light wave band, the scheme has good performance in a wide wave band, the limitation of observation conditions is greatly reduced, and the application range of the liquid crystal molecules is wider.
The present invention solves the following problems:
(1) the element design is flexible, the two binary gray patterns can be designed respectively, and the two binary gray patterns are completely independent and have no crosstalk.
(2) The invention has the capability of switching two unrelated images, can realize double anti-counterfeiting and has good concealment.
(3) Due to the excellent optical field regulation and control capability of the liquid crystal, the invention realizes the integration of multiple functions, solves the problems of large volume, complex optical path and the like of the traditional optical device, and is suitable for the integration and planarization development of optical elements.
(4) The liquid crystal element is relatively simple in production and low in cost because the processing and manufacturing process of the liquid crystal is relatively mature and can be produced in batches.
Example (b):
in the optical anti-counterfeiting liquid crystal element designed by the embodiment, when linearly polarized light passes through the liquid crystal element and the analyzer (the difference between the polarization angle and the polarization angle of incident light is pi/2), the surface of the element can display an image of the channel 1, and then the element rotates counterclockwise around the optical axis by a rotation angle beta, and the surface of the element can display an image of the channel 2.
In this embodiment, the optical security liquid crystal element includes a substrate and a liquid crystal array thereon. At the working wavelength of 638nm, each liquid crystal molecule has high polarization conversion efficiency. The substrate can be made of fused silica glass material and is divided into a plurality of units with the same period size, and liquid crystal molecules with the same rotation angle are coated on each unit in a spin mode. As shown in fig. 1(a), the light intensities of the channel 1 and the channel2 regularly change with the change of the rotation angle θ of the liquid crystal molecules. The liquid crystal element comprises two channels, incident light is linearly polarized light under the channel 1, and after the linearly polarized light passes through the liquid crystal element, the linearly polarized light is analyzed by an analyzer with the difference between an analyzing angle and the polarizing angle of the incident light being pi/2, so that a flower image is displayed on the surface of the element. After the liquid crystal element is rotated by β along the optical axis at this time, the channel is switched to channel2, and at this time, incident light passes through the optical path in line with channel 1, and the surface of the element displays an image of the insect.
In channel 1, incident light (alpha) is linearly polarized 1 ) Passing through liquid crystal molecules and an analyzer (alpha) 2 ) Then, the emergent light intensity is as follows:
wherein theta is the included angle between the liquid crystal molecules and the x axis, I 0 Is the intensity of incident light, I 1 For channel 1, the intensity of the light emitted, l and s are the major and minor axes of the liquid crystal molecules, respectively, and t l And t s Respectively representing the transmission of the major and minor axes of the liquid crystal moleculesAnd (4) the coefficient. At this time, the liquid crystal element rotates counterclockwise by an angle β around the optical axis, and when entering the channel2, the emergent light intensity is:
wherein, I 2 The intensity of the light emitted from channel 2. Regarding each unit of the liquid crystal element as a pixel, and modulating the rotation angle of liquid crystal molecules on each pixel point one by one according to the following scheme:
the rotation angle of the liquid crystal molecules of the binary gray image 'flower' in the channel 1 is designed (the normalized intensity distribution satisfies sin 2 (2 θ)): when alpha is 1 And alpha 2 Satisfies | α 1 -α 2 When the liquid crystal element has a rotation angle of 0, | π/2, the normalized intensity distribution of the emergent light intensity satisfies sin 2 (2 θ), as shown by the channel 1 curve in FIG. 1. Defining the value of the pixel with smaller light intensity (normalized intensity is less than 0.3) in the binary image as 0, and defining the candidate rotation angle corresponding to the liquid crystal molecules as theta 1 And theta 4 (ii) a Defining the value of the pixel with larger light intensity (normalized intensity is larger than 0.7) as 1, and the candidate rotation angle corresponding to the liquid crystal molecules is theta 2 And theta 3 . It is noted here that the choice of 0.3 or 0.7 is not exclusive, as long as the contrast of the two intensities is sufficiently resolved, as in the grey portion of fig. 1 (a).
The rotation angle of the liquid crystal molecules of the binary gray level image insect in the channel2 is designed (the normalized intensity distribution meets sin 2 (2 θ -2 β)): when alpha is 1 And alpha 2 Satisfies | α 1 -α 2 When | ═ π/2 and the rotation angle of the liquid crystal element is β, the normalized intensity distribution of the light intensity of the outgoing light satisfies sin 2 (2. theta. -2. beta.). As shown in the channel2 curve in fig. 1, the value of the pixel with small light intensity (normalized intensity less than 0.3) in the binary image is defined as 0, and the candidate rotation angle corresponding to the liquid crystal molecule is θ 1 And theta 2 (ii) a Defining the value of the pixel with larger light intensity (normalized intensity is larger than 0.7) as 1, and the candidate rotation angle corresponding to the liquid crystal molecules is theta 3 And theta 4 . It is noted here that the choice of 0.3 or 0.7 is not exclusive, as long as the contrast of the two intensities is sufficiently resolved, as in the grey portion of fig. 1 (a).
The binary grey map of the two channels can then be coded into 4 2-ary codes: the codes are 00, 10, 11 and 01, each code corresponds to the light intensity distribution of the same pixel point of the channel 1 and the channel2, and 4 codes correspond to liquid crystal molecules with 4 different rotation angles one by one. As shown in FIG. 1, when the code is "00", the light intensity of each of the channel 1 and the channel2 is required to be less than the threshold value of 0.3, and when the rotation angle of the liquid crystal molecules is θ 1 In time, sin 2 (2θ 1 ) And sin 2 (2θ 1 Values of-2 β) are all less than 0.3, so θ 1 Corresponding to "00" in binary coding; similarly, when the code is "10", the light intensity of channel 1 is greater than the threshold value 0.7, and the light intensity of channel2 is less than the threshold value 0.3, and when the rotation angle of the liquid crystal molecules is θ 2 In time, sin 2 (2θ 2 ) A value of greater than 0.7 and sin 2 (2θ 2 Value of-2 β) is less than 0.3, so θ 2 Corresponding to "10" in binary coding; when the code is "11", the light intensity of each of the channel 1 and the channel2 is greater than the threshold value of 0.7, and when the rotation angle of the liquid crystal molecules is θ 3 In time, sin 2 (2θ 3 ) And sin 2 (2θ 3 Values of-2 β) are all greater than 0.7, so θ 3 Corresponding to "11" in binary encoding; when the code is "01", the light intensity of the channel 1 is less than the threshold value 0.3, and the light intensity of the channel2 is greater than the threshold value 0.7, and when the rotation angle of the liquid crystal molecules is θ 4 In time, sin 2 (2θ 4 ) Value of less than 0.3 and sin 2 (2θ 4 -2 β) is greater than 0.7, so θ 4 Corresponding to "01" in binary encoding. It is worth noting that the candidate rotation angle θ of the liquid crystal molecule in FIG. 1 1 ，θ 2 ，θ 3 And theta 4 The angles are not limited to these angles, and the angles can be candidates as long as the rotation angle satisfies the above condition and the contrast of each channel intensity is sufficiently resolved.
Based on the principle and design, the designed optical anti-counterfeiting liquid crystal element can realize the switching of two binary gray level images by arranging the rotation angles of liquid crystal molecules pixel by pixel. The liquid crystal element may be manufactured by a Digital Micro-mirror Device (DMD) system. In order to manufacture high-quality components, the whole process should be carried out in a dust-free environment, and the specific process is as follows: 1. carrying out ultrasonic cleaning, sufficient heating, ultraviolet irradiation and compressed air drying on a glass substrate with the thickness of 1.1 mm; 2. dropping a Solution prepared from sulfonated azo dye (Solution of sulfonated azo-dye, SD1, 0.5%) and dimethyl formamide (DMF, 99.5%) on a glass substrate and carrying out spin coating at a proper speed to generate an orientation layer with uniform distribution; 3. the optical orientation of SD1 was modulated with a DMD and different linearly polarized light, resulting in different patterns; 4. a solution incorporating liquid crystal material RM257 (14%), light inducer (Irgacure184 (1%)), toluene (85%) was dropped uniformly on the SD1 layer, where the photo-alignment material SD1 already provided the alignment direction of the liquid crystal molecules (perpendicular to the polarization direction of linearly polarized light); 5. the liquid crystal was polymerized by irradiation with unpolarized light having a wavelength of 365nm to obtain a desired element. The processing scheme is mature, and can be used for mass production on the premise of lower cost.
In this embodiment, "flower" is used as the image of the channel 1, and "worm" is used as the image of the channel2, and the effect is shown in fig. 2. Since the display of the two images is only related to the rotation angle of the liquid crystal molecules and independent of each other, no crosstalk exists, so that the images have no relevance and can be used for encrypted display. And as shown in fig. 3, the liquid crystal molecules have the highest polarization conversion efficiency at the wavelength of 633nm, and the visible light band has very high polarization conversion rate without considering material dispersion, so the element has good performance on a wide band, which greatly reduces the limitation of observation conditions, and makes the application range of the element wider. The invention designs an optical anti-counterfeiting liquid crystal element which can realize the display and free switching of two binary gray level images.
Claims (3)
1. A design method of an optical anti-counterfeiting liquid crystal element is characterized by comprising the following steps:
step one, constructing a liquid crystal array:
dividing a plurality of units with the same period size on a substrate, wherein liquid crystal molecules with the same rotation angle are coated on each unit in a spinning mode, so that a liquid crystal array is formed, the substrate and the liquid crystal array on the substrate form a liquid crystal element, the liquid crystal element is provided with two display channels which are a channel 1 and a channel2 respectively, and the light intensity of the channel 1 and the channel2 regularly changes along with the change of the rotation angle of the liquid crystal molecules;
step two, when linearly polarized light vertically enters and passes through the liquid crystal molecules and the analyzer, the emergent light field can be expressed as:
wherein alpha is 1 Is the angle of polarization, α 2 For the angle of polarization detection, l and s are the major and minor axes of the liquid crystal molecules, t l And t s The transmission coefficients of the long axis and the short axis of the liquid crystal molecules are shown, and theta is an included angle between the long axis and the x axis of the liquid crystal molecules in the x-y plane;
thirdly, carrying out gray level design on the light intensity of the channel 1 in the liquid crystal element:
when linearly polarized incident light passes through the liquid crystal molecules and the analyzer, the intensity of the emergent light is as follows:
wherein, I 0 Is the intensity of incident light, I 1 The light intensity of emergent light of the channel 1;
fourthly, gray level design is carried out on the light intensity of the channel2 in the liquid crystal element:
rotating the liquid crystal element around the optical axis by a counterclockwise rotation angle beta, wherein the emergent light intensity is as follows:
wherein, I 2 The light intensity of emergent light of the channel 2;
step five, designing the rotation angle of the liquid crystal molecules of the binary gray image 1 in the channel 1:
when alpha is 1 And alpha 2 Satisfies the relation of | α 1 -α 2 When | ═ π/2 and the rotation angle of the liquid crystal element is 0, the normalized intensity distribution of the light intensity of the outgoing light satisfies sin 2 (2 theta), defining the value of the pixel with smaller light intensity in the binary image as 0, and defining the candidate rotation angle corresponding to the liquid crystal molecules as theta 1 And theta 4 (ii) a The value of the pixel with the higher light intensity is defined as 1, and the candidate rotation angle corresponding to the liquid crystal molecules is theta 2 And theta 3 ；
Sixthly, designing the rotation angle of the liquid crystal molecules of the binary gray level image 2 in the channel 2:
when alpha is 1 And alpha 2 Satisfies the relation of | α 1 -α 2 When | ═ pi/2 and the rotation angle of the liquid crystal element is beta, the normalized intensity distribution of the intensity of the emergent light satisfies sin 2 (2 theta-2 beta), the value of the pixel with smaller light intensity in the binary image is defined as 0, and the candidate rotation angle corresponding to the liquid crystal molecules is theta 1 And theta 2 (ii) a The value of the pixel with larger light intensity is defined as 1, and the candidate rotation angle corresponding to the liquid crystal molecules is theta at the moment 3 And theta 4 ；
Step seven, combining the step five and the step six, coding the binary gray level images of the channel 1 and the channel2 into 4 2-system codes: the codes are 00, 10, 11 and 01, each code respectively corresponds to the light intensity distribution of the same pixel point of the channel 1 and the channel2, and 4 codes correspond to liquid crystal molecules with 4 different rotation angles one by one;
step eight, regarding each unit of the liquid crystal element as a pixel, modulating the rotation angle of liquid crystal molecules on each pixel point one by one according to the method of the step five to the step seven, when linearly polarized light enters the liquid crystal element, modulating the polarization and the light intensity of the incident light, after transmission, collecting the binary gray image of the channel 1 through an analyzer with the difference of the polarization angle and the polarization angle of the incident light being pi/2, and collecting the binary gray image of the channel2 after the element rotates anticlockwise around the optical axis by beta;
and step nine, obtaining the rotation angle of the liquid crystal molecules in each pixel according to the step eight, and manufacturing the liquid crystal element through a digital micro-mirror device system.
2. The method for designing an optically forgery-preventive liquid crystal cell according to claim 1, wherein said substrate is glass.
3. The method for designing an optically antiforgery liquid crystal cell according to claim 1, wherein said liquid crystal molecules are rotated at an angle θ 1 When θ 1 Corresponding to "00" in binary coding; the rotation angle of the liquid crystal molecules is theta 2 When theta is greater than theta 2 Corresponding to "10" in binary coding; the rotation angle of the liquid crystal molecules is theta 3 When theta is greater than theta 3 Corresponding to "11" in binary encoding; the rotation angle of the liquid crystal molecules is theta 4 When θ 4 Corresponding to "01" in binary encoding.
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