CN116149101A - FPGA control-based adjustable-focus liquid crystal lens and design method - Google Patents
FPGA control-based adjustable-focus liquid crystal lens and design method Download PDFInfo
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
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- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
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- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
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- G—PHYSICS
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
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- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
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- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
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- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
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Abstract
The invention relates to an adjustable-focus liquid crystal lens based on FPGA control and a design method thereof. According to the change characteristics, a stripe electrode structure for controlling voltage change is designed on ITO glass for manufacturing the liquid crystal box, the voltage of the stripe electrode on the liquid crystal box is controlled to be changed in a gradient mode through the FPGA, the refractive index inside liquid crystal is changed, phase resonance is caused, and the function of tunable focal length of the liquid crystal lens is achieved. Meanwhile, different wave bands in the time domain are used for carrying out specific stripe partition and controlling stripe electrode voltage, so that superposition of focuses of different wave bands is realized, and basic research work is provided for achromatism experiments of different wavelengths. More adjustable focal lengths are obtained without complicating the manufacture of the liquid crystal lens to optimize the effect of time domain achromatism.
Description
Technical Field
The invention relates to a focusing technology, in particular to an adjustable-focus liquid crystal lens based on FPGA control and a design method.
Background
While conventional optical lenses cannot solve the chromatic aberration problem of different wavelengths without an autofocus function, adjustable-focus liquid crystal lens technology can improve this situation. The liquid crystal lens has the advantages of small volume, thin thickness, easy integration, good imaging quality, quick response time and the like, and compared with the traditional single refractive index and fixed focal length glass lens, the liquid crystal micro lens can realize the zooming effect under the adjustment of an electric field within millisecond response time.
Subsequently, the design of the electrode structure of the liquid crystal cell is more complex due to the development of etching technology, and two electrode structures are derived. One is that Wonsuk Choi et al propose a high fill factor Liquid Crystal (LC) lens array fabricated using imprint techniques, but the lenses of this construction do not prevent thickness loss nor provide sufficient focusing effect for large aperture; the other electrode structure adopts a Fresnel lens structure, namely, the voltages of adjacent annular bands are precisely controlled according to the phase difference, so that the lens function is realized. The lens has low cost, small thickness and large aperture, and can avoid the problems of overlong response time and the like caused by the increase of the thickness.
In recent years, many reports on a liquid crystal lens based on a ring phase have been made. Huang et al propose a liquid crystal fresnel lens with a diffraction efficiency as high as 39%, lou et al uses binary optical stepping precision harmonics to bring the diffraction efficiency of the fresnel zone plate lens close to 40.4%. In addition, the united states kente liquid crystal institute (Kent Liquid Crystal Institute) reported a liquid crystal lens with a floating electrode structure for controlling the phase distribution, which adds a unique resistive network design between adjacent electrodes, which are connected by nickel wires, forming an addressing network, as compared to conventional coaxial ring electrodes. While this can improve image contrast, an overly complex electrode structure will increase the difficulty and cost of lens manufacturing.
Disclosure of Invention
Aiming at the urgent demand of the current optical system for adjustable focusing and achromatism, an adjustable focusing liquid crystal lens based on FPGA control and a design method are provided, and more adjustable focusing distances are obtained under the condition that the manufacturing of the liquid crystal lens is not complicated, so as to optimize the time domain achromatism effect.
The technical scheme of the invention is as follows: the utility model provides a liquid crystal lens of adjustable focusing based on FPGA control, the surface contains the liquid crystal lens of etching even n ITO stripe electrode, and n ITO stripe electrode is arranged according to variable interval grating and is distributed, and n ITO stripe electrode is connected with FPGA logic gate circuit winding displacement, and n ITO stripe electrode divide into one or more group, and the automatically controlled gradient voltage that will be given on any one group ITO stripe electrode of FPGA, light pass through the liquid crystal box and realize achromatism in the time domain of different wavelength, the coincidence of different wave band focuses.
Preferably, the ITO stripe electrodes are arranged and distributed according to the form of Fresnel half wave bands to form a 128-stripe variable-pitch grating structure, so that light passing through the structure generates a focusing effect, the phase difference between stripes is a multiple of pi, the voltages of different channel electrodes are changed, the light passing through the channel stripes of each electrode is changed in pi phase difference, and the light is focused.
Preferably, the interval between the ITO stripe electrode stripes is gradually reduced from the center to the edge, the structure guides the autonomous focusing of the liquid crystal lens, and different voltages are applied to each channel of the ITO stripe electrode structure to control different refractive indexes of corresponding liquid crystal phase units, so that liquid crystal phase distribution based on gradient refractive indexes is formed.
Preferably, the maximum pitch of the 128-stripe variable pitch grating is 631 μm, the minimum pitch is 20 μm, the size of the whole etching area is 10mm x 10mm, the selected filling liquid crystal is E7 liquid crystal, and the thickness of a liquid crystal box is 5 μm.
A preparation method of an adjustable-focus liquid crystal lens based on FPGA control specifically comprises the following steps:
1) Based on the stripe structure designed by the one-dimensional adjustable-focus cylindrical liquid crystal lens based on the FPGA control liquid crystal box of claim 4, the specific steps of electrode etching on ITO glass are as follows:
1.1 ITO surface cleaning: firstly scrubbing with a cotton ball serving as a detergent, then ultrasonically cleaning with acetone and distilled water twice for 10min each time, and finally drying in an oven for standby;
1.2 Glue spreading: the following photoresist: photoresist thinner = 1:1, gluing by a spin coater;
1.3 Pre-baking: placing the ITO glass subjected to the gluing in an oven for drying to remove the solvent and enhance the adhesiveness of the photoresist;
1.4 Exposure, namely, the area of the photoetching plate is 10mm multiplied by 10mm, an image is projected on the adhesive by ultraviolet light, and photochemical reaction is caused in a light-transmitting place;
1.5 Developing: placing the ITO glass into a developing solution, so that glue which is not exposed is left on the ITO glass;
1.6 Film hardening): washing the developed ITO glass, and placing the ITO glass in an oven for hardening;
1.7 Etching: selecting the post-process lithographyThe glue remains the complete ITO glass, using HCl: H 2 O=1: 1, and adding a certain amount of FeCl 3 Etching the ITO glass, and transferring the designed photoetching pattern to the ITO glass;
1.8 Photoresist stripping: adopting 4% NaOH solution to carry out photoresist removal treatment on the etched ITO glass;
1.9 Detecting: testing whether an etched electrode on the ITO glass has a short circuit or a break circuit, and selecting a normal electrode structure for a next experiment;
2) The liquid crystal box is manufactured by taking etched ITO glass as a substrate, and specifically comprises the following steps:
2.1 Cleaning: cleaning the etched ITO glass with purified water, drying in a drying oven at 180 ℃ for one hour, and taking out for later use;
2.2 Spin coating: fixing the dried ITO glass on a spin coater, and spin-coating PI liquid drops on the glass to achieve the effect of uniform thickness;
2.3 Drying: placing the spin-coated ITO glass into a drying oven for drying treatment, wherein the treatment steps are the same as the step 1);
2.4 Friction): after the drying is finished, friction cloth is used for friction in one direction, and the direction of liquid crystals is controlled;
2.5 Spacer microsphere): placing the rubbed ITO glass into a powder spraying machine, placing spacer microspheres with required thickness into a container at the bottom of the powder spraying machine, and diffusing the spacer microspheres into a closed space in which the container is diffused, and naturally falling onto the ITO glass;
2.6 Packaging: placing two pieces of ITO glass in an overlapping manner, only etching one piece, sealing two ends of the two pieces by using AB glue, and filling the other two ends with liquid crystal;
2.7 Filling: filling E7 liquid crystal into the packaged liquid crystal box to obtain a filled liquid crystal box;
3) And (3) carrying out wire arrangement on the manufactured liquid crystal box and ITO glass etched with 128 variable-pitch gratings on an FPGA logic gate circuit system to form a complete electric control liquid crystal box.
A focusing system of an adjustable-focus liquid crystal lens based on FPGA control is characterized in that light emitted by light source laser sequentially passes through an objective lens, a small hole, a lens, a diaphragm, a half wave plate and a liquid crystal lens with the same optical axis, ITO stripe electrode voltage on the FPGA electronic control liquid crystal lens changes phase distribution inside the liquid crystal lens, different focusing effects are obtained, and finally images are formed on a receiving screen.
After the voltage-refractive index change relation of a liquid crystal phase unit is obtained through simulation analysis, an ITO stripe electrode structure with 128 channels is designed based on the Fresnel zone plate principle, different voltages are applied to different stripe electrode channels in different areas on an FPGA electric control system, so that the refractive index in liquid crystal changes, phase resonance is caused, tunable focusing is achieved, and the liquid crystal lens has discrete zooming capability.
According to the design method of the adjustable-focus liquid crystal lens based on FPGA control, specific gradient voltages are applied to enable different wave bands to have the same focus after specific stripe partitioning is carried out on the different wave bands in a time domain range, and achromatism can be achieved when the response time of filling liquid crystal is smaller than the retention time of an image observed by human eyes.
The invention has the beneficial effects that: according to the adjustable-focus liquid crystal lens based on FPGA control and the design method, the conditions of liquid crystal refractive index and phase change under different voltage conditions are obtained through analysis and simulation. According to the change characteristics, a stripe electrode structure for controlling voltage change is designed on ITO glass for manufacturing the liquid crystal box, the voltage of the stripe electrode on the liquid crystal box is controlled to be changed in a gradient mode through the FPGA, the refractive index inside liquid crystal is changed, phase resonance is caused, and the function of tunable focal length of the liquid crystal lens is achieved. Meanwhile, different wave bands in the time domain are used for carrying out specific stripe partition and controlling stripe electrode voltage, so that superposition of focuses of different wave bands is realized, and basic research work is provided for achromatism experiments of different wavelengths.
Drawings
FIG. 1 is a schematic diagram of liquid crystal main tube deflection in a liquid crystal phase cell at a specified voltage of an electrode;
FIG. 2a is a graph showing the simulation of the electric field intensity distribution of a liquid crystal phase cell at an electrode voltage (3V);
FIG. 2b is a simulated view of the refractive index distribution of the liquid crystal corresponding to FIG. 2 a;
FIG. 3 is a graph showing the average refractive index response curve of the entire unit according to the present invention as a function of externally applied voltage;
FIG. 4 is a graph of the gradient phase distribution calculation of the present invention;
FIG. 5 is a schematic diagram of the structure of an ITO striped electrode of the present invention;
FIG. 6 is a schematic diagram of a liquid crystal lens of the present invention applied to test focal length tuning;
FIG. 7 is a schematic view of a zooming effect of a liquid crystal lens;
FIG. 8 is a plot of focal position and imaging conditions for the present invention divided into 64 electrode areas under a 405nm laser;
FIG. 9 is a plot of focal position and imaging conditions for the present invention divided into 42 electrode areas with a 633nm laser;
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical scheme of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following examples.
The invention provides an adjustable-focus liquid crystal lens based on FPGA control, which is characterized in that after the voltage-refractive index change relation of a liquid crystal phase unit is obtained through analog analysis, an ITO stripe electrode structure with 128 channels is designed based on the Fresnel zone plate principle, different voltages are applied to different stripe electrode channels in different areas on an FPGA electric control system, so that the refractive index in the liquid crystal is changed, phase resonance is caused, a tunable focusing effect is achieved, and the liquid crystal lens has discrete zooming capability. Meanwhile, in the time domain range, different wave bands can have the same focus by applying specific gradient voltage after specific stripe partitioning is carried out on the different wave bands, and when the response time of filling liquid crystal is smaller than the retention time of the image observed by human eyes, the achromatic function can be achieved.
1. Analytical simulations were performed for the liquid crystal phase cells (each liquid crystal cell whose refractive index changes due to external voltage). Assuming that the long axis of the liquid crystal is uniform before the voltage is applied, the overall refractive index thereof is maintained uniform in one direction. If the space direction of the liquid crystal in the two-dimensional condition is represented by using the inclination angle theta (the included angle between the incident light and the optical axis of the liquid crystal) as a unique parameter, a free energy expression equation of the liquid crystal in the low-frequency electric field can be obtained, and on the basis of the formula, a corresponding Euler-Lagrange equation can be obtained by using a free energy variation method:
wherein x and y are two space directions, k, of incident light perpendicular to each other in a two-dimensional coordinate system 11 、k 33 The parameters of the splay and bend elasticity are respectively, and delta epsilon is the difference between the two relative dielectric constants parallel to the director and perpendicular to the director 0 Is the dielectric constant under vacuum state, E x 、E y The electric field components of the electric field corresponding to the x and y directions respectively.
The Euler-Lagrangian equation satisfies the minimum free energy case of the system. And for the applied external electric field, the Poisson equation is utilized to bring the relative allowable tensor into two-dimensional coordinates, so that the partial differential square field of the coupling electric field can be obtained.
From the above derived set of coupled partial differential equations, it is known that the liquid crystal director is determined by its own coupling with the internal electric field director. If these partial differential equations are solved by finite element method, the direction of the liquid crystal molecular vector of a certain point inside and the refractive index of that point can be determined. As shown in fig. 1, a liquid crystal main tube in a liquid crystal phase cell deflects at a specified voltage of an electrode.
Meanwhile, in the case of clearly filling a liquid crystal material (e.g., E7), if a beam of light enters the liquid crystal and its vibration direction is parallel to the X-axis, the effective refractive index formula is as follows:
wherein n is 0 、n e The refractive index of the ordinary ray and the refractive index of the extraordinary ray of the adopted liquid crystal material are respectively, and theta is the included angle between the incident light and the optical axis of the liquid crystal.
According to the formula (2), a refractive index distribution curve of the liquid crystal phase unit under a specific voltage can be obtained, such as a simulated graph of electric field intensity distribution of the liquid crystal phase unit under an electrode voltage (3V) as shown in fig. 2a, and a simulated graph of refractive index distribution of the liquid crystal corresponding to fig. 2a as shown in fig. 2 b.
2. And designing the phase regulation of the whole crystal lens. Analysis of 1 shows that the refractive index profile of the liquid crystal phase unit at a specific voltage shows that the liquid crystal molecules in the liquid crystal phase unit react differently to different electric fields, are sensitive to changes near the electrodes, and tend to maintain the original orientation in the central region. Thus by controlling the change of the voltage, a change of the refractive index of the sensitive area and a change of the average refractive index of the liquid crystal phase cell at different voltages can be obtained, respectively. The average refractive index response curve of the entire liquid crystal phase cell as shown in fig. 3 is plotted as a function of the applied voltage. Meaning that it can be determined from the map how to control the externally applied voltage to obtain the desired phase change of the liquid crystal.
The gradient index liquid crystal lens can be programmed with the difference in response amplitude of the liquid crystal steering based on the analysis described above. An ITO stripe electrode structure is designed on the basis of the Fresnel zone plate principle to serve as a phase control substrate of liquid crystal (the stripe number is variable, and the invention designs the stripe electrode structure with 128 channels). The stripes of the substrate taper from center to edge so that the ITO electrode can provide a basic structure to guide autonomous focusing of the liquid crystal lens and can be used to adjust the phase. According to the refractive index curve corresponding to the voltage in fig. 3, different voltages are applied to each channel of the ITO stripe electrode structure to control different refractive indexes of the corresponding liquid crystal phase units, so that the refractive index liquid crystal phase distribution of the whole lens can be obtained.
3. Focusing mode. Based on the electric control liquid crystal phase modulation principle of 1 and 2, the phase of light waves passing through liquid crystal is obtained, and a phase resonance effect is generated on the whole lens, so that focusing is realized. By switching the existence of channel voltage in the ITO stripe electrode structure, the focal length formula of the liquid crystal lens can be expressed as follows:
where R is the radius of the liquid crystal lens, m is the number of areas, and λ is the incident wavelength.
Wherein the number of phase change regions m in the liquid crystal can be artificially adjusted by controlling the number of voltages applied to the electrode channels. Each region contains n (n is an even number) electrode channels. Since each set of electrode channels is a binary-change period, the phase difference of half channels in the set is pi, so that the focal length of the liquid crystal lens can be changed along with the phase change caused by different area numbers. The phase change in this case still follows the characteristics of a binary optical element, resulting in a significant variability in the focal length change during zooming, with the number of regions m in decisive positions. Therefore, the introduction of the gradient index method is considered below to optimize the focusing function of the lens.
As described above, the different voltages correspond to the different refractive index changes, and this reaction mechanism of the liquid crystal provides a continuously varying gradient voltage for each electrode channel, which makes it possible for one region to gradually vary in the form of a gradient with a phase difference of pi (the optical path difference to the focus is 2pi), instead of 0 or pi, as shown in the gradient phase distribution calculation chart of fig. 4.
Since the phase distribution of the liquid crystal needs to fluctuate in the range of 0 to 2 pi, it is also necessary to control the phase distribution of the liquid crystal in this range, controlling the liquid crystal to form each gradient region. The focal length of the diffraction field at this time is specifically expressed by the following formula:
m' is the new partition number, L is the sub-partition index of each partition, and L is the total number of phases of each partition.
In formula (4), since the region number m is replaced by a new region number m', the focal length of the lens is not directly determined by m, but is determined together with the sub-division index l caused by the refractive index gradient-index, so that the lens can optimize the diffraction field and achieve fine adjustment of the focal length.
Thus, the gradient refractive index lens based on electronically controlled liquid crystal phase is realized. By means of different responses of liquid crystal to the electric field of the strip-shaped electrodes, the lens forms liquid crystal phase distribution based on gradient refractive index in the x direction, so that the focal length of the liquid crystal lens is adjustable, and the change depends on the subarea m' and the subarea l of the refractive index.
Example 1
An adjustable-focus liquid crystal lens based on FPGA control. The liquid crystal display consists of a liquid crystal box with 128 etched electrode channels and ITO glass on the surface, and the 128 electrode channels and FPGA logic gate circuit flat cables. Wherein the maximum pitch of 128 variable pitch gratings is 631 μm, the minimum pitch is 20 μm, the size of the whole etching area is 10mm by 10mm, and the schematic diagram of the variable pitch gratings is shown in fig. 5. The filling liquid crystal adopted by the invention is E7 liquid crystal, and the thickness of the liquid crystal box is controlled to be 5 mu m. The preparation method comprises the following steps:
1. design and preparation of ITO glass surface electrode
1) The ITO stripe electrode structure with 128 channels used in the invention is designed according to the Fresnel zone plate principle. The normal fresnel zone plate is composed of a series of concentric rings with alternate brightness, the area of each ring is equal, and the optical path difference between any two adjacent rings is lambda/2, so the fresnel zone plate can be also called a half-wave zone, according to the physical optical principle (phase difference=2pi×optical path difference/lambda), the light beam reaches the diffraction focus through the half-wave zone and has pi phase difference with the adjacent half-wave zone, meanwhile, because the adjacent half-wave zones are alternate brightness, only the light beams with the same phase difference can strike the focus position, and the light beams are overlapped with each other to generate a maximum value. According to the diffraction light-gathering property of the Fresnel zone plate, the ITO strip electrode structure is arranged and distributed according to the Fresnel half-wave band mode by adopting the thought, which is equivalent to a variable-pitch grating structure with 128 strips, as shown in figure 5, the light passing through the structure can generate a focusing effect, the phase difference between the strips is a multiple of pi, and the voltage of the electrodes passing through different channels is changed on the basis, so that the light passing through the electrode channels is changed in pi phase difference, and the light can be ensured to be focused correctly.
2) Based on the stripe structure designed in 1), the specific steps of electrode etching on the ITO glass are as follows:
(1) ITO surface cleaning:
(2) gluing: the following photoresist: photoresist thinner = 1:1, gluing by a spin coater;
(3) pre-baking: placing the ITO glass subjected to the gluing in an oven for drying to remove the solvent and enhance the adhesiveness of the photoresist;
(4) exposing, namely, the area of the photoetching plate is 10mm multiplied by 10mm, an image is projected on the adhesive by ultraviolet light, and photochemical reaction is caused in a light-transmitting place;
(5) developing: placing the ITO glass into a developing solution, so that glue which is not exposed is left on the ITO glass;
(6) hardening: washing the developed ITO glass, and placing the ITO glass in an oven for hardening;
(7) etching: the photoresist is selected to keep the complete ITO glass after the process, and HCl: H is utilized 2 O=1: 1, and adding a certain amount of FeCl 3 Etching the ITO glass, and transferring the designed photoetching pattern to the ITO glass;
(8) removing photoresist: adopting 4% NaOH solution to carry out photoresist removal treatment on the etched ITO glass;
(9) and (3) detection: and testing whether the etched electrode on the ITO glass has short circuit or open circuit, and selecting a normal electrode structure for the next experiment.
2. The liquid crystal box is manufactured by taking etched ITO glass as a substrate, and specifically comprises the following steps:
1) Cleaning: cleaning the etched ITO glass with purified water, drying in a drying oven at 180 ℃ for one hour, and taking out for later use;
2) Spin coating: fixing the dried ITO glass on a spin coater, and spin-coating PI liquid drops on the glass to achieve the effect of uniform thickness;
3) And (3) drying: placing the spin-coated ITO glass into a drying oven for drying treatment, wherein the treatment steps are the same as the step 1);
4) Friction: after the drying is finished, friction cloth is used for friction in one direction, and the direction of liquid crystals is controlled;
5) Spacer microspheres: placing the rubbed ITO glass into a powder spraying machine, placing spacer microspheres (5 mu m,10 mu m,20 mu m and the like) with required thickness into a container at the bottom of the powder spraying machine, and diffusing the spacer microspheres into a closed space in the container until the spacer microspheres naturally fall onto the ITO glass;
6) And (3) packaging: placing two pieces of ITO glass in an overlapping manner (only one piece is etched), sealing two ends of the two pieces of ITO glass by using AB glue, and filling liquid crystals at the other two ends;
7) Filling: filling E7 liquid crystal into the packaged liquid crystal box to obtain a filled liquid crystal box
3. And (3) carrying out wire arrangement on the manufactured liquid crystal box and ITO glass etched with 128 variable-pitch gratings on an FPGA logic gate circuit system to form a complete electric control liquid crystal box.
The prepared liquid crystal lens capable of utilizing the stripe electrode structure to discretely control voltage is connected with an FPGA logic gate circuit system to form a complete adjustable-focus liquid crystal lens based on FPGA control. The electric control liquid crystal lens is put into the following light path for experiments, the focusing capability of the electric control liquid crystal lens is shown, and the light path diagram is shown in figure 6. In the light path experiment, a 633nm light source is used as a test light source, and laser light sequentially passes through an objective lens, a small hole, a lens, a diaphragm, a half wave plate and a liquid crystal lens with the same optical axis after being emitted, and finally is imaged on a receiving screen. In the experimental process, according to the analysis in the above technical scheme, the phase distribution inside the liquid crystal lens is changed by controlling the stripe electrode voltage, so as to obtain different focusing effects, as shown in fig. 7. After the focusing conditions of the phase distribution under different electric control conditions are obtained, the positions of the receiving screen from the lens (120 cm and 240cm from the lens respectively) are adjusted in an experiment, and then the focusing effect is recorded, so that the liquid crystal lens has the effect that under the condition of different phase distribution based on the electrode channel, the corresponding images can be scaled to different degrees at the specific positions of the receiving screen due to different focal lengths. Through the experiment, the liquid crystal lens can realize the focusing function.
Example 2
For the liquid crystal lens in the present invention, the focal length is determined by the number of segments m' and the wavelength λ (according to the formula (3) in the technical scheme, the total number of phases L and the sub-segment index L have less influence on the focal length). Therefore, at different area numbers, two light waves with different wavelengths can reach the same focal length. By applying the principle, the focus of the two light waves can be adjusted to one place under the condition of persistence of vision, so that the achromatic effect is realized in the time domain.
Thus on the basis of the device manufacturing process and the light path construction of example 1. Unlike the single laser light source used in the optical path of example 1, achromatic function verification was performed using lasers of both 405nm and 633nm wavelengths in this example. For a 405nm laser, 128 electrode stripes are divided into 64 areas, different voltages are applied to different areas, and the focal position and imaging condition of the laser are observed, as shown in fig. 8. For a 633nm laser, 128 electrode stripes are divided into 42 areas, different voltages are applied to different areas, and the focal position and imaging condition of the laser are observed, as shown in fig. 9. The experiment shows that the achromatic effect of the liquid crystal lens in the time domain can be realized by adjusting the focal length of the corresponding wavelength. While considering that the human eye can hold an image for less than 200ms, the refresh time of the lens is set to be changed once every 100ms (the response time of the E7 liquid crystal is less than 100 ms). Thus, two different wavelengths of color alternate in the same place, and the brain can superimpose them into a composite new color. Thereby realizing achromatic effect in time domain through the electrically controlled liquid crystal lens.
The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (8)
1. The utility model provides a but focusing liquid crystal lens based on FPGA control, its characterized in that, the surface contains the liquid crystal lens of etching even n ITO stripe electrodes, and n ITO stripe electrodes are arranged according to variable interval grating and are distributed, and n ITO stripe electrodes are connected with FPGA logic gate circuit winding displacement, and n ITO stripe electrodes divide into one or more group, and the automatically controlled gradient voltage that applies on arbitrary group ITO stripe electrode of FPGA, light pass through the liquid crystal box and realize achromatism in the different wavelength time domain, coincidence of different wave band focuses.
2. The FPGA controlled adjustable focus liquid crystal lens of claim 1, wherein the ITO stripe electrodes are arranged and distributed according to fresnel half-wave band to form a 128 stripe variable pitch grating structure, so that light passing through the structure generates a focusing effect and the phase difference between stripes is a multiple of pi, and voltages of different channel electrodes are changed, so that light passing through the electrode channel stripes is changed in pi phase difference, and light is focused.
3. The FPGA-controlled adjustable-focus liquid crystal lens of claim 2, wherein the ITO stripe electrode stripe spacing is gradually reduced from the center to the edge, the structure directs autonomous focusing of the liquid crystal lens, and different voltages are applied to each channel of the ITO stripe electrode structure to control different refractive indices of the corresponding liquid crystal phase cells, forming a gradient refractive index-based liquid crystal phase distribution.
4. The FPGA control-based adjustable-focus liquid crystal lens of claim 3, wherein the 128 stripe variable-pitch grating has a maximum pitch of 631 μm, a minimum pitch of 20 μm, a size of the entire etched area of 10mm x 10mm, and the selected filling liquid crystal is E7 liquid crystal, and a thickness of a liquid crystal cell is 5 μm.
5. The preparation method of the adjustable-focus liquid crystal lens based on FPGA control is characterized by comprising the following steps:
1) Based on the stripe structure designed by the one-dimensional adjustable-focus cylindrical liquid crystal lens based on the FPGA control liquid crystal box of claim 4, the specific steps of electrode etching on ITO glass are as follows:
1.1 ITO surface cleaning: firstly scrubbing with a cotton ball serving as a detergent, then ultrasonically cleaning with acetone and distilled water twice for 10min each time, and finally drying in an oven for standby;
1.2 Glue spreading: the following photoresist: photoresist thinner = 1:1, gluing by a spin coater;
1.3 Pre-baking: placing the ITO glass subjected to the gluing in an oven for drying to remove the solvent and enhance the adhesiveness of the photoresist;
1.4 Exposure, namely, the area of the photoetching plate is 10mm multiplied by 10mm, an image is projected on the adhesive by ultraviolet light, and photochemical reaction is caused in a light-transmitting place;
1.5 Developing: placing the ITO glass into a developing solution, so that glue which is not exposed is left on the ITO glass;
1.6 Film hardening): washing the developed ITO glass, and placing the ITO glass in an oven for hardening;
1.7 Etching: the photoresist is selected to keep the complete ITO glass after the process, and HCl: H is utilized 2 O=1: 1, and adding a certain amount of FeCl 3 Etching the ITO glass, and transferring the designed photoetching pattern to the ITO glass;
1.8 Photoresist stripping: adopting 4% NaOH solution to carry out photoresist removal treatment on the etched ITO glass;
1.9 Detecting: testing whether an etched electrode on the ITO glass has a short circuit or a break circuit, and selecting a normal electrode structure for a next experiment;
2) The liquid crystal box is manufactured by taking etched ITO glass as a substrate, and specifically comprises the following steps:
2.1 Cleaning: cleaning the etched ITO glass with purified water, drying in a drying oven at 180 ℃ for one hour, and taking out for later use;
2.2 Spin coating: fixing the dried ITO glass on a spin coater, and spin-coating PI liquid drops on the glass to achieve the effect of uniform thickness;
2.3 Drying: placing the spin-coated ITO glass into a drying oven for drying treatment, wherein the treatment steps are the same as the step 1);
2.4 Friction): after the drying is finished, friction cloth is used for friction in one direction, and the direction of liquid crystals is controlled;
2.5 Spacer microsphere): placing the rubbed ITO glass into a powder spraying machine, placing spacer microspheres with required thickness into a container at the bottom of the powder spraying machine, and diffusing the spacer microspheres into a closed space in which the container is diffused, and naturally falling onto the ITO glass;
2.6 Packaging: placing two pieces of ITO glass in an overlapping manner, only etching one piece, sealing two ends of the two pieces by using AB glue, and filling the other two ends with liquid crystal;
2.7 Filling: filling E7 liquid crystal into the packaged liquid crystal box to obtain a filled liquid crystal box;
3) And (3) carrying out wire arrangement on the manufactured liquid crystal box and ITO glass etched with 128 variable-pitch gratings on an FPGA logic gate circuit system to form a complete electric control liquid crystal box.
6. A focusing system of an adjustable-focus liquid crystal lens based on FPGA control is characterized in that light emitted by light source laser sequentially passes through an objective lens, a small hole, a lens, a diaphragm, a half-wave plate and a liquid crystal lens with the same optical axis, ITO stripe electrode voltage on the FPGA electronic control liquid crystal lens changes phase distribution inside the liquid crystal lens, different focusing effects are obtained, and finally images are formed on a receiving screen.
7. A design method of an adjustable-focus liquid crystal lens based on FPGA control is characterized in that after the voltage-refractive index change relation of a liquid crystal phase unit is obtained through analog analysis, an ITO stripe electrode structure with 128 channels is designed based on the Fresnel zone plate principle, different voltages are applied to different stripe electrode channels in different areas on an FPGA electric control system, so that the refractive index in the liquid crystal is changed, phase resonance is caused, tunable focusing is achieved, and the liquid crystal lens has discrete zoom capability.
8. The FPGA control-based tunable liquid crystal lens design method of claim 7, wherein, in the time domain, different bands have the same focus by applying a specific gradient voltage after specific stripe division is performed on the different bands, and achromatism is achieved when the response time of filling the liquid crystal is less than the retention time of the human eye observation image.
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