Focus-adjustable liquid crystal lens based on FPGA control and design method

Abstract

The present invention relates to a focus-adjustable liquid crystal lens and a design method based on FPGA control. Through analysis and simulation, the changes of the refractive index and phase of liquid crystal under different voltage conditions are obtained. According to the change characteristics, a stripe electrode structure for controlling the voltage change is designed on the ITO glass for making a liquid crystal box. The voltage of the stripe electrode on the liquid crystal box is controlled by FPGA to change in a gradient, so that the refractive index inside the liquid crystal changes, thereby causing phase resonance, and realizing the focal length tunable function of the liquid crystal lens. At the same time, in different bands in the time domain, specific stripe partitioning and control of the stripe electrode voltage are performed to realize the overlap of the focus of different bands, which provides basic research work for achromatic experiments of different wavelengths. More adjustable focal lengths are obtained without complicating the manufacture of liquid crystal lenses to optimize the effect of time domain achromatism.

Description

Technical Field

[0001] The invention relates to a focusing technology, and in particular to a focus-adjustable liquid crystal lens based on FPGA control and a design method thereof. Background Art

[0002] Traditional optical lenses cannot solve the chromatic aberration problem of different wavelengths without the autofocus function, but the adjustable focus liquid crystal lens technology can improve this situation. Liquid crystal lenses have the advantages of small size, thin thickness, easy integration, good imaging quality, and fast response time. Compared with traditional single refractive index, fixed focal length glass lenses, liquid crystal micro lenses can achieve a zoom effect under electric field regulation within a millisecond response time.

[0003] Subsequently, due to the development of etching technology, the design of the electrode structure of the liquid crystal box has become more complicated, and two electrode structures have been derived. One is that Wonsuk Choi et al. proposed a high filling factor liquid crystal (LC) lens array made by imprinting technology, but the lens of this structure cannot prevent the loss of thickness, nor is it sufficient to provide a large aperture focusing effect; the other electrode structure uses a Fresnel lens structure, that is, the voltage of adjacent ring bands is accurately controlled according to the phase difference to achieve the lens function. This lens is not only low in cost, small in thickness, and large in aperture, but also can avoid problems such as long response time caused by increased thickness.

[0004] In recent years, many reports on liquid crystal lenses based on annular phase have emerged. Huang et al. proposed a liquid crystal Fresnel lens with a diffraction efficiency of up to 39%, and Lou et al. used binary optical stepping precision harmonics to make the diffraction efficiency of the Fresnel zone plate lens close to 40.4%. In addition, the Kent Liquid Crystal Institute in the United States reported a liquid crystal lens with a floating electrode structure for controlling phase distribution. Compared with the traditional coaxial annular electrode, the liquid crystal lens adds a unique resistor network design between adjacent electrodes. The electrodes are connected by nickel wires to form an addressing network. Although this can improve image contrast, the overly complex electrode structure will increase the difficulty and cost of lens manufacturing. Summary of the invention

[0005] In view of the urgent need for adjustable focus and achromatism in current optical systems, a focus-adjustable liquid crystal lens and design method based on FPGA control are proposed to obtain more adjustable focal lengths without complicating the manufacturing of the liquid crystal lens, so as to optimize the effect of time-domain achromatism.

[0006] The technical solution of the present invention is: a focus-adjustable liquid crystal lens based on FPGA control, a liquid crystal lens with an even number n ITO stripe electrodes etched on the surface, the n ITO stripe electrodes are arranged and distributed according to a variable spacing grating, the n ITO stripe electrodes are connected to the FPGA logic gate circuit wiring, the n ITO stripe electrodes are divided into one or more groups, the FPGA electronic control applies a gradient voltage to any group of ITO stripe electrodes, and the light passes through the liquid crystal box to achieve achromatic aberration in different wavelength time domains and overlap of focal points in different bands.

[0007] Preferably, the ITO stripe electrodes are arranged and distributed in the form of Fresnel half-wave bands to form a 128-strip variable-pitch grating structure, so that the light passing through the structure produces a focusing effect and the phase difference between the stripes is a multiple of π. The voltage of different channel electrodes changes, so that the light passing through each electrode channel stripe changes with a phase difference of π, and the light is focused.

[0008] Preferably, the interval between the ITO stripe electrodes gradually decreases from the center to the edge, and the structure guides the autonomous focusing of the liquid crystal lens. Different voltages are applied to each channel of the ITO stripe electrode structure to control the different refractive indices of the corresponding liquid crystal phase units, forming a liquid crystal phase distribution based on a gradient refractive index.

[0009] Preferably, the maximum pitch of the 128-strip variable pitch grating is 631 μm, the minimum pitch is 20 μm, the size of the entire etched area is 10 mm*10 mm, the selected filling liquid crystal is E7 liquid crystal, and the thickness of the liquid crystal box is 5 μm.

[0010] A method for preparing a focus-adjustable liquid crystal lens based on FPGA control, specifically comprising the following steps: 1) Based on the stripe structure of the one-dimensional focus-adjustable cylindrical liquid crystal lens designed based on FPGA-controlled liquid crystal cell as claimed in claim 4, the specific steps of electrode etching on ITO glass are as follows:

[0011] 1.1) ITO surface cleaning: First, scrub with a cotton ball with detergent, then ultrasonically clean twice with acetone and distilled water, each time for 10 minutes, and finally put it in an oven to dry for later use;

[0012] 1.2) Glue coating: Glue coating is performed by a glue spreader according to the ratio of photoresist to photoresist diluent = 1:1;

[0013] 1.3) Pre-baking: Put the ITO glass after coating into the oven for drying to remove the solvent and enhance the adhesion of the photoresist;

[0014] 1.4) Exposure: The photomask area is 10mm×10mm, and the image is projected onto the glue using ultraviolet light, causing a photochemical reaction in the light-transmitting area;

[0015] 1.5) Development: put the ITO glass into the developer so that the glue that has not been exposed to light remains on the ITO glass; 1.6) Hardening: rinse the developed ITO glass and put it in an oven to harden the film;

[0016] 1.7) Etching: After the above process, the photoresist retains the complete ITO glass, and HCl:H2O=1:1 is used, and a certain amount of FeCl3 is added thereto to etch the ITO glass, and the designed photolithography pattern is transferred to the ITO glass;

[0017] 1.8) Debonding: Use 4% NaOH solution to debond the etched ITO glass;

[0018] 1.9) Detection: Test whether the electrodes etched on the ITO glass are short-circuited or open-circuited, and select the normal electrode structure for the next experiment;

[0019] 2) Using the etched ITO glass as a substrate to make a liquid crystal cell, specifically including the following steps:

[0020] 2.1) Cleaning: Wash the etched ITO glass with clean water, and then put it into a drying oven at 180°C for one hour. After completion, take it out for use;

[0021] 2.2) Spin coating: The dried ITO glass is fixed on the spin coater, and the PI droplets are spin-coated on the glass to achieve a uniform thickness;

[0022] 2.3) Drying: The spin-coated ITO glass is placed in a drying oven for drying, and the processing steps are the same as step 1);

[0023] 2.4) Friction: After drying, use a friction cloth to rub in one direction to control the direction of the liquid crystal;

[0024] 2.5) Spacer microspheres: put the rubbed ITO glass into a powder sprayer, put spacer microspheres of required thickness into the container at the bottom of the powder sprayer, diffuse them into the closed space in the container, and wait for them to naturally fall onto the ITO glass;

[0025] 2.6) Packaging: Place two ITO glass sheets on top of each other, etch only one of them, seal both ends of the sheet with AB glue, and use the other two ends to fill the liquid crystal;

[0026] 2.7) Filling: Fill the packaged liquid crystal box with E7 liquid crystal to obtain a filled liquid crystal box; 3) Arrange the prepared liquid crystal box and the ITO glass etched with 128 variable-pitch gratings on the FPGA logic gate circuit system to form a complete electrically controlled liquid crystal box.

[0027] A focusing system of a focus-adjustable liquid crystal lens based on FPGA control. The light emitted by the light source laser passes through the objective lens, pinhole, lens, aperture, half-wave plate, and liquid crystal lens on the same optical axis in sequence. The FPGA electrically controls the voltage of the ITO stripe electrode on the liquid crystal lens to change the phase distribution inside the liquid crystal lens to obtain different focusing effects, and finally an image is formed on the receiving screen.

[0028] A design method for a focus-adjustable liquid crystal lens based on FPGA control is disclosed. After obtaining the voltage-refractive index change relationship of the liquid crystal phase unit through simulation analysis, an ITO stripe electrode structure with 128 channels is designed based on the Fresnel zone plate principle, and different voltages are applied to different stripe electrode channels in different regions on the FPGA electric control system, so that the refractive index inside the liquid crystal changes, thereby causing phase resonance, achieving tunable focusing, and enabling the liquid crystal lens to have discrete zoom capability.

[0029] The design method of the focus-adjustable liquid crystal lens based on FPGA control is to perform specific stripe partitioning on different bands within the time domain, and then apply a specific gradient voltage to make different bands have the same focus. When the response time of the filled liquid crystal is less than the retention time of the human eye observing the image, achromatism can be achieved.

[0030] The beneficial effects of the present invention are as follows: the present invention is based on the FPGA-controlled adjustable focus liquid crystal lens and design method, and through analysis and simulation, obtains the changes in the refractive index and phase of the liquid crystal under different voltage conditions. According to its change characteristics, a stripe electrode structure for controlling voltage changes is designed on the ITO glass for making the liquid crystal box, and the voltage of the stripe electrode on the liquid crystal box is controlled by FPGA to change in a gradient, so that the refractive index inside the liquid crystal changes, thereby causing phase resonance, and realizing the focal length tunable function of the liquid crystal lens. At the same time, in different bands in the time domain, specific stripe partitioning and control of the stripe electrode voltage realize the overlap of the focus of different bands, which provides basic research work for achromatic experiments of different wavelengths. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the deflection of the liquid crystal main tube in the liquid crystal phase unit under a specified voltage of the electrode;

[0032] Figure 2a Simulation diagram of the electric field intensity distribution of the liquid crystal phase unit under electrode voltage (3V);

[0033] Figure 2b for Figure 2a The corresponding simulation diagram of the liquid crystal refractive index distribution;

[0034] Figure 3 is a linear variation diagram of the average refractive index response curve of the entire unit of the present invention with external applied voltage;

[0035] Figure 4 It is the gradient phase distribution calculation diagram of the present invention;

[0036] Figure 5 This is a simulation diagram of the ITO stripe electrode structure of the present invention;

[0037] Figure 6 This is a light path diagram of the liquid crystal lens of the present invention used for testing focal length tuning;

[0038] Figure 7 Schematic diagram of the zoom effect of the liquid crystal lens;

[0039] Figure 8 The present invention is divided into 64 electrode areas under 405nm laser and imaging condition diagram;

[0040] Fig. 9 The present invention is divided into 42 electrode areas under 633nm laser and imaging condition diagram; DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0042] The present invention proposes a focus-adjustable liquid crystal lens based on FPGA control. After obtaining the voltage-refractive index change relationship of the liquid crystal phase unit through simulation analysis, an ITO stripe electrode structure with 128 channels is designed based on the Fresnel zone plate principle, and different voltages are applied to different stripe electrode channels in different regions on the FPGA electric control system, so that the refractive index inside the liquid crystal changes, thereby causing phase resonance, achieving a tunable focusing effect, and enabling the liquid crystal lens to have discrete zoom capability. At the same time, in the time domain, different bands can have the same focus by applying specific gradient voltages after specific stripe partitions for different bands. When the response time of the filled liquid crystal is less than the retention time of the human eye observing the image, the function of achromatic aberration can be achieved.

[0043] 1. Perform an analytical simulation on the liquid crystal phase unit (each liquid crystal unit whose refractive index changes due to external voltage). Assume that before the voltage is applied, the long axis of the liquid crystal is consistent and its overall refractive index remains uniform in one direction. If the inclination angle θ (the angle between the incident light and the optical axis of the liquid crystal) is used as the only parameter to represent its spatial direction in two dimensions, the free energy expression equation of the liquid crystal under a low-frequency electric field can be obtained. Based on this formula, the corresponding Euler-Lagrange equation can be obtained using the variational method of free energy:

[0044]

[0045] Among them, x and y are two spatial directions of the incident light that are perpendicular to each other in the two-dimensional coordinate system, and k 11 , k 33 are the splay and bending elastic parameters, △ε is the difference between the two relative dielectric constants parallel to the director and perpendicular to the director, ε0 is the dielectric constant in vacuum, E x 、E y are the electric field components corresponding to the x and y directions respectively.

[0046] The Euler-Lagrange equation satisfies the minimum free energy of the system. For the applied external electric field, the Poisson equation is used to bring the relative permissible tensor into the two-dimensional coordinates to obtain the partial differential square field of the coupled electric field.

[0047] From the above derivation of the coupled partial differential equations, we can know that the liquid crystal director is determined by the coupling between itself and the internal electric field director. If these partial differential equations are solved iteratively using the finite element method, the direction of the liquid crystal molecule vector at a certain point inside and the refractive index at that point can be determined. Figure 1 Schematic diagram showing the deflection of a liquid crystal main in a liquid crystal phase unit under a specified voltage of the electrodes.

[0048] At the same time, in the case of clear filling of liquid crystal material (such as 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:

[0049]

[0050] Among them, n0, n e are the ordinary light refractive index and extraordinary light refractive index of the liquid crystal material used, and θ is the angle between the incident light and the optical axis of the liquid crystal.

[0051] According to formula (2), the refractive index distribution curve of the liquid crystal phase unit under a specific voltage can be obtained, such as Figure 2a The electric field intensity distribution simulation diagram of the liquid crystal phase unit under the electrode voltage (3V) shown in the figure, Figure 2b Shown Figure 2a Corresponding simulation diagram of liquid crystal refractive index distribution.

[0052] 2. Design the phase control of the entire liquid crystal lens. From the analysis in 1, we can know the distribution curve of the refractive index of the liquid crystal phase unit under a specific voltage, and show that the liquid crystal molecules in the liquid crystal phase unit have different responses to different electric fields. Near the electrode, its changes are very sensitive, while in the central area it tends to maintain the original orientation. Therefore, by controlling the change of voltage, the refractive index change of the sensitive area under different voltages and the average refractive index change of the liquid crystal phase unit can be obtained respectively. As shown in the attached figure Figure 3The average refractive index response curve of the entire liquid crystal phase unit changes linearly with the external applied voltage. This means that it is possible to determine how to control the external applied voltage to obtain the desired liquid crystal phase change through this graph.

[0053] Based on the above analysis, the difference in response amplitude of the liquid crystal guide can be used to plan the gradient index liquid crystal lens. Based on the principle of Fresnel zone plate, an ITO stripe electrode structure is designed as the phase control substrate of the liquid crystal (the number of stripes can be changed, and the present invention is a stripe electrode structure with 128 channels). The stripes of the substrate gradually shrink from the center to the edge, so that the ITO electrode can provide a basic structure to guide the autonomous focusing of the liquid crystal lens, and the ITO stripe electrode structure can be used to adjust the phase. According to Figure 3 The refractive index curve corresponding to the medium voltage is obtained by applying different voltages to each channel of the ITO stripe electrode structure to control the different refractive indices of the corresponding liquid crystal phase units, and the refractive index liquid crystal phase distribution of the entire lens can be obtained.

[0054] 3. Focusing method. Based on the above 1 and 2 principles of electrically controlled liquid crystal phase modulation, the phase of the light wave passing through the liquid crystal is obtained, and a phase resonance effect is generated on the entire lens, thereby achieving focusing. By switching the presence or absence of the channel voltage in the ITO stripe electrode structure, the focal length formula of the liquid crystal lens can be expressed as:

[0055]

[0056] Where R is the radius of the liquid crystal lens, m is the number of regions, and λ is the incident wavelength.

[0057] By controlling the number of voltages applied to the electrode channels, the number of phase change regions m inside the liquid crystal can be artificially adjusted. Each region contains n (n is an even number) electrode channels. Because each group of electrode channels is a binary change cycle, the phase difference of half of the channels in the group is π, so the focal length of the liquid crystal lens can change with the phase change caused by the different number of regions. However, the phase change in this case still follows the characteristics of binary optical elements, resulting in the number of regions m being in a decisive position during the zoom process, and the focal length change has obvious discreteness. Therefore, the following considers introducing the gradient index method to optimize the focusing function of the lens.

[0058] As mentioned above, different voltages correspond to different refractive index changes. If the reaction mechanism of liquid crystal provides a continuously changing gradient voltage for each electrode channel, it is possible for an area to gradually change in the form of a gradient with a phase difference of π (the optical path difference to the focus is 2π) instead of 0 or π, as shown in the attached figure. Figure 4 Calculation diagram of gradient phase distribution shown.

[0059] Since the phase distribution of the liquid crystal needs to fluctuate within the range of 0-2π, it is also necessary to control the phase distribution of the liquid crystal within this range to control the liquid crystal to form each gradient zone. At this time, the focal length of the diffraction field is specifically expressed by the following formula:

[0060]

[0061] m' is the number of new partitions, l is the sub-partition index of each partition, and L is the total number of phase levels of each partition.

[0062] In formula (4), since the region number m is replaced by the new region number m', the focal length of the lens is no longer directly determined by m, but is determined together with the sub-partition index l caused by the refractive index gradient-index, so that the lens can optimize the diffraction field and achieve fine-tuning of the focal length.

[0063] Thus, a gradient refractive index lens based on electronically controlled liquid crystal phase is realized. Through the different responses of liquid crystal to the electric field of the strip electrode, the lens forms a liquid crystal phase distribution based on a 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 refractive index partition m' and sub-partition l.

[0064] Example 1

[0065] A focus-adjustable liquid crystal lens based on FPGA control. It consists of a liquid crystal box with 128 electrode channels etched on the surface of ITO glass, and the 128 electrode channels are wired with FPGA logic gate circuits. The maximum spacing of the 128 variable-pitch gratings is 631μm, the minimum spacing is 20μm, and the size of the entire etched area is 10mm*10mm. The schematic diagram of the variable-pitch grating is as shown in the attached figure. Figure 5 As shown. The filling liquid crystal selected in the present invention is E7 liquid crystal, and the thickness of the liquid crystal box is controlled to be 5 μm. The specific preparation includes the following steps:

[0066] 1. Design and preparation of ITO glass surface electrode

[0067] 1) The ITO stripe electrode structure with 128 channels used in the present invention is designed according to the principle of Fresnel zone plate. A normal Fresnel zone plate is composed of a series of concentric rings that alternate between light and dark. The area of ​​each ring is equal, and the optical path difference between any two adjacent rings is λ / 2, so it can also be called a half-wave band. According to the principle of physical optics (phase difference = 2π*optical path difference / λ), when a light beam passes through a half-wave band and reaches the diffraction focus, there will be a phase difference of π with the adjacent half-wave band. At the same time, because the adjacent half-wave bands are alternately light and dark, only light beams with the same phase difference will hit the focal position, and the light beams are superimposed on each other to produce a maximum value. Based on the diffraction and focusing properties of the Fresnel zone plate, this idea is adopted to arrange and distribute the ITO stripe electrode structure in the form of a Fresnel half-wave band, which is equivalent to a variable-pitch grating structure with 128 stripes, as shown in the attached figure. Figure 5 As shown, the light passing through the structure will produce a focusing effect and the phase difference between the stripes is a multiple of π. On this basis, the voltage of different channel electrodes is changed so that the light passing through each electrode channel stripe changes with a phase difference of π, ensuring that the light can be focused correctly.

[0068] 2) Based on the stripe structure designed in 1), the specific steps of etching the electrode on the ITO glass are as follows:

[0069] ①ITO surface cleaning:

[0070] ② Gluing: Glue coating is performed by a glue spreader according to the ratio of photoresist to photoresist diluent = 1:1;

[0071] ③ Pre-baking: Put the ITO glass after coating into the oven for drying to remove the solvent and enhance the adhesion of the photoresist;

[0072] ④Exposure: The photolithography plate has an area of ​​10mm×10mm. The image is projected onto the glue using ultraviolet light, causing a photochemical reaction in the light-transmitting area.

[0073] ⑤ Development: Place the ITO glass in the developer so that the glue that has not been exposed to light remains on the ITO glass;

[0074] ⑥ Hardening film: Rinse the developed ITO glass and put it in an oven to harden the film;

[0075] ⑦ Etching: After the above process, the photoresist retains the complete ITO glass, and HCl:H2O=1:1 is used, and a certain amount of FeCl3 is added to it to etch the ITO glass, and the designed photolithography pattern is transferred to the ITO glass;

[0076] ⑧ Debonding: Use 4% NaOH solution to debond the etched ITO glass;

[0077] ⑨Detection: Test whether the electrodes etched on the ITO glass are short-circuited or open-circuited, and select the normal electrode structure for the next experiment.

[0078] 2. Using the etched ITO glass as a substrate to make a liquid crystal cell, specifically including the following steps:

[0079] 1) Cleaning: Wash the etched ITO glass with clean water, and then put it into a drying oven at 180°C for one hour. After completion, take it out for use;

[0080] 2) Spin coating: The dried ITO glass is fixed on the spin coater, and the PI droplets are spin-coated on the glass to achieve a uniform thickness;

[0081] 3) Drying: The spin-coated ITO glass is placed in a drying oven for drying, and the processing steps are the same as step 1);

[0082] 4) Friction: After drying, use a friction cloth to rub in one direction to control the direction of the liquid crystal;

[0083] 5) Spacer microspheres: Put the rubbed ITO glass into a powder sprayer, put spacer microspheres of required thickness (5μm, 10μm, 20μm, etc.) into the container at the bottom of the powder sprayer, diffuse them into the closed space in the container, and wait for them to naturally fall onto the ITO glass;

[0084] 6) Packaging: Place two ITO glasses on top of each other (only one of them is etched), seal the two ends of the glass with AB glue, and use the other two ends to fill the liquid crystal;

[0085] 7) Filling: Fill the packaged liquid crystal box with E7 liquid crystal to obtain a filled liquid crystal box. 3) Arrange the prepared liquid crystal box and the ITO glass etched with 128 variable-pitch gratings on the FPGA logic gate circuit system to form a complete electrically controlled liquid crystal box.

[0086] The prepared liquid crystal lens that can use the striped electrode structure to discretely control the voltage is connected to the FPGA logic gate circuit system to form a complete FPGA-controlled adjustable focus liquid crystal lens. The electrically controlled liquid crystal lens is placed in the following optical path for experiment to demonstrate its focusing ability. The optical path diagram is attached. Figure 6 In the optical path experiment, a 633nm light source is used as the test light source. After the laser is emitted, it passes through the objective lens, pinhole, lens, aperture, half-wave plate, liquid crystal lens on the same optical axis in sequence, and finally forms an image on the receiving screen. During the experiment, according to the analysis in the above technical solution, 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 the attached figure. Figure 7As shown. After obtaining the focusing conditions of the phase distribution under different electric control conditions, the position of the receiving screen from the lens is adjusted in the experiment (120 cm and 240 cm from the lens respectively), and then the focusing effect is recorded. From the effect, it can be seen that under different phase distribution conditions based on the electrode channel, due to different focal lengths, the corresponding image at the specific position of the receiving screen will produce different degrees of zooming. Through this experiment, it can be verified that the liquid crystal lens of the present invention can realize the adjustable focus function.

[0087] Example 2

[0088] For the liquid crystal lens in the present invention, the focal length is determined by the number of zones m' and the wavelength λ (according to formula (3) in the technical solution, the total number of phase levels L and the sub-zone index l have little effect on the focal length). Therefore, in different zone numbers, two light waves of different wavelengths can achieve the same focal length. Applying this principle, the focus of the two light waves can be adjusted to one place under the condition of visual persistence, thereby achieving an achromatic effect in the time domain.

[0089] Therefore, based on the device preparation process and optical path construction of Example 1. Different from the single laser light source used in the optical path of Example 1, this example uses two wavelengths of lasers, 405nm and 633nm, to verify the achromatic function. For the 405nm laser, its 128 electrode stripes are divided into 64 areas, different voltages are applied to different areas, and its focus position and imaging are observed, as shown in the attached figure. Figure 8 For a 633nm laser, its 128 electrode stripes are divided into 42 areas, different voltages are applied to different areas, and its focal position and imaging are observed, as shown in the attached figure. Fig. 9 As shown. The experimental results show that by adjusting the focal length of the corresponding wavelength, the achromatic effect of the liquid crystal lens in the time domain can be achieved. At the same time, considering that the human eye can retain an image for less than 200ms, the refresh time of the lens is set to change every 100ms (the response time of the E7 liquid crystal is less than 100ms). In this way, two colors of different wavelengths appear alternately in the same place, and the brain can superimpose them into a composite new color. Thus, the achromatic effect is achieved in the time domain through the electrically controlled liquid crystal lens.

[0090] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A focus-adjustable liquid crystal lens based on FPGA control, characterized in that: The surface of the liquid crystal lens contains an even number of n ITO stripe electrodes etched, the n ITO stripe electrodes are arranged and distributed according to a variable pitch grating, the n ITO stripe electrodes are connected to the FPGA logic gate circuit wiring, the n ITO stripe electrodes are divided into one or more groups, the FPGA electronic control applies a gradient voltage to any group of ITO stripe electrodes, and the light passes through the liquid crystal box to achieve achromatic aberration in different wavelength time domains and coincidence of focal points in different bands; Specific focusing method: Based on the principle of electrically controlled liquid crystal phase modulation, the phase of the light wave passing through the liquid crystal is obtained, and a phase resonance effect is generated on the entire lens to achieve focusing. By switching the presence or absence of the channel voltage in the ITO stripe electrode structure, the focal length formula of the liquid crystal lens is expressed as: （3） in R is the radius of the liquid crystal lens, m is the number of regions, λ is the incident wavelength; The phase change region inside the liquid crystal is adjusted by controlling the number of voltages applied to the electrode channels. m Each area contains n Electrode channels, n is an even number, because each group of electrode channels is a binary change cycle, and the phase difference of half of the channels in the group is π , so the focal length of the liquid crystal lens changes with the phase change caused by the different number of regions; The gradient index method is introduced to optimize the focusing function of the lens: Since the phase distribution of the liquid crystal needs to fluctuate within the range of 0-2π, it is also necessary to control the phase distribution of the liquid crystal within this range to control the liquid crystal to form each gradient zone. At this time, the focal length of the diffraction field is specifically expressed by the following formula: （4） m ' is the new partition number, l is the sub-division index of each partition, L is the total number of phase levels of each partition, In formula (4), since the area number m The new area number m ' is replaced by the focal length of the lens. m Directly determined, but with the subpartition index l Determined together, the lens can optimize the diffraction field and achieve fine adjustment of the focal length; Thus, a gradient refractive index lens based on electronically controlled liquid crystal phase is realized. Through the different responses of liquid crystal to the electric field of the strip electrode, the lens x A liquid crystal phase distribution based on a gradient refractive index is formed in the direction, so that the focal length of the liquid crystal lens is adjustable, and the change depends on the partition of the refractive index. m ' and sub-partitions l .

2. The focus-adjustable liquid crystal lens based on FPGA control according to claim 1, characterized in that: The ITO stripe electrodes are arranged and distributed in the form of Fresnel half-wave bands to form a 128-strip variable-pitch grating structure, so that the light passing through the structure produces a focusing effect and the phase difference between the stripes is π The voltage of different channel electrodes changes by multiples, making the light passing through each electrode channel stripe π The phase difference changes and the light is focused.

3. The focus-adjustable liquid crystal lens based on FPGA control according to claim 2, characterized in that: The ITO stripe electrode stripe interval gradually decreases from the center to the edge, and the structure guides the autonomous focusing of the liquid crystal lens. Different voltages are applied to each channel of the ITO stripe electrode structure to control the different refractive indices of the corresponding liquid crystal phase units, forming a liquid crystal phase distribution based on a gradient refractive index.

4. The focus-adjustable liquid crystal lens based on FPGA control according to claim 3, characterized in that: The maximum pitch of the 128-fringe variable-pitch grating is 631 μm , the minimum spacing is 20 μm The entire etching area size is 10mm*10mm, the selected filling liquid crystal is E7 liquid crystal, and the liquid crystal box thickness is 5 μm .

5. A method for preparing a focus-adjustable liquid crystal lens based on FPGA control, characterized in that: The specific steps include: 1) Based on the stripe structure of the one-dimensional adjustable focus cylindrical liquid crystal lens designed based on FPGA-controlled liquid crystal cell as described in claim 4, the specific steps of etching the electrode on the ITO glass are as follows: 1.1) ITO surface cleaning: First, scrub with a cotton ball with detergent, then use acetone and distilled water for ultrasonic cleaning twice, each time for 10 minutes, and finally put it in an oven to dry for later use; 1.2) Glue coating: Glue is coated by a glue spreader according to the ratio of photoresist to photoresist diluent = 1:1; 1.3) Pre-baking: Put the ITO glass after coating into the oven for drying to remove the solvent and enhance the adhesion of the photoresist; 1.4) Exposure: The photolithography plate has an area of ​​10mm×10mm. The image is projected onto the glue using ultraviolet light, causing a photochemical reaction in the light-transmitting area. 1.5) Development: Place the ITO glass in the developer so that the glue that has not been exposed to light remains on the ITO glass; 1.6) Hardening: Rinse the developed ITO glass and place it in an oven to harden the film; 1.7) Etching: After the above process, the photoresist retains the complete ITO glass, and HCl:H2O=1:1 is used, and a certain amount of FeCl3 is added to it to etch the ITO glass, and the designed photolithography pattern is transferred to the ITO glass; 1.8) Degumming: Use 4% NaOH solution to degumming the etched ITO glass; 1.9) Detection: Test whether the electrodes etched on the ITO glass are short-circuited or open-circuited, and select the normal electrode structure for the next experiment; 2) Using the etched ITO glass as the substrate to make a liquid crystal cell, the specific steps include: 2.1) Cleaning: Wash the etched ITO glass with clean water, and then put it into a drying oven at 180°C for one hour. After completion, take it out for use; 2.2) Spin coating: The dried ITO glass is fixed on the spin coater, and the PI droplets are spin-coated on the glass to achieve a uniform thickness; 2.3) Drying: The spin-coated ITO glass is placed in a drying oven for drying, and the processing steps are the same as step 1); 2.4) Friction: After drying, use a friction cloth to rub in one direction to control the direction of the liquid crystal; 2.5) Spacer microspheres: Put the rubbed ITO glass into the powder sprayer, put the spacer microspheres of required thickness into the container at the bottom of the powder sprayer, diffuse them into the closed space in the container, and wait for them to fall naturally onto the ITO glass; 2.6) Packaging: Place two ITO glass sheets on top of each other, etch only one of them, seal both ends of the sheet with AB glue, and use the other two ends to fill the liquid crystal; 2.7) Filling: Fill the packaged liquid crystal box with E7 liquid crystal to obtain a filled liquid crystal box; 3) Arrange the prepared liquid crystal box and the ITO glass with 128 variable-pitch gratings etched on the FPGA logic gate circuit system to form a complete electrically controlled liquid crystal box.

6. A focusing system of a focus-adjustable liquid crystal lens based on FPGA control, characterized in that: The focus-adjustable liquid crystal lens based on FPGA control as described in claim 1 is selected, and the light emitted by the light source laser passes through the objective lens, pinhole, lens, aperture, half-wave plate, and liquid crystal lens on the same optical axis in sequence. The FPGA electrically controls the voltage of the ITO stripe electrode on the liquid crystal lens to change the phase distribution inside the liquid crystal lens to obtain different focusing effects, and finally an image is formed on the receiving screen.

7. A method for designing a focus-adjustable liquid crystal lens based on FPGA control, characterized in that: After obtaining the voltage-refractive index change relationship of the liquid crystal phase unit through simulation analysis, an ITO stripe electrode structure with 128 channels is designed based on the Fresnel zone plate principle, and different voltages are applied to different stripe electrode channels in different regions on the FPGA electronic control system, so that the refractive index inside the liquid crystal changes, thereby causing phase resonance, achieving tunable focusing, and making the liquid crystal lens have discrete zoom capability, thereby obtaining the FPGA-controlled adjustable focus liquid crystal lens described in claim 1.

8. The method for designing a focus-adjustable liquid crystal lens based on FPGA control according to claim 7, characterized in that: In the time domain, by partitioning different bands into specific stripes and applying specific gradient voltages to make different bands have the same focus, achromatism can be achieved when the response time of the filled liquid crystal is less than the retention time of the human eye observing the image.

Images