Monolithic two-dimensional transmission-type liquid crystal optical phased array device

Abstract

The invention discloses a monolithic two-dimensional transmission-type liquid crystal optical phased array device which comprises a multi-layer sandwich structure, the multi-layer sandwich structure comprises a lower array electrode layer, and the lower array electrode layer comprises a plurality of pixel electrodes arranged in a rectangular array, a driving chip used for controlling the pixel electrodes and a flexible circuit board connected with an external liquid crystal driving circuit. The flexible circuit board is connected with the pixel electrode through the driving chip; the output pin and the input pin of the driving chip are respectively connected with the pixel electrode and the output pin of the flexible circuit board; the plurality of pixel electrodes are arranged in a square matrix, each pixel electrode is square, and the order of the square matrix is not less than 8; according to the device, angle deflection and scanning of incident light in the two-dimensional direction can be realized through a single chip.

Description

Technical Field

[0001] The invention relates to a liquid crystal optical phased array device, in particular to a single-chip two-dimensional transmission type liquid crystal optical phased array device. Background Art

[0002] In applications such as free-space laser optical communications, laser sensing, and lidar, high-precision capture, tracking, and targeting (ATP) of laser beams is a very important key technology and difficulty. Traditional ATP solutions usually use mechanical methods such as universal joints. Due to factors such as large size, heavy weight, high power consumption, and mechanical wear, non-mechanical ATP technology has gradually attracted attention. Currently, the commonly used non-mechanical beam scanning adjustment and control methods mainly include microlens array technology, MEMS (micro-electromechanical system) technology, electrowetting microprism technology, and liquid crystal optical phased array technology. Among them, liquid crystal optical phased array technology is currently the most practical technical solution.

[0003] At present, a single liquid crystal optical phased array device is usually a one-dimensional grating device, which can achieve angle deflection and scanning in one dimension. To achieve angle deflection and scanning in two dimensions, the existing technical solution is to stack two liquid crystal optical phased array devices orthogonally, and place a half-wave plate between the two, and the angle between its crystal axis direction and the liquid crystal orientation direction of the two orthogonally placed liquid crystal optical phased array devices in front and behind is 45°.

[0004] The Chinese invention patent application with publication number CN117970722A discloses an integrated structure of a two-dimensional liquid crystal optical phased array device, which includes two unit devices stacked in sequence, namely, a first unit liquid crystal optical phased array device and a second unit liquid crystal optical phased array device from top to bottom, which are 7-layer sandwich structures and 9-layer sandwich structures respectively. The two unit devices are bonded by optical glue, and a liquid crystal polymer film is embedded inside the second liquid crystal optical phased array as a half-wave plate, so that the polarization direction required by the two one-dimensional liquid crystal optical phased arrays in the cascade process is rotated by 90°. The integrated structure of the invention is more compact, thinner, and has lower light intensity loss, and the assembly process of the independent unit device of the half-wave plate is omitted, thereby reducing the manufacturing cost.

[0005] Although the above device omits the half-wave plate, two liquid crystal optical phased array devices are still required, and one of the devices also needs to integrate a liquid crystal polymer film as a half-wave plate. The number of devices is large, the structure is complex and the cost is high. In addition to the structure of the above device, there is also a single-chip transmissive two-dimensional liquid crystal spatial light modulator with an active electrode structure of TFT, which requires a complex semiconductor manufacturing process and has very high R&D and manufacturing costs. Secondly, existing two-dimensional liquid crystal optical phased array devices generally use nematic liquid crystal materials. When the operating wavelength is longer, the thickness of the liquid crystal box increases, which limits the improvement of the response speed of the liquid crystal device. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a single-chip two-dimensional transmissive liquid crystal optical phased array device that can achieve angular deflection and scanning of incident light in two-dimensional directions.

[0007] Technical solution: The monolithic two-dimensional transmissive liquid crystal optical phased array device described in the present invention comprises a multi-layer sandwich structure, including a lower array electrode layer, wherein the lower array electrode layer comprises a plurality of pixel electrodes arranged in a rectangular array, a driving chip for controlling the pixel electrodes and a flexible circuit board connected to an external liquid crystal driving circuit, wherein the flexible circuit board is connected to the pixel electrodes through the driving chip; a plurality of pixel electrodes can be combined to form a closed area.

[0008] Based on the above technical solution, by arranging a plurality of pixel electrodes in a rectangular array on the lower array electrode layer, a two-dimensional distribution of electrodes can be realized on a single-chip liquid crystal optical phased array device, and the angle deflection and scanning of the incident light in the two-dimensional direction can be realized. Compared with the single-chip device using parallel strip pixel electrodes in a single direction, which requires two pieces to be superimposed to form a two-dimensionally distributed pixel electrode, the present device can realize the functions of two pieces only through a single-chip device, and the structure is simpler and more compact, saving costs. Moreover, the present device does not need to integrate a thin film transistor for each liquid crystal pixel point like a TFT structure to drive, and the research and development and manufacturing costs are low; secondly, a driving chip is arranged between the flexible circuit board connected to the external liquid crystal driving circuit and the pixel electrode, because the driving chip can process the signal internally and then output it accordingly, it only needs to set a few fixed number of input terminals, and there is no need to set the number of its input terminals according to the number of pixel electrodes. In this way, the width of the flexible circuit board wiring can be greatly reduced, the complexity of the connection structure with the external driving circuit can be reduced, the manufacturing cost can be reduced, and the overall integration of the device can be improved, thereby making the number of electrodes independently controlled by the device greater.

[0009] Preferably, the output pin and the input pin of the driving chip are connected to the pixel electrode and the output pin of the flexible circuit board respectively.

[0010] Preferably, the plurality of pixel electrodes are arranged in a square matrix, and each pixel electrode is in a square shape.

[0011] Preferably, the order of the square matrix is ​​not less than 8.

[0012] If the order of the array is not less than 8, the diffraction efficiency of the device for incident light can be above 95%.

[0013] Preferably, a lower glass substrate layer is provided below the lower array electrode layer, and the driving chip is packaged on the lower glass substrate layer through a COG process.

[0014] Preferably, the multi-layer sandwich structure also includes an upper glass base layer and a liquid crystal layer in the middle layer. The liquid crystal layer uses a polymer network liquid crystal material. The upper glass substrate layer and the lower glass substrate layer apply a shear force to the liquid crystal layer along the length or width direction of the rectangular array in which the pixel electrodes are arranged so that the orientation of the polymer network liquid crystal material is consistent with the shear direction.

[0015] Applying a lateral shear force between the two glass substrates can cause a certain distance of misalignment and translation between the upper and lower glass substrates, thereby straightening the polymer network of the polymer network liquid crystal material in a unified direction, making the liquid crystal domains between the polymer networks evenly oriented, and finally forming a stress polymer network liquid crystal material. The response time of the stress polymer network liquid crystal material can reach ms level or even shorter, and the response time is independent of the thickness of the liquid crystal. For longer wavelength bands such as mid-infrared and long-wave infrared, the liquid crystal thickness needs to be set larger, which can effectively improve the response speed.

[0016] Preferably, the polymer network liquid crystal material is prepared by mixing a nematic liquid crystal material, a photosensitive polymer material, a photoinitiator and an optical glue and polymerizing the mixture through ultraviolet light irradiation.

[0017] Preferably, the nematic liquid crystal material, photosensitive polymer material, photoinitiator and optical glue are 5CB, RM82, Irg651 and NOA65 respectively, which are mixed in a mass ratio of 90:2:0.2:7.8.

[0018] Preferably, after the nematic liquid crystal material, photosensitive polymer material, photoinitiator and optical glue are mixed, they are irradiated with ultraviolet light at 50° C. and a power density of 20 mW / cm 2 for half an hour.

[0019] Preferably, the spacing between the pixel electrodes is greater than 5 μm.

[0020] The pitch of the pixel electrodes being greater than 5 μm can ensure that the wires connecting the pixel electrodes and the driving chip will not contact each other, maintain an independent insulation state, and will not interfere with each other.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant effects: by arranging pixel electrodes arranged in a rectangular array in the lower array electrode layer, a single-chip liquid crystal optical phased array device can realize a two-dimensional arrangement of electrodes and thus realize an angle deflection and scanning of the incident light in a two-dimensional direction, without the need for a combination of multiple devices, which greatly simplifies the structure; secondly, by adding a driving chip between the flexible circuit board and the pixel electrode, the integration of the device is improved, the device is simplified, and the cost is reduced; in addition, the liquid crystal layer uses a polymer network liquid crystal material to achieve rapid response at a longer operating wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a side sectional view of the device; Figure 2 Schematic diagram of the lower electrode layer structure. DETAILED DESCRIPTION

[0023] As shown in the figure, the monolithic two-dimensional transmissive liquid crystal optical phased array device described in the present invention includes a multi-layer sandwich structure, which may be 7 layers, including a lower array electrode layer 1, wherein the lower array electrode layer 1 includes a plurality of pixel electrodes 1-1 arranged in a rectangular array, a driving chip 1-2 for controlling the pixel electrode 1-1, and a flexible circuit board 1-3 connected to an external liquid crystal driving circuit, and the flexible circuit board 1-3 is connected to the pixel electrode 1-1 through the driving chip 1-2.

[0024] The 7-layer sandwich structure comprises, from top to bottom, an upper glass substrate layer 3, an upper common electrode layer 5, an upper orientation layer 6, a liquid crystal layer 4, a lower orientation layer 7, a lower array electrode layer 1 and a lower glass substrate layer 2; the existing liquid crystal optical phased array device also has the same structure, the upper glass substrate layer 3 and the lower glass substrate layer 2 are flat glass, such as fused quartz glass, sapphire glass, etc.; the upper common electrode layer 5 and the lower array electrode layer 1 are transparent conductive electrodes, the upper orientation layer 6 and the lower orientation layer 7 can be prepared by rubbing orientation agent or photo orientation agent material through processes such as coating, curing, rubbing or photo orientation exposure, and their orientation directions are consistent, which is the X-axis direction. Under the joint action of the two, the direction of the molecular director of the liquid crystal layer 5 sandwiched therebetween is consistent with the orientation directions of the upper orientation layer 6 and the lower orientation layer 7, which is also the X-axis direction; the upper common electrode layer 5 is a whole piece of continuous transparent conductive electrode, and the lower array electrode layer 1 of the present invention is different from the existing device.

[0025] The lower array electrode layer 1 includes a plurality of pixel electrodes 1-1 arranged in a rectangular array, and the pixel electrodes 1-1 can be manufactured by conventional photolithography and etching processes; the pixel electrodes 1-1 are arranged at intervals from each other; the pixel electrodes 1-1 and the upper common electrode layer 5 act together after voltage is applied, so that the liquid crystal layer 5 sandwiched between the two is subjected to different spatially distributed voltages, thereby forming a phase spatial modulation of the incident light wave according to the electro-optical effect of the liquid crystal material.

[0026] The pixel electrodes 1-1 can be arranged in a square array, each pixel electrode 1-1 is square, the spacing between adjacent pixel electrodes 1-1 is equal, and each adjacent four pixel electrodes 1-1 can enclose a rectangular closed area; the size of the square array is between 4*4 and 20*20, and the spacing between the pixel electrodes 1-1 generally needs to be greater than 5μm; for example, the pixel electrode 1-1 can be designed as a square array structure with 8 rows and 8 columns, that is, the order of the square array is 8, and this order can achieve a diffraction efficiency of more than 95%. The order can be set higher to further improve the diffraction efficiency, but the order higher than 8 is not very effective in improving the diffraction efficiency, and too large an order will increase the complexity of the device. On a limited area, too high an order will greatly increase the manufacturing cost and driving complexity, so setting the order to 8 is the best choice that can take into account both diffraction efficiency and device complexity.

[0027] The length and width of each pixel electrode 1 - 1 are both a=1 mm, and the distance between two pixel electrodes 1 - 1 is b=30 um, so the spatial period of the pixel unit is T=a+b=1.03 mm.

[0028] The output pin and input pin of the driving chip 1-2 are respectively connected to the output pins of the pixel electrode 1-1 and the flexible circuit board 1-3, and the wires connecting the driving chip 1-2 to each pixel electrode 1-1 are independent of each other and remain insulated; similarly, all wires connecting the driving chip 1-2 to the flexible circuit board 1-3 are also independent of each other and insulated; the driving chip 1-2 is encapsulated on the lower glass substrate layer 2 through the COG process.

[0029] The liquid crystal layer 4 is made of polymer network liquid crystal material. A shear force is applied to the upper glass substrate layer 3 and the lower glass substrate layer 2 along the length or width direction of the rectangular array of pixel electrodes 1-1. The shear force is transmitted to the liquid crystal layer 4 pressed between the two glass substrate layers through the electrode layer and the orientation layer in turn, so that the orientation of the polymer network liquid crystal material is consistent with the direction of the shear force.

[0030] The polymer network liquid crystal material is formed by mixing nematic liquid crystal material, photosensitive polymer material, photoinitiator, optical glue and other materials, and is polymerized by ultraviolet light to form a composite material of liquid crystal and polymer network. Microscopically, in the composite material, the liquid crystal is divided into many small areas by the polymer network, also called liquid crystal domains. Macroscopically, the composite material is poured between two glass substrates to form a liquid crystal box before polymerization. After polymerization, a lateral misalignment displacement is applied through the upper and lower glass substrates, and the polymer network is straightened along a uniform direction, so that the liquid crystal domains between the polymer networks are uniformly oriented by stretching in a uniform direction. In order to achieve a better orientation effect, the direction of the lateral misalignment displacement in the present invention is consistent with the orientation direction of the liquid crystal orientation layer. The response time of the stress polymer liquid crystal is very short, about ms or even shorter, and the response time is independent of the thickness of the liquid crystal box. This characteristic has a high application value for longer wavelength bands such as mid-infrared and long-wave infrared.

[0031] The typical material ratio is: nematic liquid crystal material 5CB: photosensitive polymer material RM82: photoinitiator Irg651: optical glue NOA65 = 90:2:0.2:7.8, and the typical UV light curing conditions are irradiation at 50°C and 20mW / cm2 power density for half an hour; after curing to form a polymer network structure, a lateral shear force is applied to the upper and lower glass substrate layers, so that a certain distance of misalignment and translation occurs between the upper and lower glass substrate layers, thereby forming a stress polymer network liquid crystal material. This misalignment and translation distance is called the shear distance, and the typical shear distance is 5-10 times the thickness of the liquid crystal layer. In this embodiment, the shear distance is 80um.

[0032] When the device is working, the external liquid crystal driving circuit controls the driving chip 1-2 through the flexible circuit board 1-3, sets the amplitude, frequency, duty cycle and other parameters of the driving voltage, and the driving chip 1-2 outputs multiple independent voltage waveforms according to the parameters of the external liquid crystal driving circuit, and loads the output voltage to each pixel electrode 1-1. Since the pixel electrode 1-1 has a rectangular array structure, it can drive the liquid crystal molecules in the liquid crystal layer 4 to have a two-dimensional spatial distribution of electrically controlled refractive index, thereby realizing programmable two-dimensional phase modulation of the incident light wave, and finally realizing two-dimensional fast and precise deflection and scanning of the laser beam.

Claims

1. A monolithic two-dimensional transmissive liquid crystal optical phased array device, comprising a multi-layer sandwich structure, including a lower array electrode layer (1), characterized in that: The lower array electrode layer (1) comprises a plurality of pixel electrodes (1-1) arranged in a rectangular array, a driving chip (1-2) for controlling the pixel electrodes (1-1), and a flexible circuit board (1-3) connected to an external liquid crystal driving circuit; the flexible circuit board (1-3) is connected to the pixel electrodes (1-1) via the driving chip (1-2).

2. The monolithic two-dimensional transmissive liquid crystal optical phased array device according to claim 1, characterized in that: The output pin and the input pin of the driving chip (1-2) are respectively connected to the pixel electrode (1-1) and the output pin of the flexible circuit board (1-3).

3. The monolithic two-dimensional transmissive liquid crystal optical phased array device according to claim 1, characterized in that: The plurality of pixel electrodes (1-1) are arranged in a square array, and each pixel electrode (1-1) is in the shape of a square.

4. The monolithic two-dimensional transmissive liquid crystal optical phased array device according to claim 3, characterized in that: The order of the square matrix is ​​not less than 8.

5. The monolithic two-dimensional transmissive liquid crystal optical phased array device according to claim 1, characterized in that: A lower glass substrate layer (2) is provided below the lower array electrode layer (1), and the driving chip (1-2) is packaged on the lower glass substrate layer (2) through a COG process.

6. The monolithic two-dimensional transmissive liquid crystal optical phased array device according to claim 5, characterized in that: The multi-layer sandwich structure further comprises an upper glass substrate layer (3) as the top layer and a liquid crystal layer (4) as the middle layer, wherein the liquid crystal layer (4) adopts a polymer network liquid crystal material, and the upper glass substrate layer (3) and the lower glass substrate layer (2) apply a shear force to the liquid crystal layer (4) along the length or width direction of the rectangular array in which the pixel electrodes (1-1) are arranged, so that the orientation of the polymer network liquid crystal material is consistent with the shear direction.

7. The monolithic two-dimensional transmissive liquid crystal optical phased array device according to claim 6, characterized in that: The polymer network liquid crystal material is prepared by mixing a nematic liquid crystal material, a photosensitive polymer material, a photoinitiator and an optical glue and polymerizing the mixture through ultraviolet light irradiation.

8. The monolithic two-dimensional transmissive liquid crystal optical phased array device according to claim 7, characterized in that: The nematic liquid crystal material, photosensitive polymer material, photoinitiator and optical glue are 5CB, RM82, Irg651 and NOA65 respectively, which are mixed in a mass ratio of 90:2:0.2:7.

8.

9. The monolithic two-dimensional transmissive liquid crystal optical phased array device according to claim 8, characterized in that: After the nematic liquid crystal material, the photosensitive polymer material, the photoinitiator and the optical glue are mixed, they are irradiated with ultraviolet light at 50° C. and a power density of 20 mW / cm 2 for half an hour.

10. The monolithic two-dimensional transmissive liquid crystal optical phased array device according to claim 1, characterized in that: The spacing between the pixel electrodes (1-1) is greater than 5 μm.

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