Non-rotating space laser communication system and communication method based on liquid crystal phase regulation and control device

Abstract

The invention relates to laser communication, in particular to a non-rotating type space laser communication system and method based on a liquid crystal phase regulation and control device, and aims to overcome the defects that in the prior art, a liquid crystal spatial light modulator is small in deflection angle and small in transmitting and receiving aperture, and the requirements for the capturing and tracking range and aperture of space laser communication are difficult to meet. The non-rotation type space laser communication system based on the liquid crystal phase regulation and control device comprises an adjustable phase delayer, a liquid crystal polarization grating module, a beam shrinking module, a liquid crystal space light modulator, a fine tracking galvanometer, a light splitting module, a coarse tracking module, a fine tracking module, a communication module and a data processing module, according to the communication method based on the system, light beam deflection is carried out through the adjustable phase delayer, the liquid crystal polarization grating module, the liquid crystal spatial light modulator and the fine tracking galvanometer, a traditional mechanical rotary table is replaced, and high-precision adjustment is achieved.

Description

Technical Field

[0001] The present invention relates to laser communication, and in particular to a non-rotating space laser communication system and a communication method based on a liquid crystal phase control device. Background Art

[0002] Space laser communication has the advantages of wide bandwidth, large information capacity, good confidentiality, strong anti-interference ability, no spectrum restriction, small size, light weight, low power consumption, etc. It can meet the growing data volume demand in detection missions and space-based communication networks. In recent years, the United States, Europe and China have repeatedly achieved on-orbit demonstration and verification of space laser communication technology between satellites and between satellites and the ground. Space laser communication technology has been widely used in low-orbit satellite constellations at home and abroad.

[0003] In the space laser communication system, the aiming, capturing and tracking subsystems are important components. The tracking subsystem can complete the rapid capture of space optical signals through the two-level capture and tracking systems of coarse tracking and fine tracking, and ensure that the optical signals enter the communication receiving system stably and efficiently in real time, so as to realize high-speed communication of data. In the existing space laser communication system, a rotating mechanical turntable is mostly used, and the coarse tracking and capturing of the light beam is realized through the mechanical rotation of the turntable. The volume, weight and power consumption of this mechanical turntable are relatively large, accounting for more than 70% of the volume, weight, power consumption and resources of the space laser communication system terminal. At the same time, there are problems such as large inertia and difficulty in expanding multi-user simultaneous communication, which limits the development of space laser communication terminals towards miniaturization, lightweight and flexible networking.

[0004] Liquid crystal spatial light modulators perform beamforming through phase modulation, which can achieve non-mechanical beam deflection. They are small in size, light in weight, and low in power consumption, and are expected to replace mechanical turntables with non-rotating structures in space laser communications. However, the current liquid crystal spatial light modulators have a small deflection angle and a small transmitting and receiving aperture, which makes it difficult to meet the requirements of tracking range and aperture in space laser communications. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art that the liquid crystal spatial light modulator has a small deflection angle and a small transmitting and receiving aperture, which makes it difficult to meet the tracking range and aperture requirements of space laser communications, and to provide a non-rotating space laser communication system and communication method based on a liquid crystal phase control device.

[0006] To achieve the above objectives, the technical solutions provided by the present invention are as follows:

[0007] A non-rotating space laser communication system based on a liquid crystal phase control device is special in that it includes an adjustable phase delay, a liquid crystal polarization grating module, a beam reduction module, a liquid crystal spatial light modulator, a fine tracking galvanometer, and a splitter module, a coarse tracking module, a fine tracking module, a communication module and a data processing module arranged in sequence along the incident light path; the adjustable phase delay is used to change the polarization state of the incident light; the liquid crystal polarization grating module is used to diffract the incident light signal and control its discrete angle deflection; the beam reduction module is used to reduce the aperture of the incident light; the liquid crystal spatial light modulator is used to phase modulate the incident light after beam reduction to achieve continuous deflection of the incident light angle; the fine tracking galvanometer is used to adjust the angle of the incident light after phase modulation; the splitter module is arranged on the reflected light path of the fine tracking galvanometer, and is used to split the reflected light of the fine tracking galvanometer and transmit it to the coarse tracking module, respectively. Tracking module, fine tracking module, communication module, at the same time, the output optical signal of the communication module is transmitted to the fine tracking galvanometer, and then sequentially output through the liquid crystal spatial light modulator, the beam reduction module, the liquid crystal polarization grating module and the adjustable phase delay; the coarse tracking module and the fine tracking module are respectively used to receive the incident light and image it; the communication module is used to receive and receive optical signals, perform photoelectric and electro-optical conversion, and perform signal modulation and demodulation; the data processing module is respectively connected to the coarse tracking module, the fine tracking module, the adjustable phase delay, the liquid crystal polarization grating module, the liquid crystal spatial light modulator and the fine tracking galvanometer, the data processing module is used to receive the imaging of the coarse tracking module and the fine tracking module, and transmit feedback voltage to the adjustable phase delay, the liquid crystal polarization grating module and the liquid crystal spatial light modulator according to the imaging of the coarse tracking module, and transmit feedback voltage to the fine tracking galvanometer according to the imaging of the fine tracking module.

[0008] Furthermore, the liquid crystal polarization grating module comprises a first liquid crystal polarization grating component and a second liquid crystal polarization grating component which are sequentially arranged along the incident light path and whose deflection directions are perpendicular to each other.

[0009] Furthermore, the first liquid crystal polarization grating assembly includes n layers of liquid crystal polarization gratings, and the deflection angle multiples of the n layers of liquid crystal polarization gratings are 1, 3, ..., (2 n -1) times, where 1≤n≤6;

[0010] The second liquid crystal polarization grating assembly comprises m layers of liquid crystal polarization gratings, and the deflection angle multiples of the m layers of liquid crystal polarization gratings are 1, 3, ..., (2 m -1) times, where 1≤m≤6.

[0011] Furthermore, it also includes a triangular reflector, which includes a first reflective surface and a second reflective surface;

[0012] The first reflection surface is located between the beam reduction module and the liquid crystal spatial light modulator, and the second reflection surface is located between the liquid crystal spatial light modulator and the fine tracking galvanometer;

[0013] The beam reduction module and the precision tracking galvanometer are coaxially arranged, and the triangular reflector is located on the central axis thereof.

[0014] Further, the beam splitter module includes a first beam splitter, a second beam splitter, and a third beam splitter, the first beam splitter is arranged on the reflected light path of the fine tracking galvanometer, and reflects and transmits the reflected light of the fine tracking galvanometer, and the coarse tracking module is arranged on the transmitted light path of the first beam splitter;

[0015] The second beam splitter is arranged on the reflection light path of the first beam splitter, and reflects and transmits the reflected light of the first beam splitter; the third beam splitter is arranged on the transmission light path of the second beam splitter, and reflects and transmits the transmitted light of the second beam splitter;

[0016] The communication module is arranged on the reflected light path of the second beam splitter and the third beam splitter; and the fine tracking module is arranged on the transmitted light path of the third beam splitter.

[0017] Furthermore, the coarse tracking module comprises a coarse tracking coupling optical component and a coarse tracking camera which are arranged in sequence; the coarse tracking coupling optical component is used to focus the light beam onto the photosensitive surface of the coarse tracking camera to form a light spot, and the coarse tracking camera images it and outputs it to the data processing module;

[0018] The fine tracking module includes a fine tracking coupling optical component and a fine tracking camera arranged in sequence; the fine tracking coupling optical component is used to focus the light beam onto the photosensitive surface of the fine tracking camera to form a light spot, and the fine tracking camera images it and outputs it to the data processing module.

[0019] Furthermore, the communication module includes a receiving coupling optical component, a transmitting coupling optical component and an optical communication transceiver, the transmitting coupling optical component is arranged on the reflection light path of the second beam splitter, the output light of the optical communication transceiver is collimated and transmitted to the second beam splitter through the transmitting coupling optical component, and then reflected by the second beam splitter and reflected to the precision tracking galvanometer through the first beam splitter;

[0020] The receiving coupling optical component is arranged on the reflected light path of the third beam splitter, corresponding to the input end of the optical communication transceiver, and focuses the reflected light of the third beam splitter to the input end of the optical communication transceiver.

[0021] Further, the coarse tracking camera is a CCD, a CMOS infrared camera or a four-quadrant detector;

[0022] The precision tracking camera is a CCD, CMOS infrared camera or a four-quadrant detector;

[0023] The shrinking ratio N of the shrinking module is 8-10, and the apertures of the adjustable phase retarder and the liquid crystal polarization grating module are both N times that of the liquid crystal spatial light modulator.

[0024] At the same time, the present invention also provides a non-rotating space laser communication method based on a liquid crystal phase control device. The non-rotating space laser communication system based on the liquid crystal phase control device is special in that it includes the following steps:

[0025] S1. According to the received initial position information of the communication target and its own initial position information, the data processing module analyzes the initial deflection angle and converts the angle information into voltage control information, which is loaded onto the adjustable phase retarder, the liquid crystal polarization grating module and the liquid crystal spatial light modulator respectively;

[0026] S2. The adjustable phase retarder, the liquid crystal polarization grating module and the liquid crystal spatial light modulator, under the action of the voltage control information, make the laser beam or beacon light emitted by the communication target incident and deflected, and the coarse tracking module receives and images it;

[0027] S3, the data processing module receives the imaging of the coarse tracking module, detects the off-target amount information of the center of mass of the light spot on it, and determines whether it meets the following conditions:

[0028] The distance between the centroid of the light spot and the central pixel of the coarse tracking module is ≤ 1 pixel;

[0029] If it meets the requirements, complete the rough tracking and proceed to the next step;

[0030] If not, the corresponding angle to be deflected is calculated according to the off-target amount information of the spot mass center, and this angle is decomposed into the angles corresponding to the adjustable phase retarder, the liquid crystal polarization grating module and the liquid crystal spatial light modulator and the corresponding voltage control information, and the process returns to step S2;

[0031] S4, the fine tracking module images the laser beam or beacon light after the rough tracking is completed;

[0032] S5, the data processing module receives the image of the fine tracking module, detects the off-target amount information of the center of mass of the light spot on it, and determines whether it meets the following conditions:

[0033] The distance between the centroid of the light spot and the central pixel of the fine tracking module is ≤ 1 pixel;

[0034] If it meets the requirements, complete the precise tracking and proceed to the next step;

[0035] If not, the corresponding angle to be deflected is calculated according to the off-target amount information of the center of mass of the light spot, and this angle is converted into the deflection angle and control voltage information of the fine tracking galvanometer, and the corresponding control voltage information is loaded on the fine tracking galvanometer. The fine tracking galvanometer rotates under the action of the control voltage information, and then returns to step S4;

[0036] S6, maintaining the fine tracking state, the laser beam passes through the spectrometer module and is received by the communication module to complete signal reception; or, maintaining the fine tracking state, the communication module outputs a beam that modulates the communication signal and deflects it to the direction of the communication target.

[0037] Beneficial effects of the present invention:

[0038] 1. In the non-rotating space laser communication system based on the liquid crystal phase control device of the present invention, an adjustable phase delay, a liquid crystal polarization grating module, a liquid crystal spatial light modulator and a coarse tracking module are arranged to realize coarse tracking, and a fine tracking galvanometer and a fine tracking module are arranged to realize fine tracking, which can replace the traditional mechanical turntable and greatly reduce the volume, weight and power consumption of the space laser communication system. The liquid crystal polarization grating and the liquid crystal spatial light modulator are cascaded to solve the problems of large volume, weight and power consumption of the traditional mechanical turntable optical antenna, small deflection angle based solely on the liquid crystal spatial light modulator, and small transmitting and receiving aperture.

[0039] 2. In the non-rotating space laser communication system based on the liquid crystal phase control device of the present invention, the coarse tracking system is decomposed, the adjustable phase delay and the liquid crystal polarization grating are placed at the front end of the telescope system, and the liquid crystal spatial light modulator is placed at the rear end of the telescope system, which solves the problem of small light aperture when the spatial light modulator is used alone as the coarse tracking system and can adapt to the application requirements of large-aperture space laser communications.

[0040] 3. In the non-rotating space laser communication system based on the liquid crystal phase control device of the present invention, a liquid crystal polarization grating and a liquid crystal spatial light modulator are used in combination, which solves the problem that the liquid crystal polarization grating can only achieve discrete angle deflection and the problem that the liquid crystal spatial light modulator can only achieve small angle deflection, and realizes arbitrary angle light beam deflection within a large angle range.

[0041] 4. The non-rotating space laser communication method based on the liquid crystal phase control device of the present invention first performs coarse tracking and then performs fine tracking. The combination of the two realizes high-precision adjustment and ensures the accuracy of the adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a structural schematic diagram of an embodiment of a non-rotating space laser communication system based on a liquid crystal phase control device of the present invention (data processing module is not shown);

[0043] Figure 2It is a schematic diagram of the principle of an adjustable phase retarder and a liquid crystal polarization grating of an embodiment of a non-rotating space laser communication system based on a liquid crystal phase control device of the present invention;

[0044] Description of reference numerals:

[0045] 1-adjustable phase retarder, 2-liquid crystal polarization grating module, 201-liquid crystal polarization grating, 202-first light beam, 203-second light beam, 204-third light beam, 3-beam reduction module, 4-triangular reflector, 5-liquid crystal spatial light modulator, 6-fine tracking galvanometer, 7-first beam splitter, 8-second beam splitter, 9-third beam splitter, 10-coarse tracking coupling optical component, 11-transmitting coupling optical component, 12-receiving coupling optical component, 13-fine tracking coupling optical component, 14-optical communication transceiver, 15-coarse tracking camera, 16-fine tracking camera. DETAILED DESCRIPTION

[0046] In the non-rotating space laser communication system based on the liquid crystal phase control device of the present invention, a liquid crystal spatial light modulator 5 is provided to realize non-rotating beam deflection, which can replace the traditional mechanical turntable and has the characteristics of small size, light weight and low power consumption. The structure is as follows Figure 1 As shown, it includes an adjustable phase retarder 1, a liquid crystal polarization grating module 2, a beam shrinking module 3, a liquid crystal spatial light modulator 5, a fine tracking galvanometer 6, a light splitting module, a coarse tracking module, a fine tracking module, a communication module and a data processing module.

[0047] An adjustable phase retarder 1, a liquid crystal polarization grating module 2, a beam reduction module 3, a liquid crystal spatial light modulator 5 and a precision tracking galvanometer 6 are arranged in sequence along the incident light path; the adjustable phase retarder 1 is used to change the polarization state of the incident light; the liquid crystal polarization grating module 2 is used to diffract the incident light passing through the adjustable phase retarder 1 and control the discrete angle deflection of the incident light, including multiple liquid crystal polarization gratings 201; the beam reduction module 3 is used to reduce the aperture of the incident light passing through the liquid crystal polarization grating module 2; the liquid crystal spatial light modulator 5 is used to phase modulate the incident light after beam reduction to achieve continuous deflection of the angle of the incident light; the precision tracking galvanometer 6 is used to adjust the angle of the incident light after phase modulation.

[0048] Reference Figure 2 The working principle of the adjustable phase retarder 1 and the liquid crystal polarization grating 201 is as follows: when different voltages are applied to the adjustable phase retarder 1, different phase delays can be applied to the optical signal to change the polarization state of the transmitted optical signal, such as Figure 2As shown, the third light beam 204 can be changed from right-handed to left-handed. Therefore, the present invention sets an adjustable phase retarder 1 for changing the polarization state of the incident light, so that it switches between left-handed circularly polarized light and right-handed circularly polarized light. When the liquid crystal polarization grating 201 is controlled without voltage, left-handed or right-handed circularly polarized light will undergo -1st or +1st order diffraction and switch to the opposite polarization state when passing through, thereby generating a discrete angle deflection in the negative direction or positive direction in the far field, such as the first light beam 202 and the third light beam 204 changing the polarization state and causing beam deflection. Under certain voltage control, the liquid crystal polarization grating 201 will lose the effect of the diffraction device, so that no discrete angle deflection will occur in the far field, such as the second light beam 203 emitting along the original direction. The discrete angle deflection of the liquid crystal polarization grating 201 is determined by its phase period, and liquid crystal polarization gratings 201 with different discrete angles can be obtained by changing the phase period.

[0049] According to the above principle, the liquid crystal polarization gratings 201 with different angles can be superimposed to achieve multiple specified angles of light beam deflection. Since the polarization state of light changes after passing through the liquid crystal polarization grating 201, when passing through two layers of liquid crystal polarization gratings 201, the light beam is forwardly deflected in the first layer of liquid crystal polarization grating 201 and then reversely deflected in the second layer of liquid crystal polarization grating 201. Therefore, in order to achieve a larger angle of deflection, the present invention sets a multi-layer liquid crystal polarization grating 201 superposition method to expand the deflection angle. In order to reduce insertion loss, when the number of layers is set to i, the number of layers is sequentially arranged according to 1, 3, ..., (2 i -1) times the angle of the regularly arranged liquid crystal polarization grating 201 can achieve the most efficient combination. Generally, when the number of stacked layers i reaches 6, the deflection angle can reach the limit range, so the value range of i is preferably 1≤i≤6.

[0050] In this embodiment, in order to achieve deflection on two axes, the liquid crystal polarization grating module 2 includes a first liquid crystal polarization grating component and a second liquid crystal polarization grating component whose deflection directions are perpendicular to each other, and the angle deflection of the two axes in the horizontal and vertical directions is achieved by superposition. The first liquid crystal polarization grating component includes four layers of liquid crystal polarization gratings 201, and the deflection angles are set to 0.75°, 2.25°, 5.25°, and 11.25° in sequence. The angular resolution is 0.75°, the maximum deflection range is -11.25° to 11.25°, and the superposition achieves a deflection range of 22.5°. The second liquid crystal polarization grating component includes three layers of liquid crystal polarization gratings 201, and the deflection angles are set to 0.75°, 2.25°, and 5.25° in sequence. The superposition achieves a deflection range of 10.5°, wherein the multiples of the deflection angle increase in sequence along the direction from the beam reduction module 3 to the adjustable phase retarder 1.

[0051] In this embodiment, the beam reduction module 3 is an 8X beam reduction module 3, which is used to compress the diameter of the optical signal to 1 / 8 or amplify it to 8 times, and at the same time amplify or reduce the angle of the off-axis light beam by 8 times accordingly. Therefore, the aperture of the adjustable phase retarder 1 and the liquid crystal polarization grating module 2 is 60 mm, and the aperture of the device behind the beam reduction module 3 is 7.5 mm. The beam reduction module 3 in this embodiment is a Maksutov catadioptric system, the lens and the reflector are spherical, the eyepiece is composed of 3 pieces, and the system can be shared by receiving and transmitting.

[0052] The working principle of the liquid crystal spatial light modulator 5 is: when an external voltage is applied to the liquid crystal spatial light modulator 5, there will be an angle deflection between the light beam reflected by the liquid crystal spatial light modulator 5 and its normal reflection direction. When different voltage values ​​are applied, the reflected laser light beam will be deflected at different angles. The angle deflection range of the liquid crystal spatial light modulator 5 is small. In this embodiment, the angular resolution of the liquid crystal polarization grating module 2 is 0.75°, which is enlarged to 6° after being 8 times contracted by the contraction module 3. The liquid crystal spatial light modulator 5 completes the deflection of any angle within its angular resolution. Therefore, the angle deflection range of the liquid crystal spatial light modulator 5 is -3° to 3°, and the angular resolution is 0.2 mrad. Together with the adjustable phase retarder 1 and the liquid crystal polarization grating module 2, it constitutes a rough tracking unit for space laser communication. The working principle of the fine tracking galvanometer 6 is: according to different input voltages, its piezoelectric actuator is driven to push and pull, and different two-dimensional angle deflections are performed, which are used for small angle high-precision adjustment under voltage control. In this embodiment, the fine tracking galvanometer 6 has a deflection angle range of 3 mrad and an angle resolution of 0.02 μrad, and can accurately adjust the direction of the optical signal.

[0053] The spectroscopic module is arranged on the reflected light path of the fine tracking galvanometer 6, and is used to split the reflected light of the fine tracking galvanometer 6, and transmit or reflect it to the coarse tracking module, the fine tracking module, and the communication module. The spectroscopic module includes a first spectroscope 7, a second spectroscope 8, and a third spectroscope 9 which are coaxially arranged. The first spectroscope 7, the second spectroscope 8, and the third spectroscope 9 are energy spectroscopes, which are used to transmit half of the energy of the optical signal through transmission and the other half through reflection. The first spectroscope 7 is arranged on the reflected light path of the fine tracking galvanometer 6, and is coaxial with the fine tracking galvanometer 6, and reflects and transmits the reflected light of the fine tracking galvanometer 6. The coarse tracking module is coaxially arranged on the transmitted light path of the first spectroscope 7; the second spectroscope 8 is arranged on the reflected light path of the first spectroscope 7, and reflects and transmits the reflected light of the first spectroscope 7; the third spectroscope 9 is arranged on the transmitted light path of the second spectroscope 8, and reflects and transmits the transmitted light of the second spectroscope 8; the communication module is arranged on the reflected light paths of the second spectroscope 8 and the third spectroscope 9; and the fine tracking module is coaxially arranged on the transmitted light path of the third spectroscope 9.

[0054] The coarse tracking module and the fine tracking module are respectively used to receive incident light and image it; the coarse tracking module includes a coarse tracking coupling optical component 10 and a coarse tracking camera 15 which are arranged in sequence; the coarse tracking coupling optical component 10 is used to focus the light beam onto the photosensitive surface of the coarse tracking camera 15 to form a light spot, and the coarse tracking camera 15 images it and outputs it to the data processing module; the fine tracking module includes a fine tracking coupling optical component 13 and a fine tracking camera 16 which are arranged in sequence; the fine tracking coupling optical component 13 is used to focus the light beam onto the photosensitive surface of the fine tracking camera 16 to form a light spot, and the fine tracking camera 16 images it and outputs it to the data processing module.

[0055] The communication module is used for receiving and transmitting optical signals, performing photoelectric and electro-optical conversion, and signal modulation and demodulation; the communication module includes a receiving coupling optical component 12, a transmitting coupling optical component 11, and an optical communication transceiver 14. The receiving coupling optical component 12 is arranged on the reflected light path of the third beam splitter 9, focuses the reflected light of the third beam splitter 9 onto the single-mode optical fiber, and transmits it to the input end of the optical communication transceiver 14; the transmitting coupling optical component 11 is arranged on the reflected light path of the second beam splitter 8, corresponding to the transmitting end of the optical communication transceiver 14, collimates and transmits the optical fiber signal light provided by the optical communication transceiver 14 to the spatial light path, and then reflects from the second beam splitter 8 and the first beam splitter 7 to the precision tracking galvanometer 6 in turn, and after being reflected by the precision tracking galvanometer 6, it is transmitted and output through the liquid crystal spatial light modulator 5, the beam reduction module 3, the liquid crystal polarization grating module 2, and the adjustable phase delay device 1 in turn.

[0056] The data processing module is respectively connected to the coarse tracking module, the fine tracking module, the adjustable phase retarder 1, the liquid crystal polarization grating module 2, the liquid crystal spatial light modulator 5 and the fine tracking galvanometer 6. The working principle is as follows: the data processing module detects the centroid position of the light spot imaged by the coarse tracking camera 15, and then detects the miss-target amount information of the center of the light spot, converts it into the corresponding angle that requires the incident light to be deflected, decomposes this angle into the angle and control voltage corresponding to the adjustable phase retarder 1, the liquid crystal polarization grating module 2 and the liquid crystal spatial light modulator 5, and then loads the corresponding control voltages to achieve coarse tracking of the light beam. The data processing module detects the centroid position of the light spot imaged by the fine tracking camera 16, and then detects the miss-target amount information of the center of the light spot, converts it into the corresponding angle and control voltage that requires the fine tracking galvanometer 6 to be deflected, and loads the corresponding control voltage to achieve fine tracking of the light beam.

[0057] In order to reduce the overall volume of the non-rotating space laser communication system, the present invention is further provided with a triangular reflector 4, which includes a first reflective surface and a second reflective surface. The first reflective surface is located between the beam reduction module 3 and the liquid crystal spatial light modulator 5 along the optical path, and the second reflective surface is located between the liquid crystal spatial light modulator 5 and the fine tracking galvanometer 6 along the optical path. The liquid crystal spatial light modulator 5 is located on the reflected optical path of the first reflective surface of the triangular reflector 4, and is located on the incident optical path of the second reflective surface; the adjustable phase delay device 1, the liquid crystal polarization grating module 2, the beam reduction module 3, and the fine tracking galvanometer 6 are coaxially arranged, and the initial angle between the fine tracking galvanometer 6 and the central axis is 45°. The corner reflector 4 is located on the central axis between the beam reduction module 3 and the precision tracking galvanometer 6, and the three angles are 43.5°, 43.5°, and 93° respectively. The angle between the first reflective surface and the central axis is 136.5°; the angle between the second reflective surface and the central axis is 43.5°. The liquid crystal spatial light modulator 5 is located on the extension line of the center line of the triangular reflector 44 and is perpendicular to the extension line, thereby reducing the angle of the incident light incident on the liquid crystal spatial light modulator 5 and improving the device performance. The first reflective surface deflects the light signal at an incident angle of 3° to the liquid crystal spatial light modulator 5, and then deflects it at the original angle on the second reflective surface to the precision tracking galvanometer 6 after reflection.

[0058] The coarse tracking camera 15 is a CCD, a CMOS infrared camera or a four-quadrant detector, and the fine tracking camera 16 is a CCD, a CMOS infrared camera or a four-quadrant detector; the shrinking ratio N of the shrinking module 3 is 8-10, and the apertures of the adjustable phase retarder 1 and the liquid crystal polarization grating 201 are both N times that of the liquid crystal spatial light modulator 5.

[0059] The non-rotating space laser communication system based on the above-mentioned liquid crystal phase control device can capture, track and communicate with space laser beams, and when used to receive the laser beam emitted by the communication target, it includes the following steps:

[0060] Step 1: According to the received initial position information of the communication target and its own initial position information, the data processing module analyzes the initial deflection angle, converts the angle information into voltage control information, and loads it to the adjustable phase retarder 1, the liquid crystal polarization grating module 2 and the liquid crystal spatial light modulator 5 respectively, and the precision tracking galvanometer 6 is placed in the initial position without adjustment;

[0061] Step 2: Under the action of voltage control information, the adjustable phase retarder 1, the liquid crystal polarization grating module 2 and the liquid crystal spatial light modulator 5 make the laser beam deflected by the initial deflection angle, and sequentially pass through the adjustable phase retarder 1, the liquid crystal polarization grating module 2, the beam reduction module 3, the first reflection surface, the liquid crystal spatial light modulator 5, the second reflection surface, the fine tracking galvanometer 6, the first beam splitter 7 and the coarse tracking coupling optical component 10, and form a light spot on the photosensitive surface of the coarse tracking camera 15, and the coarse tracking camera 15 images it;

[0062] Step 3: The data processing module receives the image of the coarse tracking camera 15, detects the off-target amount information of the center of mass of the light spot, and determines whether it meets the following conditions:

[0063] The distance between the centroid of the light spot and the central pixel of the coarse tracking camera 15 is ≤1 pixel;

[0064] If it meets the requirements, complete the rough tracking and proceed to the next step;

[0065] If not, the corresponding angle to be deflected is calculated according to the off-target amount information of the spot mass center, and this angle is decomposed into the angles corresponding to the adjustable phase retarder 1, the liquid crystal polarization grating module 2 and the liquid crystal spatial light modulator 5 and the corresponding voltage control information, and then the process returns to step 2;

[0066] Step 4, the laser beam passes through the first beam splitter 7, the second beam splitter 8, the third beam splitter 9 and the fine tracking coupling optical component 13, and forms a light spot on the photosensitive surface of the fine tracking camera 16, and the fine tracking camera 16 images it;

[0067] Step 5, the fine tracking camera 16 outputs the image to the data processing module, and the data processing module detects the miss amount information of the center of mass of the light spot to determine whether it meets the following conditions:

[0068] The distance between the centroid of the light spot and the central pixel of the fine tracking camera 16 is ≤1 pixel;

[0069] If it meets the requirements, complete the precise tracking and proceed to the next step;

[0070] If not, the corresponding deflection angle is calculated according to the off-target amount information of the spot mass center, and this angle is converted into the deflection angle and control voltage information of the fine tracking galvanometer 6, and the corresponding control voltage information is loaded on the fine tracking galvanometer 6. The fine tracking galvanometer 6 rotates under the action of the control voltage information, and then returns to step 4;

[0071] Step 6, keep the center of mass of the light spot always located at the center position of the fine tracking camera 16 unchanged, and continue to maintain the fine tracking state. At this time, the laser beam is reflected by the third beam splitter 9 and coupled into the optical communication transceiver 14 by the receiving coupling optical component 12.

[0072] When used to emit a laser beam for communication purposes, the following steps are included:

[0073] Step 1: According to the received initial position of the communication target and its own initial position information, the data processing module analyzes the initial deflection angle and converts the angle information into voltage control information, which is loaded onto the adjustable phase retarder 1, the liquid crystal polarization grating module 2 and the liquid crystal spatial light modulator 5 respectively, and the precision tracking galvanometer 6 is placed at the initial position;

[0074] Step 2: Under the action of voltage control information, the adjustable phase retarder 1, the liquid crystal polarization grating module 2 and the liquid crystal spatial light modulator 5 make the beacon light of the communication target deflected by the initial deflection angle to form a light spot on the photosensitive surface of the coarse tracking camera 15, and the coarse tracking camera 15 images it;

[0075] Step 3: The data processing module receives the image of the coarse tracking camera 15, detects the off-target amount information of the center of mass of the light spot, and determines whether it meets the following conditions:

[0076] The distance between the centroid of the light spot and the central pixel of the coarse tracking camera 15 is ≤1 pixel;

[0077] If it meets the requirements, complete the rough tracking and proceed to the next step;

[0078] If not, the corresponding angle to be deflected is calculated according to the off-target amount information of the spot mass center, and this angle is decomposed into the angles corresponding to the adjustable phase retarder 1, the liquid crystal polarization grating module 2 and the liquid crystal spatial light modulator 5 and the corresponding voltage control information, and then the process returns to step 2;

[0079] Step 4: The beacon light enters the fine tracking module, forms a light spot on the photosensitive surface of the fine tracking camera 16, and the fine tracking camera 16 images it;

[0080] Step 5, the fine tracking camera 16 outputs the image to the data processing module, and the data processing module detects the miss amount information of the center of mass of the light spot to determine whether it meets the following conditions:

[0081] The distance between the centroid of the light spot and the central pixel of the fine tracking camera 16 is ≤1 pixel;

[0082] If it meets the requirements, complete the precise tracking and proceed to the next step;

[0083] If not, the corresponding deflection angle is calculated according to the off-target amount information of the spot mass center, and this angle is converted into the deflection angle and control voltage information of the fine tracking galvanometer 6, and the corresponding control voltage information is loaded on the fine tracking galvanometer 6. The fine tracking galvanometer 6 rotates under the action of the control voltage information, and then returns to step 4;

[0084] Step 6, keep the center of mass of the light spot always located at the center position of the fine tracking camera 16 unchanged, and continue to maintain the fine tracking state; the optical communication transceiver 14 outputs a light beam that modulates the communication signal, which passes through the emission coupling optical component 11, the second beam splitter 8, the first beam splitter 7, the fine tracking galvanometer 6, the second reflection surface, the liquid crystal spatial light modulator 5, the first reflection surface, the beam reduction module 3, the liquid crystal polarization grating module 2, and the adjustable phase delay device 1 in sequence, and then deflects to the direction of the communication target.

[0085] Through the above embodiments, it can be seen that the non-rotating space laser communication system based on the liquid crystal phase control device of the present invention can replace the traditional mechanical turntable, and the adjustable phase delay device 1, the liquid crystal polarization grating 201 and the liquid crystal spatial light modulator 5 are combined to form a non-rotating coarse tracking system, which greatly reduces the volume, weight and power consumption of the space laser communication system; at the same time, the coarse tracking system is decomposed, the adjustable phase delay device 1 and the liquid crystal polarization grating module are placed at the front end of the beam reduction module 3, and the liquid crystal spatial light modulator 5 is placed at the rear end of the telescope system, which solves the problem of small aperture when the spatial light modulator is used alone as the coarse tracking system, and can adapt to the application requirements of large-aperture space laser communication; in addition, the combination of the liquid crystal polarization grating 201 and the liquid crystal spatial light modulator 5 solves the problem that the liquid crystal polarization grating 201 can only achieve discrete angle deflection and the problem that the liquid crystal spatial light modulator 5 can only achieve small angle deflection, and realizes arbitrary angle beam deflection within a large angle range.

Claims

1. A non-rotating space laser communication system based on a liquid crystal phase control device, characterized in that: It comprises an adjustable phase delay device (1), a liquid crystal polarization grating module (2), a beam reduction module (3), a liquid crystal spatial light modulator (5), a fine tracking galvanometer (6), a light splitting module, a coarse tracking module, a fine tracking module, a communication module and a data processing module, which are sequentially arranged along the incident light path; The adjustable phase retarder (1) is used to change the polarization state of the incident light; the liquid crystal polarization grating module (2) is used to diffract the incident light signal and control its discrete angle deflection; the beam reduction module (3) is used to reduce the aperture of the incident light; the liquid crystal spatial light modulator (5) is used to perform phase modulation on the incident light after beam reduction and realize continuous deflection of the angle of the incident light; the precision tracking galvanometer (6) is used to adjust the angle of the incident light after phase modulation; The light splitting module is arranged on the reflected light path of the fine tracking galvanometer (6), and is used to split the reflected light of the fine tracking galvanometer (6), and transmit the light to the coarse tracking module, the fine tracking module, and the communication module respectively. At the same time, the output light signal of the communication module is transmitted to the fine tracking galvanometer (6), and then sequentially outputted through the liquid crystal spatial light modulator (5), the beam reduction module (3), the liquid crystal polarization grating module (2), and the adjustable phase delay device (1); The coarse tracking module and the fine tracking module are respectively used to receive incident light and image it; the communication module is used to transmit and receive optical signals, perform photoelectric and electro-optical conversion, and perform signal modulation and demodulation; The data processing module is respectively connected to the coarse tracking module, the fine tracking module, the adjustable phase retarder (1), the liquid crystal polarization grating module (2), the liquid crystal spatial light modulator (5) and the fine tracking galvanometer (6); the data processing module is used to receive the imaging of the coarse tracking module and the fine tracking module, transmit feedback voltage to the adjustable phase retarder (1), the liquid crystal polarization grating module (2) and the liquid crystal spatial light modulator (5) according to the imaging of the coarse tracking module, and transmit feedback voltage to the fine tracking galvanometer (6) according to the imaging of the fine tracking module.

2. According to claim 1, the non-rotating space laser communication system based on the liquid crystal phase control device is characterized by: The liquid crystal polarization grating module (2) comprises a first liquid crystal polarization grating component and a second liquid crystal polarization grating component which are arranged in sequence along the incident light path and whose deflection directions are perpendicular to each other.

3. According to claim 2, the non-rotating space laser communication system based on the liquid crystal phase control device is characterized in that: The first liquid crystal polarization grating component comprises n layers of liquid crystal polarization gratings (201), and the deflection angle multiples of the n layers of liquid crystal polarization gratings (201) are 1, 3, ..., (2 n -1) times, where 1≤n≤6; The second liquid crystal polarization grating component comprises m layers of liquid crystal polarization gratings (201), and the deflection angle multiples of the m layers of liquid crystal polarization gratings (201) are 1, 3, ..., (2 m -1) times, where 1≤m≤6.

4. According to claim 3, the non-rotating space laser communication system based on the liquid crystal phase control device is characterized in that: It also includes a triangular reflector (4), which includes a first reflective surface and a second reflective surface; The first reflection surface is located between the beam reduction module (3) and the liquid crystal spatial light modulator (5), and the second reflection surface is located between the liquid crystal spatial light modulator (5) and the fine tracking galvanometer (6); The beam reduction module (3) and the precision tracking galvanometer (6) are coaxially arranged, and the triangular reflector (4) is located on the central axis thereof.

5. The non-rotating space laser communication system based on a liquid crystal phase control device according to any one of claims 1 to 4, characterized in that: The light splitting module comprises a first light splitter (7), a second light splitter (8), and a third light splitter (9); the first light splitter (7) is arranged on the reflection light path of the fine tracking galvanometer (6) to reflect and transmit the reflection light of the fine tracking galvanometer (6); and the coarse tracking module is arranged on the transmission light path of the first light splitter (7); The second beam splitter (8) is arranged on the reflection light path of the first beam splitter (7) to reflect and transmit the reflected light of the first beam splitter (7); the third beam splitter (9) is arranged on the transmission light path of the second beam splitter (8) to reflect and transmit the transmitted light of the second beam splitter (8); The communication module is arranged on the reflected light path of the second beam splitter (8) and the third beam splitter (9); and the fine tracking module is arranged on the transmitted light path of the third beam splitter (9).

6. The non-rotating space laser communication system based on the liquid crystal phase control device according to claim 5, characterized in that: The coarse tracking module comprises a coarse tracking coupling optical component (10) and a coarse tracking camera (15) which are arranged in sequence; the coarse tracking coupling optical component (10) is used to focus a light beam onto a photosensitive surface of the coarse tracking camera (15) to form a light spot, and the coarse tracking camera (15) images the light spot and outputs the image to the data processing module; The fine tracking module comprises a fine tracking coupling optical component (13) and a fine tracking camera (16) which are arranged in sequence; the fine tracking coupling optical component (13) is used to focus a light beam onto a photosensitive surface of the fine tracking camera (16) to form a light spot, and the fine tracking camera (16) images the light spot and outputs the image to the data processing module.

7. The non-rotating space laser communication system based on the liquid crystal phase control device according to claim 6 is characterized in that: The communication module comprises a receiving coupling optical component (12), a transmitting coupling optical component (11) and an optical communication transceiver (14); the transmitting coupling optical component (11) is arranged on the reflection light path of the second beam splitter (8); the output light of the optical communication transceiver (14) is collimated and transmitted to the second beam splitter (8) through the transmitting coupling optical component (11), and after being reflected by the second beam splitter (8), it is reflected to the precision tracking galvanometer (6) through the first beam splitter (7); The receiving coupling optical component (12) is arranged on the reflected light path of the third beam splitter (9), corresponding to the input end of the optical communication transceiver (14), and focuses the reflected light of the third beam splitter (9) to the input end of the optical communication transceiver (14).

8. The non-rotating space laser communication system based on the liquid crystal phase control device according to claim 7 is characterized in that: The coarse tracking camera (15) is a CCD, a CMOS infrared camera or a four-quadrant detector; The precision tracking camera (16) is a CCD, CMOS infrared camera or a four-quadrant detector; The shrinking ratio N of the shrinking module (3) is 8-10, and the apertures of the adjustable phase retarder (1) and the liquid crystal polarization grating module are both N times that of the liquid crystal spatial light modulator (5).

9. A non-rotating space laser communication method based on a liquid crystal phase control device, based on the non-rotating space laser communication system based on a liquid crystal phase control device according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. According to the received initial position information of the communication target and its own initial position information, the data processing module analyzes the initial deflection angle and converts the angle information into voltage control information, which is loaded onto the adjustable phase retarder (1), the liquid crystal polarization grating module (2) and the liquid crystal spatial light modulator (5); S2. The adjustable phase retarder (1), the liquid crystal polarization grating module (2) and the liquid crystal spatial light modulator (5) cause the laser beam or beacon light emitted by the communication target to be incident and deflected under the action of voltage control information, and the coarse tracking module receives and images the laser beam or beacon light; S3, the data processing module receives the imaging of the coarse tracking module, detects the off-target amount information of the center of mass of the light spot on it, and determines whether it meets the following conditions: The distance between the centroid of the light spot and the central pixel of the coarse tracking module is ≤ 1 pixel; If it meets the requirements, complete the rough tracking and proceed to the next step; If not, the angle to be deflected is calculated according to the off-target amount information of the center of mass of the light spot, and the angle is decomposed into the angles corresponding to the adjustable phase retarder (1), the liquid crystal polarization grating module (2) and the liquid crystal spatial light modulator (5) and the corresponding voltage control information, and the process returns to step S2; S4, the fine tracking module images the laser beam or beacon light after the rough tracking is completed; S5, the data processing module receives the image of the fine tracking module, detects the off-target amount information of the center of mass of the light spot on it, and determines whether it meets the following conditions: The distance between the centroid of the light spot and the central pixel of the fine tracking module is ≤ 1 pixel; If it meets the requirements, complete the precise tracking and proceed to the next step; If not, the angle to be deflected is calculated according to the off-target amount information of the center of mass of the light spot, and the angle is converted into the deflection angle and control voltage information of the fine tracking galvanometer (6), and the corresponding control voltage information is loaded on the fine tracking galvanometer (6), and the fine tracking galvanometer (6) rotates under the action of the control voltage information, and then returns to step S4; S6, maintaining the fine tracking state, the laser beam passes through the spectrometer module and is received by the communication module to complete signal reception; or, maintaining the fine tracking state, the communication module outputs a beam that modulates the communication signal and deflects it to the direction of the communication target.

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