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

Abstract

The present application relates to laser communication, in particular to a non-rotating space laser communication system and communication method based on liquid crystal phase control device, in order to solve the problem of small deflection angle of liquid crystal space light modulator, small transmitting and receiving aperture, and difficult to meet the requirements of space laser communication tracking range and aperture in the prior art, the non-rotating space laser communication system based on liquid crystal phase control device comprises an adjustable phase retarder, a liquid crystal polarization grating module, a beam-reducing 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 arranged in sequence along the incident light path; the communication method based on the above system deflects the light beam through the adjustable phase retarder, the liquid crystal polarization grating module, the liquid crystal space light modulator and the fine tracking galvanometer, replaces the traditional mechanical turntable, and realizes high-precision adjustment.

Description

TECHNICAL FIELD

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

[0002] Space laser communication has the advantages of wide frequency band, large information capacity, good secrecy, strong anti-interference ability, no spectrum limitation, small volume, light weight and low power consumption, and can meet the increasing data demand of detection tasks and space-based communication networks. In recent years, the United States, Europe and China have all realized on-orbit demonstration and verification of inter-satellite and space-ground space laser communication technology, and space laser communication technology has been widely used in low-orbit satellite constellations at home and abroad.

[0003] In a space laser communication system, the aiming, acquisition and tracking subsystem is an important component. The tracking subsystem can complete the rapid acquisition of space optical signals through a two-stage coarse tracking and fine tracking acquisition system, and ensure that the optical signal enters the communication receiving system stably and efficiently in real time to realize high-speed data communication. The existing space laser communication system mainly uses a rotating mechanical turntable to realize coarse tracking and acquisition of the optical beam through mechanical rotation of the turntable. Such a mechanical turntable has a large volume, weight and power consumption, and occupies more than 70% of the volume, weight and power consumption and resources of the space laser communication system terminal. At the same time, it has the problems of large inertia and difficulty in expanding multi-user simultaneous communication, which limits the development of space laser communication terminals towards miniaturization, light weight and flexible networking.

[0004] A liquid crystal spatial light modulator can realize beam shaping through phase modulation and non-mechanical beam deflection, and has the characteristics of small volume, light weight and low power consumption, and is expected to replace the mechanical turntable in space laser communication with a non-rotating structure. However, the deflection angle of the liquid crystal spatial light modulator is small, and the transmitting and receiving aperture is small, which cannot meet the requirements of the acquisition and tracking range and aperture of space laser communication. SUMMARY

[0005] The purpose of the present application is to solve the problems of small deflection angle and small transmitting and receiving aperture of the liquid crystal spatial light modulator in the prior art, and to provide a non-rotating space laser communication system and a communication method based on a liquid crystal phase control device.

[0006] To achieve the above-mentioned purpose, the technical solution provided by the present application is 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, as well as a spectrometer module, a coarse tracking module, a fine tracking module, a communication module and a data processing module, which are 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 spectrometer 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 and the fine 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 includes 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 includes 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 reflecting surface is located between the beam-reducing module and the liquid crystal spatial light modulator, and the second reflecting surface is located between the liquid crystal spatial light modulator and the fine tracking galvanometer.

[0013] The beam-reducing module and the fine tracking galvanometer are coaxially arranged, and the triangular reflecting mirror is located on the central axis.

[0014] Further, the light splitting module comprises a first light splitting mirror, a second light splitting mirror and a third light splitting mirror, the first light splitting mirror 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 light splitting mirror.

[0015] The second light splitting mirror is arranged on the reflected light path of the first light splitting mirror and reflects and transmits the reflected light of the first light splitting mirror, and the third light splitting mirror is arranged on the transmitted light path of the second light splitting mirror and reflects and transmits the transmitted light of the second light splitting mirror.

[0016] The communication module is arranged on the reflected light path of the second light splitting mirror and the third light splitting mirror, and the fine tracking module is arranged on the transmitted light path of the third light splitting mirror.

[0017] Further, the coarse tracking module comprises a coarse tracking coupling optical assembly and a coarse tracking camera arranged in sequence, the coarse tracking coupling optical assembly is used for focusing a light beam on a light-sensitive surface of the coarse tracking camera to form a light spot, the coarse tracking camera images the light spot and outputs the image to the data processing module.

[0018] The fine tracking module comprises a fine tracking coupling optical assembly and a fine tracking camera arranged in sequence, the fine tracking coupling optical assembly is used for focusing a light beam on a light-sensitive surface of the fine tracking camera to form a light spot, and the fine tracking camera images the light spot and outputs the image to the data processing module.

[0019] Further, the communication module comprises a receiving coupling optical assembly, a transmitting coupling optical assembly and an optical communication transceiver, the transmitting coupling optical assembly is arranged on the reflected light path of the second light splitting mirror, the output light of the optical communication transceiver is collimated and transmitted through the transmitting coupling optical assembly to the second light splitting mirror, and the reflected light is reflected by the second light splitting mirror and then reflected by the first light splitting mirror to the fine tracking galvanometer.

[0020] The receiving coupling optical assembly is arranged on the reflected light path of the third light splitting mirror, and the receiving coupling optical assembly is arranged corresponding to the input end of the optical communication transceiver to focus the reflected light of the third light splitting mirror 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 fine tracking camera is a CCD, a CMOS infrared camera or a four-quadrant detector.

[0023] The pinching ratio N of the pinching module is 8-10, and the aperture of the adjustable phase retarder and the liquid crystal polarization grating module is N times of the aperture of the liquid crystal spatial light modulator.

[0024] Meanwhile, the application also provides a non-rotating space laser communication method based on the liquid crystal phase control device, and the non-rotating space laser communication system based on the liquid crystal phase control device, which is characterized by comprising the following steps:

[0025] S1. According to the received initial position of the communication target and the initial position information of itself, the data processing module analyzes the initial deflection angle and converts the angle information into voltage control information, which is loaded on 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 make the laser beam or beacon light emitted by the communication target incident and deflected under the action of the voltage control information, and the coarse tracking module receives and images the laser beam or beacon light;

[0027] S3. The data processing module receives the imaging of the coarse tracking module, detects the off-target amount information of the spot centroid thereon, and judges whether the off-target amount information meets the following conditions:

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

[0029] If yes, the coarse tracking is completed, and the next step is entered;

[0030] If no, the angle corresponding to the deflection required is calculated according to the off-target amount information of the spot centroid, the angle is decomposed into the angle 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 step S2 is returned;

[0031] S4. The fine tracking module images the laser beam or beacon light after the coarse tracking is completed;

[0032] S5. The data processing module receives the imaging of the fine tracking module, detects the off-target amount information of the spot centroid thereon, and judges whether the off-target amount information meets the following conditions:

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

[0034] If yes, the fine tracking is completed, and the next step is entered;

[0035] If not, the angle corresponding to the required deflection is calculated according to the off-target amount information of the spot center, the angle is converted into the angle and control voltage information of the fine tracking galvanometer deflection, the corresponding control voltage information is loaded to the fine tracking galvanometer, the fine tracking galvanometer rotates under the action of the control voltage information, and then the step S4 is returned to;

[0036] S6, maintaining the fine tracking state, the laser beam passes through the light splitting module, is received by the communication module, and signal reception is completed; or, maintaining the fine tracking state, the communication module outputs the modulated communication signal beam, and the beam is deflected to the communication target direction.

[0037] The present application has the following beneficial effects:

[0038] 1. In the non-rotating space laser communication system based on the liquid crystal phase control device, the adjustable phase delay device, the liquid crystal polarization grating module, the liquid crystal spatial light modulator and the coarse tracking module are combined to realize coarse tracking, and the fine tracking galvanometer and the fine tracking module are combined to realize fine tracking, so that the traditional mechanical turntable can be replaced, and the volume, weight and power consumption of the space laser communication system are greatly reduced.

[0039] 2. In the non-rotating space laser communication system based on the liquid crystal phase control device, the coarse tracking system is decomposed, the adjustable phase delay device 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, so that the problem of small light aperture of the spatial light modulator as the coarse tracking system is solved, and the space laser communication application demand of large aperture can be adapted.

[0040] 3. In the non-rotating space laser communication system based on the liquid crystal phase control device, the liquid crystal polarization grating and the liquid crystal spatial light modulator are combined for use, so that the problems of discrete angle deflection of the liquid crystal polarization grating and small angle deflection of the liquid crystal spatial light modulator are solved, and arbitrary angle beam deflection in a large angle range is realized.

[0041] 4. The non-rotating space laser communication method based on the liquid crystal phase control device decomposes the coarse tracking and the fine tracking, combines the two to realize high-precision adjustment, and ensures the accuracy of the adjustment. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a structural schematic diagram of the non-rotating space laser communication system based on the liquid crystal phase control device of the present application (without showing the data processing module);

[0043] Figure 2Fig. 1 is a schematic diagram of the adjustable phase retarder and liquid crystal polarization grating according to the embodiment of the non-rotating space laser communication system based on the liquid crystal phase control device of the application;

[0044] Marked for explanation:

[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 shrinking module, 4-triangular mirror, 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 assembly, 11-transmission coupling optical assembly, 12-reception coupling optical assembly, 13-fine tracking coupling optical assembly, 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 application, the non-rotating beam deflection is realized by setting the liquid crystal spatial light modulator 5, which can replace the traditional mechanical turntable, has the characteristics of small size, light weight and low power consumption, and its structure is shown in Figure 1 Fig. 1, which 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 beam splitting module, a coarse tracking module, a fine tracking module, a communication module and a data processing module.

[0047] The adjustable phase retarder 1, the liquid crystal polarization grating module 2, the beam shrinking module 3, the liquid crystal spatial light modulator 5 and the fine tracking galvanometer 6 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 through the adjustable phase retarder 1 to control the discrete angle deflection of the incident light, and includes a plurality of liquid crystal polarization gratings 201; the beam shrinking module 3 is used to reduce the aperture of the incident light 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 shrinking to realize continuous deflection of the incident light angle; and the fine tracking galvanometer 6 is used to adjust the incident light angle after phase modulation.

[0048] Reference Figure 2 The working principle of the adjustable phase retarder 1 and the liquid crystal polarization grating 201 is that when different voltages are applied to the adjustable phase retarder 1, different phase delays can be loaded on the optical signal, and the polarization state of the transmitted light signal is changed, as shown in Figure 2As shown, the third light beam 204 can be changed from right-handed to left-handed. Therefore, the present application provides an adjustable phase retarder 1 for changing the polarization state of the incident light to switch between left-handed circularly polarized light and right-handed circularly polarized light. Under the control of no voltage, the liquid crystal polarization grating 201 diffracts the left-handed or right-handed circularly polarized light by-1 order or +1 order and switches to the opposite polarization state, thereby producing discrete angular deflection in the far field in the negative direction or the positive direction, such as the first light beam 202 and the third light beam 204 changing the polarization state and deflection. Under the control of a certain voltage, the liquid crystal polarization grating 201 loses the effect of the diffractive device, thereby not producing discrete angular deflection in the far field, such as the second light beam 203 exiting in the original direction. The discrete angular deflection of the liquid crystal polarization grating 201 is determined by its phase period, and different discrete angles of the liquid crystal polarization grating 201 can be obtained by changing the phase period.

[0049] According to the above principle, the superposition of liquid crystal polarization gratings 201 with different angles can realize the deflection of light beams with multiple specified angles. Since the polarization state of light changes after passing through the liquid crystal polarization grating 201, when the light passes through two layers of liquid crystal polarization gratings 201, the light beam is positively deflected in the first layer of liquid crystal polarization grating 201 and negatively deflected in the second layer of liquid crystal polarization grating 201. Therefore, in order to realize larger angle deflection, the present application provides a way of superimposing multiple layers of liquid crystal polarization gratings 201 to expand the deflection angle. In order to reduce the insertion loss, when the number of layers is i, the angles of the liquid crystal polarization gratings 201 are arranged in the order of 1, 3, …, (2 i -1) times, which can achieve the most efficient combination. Generally, when the number of superimposed 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 realize deflection on two axes, the liquid crystal polarization grating module 2 includes a first liquid crystal polarization grating assembly and a second liquid crystal polarization grating assembly whose deflection directions are perpendicular to each other, and the horizontal and vertical two-axis angular deflection is realized by superimposing them. The first liquid crystal polarization grating assembly includes four liquid crystal polarization gratings 201, and the deflection angles are arranged in the order of 0.75°, 2.25°, 5.25°, and 11.25°, the angular resolution is 0.75°, the maximum deflection range is -11.25° to 11.25°, and the superposition realizes a deflection range of 22.5°. The second liquid crystal polarization grating assembly includes three liquid crystal polarization gratings 201, and the deflection angles are arranged in the order of 0.75°, 2.25°, and 5.25°, and the superposition realizes a deflection range of 10.5°. Among them, the multiples of the deflection angles increase in the direction from the beam shrinking module 3 to the adjustable phase retarder 1.

[0051] In this embodiment, the beam-reducing module 3 is an 8X beam-reducing module 3, which is used to compress the diameter of the optical signal to 1 / 8 or enlarge it to 8 times, and at the same time, the angle of the off-axis light beam is enlarged or reduced by 8 times. Therefore, the aperture of the adjustable phase delay device 1 and the liquid crystal polarization grating module 2 is 60 mm, and the aperture of the device after the beam-reducing module 3 is 7.5 mm. The beam-reducing module 3 in this embodiment is a Maksutov catadioptric system, and the lenses and mirrors are all spherical. The eyepiece is composed of three pieces, and this system can be shared by receiving and transmitting.

[0052] The working principle of the liquid crystal spatial light modulator 5 is that when an external voltage is applied to the liquid crystal spatial light modulator 5, the reflected light beam after passing through the liquid crystal spatial light modulator 5 will be deflected at an angle from the normal reflection direction. Different voltage values will cause the reflected laser beam to 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 8 times beam reduction by the beam-reducing module 3. The liquid crystal spatial light modulator 5 can complete the deflection at 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. The liquid crystal spatial light modulator 5, together with the adjustable phase delay device 1 and the liquid crystal polarization grating module 2, constitutes a spatial laser communication coarse tracking unit. The working principle of the fine tracking galvanometer 6 is that according to different input voltages, it drives the piezoelectric actuator to push and pull to perform different two-dimensional angle deflection, which is used for small-angle high-precision adjustment under voltage control. In this embodiment, the deflection angle range of the fine tracking galvanometer 6 is 3 mrad, and the angular resolution is 0.02 μrad, which can accurately adjust the direction of the optical signal.

[0053] The beam-splitting module is arranged on the reflected light path of the fine tracking galvanometer 6, and is used for splitting the reflected light of the fine tracking galvanometer 6 and transmitting or reflecting it to the coarse tracking module, the fine tracking module and the communication module. The beam-splitting module includes coaxially arranged first, second and third beam splitters 7, 8 and 9. The first, second and third beam splitters 7, 8 and 9 are energy beam splitters, which are used for transmitting half of the energy of the optical signal and reflecting the other half. The first beam splitter 7 is arranged on the reflected light path of the fine tracking galvanometer 6 and is coaxial with the fine tracking galvanometer 6. It reflects and transmits the reflected light of the fine tracking galvanometer 6. The coarse tracking module is coaxially arranged on the transmission light path of the first beam splitter 7. The second beam splitter 8 is arranged on the reflected light path of the first beam splitter 7 and reflects and transmits 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 and reflects and transmits the transmitted light of the second beam splitter 8. The communication module is arranged on the reflected light path of the second and third beam splitters 8 and 9. The fine tracking module is coaxially arranged on the transmission light path of the third beam splitter 9.

[0054] The coarse tracking module and the fine tracking module are respectively used for receiving incident light and imaging the incident light; the coarse tracking module comprises a coarse tracking coupling optical assembly 10 and a coarse tracking camera 15 arranged in sequence; the coarse tracking coupling optical assembly 10 is used for focusing a light beam on a light-sensitive 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 light spot to a data processing module; the fine tracking module comprises a fine tracking coupling optical assembly 13 and a fine tracking camera 16 arranged in sequence; the fine tracking coupling optical assembly 13 is used for focusing a light beam on a light-sensitive 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 light spot to the data processing module.

[0055] The communication module is used for transceiving optical signals, performing photoelectric and electro-optical conversion, and signal modulation and demodulation; the communication module comprises a receiving coupling optical assembly 12, a transmitting coupling optical assembly 11 and an optical communication transceiver 14; the receiving coupling optical assembly 12 is arranged on a reflection light path of the third beam splitter 9 and focuses reflected light of the third beam splitter 9 to a single-mode optical fiber and transmits the reflected light to an input end of the optical communication transceiver 14; the transmitting coupling optical assembly 11 is arranged on a reflection light path of the second beam splitter 8 and is arranged corresponding to a transmitting end of the optical communication transceiver 14 to collimate and transmit fiber signal light provided by the optical communication transceiver 14 to a spatial light path, and then the fiber signal light is reflected by the second beam splitter 8, the first beam splitter 7 and the fine tracking galvanometer 6 in sequence, and then the fiber signal light is transmitted by the liquid crystal spatial light modulator 5, the beam shrinking module 3, the liquid crystal polarization grating module 2 and the adjustable phase retarder 1 in sequence and is output.

[0056] The data processing module is connected with 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 respectively, and the working principle is as follows: the data processing module detects a light spot centroid position imaged by the coarse tracking camera 15, further detects off-target amount information of a light spot center, converts the off-target amount information into an angle corresponding to deflection of incident light, decomposes the angle into angles and control voltages 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 corresponding control voltages to realize coarse tracking of the light beam. The data processing module detects a light spot centroid position imaged by the fine tracking camera 16, further detects off-target amount information of a light spot center, converts the off-target amount information into an angle and a control voltage corresponding to deflection of the fine tracking galvanometer 6, and then loads the corresponding control voltage to realize fine tracking of the light beam.

[0057] In order to reduce the overall volume of the non-rotating space laser communication system, the triangular reflector 4 is further arranged, the triangular reflector 4 comprises a first reflecting surface and a second reflecting surface, the first reflecting surface is located between the beam-reducing module 3 and the liquid crystal spatial light modulator 5 along the light path, the second reflecting surface is located between the liquid crystal spatial light modulator 5 and the fine tracking galvanometer 6 along the light path, the liquid crystal spatial light modulator 5 is located on the reflected light path of the first reflecting surface of the triangular reflector 4 and on the incident light path of the second reflecting surface; the adjustable phase retarder 1, the liquid crystal polarization grating module 2, the beam-reducing module 3 and the fine tracking galvanometer 6 are coaxially arranged, the initial included angle between the fine tracking galvanometer 6 and the central axis is 45°, the triangular reflector 4 is located on the central axis between the beam-reducing module 3 and the fine tracking galvanometer 6, the three angles are 43.5°, 43.5° and 93° respectively, the included angle between the first reflecting surface and the central axis is 136.5°, the included angle between the second reflecting surface and the central axis is 43.5°, the liquid crystal spatial light modulator 5 is located on the extension line of the middle line of the triangular reflector 4 and is perpendicular to the extension line, so that the angle of the incident light entering the liquid crystal spatial light modulator 5 is reduced, the device performance is improved, the first reflecting surface deflects the optical signal to the liquid crystal spatial light modulator 5 at an incident angle of 3°, the optical signal is reflected by the liquid crystal spatial light modulator 5 and is deflected to the fine tracking galvanometer 6 on the second reflecting surface at the original angle.

[0058] The coarse tracking camera 15 is a CCD, CMOS infrared camera or a four-quadrant detector, and the fine tracking camera 16 is a CCD, CMOS infrared camera or a four-quadrant detector; the beam-reducing ratio N of the beam-reducing module 3 is 8-10, and the apertures of the adjustable phase retarder 1 and the liquid crystal polarization grating 201 are N times of the aperture 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 the space laser beam, and when receiving the laser beam emitted by the communication target, the following steps are included:

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

[0061] Step 2: Under the action of the 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 pass through the initial deflection angle, and the laser beam passes through the adjustable phase retarder 1, the liquid crystal polarization grating module 2, the beam-reducing module 3, the first reflecting surface, the liquid crystal spatial light modulator 5, the second reflecting surface, the fine tracking galvanometer 6, the first beam splitter 7 and the coarse tracking coupling optical assembly 10 in sequence, and forms a light spot on the light-sensitive surface of the coarse tracking camera 15, and the coarse tracking camera 15 images the light spot.

[0062] Step 3, the data processing module receives the imaging of the coarse tracking camera 15, detects the off-target information of the spot centroid, and determines whether it meets the following conditions:

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

[0064] If it meets, the coarse tracking is completed, and the next step is entered;

[0065] If it does not meet, the corresponding angle of deflection is calculated according to the off-target information of the spot centroid, the angle is decomposed into the angle 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 is returned 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 assembly 13, and forms a spot on the light-sensitive surface of the fine tracking camera 16, which images it;

[0067] Step 5, the fine tracking camera 16 outputs the imaging to the data processing module, which detects the off-target information of the spot centroid and determines whether it meets the following conditions:

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

[0069] If it meets, the fine tracking is completed, and the next step is entered;

[0070] If it does not meet, the corresponding angle of deflection is calculated according to the off-target information of the spot centroid, the angle is converted into the angle of deflection of the fine tracking galvanometer 6 and the control voltage information, the fine tracking galvanometer 6 is loaded with the corresponding control voltage information, and the fine tracking galvanometer 6 rotates under the action of the control voltage information, and then returns to step 4;

[0071] Step 6, the spot centroid is kept at the center of the fine tracking camera 16, and the fine tracking state is continuously maintained. At this time, the laser beam passes through the third beam splitter 9 and is coupled into the optical communication transceiver 14 by the receiving coupling optical assembly 12.

[0072] When transmitting a communication target laser beam, the following steps are included:

[0073] Step 1, according to the received initial position of the communication target and the initial position information of itself, 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 fine tracking galvanometer 6 is placed at the initial position;

[0074] Step 2, the adjustable phase delay device 1, the liquid crystal polarization grating module 2 and the liquid crystal spatial light modulator 5 are controlled by the voltage control information, and the beacon light of the communication target is deflected by an initial deflection angle to form a light spot on the light-sensitive surface of the coarse tracking camera 15, and the coarse tracking camera 15 images the light spot;

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

[0076] The distance between the light spot centroid and the center pixel of the coarse tracking camera 15 is less than or equal to 1 pixel;

[0077] If the conditions are met, the coarse tracking is completed, and the next step is entered;

[0078] If the conditions are not met, the angle corresponding to the deflection is calculated according to the off-target amount information of the light spot centroid, the angle is decomposed into the angles corresponding to the adjustable phase delay device 1, the liquid crystal polarization grating module 2 and the liquid crystal spatial light modulator 5, and the corresponding voltage control information is returned to step 2;

[0079] Step 4, the beacon light enters the fine tracking module to form a light spot on the light-sensitive surface of the fine tracking camera 16, and the fine tracking camera 16 images the light spot;

[0080] Step 5, the fine tracking camera 16 outputs the image to the data processing module, and the data processing module detects the off-target amount information of the light spot centroid and judges whether the off-target amount information meets the following conditions:

[0081] The distance between the light spot centroid and the center pixel of the fine tracking camera 16 is less than or equal to 1 pixel;

[0082] If the conditions are met, the fine tracking is completed, and the next step is entered;

[0083] If the conditions are not met, the angle corresponding to the deflection is calculated according to the off-target amount information of the light spot centroid, the angle is converted into the angle of the fine tracking galvanometer 6 and the control voltage information, the fine tracking galvanometer 6 is loaded with the corresponding control voltage information, the fine tracking galvanometer 6 rotates under the action of the control voltage information, and then the step 4 is returned;

[0084] Step 6, the light spot centroid is kept at the center of the fine tracking camera 16, and the fine tracking state is maintained. The light communication transceiver 14 outputs the modulated communication signal light beam, which passes through the transmitting coupling optical assembly 11, the second beam splitter 8, the first beam splitter 7, the fine tracking galvanometer 6, the second reflecting surface, the liquid crystal spatial light modulator 5, the first reflecting surface, the beam shrinking module 3, the liquid crystal polarization grating module 2 and the adjustable phase delay device 1 in sequence, and is deflected to the communication target direction.

[0085] Through the above examples, it can be seen that the non-rotating space laser communication system based on the liquid crystal phase control device of the present application can replace the traditional mechanical turntable, and a coarse tracking system of the non-rotating type is formed by combining the adjustable phase delay device 1, the liquid crystal polarization grating 201 and the liquid crystal spatial light modulator 5, thereby greatly reducing the volume, weight and power consumption of the space laser communication system. Meanwhile, 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-reducing module 3, and the liquid crystal spatial light modulator 5 is placed at the rear end of the telescope system, thereby solving the problem of a small light aperture of the coarse tracking system using only the spatial light modulator, and the space laser communication application requirement of a large aperture can be met. In addition, the combination of the liquid crystal polarization grating 201 and the liquid crystal spatial light modulator 5 solves the problems that the liquid crystal polarization grating 201 can only realize discrete angle deflection and the liquid crystal spatial light modulator 5 can only realize small-angle deflection, and arbitrary angle beam deflection in a large angle range is realized.

Claims

1. A non-rotating space laser communication system based on liquid crystal phase control device, characterized in that: it comprises an adjustable phase retarder (1), a liquid crystal polarization grating module (2), a beam-reducing 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 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 through the adjustable phase retarder (1) to control the discrete angle deflection thereof; the beam-reducing module (3) is used to reduce the aperture of the incident light 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 realize continuous deflection of the angle of the incident light; the fine 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 deliver it to the coarse tracking module, the fine tracking module and the communication module respectively, while delivering the output optical signal of the communication module to the fine tracking galvanometer (6) and then sequentially through the liquid crystal spatial light modulator (5), the beam-reducing module (3), the liquid crystal polarization grating module (2) and the adjustable phase retarder (1) for output. It further comprises a triangular reflector (4) comprising a first reflecting surface and a second reflecting surface. The first reflecting surface is located between the beam-reducing module (3) and the liquid crystal spatial light modulator (5), and the second reflecting surface is located between the liquid crystal spatial light modulator (5) and the fine tracking galvanometer (6). The beam-reducing module (3) and the fine tracking galvanometer (6) are coaxially arranged, and the triangular reflector (4) is located on the central axis thereof. 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 transmit optical signals, perform photoelectric and electro-optical conversion, and perform signal modulation and demodulation. The data processing module is 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) respectively, and is used to receive the imaging of the coarse tracking module and the fine tracking module, emit 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 emit feedback voltage to the fine tracking galvanometer (6) according to the imaging of the fine tracking module. 2.The non-rotating space laser communication system based on liquid crystal phase control device according to claim 1, characterized in that: the liquid crystal polarization grating module (2) comprises a first liquid crystal polarization grating assembly and a second liquid crystal polarization grating assembly arranged in sequence along the incident light path and having perpendicular deflection directions. 3.The non-rotating space laser communication system based on liquid crystal phase control device according to claim 2, characterized in that: 4.The non-rotating space laser communication system based on liquid crystal phase control device according to any one of claims 1-3, characterized in that: ​ ​ The first liquid crystal polarization grating component includes 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 in turn from the beamlet module (3) to the adjustable phase retarder (1), where 1≤n≤6. The second liquid crystal polarization grating component includes 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 in turn from the beamlet module (3) to the adjustable phase retarder (1), where 1≤m≤6. ​ The light splitting module comprises a first light splitting mirror (7), a second light splitting mirror (8), and a third light splitting mirror (9); the first light splitting mirror (7) is arranged on the reflection light path of the fine tracking galvanometer (6) and reflects and transmits the reflected light of the fine tracking galvanometer (6); the coarse tracking module is arranged on the transmission light path of the first light splitting mirror (7); The second light splitting mirror (8) is arranged on the reflection light path of the first light splitting mirror (7) and reflects and transmits the reflected light of the first light splitting mirror (7); the third light splitting mirror (9) is arranged on the transmission light path of the second light splitting mirror (8) and reflects and transmits the transmitted light of the second light splitting mirror (8); The communication module is arranged on the reflection light path of the second light splitting mirror (8) and the third light splitting mirror (9); and the fine tracking module is arranged on the transmission light path of the third light splitting mirror (9).

5. The non-rotating space laser communication system based on the liquid crystal phase control device according to claim 4, characterized in that: The coarse tracking module comprises a coarse tracking coupling optical assembly (10) and a coarse tracking camera (15) arranged in sequence; the coarse tracking coupling optical assembly (10) is used for focusing the light beam onto the light-sensitive 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 assembly (13) and a fine tracking camera (16) arranged in sequence; the fine tracking coupling optical assembly (13) is used for focusing the light beam onto the light-sensitive 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.

6. The non-rotating space laser communication system based on the liquid crystal phase control device according to claim 5, characterized in that: The communication module comprises a receiving coupling optical assembly (12), a transmitting coupling optical assembly (11), and an optical communication transceiver (14); the transmitting coupling optical assembly (11) is arranged on the reflection light path of the second light splitting mirror (8); the output light of the optical communication transceiver (14) is collimated and transmitted through the transmitting coupling optical assembly (11) to the second light splitting mirror (8), reflected by the second light splitting mirror (8), and then reflected by the first light splitting mirror (7) to the fine tracking galvanometer (6); The receiving coupling optical assembly (12) is arranged on the reflection light path of the third light splitting mirror (9) and is arranged corresponding to the input end of the optical communication transceiver (14) to focus the reflected light of the third light splitting mirror (9) to the input end of the optical communication transceiver (14).

7. The non-rotating space laser communication system based on the liquid crystal phase control device according to claim 6, characterized in that: The coarse tracking camera (15) is a CCD, CMOS infrared camera, or a four-quadrant detector; The fine tracking camera (16) is a CCD, CMOS infrared camera, or a four-quadrant detector; The beam-reducing ratio N of the beam-reducing module (3) is 8-10, and the apertures of the adjustable phase delay device (1) and the liquid crystal polarization grating module are N times of the aperture of the liquid crystal spatial light modulator (5).

8. A non-rotating space laser communication method based on the liquid crystal phase control device, based on the non-rotating space laser communication system based on the liquid crystal phase control device according to any one of claims 1-7, characterized in that, The method comprises the following steps: S1. According to the received initial position of the communication target and the initial position information of itself, the data processing module analyzes the initial deflection angle and converts the angle information into voltage control information, which is loaded on the adjustable phase delay device (1), the liquid crystal polarization grating module (2) and the liquid crystal spatial light modulator (5) respectively; S2. The adjustable phase delay device (1), the liquid crystal polarization grating module (2) and the liquid crystal spatial light modulator (5) make the laser beam or beacon light emitted by the communication target incident and deflect under the action of the voltage control information, and the coarse tracking module receives and images it; S3. The data processing module receives the imaging of the coarse tracking module, detects the off-target amount information of the spot centroid thereon, and judges whether it meets the following conditions: The distance between the spot centroid and the center pixel of the coarse tracking module is ≤1 pixel; If it meets, the coarse tracking is completed, and the next step is entered; If it does not meet, the angle corresponding to the deflection required is calculated according to the off-target amount information of the spot centroid, the angle is decomposed into the corresponding angle of the adjustable phase delay device (1), the liquid crystal polarization grating module (2) and the liquid crystal spatial light modulator (5), and the corresponding voltage control information is returned to step S2; S4. The fine tracking module images the laser beam or beacon light after the coarse tracking is completed; S5. The data processing module receives the imaging of the fine tracking module, detects the off-target amount information of the spot centroid thereon, and judges whether it meets the following conditions: The distance between the spot centroid and the center pixel of the fine tracking module is ≤1 pixel; If it meets, the fine tracking is completed, and the next step is entered; If it does not meet, the angle corresponding to the deflection required is calculated according to the off-target amount information of the spot centroid, the angle is converted into the deflection angle and control voltage information of the fine tracking galvanometer (6), 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 S4; S6. The fine tracking state is maintained, the laser beam passes through the light splitting module, and the communication module receives it to complete the signal reception; or the fine tracking state is maintained, the communication module outputs the modulated communication signal beam, which is deflected to the direction of the communication target.

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