Spatial laser communication method and system based on cascaded liquid crystal polarization grating device

Abstract

This invention discloses a space laser communication method and system based on cascaded liquid crystal polarization grating devices, belonging to the field of space laser communication technology. The cascaded liquid crystal polarization grating module performs discrete deflection based on the phase of an electronically controlled liquid crystal to output a coarse pointing beam, while a fine tracking deflection module performs continuous angle compensation. The control module generates a status code based on the coarse tracking error and outputs a grating drive signal by looking up a table; it drives the fine tracking deflection module based on the fine tracking error, and when the continuous compensation angle reaches its upper limit or the pointing error exceeds the limit, it updates the status code based on the continuous compensation angle or pointing error, drives the grating to discrete deflection, and resets the fine tracking deflection module to zero. This invention achieves wide-range, high-precision, and stable pointing control through the synergy of non-mechanical discrete coarse pointing and continuous fine tracking, combined with lookup table driving, saturation unloading, and pointing monitoring mechanisms. Furthermore, the combination of multi-channel waveform pre-emphasis driving and Gray code encoding effectively suppresses transient disturbances during state switching.

Description

Technical Field

[0001] This invention relates to the field of space laser communication, specifically to a space laser communication method and system based on cascaded liquid crystal polarization grating devices. Background Technology

[0002] The establishment and maintenance of space laser communication links typically rely on the coordinated control of acquisition, coarse tracking, and fine tracking. The coarse pointing stage often employs a turntable, pan-tilt unit, or mechanical scanning mechanism to achieve wide-range pointing, but this suffers from limitations in inertia, response speed, lifespan and reliability, and micro-vibration coupling. The fine tracking stage often uses fast-reflection mirrors or other fine tracking deflection modules to achieve high-bandwidth continuous angle compensation. However, the compensation angle range of these modules is limited. When the coarse pointing deviation is large or external disturbances are strong, the fine tracking deflection module easily reaches its compensation angle limit, leading to decreased closed-loop stability or even link loss.

[0003] To overcome the limitations of mechanical beam control, the industry has begun exploring non-mechanical beam deflection technologies based on electronically controlled devices. Among these, liquid crystal phase modulation devices, especially liquid crystal polarization gratings, have shown promising application prospects. These devices modulate the phase of incident light by changing the applied electric field to control the alignment of liquid crystal molecules, thereby achieving beam deflection. They possess potential advantages such as no inertia, flexible control, and low power consumption.

[0004] However, when used for pointing control in space laser communication, it is still necessary to solve the deterministic driving of discrete deflection states, the mapping relationship between discrete states and control signals, the unloading and coarse pointing takeover when fine tracking compensation is saturated, and the monitoring and triggering mechanism for abnormal pointing errors, so as to ensure the continuity and stability of the pointing control process. Summary of the Invention

[0005] The purpose of this invention is to provide a solution to one of the aforementioned problems existing in the prior art. Specifically, this invention is achieved through the following technical solution: The space laser communication method based on cascaded liquid crystal polarization grating devices includes the following steps: Step 1: The optical antenna receives the incident beam, the beam-shrinking module shrinks the incident beam to obtain the beam-shrinking beam, and the cascaded liquid crystal polarization grating module performs phase modulation on the beam-shrinking beam based on the electronically controlled liquid crystal phase and discretely deflects it to output a coarse pointing beam. Step 2: The first beam splitting module splits the coarse pointing beam to obtain a coarse sampled beam, and the coarse tracking detector outputs a coarse tracking error signal to the control module based on the coarse sampled beam. Step 3: The fine tracking deflection module continuously compensates the coarse pointing beam to output a fine pointing beam, the second beam splitting module splits the fine pointing beam to obtain a fine sampling beam, and the fine tracking detector outputs a fine tracking error signal to the control module and the pointing monitoring module based on the fine sampling beam. Step 4: The control module stores the status code mapping table, generates a status code based on the coarse tracking error signal, and performs a table lookup output. The table lookup output is the output of the grating drive signal to the cascaded liquid crystal polarization grating module based on the status code in the status code mapping table. Step 5: The control module calculates the continuous compensation angle and its absolute value based on the fine tracking error signal, and outputs the fast-reflection mirror drive signal to the fine tracking deflection module. When the absolute value of the continuous compensation angle reaches the upper limit of the compensation angle of the fine tracking deflection module, the control module calculates the status code update amount based on the continuous compensation angle and updates the status code, resets the continuous compensation angle to 0 angle, and outputs the fast-reflection mirror drive signal to the fine tracking deflection module. The control module performs a table lookup output based on the updated status code. Step 6: The pointing monitoring module calculates the pointing error amplitude based on the fine tracking error signal. When the pointing error amplitude is greater than the pointing error threshold, the control module calculates the status code update amount based on the pointing error amplitude and updates the status code. The continuous compensation angle is reset to 0 angle and the fast-reflection mirror drive signal is output to the fine tracking deflection module. The control module performs a lookup table output based on the updated status code.

[0006] Furthermore, the beam-shrinking module shrinks the incident beam to obtain a beam-shrinking beam, including: a reflective telescope system, which compresses the incident beam to the aperture range of the cascaded liquid crystal polarization grating module.

[0007] Furthermore, the cascaded liquid crystal polarization grating module is a multi-layer stacked structure consisting of multiple electrically controlled liquid crystal half-wave plate layers and multiple liquid crystal polarization grating (LCPG) layers stacked alternately.

[0008] Furthermore, the cascaded liquid crystal polarization grating module performs phase modulation on the beam-contracting beam based on the electronically controlled liquid crystal phase and discretely deflects it to output a coarse pointing beam, including: The deflection angle of the coarse pointing beam belongs to the discrete deflection angle set, which is based on the grating period setting of the liquid crystal polarization grating (LCPG) layer.

[0009] Furthermore, the first beam splitting module splits the coarse pointing beam to obtain a coarse sampled beam, comprising: the first beam splitting module is disposed between the output optical path of the cascaded liquid crystal polarization grating module and the incident optical path of the fine tracking deflection module.

[0010] Furthermore, the second beam splitting module splits the finely pointing beam to obtain a finely sampled beam, including: the second beam splitting module is set in the output optical path of the fine tracking deflection module.

[0011] Furthermore, the fine tracking deflection module outputs a fine pointing beam after continuous angle compensation of the coarse pointing beam, including: a fast reflecting mirror and a fast reflecting mirror driver, wherein the fast reflecting mirror driver drives the fast reflecting mirror to perform continuous angle compensation based on the fast reflecting mirror drive signal.

[0012] Furthermore, the grating driving signal includes: The grating driving signal is a multi-channel voltage waveform signal, which includes a first voltage waveform sub-signal and a second voltage waveform sub-signal. The first voltage waveform sub-signal is loaded onto multiple electrically controlled liquid crystal half-wave plate layers, and the second voltage waveform sub-signal is loaded onto multiple liquid crystal polarization grating (LCPG) layers. When updating the status code, the first voltage waveform sub-signal and the second voltage waveform sub-signal sequentially include a pre-emphasis voltage segment, a steady-state voltage segment, and a reverse pre-emphasis voltage segment. The voltage amplitude of the pre-emphasis voltage segment is greater than that of the steady-state voltage segment, and the voltage amplitude of the reverse pre-emphasis voltage segment is greater than that of the steady-state voltage segment.

[0013] Furthermore, the status codes are encoded using Gray code, including a bit flip of 1 between adjacent status codes.

[0014] A space laser communication system based on cascaded liquid crystal polarization grating devices, using the aforementioned space laser communication method based on cascaded liquid crystal polarization grating devices, includes: an optical antenna, a beam-shrinking module, a cascaded liquid crystal polarization grating module, a first beam-splitting module, a coarse tracking detector, a fine tracking deflection module, a second beam-splitting module, a fine tracking detector, a control module, and a pointing monitoring module. An optical antenna, a beam-shrinking module, a cascaded liquid crystal polarization grating module, and a fine tracking deflection module are sequentially connected along the main optical path; a first beam-splitting module is located between the output optical path of the cascaded liquid crystal polarization grating module and the incident optical path of the fine tracking deflection module, and a second beam-splitting module is located in the output optical path of the fine tracking deflection module. The coarse tracking detector is used to output a coarse tracking error signal to the control module based on the coarse sampled beam obtained by the first beam splitting module, and the fine tracking detector is used to output a fine tracking error signal to the control module and the pointing monitoring module based on the fine sampled beam obtained by the second beam splitting module. The control module is used to store the status code mapping table. The control module is used to generate status codes based on the coarse tracking error signal and perform table lookup output. The table lookup output is to look up the status code in the status code mapping table and output the grating drive signal to the cascaded liquid crystal polarization grating module. The control module is used to calculate the continuous compensation angle based on the fine tracking error signal, calculate the absolute value of the continuous compensation angle, and output the fast-reflection mirror drive signal to the fine tracking deflection module. When the absolute value of the continuous compensation angle reaches the upper limit of the compensation angle of the fine tracking deflection module, the control module is used to calculate the status code update amount based on the continuous compensation angle, update the status code, reset the continuous compensation angle to 0 angle, output the fast-reflection mirror drive signal to the fine tracking deflection module, and perform table lookup output based on the updated status code. The pointing monitoring module is used to calculate the pointing error amplitude based on the fine tracking error signal. When the pointing error amplitude is greater than the pointing error threshold, it triggers the control module to calculate the status code update amount based on the pointing error amplitude, update the status code, reset the continuous compensation angle to 0 angle, and output the fast-reflection mirror drive signal to the fine tracking deflection module. It also performs a table lookup output based on the updated status code.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: The cascaded liquid crystal polarization grating module, as a non-mechanical coarse pointing actuator, realizes discrete coarse pointing and features no inertia and fast response. The fine tracking deflection module realizes continuous angle compensation to meet the requirements of high-precision fine tracking. Through the status code mapping table and lookup table output mechanism, the deterministic mapping between discrete states and grating drive signals is realized. Through the status code update triggered by the compensation angle upper limit and the pointing error threshold and the fine tracking zero return mechanism, the fine tracking saturation unloading and coarse pointing takeover are realized, improving the continuity and stability of the pointing control process. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of a space laser communication method based on cascaded liquid crystal polarization grating devices. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are for illustrative purposes only and are not intended to limit the invention. It should be noted that this invention is already in the actual research and development stage.

[0018] Example 1 like Figure 1 As shown, the space laser communication method based on cascaded liquid crystal polarization grating devices includes the following steps: Step 1: The optical antenna receives the incident beam, the beam-shrinking module shrinks the incident beam to obtain the beam-shrinking beam, and the cascaded liquid crystal polarization grating module performs phase modulation on the beam-shrinking beam based on the electronically controlled liquid crystal phase and discretely deflects it to output a coarse pointing beam. Step 2: The first beam splitting module splits the coarse pointing beam to obtain a coarse sampled beam, and the coarse tracking detector outputs a coarse tracking error signal to the control module based on the coarse sampled beam. Step 3: The fine tracking deflection module continuously compensates the coarse pointing beam to output a fine pointing beam, the second beam splitting module splits the fine pointing beam to obtain a fine sampling beam, and the fine tracking detector outputs a fine tracking error signal to the control module and the pointing monitoring module based on the fine sampling beam. Step 4: The control module stores the status code mapping table, generates a status code based on the coarse tracking error signal, and performs a table lookup output. The table lookup output is the output of the grating drive signal to the cascaded liquid crystal polarization grating module based on the status code in the status code mapping table. Step 5: The control module calculates the continuous compensation angle and its absolute value based on the fine tracking error signal, and outputs the fast-reflection mirror drive signal to the fine tracking deflection module. When the absolute value of the continuous compensation angle reaches the upper limit of the compensation angle of the fine tracking deflection module, the control module calculates the status code update amount based on the continuous compensation angle and updates the status code, resets the continuous compensation angle to 0 angle, and outputs the fast-reflection mirror drive signal to the fine tracking deflection module. The control module performs a table lookup output based on the updated status code. Step 6: The pointing monitoring module calculates the pointing error amplitude based on the fine tracking error signal. When the pointing error amplitude is greater than the pointing error threshold, the control module calculates the status code update amount based on the pointing error amplitude and updates the status code. The continuous compensation angle is reset to 0 angle and the fast-reflection mirror drive signal is output to the fine tracking deflection module. The control module performs a lookup table output based on the updated status code.

[0019] Specifically, the optical antenna receives the incident light beam and couples it into the beam-shrinking module. The beam-shrinking module compresses the incident light beam to the aperture range of the cascaded liquid crystal polarization grating module. The cascaded liquid crystal polarization grating module is a non-mechanical beam deflection device based on the phase of an electrically controlled liquid crystal. It modulates the phase of the transmitted light wavefront by adjusting the alignment of liquid crystal molecules with voltage, thereby producing a discrete and quantitative coarse beam deflection effect.

[0020] The discrete deflection angle set is set according to the grating period of the LCPG layer; under the selected operating wavelength and diffraction order, the grating period is used to configure the available angle set range of the discrete deflection angle set: in, For the first Discrete deflection angles corresponding to first-order diffraction. For the operating wavelength, The grating period of the liquid crystal polarization grating (LCPG) layer. This refers to the diffraction order.

[0021] To ensure the reproducibility of the quantization calculation of the status code update, this embodiment defines the angle step size based on a discrete set of deflection angles: in, The angle step size is the set of discrete deflection angles. For the set of discrete deflection angles, the first Each angle element For the set of discrete deflection angles, the first Each angle element This is the index of the angle element.

[0022] The discrete deflection angle set is generated from a pre-specified set of diffraction orders. The control module stores the set of diffraction orders and the working wavelength as task configuration parameters and establishes an index sequence for the discrete deflection angle set accordingly. The index sequence is used for subsequent status code generation and updating.

[0023] In one reproducible implementation, the angle step size of the discrete deflection angle set is taken as the average of the adjacent angle differences of the discrete deflection angle set, while in another reproducible implementation, the angle step size of the discrete deflection angle set is taken as the preset step size configured for the task.

[0024] The first beam splitting module splits the coarse pointing beam to obtain a coarse sampled beam, and the coarse tracking detector outputs a coarse tracking error signal to the control module based on the coarse sampled beam.

[0025] In a reproducible implementation, the coarse tracking detector outputs image plane displacement. The control module is based on the equivalent focal length of the coarse tracking imaging optical path. Converted to equivalent angular error components : in, To coarsely track the first axial equivalent angular error component, To coarsely track the equivalent angular error component of the second axis, To coarsely track the displacement of the first axial image plane, To coarsely track the displacement of the second axial image plane, This is the equivalent focal length of the coarse tracking imaging optical path.

[0026] The control module generates status codes based on the coarse tracking error signal. In a reproducible implementation, the control module will... The target pointing angle vector is mapped to the target index of the discrete deflection angle set, and the nearest neighbor quantization is used to map the target pointing angle vector to the target index. The status code corresponding to the target index is used as the generation result.

[0027] In one implementation, the quantization step size for nearest-neighbor quantization is taken as the angle step size of the discrete deflection angle set. In another implementation, the quantization step size for nearest-neighbor quantization is taken as the adjacent angle difference table derived from the index sequence of the discrete deflection angle set.

[0028] The fine tracking deflection module continuously compensates the coarse pointing beam to output a fine pointing beam. The second beam splitting module splits the fine pointing beam to obtain a fine sampling beam. The fine tracking detector outputs a fine tracking error signal to the control module and the pointing monitoring module based on the fine sampling beam.

[0029] The fine-tracking detector outputs image plane displacement in a feasible manner. The control module is based on the equivalent focal length of the fine-tracking imaging optical path. Converted to equivalent angular error components : in, To accurately track the first axial equivalent angular error component, To accurately track the equivalent angular error component of the second axis, To accurately track the displacement of the first axial image plane, To accurately track the displacement of the second axial image plane, Equivalent focal length for precise tracking imaging optical path: in, This is the equivalent angle error for precise tracking used by the control module for continuous compensation calculation.

[0030] The control module calculates the continuous compensation angle based on the fine tracking error signal, and generates a fast-reflection mirror drive signal from the continuous compensation angle, which is then output to the fine tracking deflection module. This embodiment provides an example of proportional control: in, For continuous compensation angles, This is the proportionality coefficient; in, This is the absolute value of the continuous compensation angle.

[0031] The upper limit of the compensation angle for the precision tracking deflection module is obtained through calibration and stored in the control module memory in angular units. The unit of the upper limit of the compensation angle is radians or milliradians; the proportional coefficient... The proportionality coefficient is determined during the calibration phase. The example value range is 0.2 to 5.0.

[0032] When the absolute value of the continuous compensation angle reaches the upper limit of the compensation angle of the fine tracking deflection module, the control module calculates the status code update amount based on the continuous compensation angle and updates the status code, resets the continuous compensation angle to 0 angle and outputs the fast-reflection mirror drive signal to achieve fine tracking return to zero; the control module then looks up the updated status code in the status code mapping table and outputs a new grating drive signal to achieve coarse pointing control.

[0033] In a reproducible implementation, the control module uses quantization updates to update status codes: in, For status code update quantity, This is the rounding function.

[0034] To ensure that the status code always falls within the range of the available discrete deflection angle set index, the control module performs boundary processing on the updated status code index.

[0035] in, For the updated status code index, This is the index of the status code before the update. The number of elements in the discrete deflection angle set. This is the amplitude limiting function.

[0036] The pointing monitoring module calculates the pointing error amplitude based on the fine tracking error signal and compares it with a pointing error threshold. In a reproducible implementation, the pointing monitoring module... Execution time window averaging filter to obtain And calculate the pointing error magnitude: in, This refers to the magnitude of the pointing error. To point to the monitoring module The first axial component is obtained by performing time-window averaging filtering. To point to the monitoring module The second axial component is obtained by performing time window averaging filtering.

[0037] The time window length is given by the task configuration, with an example range of 1 ms to 100 ms. When the pointing error amplitude exceeds the pointing error threshold, the pointing monitoring module triggers the control module to calculate the status code update based on the pointing error amplitude, update the status code, reset the continuous compensation angle to 0, and output the fast-reflection mirror drive signal. The control module looks up the updated status code in the status code mapping table and outputs the grating drive signal to achieve coarse pointing reconfiguration. The pointing error threshold is set by the task configuration method and stored in angle units; an example range of 0.2 mrad to 2.0 mrad for the pointing error threshold; and an example range of 0.5 mrad to 5.0 mrad for the upper limit of the compensation angle of the fine tracking deflection module.

[0038] The control module stores a status code mapping table. The status code mapping table uses the status code as the index key, and each mapping record includes at least the set of grating drive signal parameters corresponding to that status code. The grating drive signal can be a single-channel voltage waveform signal or a multi-channel voltage waveform signal. When a single-channel voltage waveform signal is used, the mapping record only configures the first sub-signal field and not the second sub-signal field. The table lookup output only outputs the pre-emphasis voltage segment amplitude, steady-state voltage segment amplitude, reverse pre-emphasis voltage segment amplitude, and the pre-emphasis voltage segment duration, steady-state voltage segment duration, and reverse pre-emphasis voltage segment duration corresponding to the first sub-signal field.

[0039] When using multi-channel voltage waveform signals, the mapping record is configured with at least two sets of sub-signal parameters. To ensure reproducible implementation, this embodiment provides an example of a mapping record field: The lookup table output timing is defined as follows: the control module at time... After completing status code generation or status code update, read the mapping record and perform a check on the first sub-signal. Output pre-emphasis voltage section, in Output steady-state voltage range, in Output reverse pre-emphasis voltage segment; for the second sub-signal in Output pre-emphasis voltage section, in Output steady-state voltage range, in Output reverse pre-emphasis voltage segment.

[0040] In one synchronous output implementation, the control module is set... , , .

[0041] In one example configuration, the duration of the pre-emphasis voltage segment is set to 0.1 ms to 2 ms, the duration of the steady-state voltage segment is set to 1 ms to 50 ms, and the duration of the reverse pre-emphasis voltage segment is set to 0.1 ms to 2 ms; these parameters are determined based on the liquid crystal layer response time constant and written into the status code mapping table during the calibration phase.

[0042] Example 2 A space laser communication system based on cascaded liquid crystal polarization grating devices, using the aforementioned space laser communication method based on cascaded liquid crystal polarization grating devices, includes: an optical antenna, a beam-shrinking module, a cascaded liquid crystal polarization grating module, a first beam-splitting module, a coarse tracking detector, a fine tracking deflection module, a second beam-splitting module, a fine tracking detector, a control module, and a pointing monitoring module. An optical antenna, a beam-shrinking module, a cascaded liquid crystal polarization grating module, and a fine tracking deflection module are sequentially connected along the main optical path; a first beam-splitting module is located between the output optical path of the cascaded liquid crystal polarization grating module and the incident optical path of the fine tracking deflection module, and a second beam-splitting module is located in the output optical path of the fine tracking deflection module. The coarse tracking detector is used to output a coarse tracking error signal to the control module based on the coarse sampled beam obtained by the first beam splitting module, and the fine tracking detector is used to output a fine tracking error signal to the control module and the pointing monitoring module based on the fine sampled beam obtained by the second beam splitting module. The control module is used to store the status code mapping table. The control module is used to generate status codes based on the coarse tracking error signal and perform table lookup output. The table lookup output is to look up the status code in the status code mapping table and output the grating drive signal to the cascaded liquid crystal polarization grating module. The control module is used to calculate the continuous compensation angle based on the fine tracking error signal, calculate the absolute value of the continuous compensation angle, and output the fast-reflection mirror drive signal to the fine tracking deflection module. When the absolute value of the continuous compensation angle reaches the upper limit of the compensation angle of the fine tracking deflection module, the control module is used to calculate the status code update amount based on the continuous compensation angle, update the status code, reset the continuous compensation angle to 0 angle, output the fast-reflection mirror drive signal to the fine tracking deflection module, and perform table lookup output based on the updated status code. The pointing monitoring module is used to calculate the pointing error amplitude based on the fine tracking error signal. When the pointing error amplitude is greater than the pointing error threshold, it triggers the control module to calculate the status code update amount based on the pointing error amplitude, update the status code, reset the continuous compensation angle to 0 angle, and output the fast-reflection mirror drive signal to the fine tracking deflection module. It also performs a table lookup output based on the updated status code.

[0043] In one extended implementation of the communication transceiver system, the space laser communication pointing control system enters the communication state after completing acquisition, coarse tracking, and fine tracking. The system further includes a communication detection unit, a communication transmitting unit, and a transceiver combining / splitting optical path. The communication detection unit performs photoelectric conversion on the communication optical signal and outputs a communication receiving signal, which is used for demodulation to obtain communication data. The communication transmitting unit modulates the local communication data onto a laser carrier and outputs a transmitted beam.

[0044] During communication reception, the beacon light signal or communication light signal emitted by the distant communication target passes sequentially through the optical antenna and beam-shrinking module along the receiving optical path, entering the cascaded liquid crystal polarization grating module to form a coarse pointing beam. This coarse pointing beam is then continuously angle-compensated by the fine tracking deflection module to form a fine pointing beam. The transmit / receive combining / splitting optical path splits the fine pointing beam using at least one of the following methods: a third beam splitting module, a color beam combining module, a polarization beam splitting module, or an optical ring structure, allowing the communication light signal in the fine pointing beam to enter the communication detection unit. The communication detection unit performs photoelectric conversion on the communication light signal and outputs a communication received signal. The control module and pointing monitoring module maintain the pointing closed loop based on the fine tracking error signal output by the fine tracking detector, ensuring that the communication detection unit continuously receives a stable communication light signal.

[0045] During communication transmission, the communication transmitting unit outputs a transmission beam. The transmit / receive combining / splitting optical path couples the transmission beam to a transmission optical path that shares or nearly shares the same aperture as the receiving optical path. This causes the transmission beam to propagate along a path opposite to the receiving optical path and be collimated by an optical antenna before being emitted towards the communication target. The transmission optical path sequentially passes through a fine-tracking deflection module and a cascaded liquid crystal polarization grating module. The control module outputs a grating drive signal based on a status code mapping table to set the discrete deflection state of the cascaded liquid crystal polarization grating module, and outputs a fast-reflection mirror drive signal to drive the fine-tracking deflection module to perform continuous angle compensation, thereby ensuring that the transmission beam and the fine-pointing beam maintain consistent pointing. To improve the acquisition and alignment efficiency of the transmission link, a nutation mirror module can be optionally installed in the transmission optical path. The nutation mirror module is used to perform small-angle periodic scanning or point advance compensation scanning of the transmission beam under the drive of the control module. The scanning parameters of the nutation mirror module are determined by the mission configuration or calibration parameters. In a reproducible implementation, the nutation mirror module and the fine tracking deflection module work together in a frequency band division of labor. The nutation mirror module is used for low-frequency scanning or acquisition assistance, while the fine tracking deflection module is used for high-bandwidth residual error suppression.

[0046] In the above-described extended communication transceiver implementation, the communication detection unit, communication transmission unit, transceiver combining and splitting optical path and nutation mirror module are optional modules used to extend the system's ability to perform communication transceiver after the pointing closed loop is stable; the core closed loop of the pointing control method is still achieved by the coordinated implementation of discrete deflection of the cascaded liquid crystal polarization grating module and continuous angle compensation of the fine tracking deflection module.

[0047] Example 3 This embodiment improves upon Embodiments 1 and 2 by refining the status code encoding rules. Gray code encoding is used for the status codes, ensuring that the number of bit flips between adjacent status codes is 1.

[0048] By reducing the number of code bit flips during status code switching, transient disturbances during switching between the control module output interface and multi-channel voltage waveform signals can be reduced, thereby mitigating the risk of transient pointing errors introduced by discrete deflection state switching and improving the stability and repeatability of coarse-fine coordinated control. The status code mapping table uses the Gray code-encoded status code as the index key, and the lookup output locates the corresponding set of grating drive signal parameters based on the Gray code status code.

[0049] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for spatial laser communication based on a cascaded liquid crystal polarization grating device, characterized in that, Includes the following steps: Step 1: The optical antenna receives the incident beam, the beam-shrinking module shrinks the incident beam to obtain the beam-shrinking beam, and the cascaded liquid crystal polarization grating module performs phase modulation on the beam-shrinking beam based on the electronically controlled liquid crystal phase and discretely deflects it to output a coarse pointing beam. Step 2: The first beam splitting module splits the coarse pointing beam to obtain a coarse sampled beam, and the coarse tracking detector outputs a coarse tracking error signal to the control module based on the coarse sampled beam; Step 3: The fine tracking deflection module continuously compensates the coarse pointing beam to output a fine pointing beam, the second beam splitting module splits the fine pointing beam to obtain a fine sampling beam, and the fine tracking detector outputs a fine tracking error signal to the control module and the pointing monitoring module based on the fine sampling beam. Step 4: The control module stores the status code mapping table, generates a status code based on the coarse tracking error signal, and performs a table lookup output. The table lookup output is the output of the grating drive signal to the cascaded liquid crystal polarization grating module based on the status code in the status code mapping table. Step 5: The control module calculates the continuous compensation angle and its absolute value based on the fine tracking error signal, and outputs the fast-reflection mirror drive signal to the fine tracking deflection module. When the absolute value of the continuous compensation angle reaches the upper limit of the compensation angle of the fine tracking deflection module, the control module calculates the status code update amount based on the continuous compensation angle and updates the status code, resets the continuous compensation angle to 0 angle, and outputs the fast-reflection mirror drive signal to the fine tracking deflection module. The control module performs a table lookup output based on the updated status code. Step 6: The pointing monitoring module calculates the pointing error amplitude based on the fine tracking error signal. When the pointing error amplitude is greater than the pointing error threshold, the control module calculates the status code update amount based on the pointing error amplitude and updates the status code. The continuous compensation angle is reset to 0 angle and the fast-reflection mirror drive signal is output to the fine tracking deflection module. The control module performs a lookup table output based on the updated status code.

2. The space laser communication method based on cascaded liquid crystal polarization grating devices according to claim 1, characterized in that, The beam-shrinking module shrinks the incident beam to obtain a beam-shrinking beam, including: a reflective telescope system, which compresses the incident beam to the aperture range of the cascaded liquid crystal polarization grating module.

3. The space laser communication method based on cascaded liquid crystal polarization grating devices according to claim 1, characterized in that, The cascaded liquid crystal polarization grating module is a multi-layered structure consisting of alternating stacks of multiple electrically controlled liquid crystal half-wave plates and multiple liquid crystal polarization grating (LCPG) layers.

4. The space laser communication method based on a cascaded liquid crystal polarization grating device according to claim 1, characterized in that, The cascaded liquid crystal polarization grating module, based on the electronically controlled liquid crystal phase modulation of the beam-contracting beam and its discrete deflection, outputs a coarsely pointing beam, including: The deflection angle of the coarse pointing beam belongs to the discrete deflection angle set, which is based on the grating period setting of the liquid crystal polarization grating (LCPG) layer.

5. The space laser communication method based on a cascaded liquid crystal polarization grating device according to claim 1, characterized in that, The first beam splitting module splits the coarse pointing beam to obtain a coarse sampled beam, comprising: the first beam splitting module is disposed between the output optical path of the cascaded liquid crystal polarization grating module and the incident optical path of the fine tracking deflection module.

6. The space laser communication method based on a cascaded liquid crystal polarization grating device according to claim 1, characterized in that, The second beam splitting module splits the finely pointing beam to obtain a finely sampled beam, including: the second beam splitting module is set in the output optical path of the fine tracking deflection module.

7. The space laser communication method based on a cascaded liquid crystal polarization grating device according to claim 1, characterized in that, The fine tracking deflection module outputs a fine pointing beam after continuous angle compensation of the coarse pointing beam, including a fast reflecting mirror and a fast reflecting mirror driver. The fast reflecting mirror driver drives the fast reflecting mirror to perform continuous angle compensation based on the fast reflecting mirror drive signal.

8. The space laser communication method based on a cascaded liquid crystal polarization grating device according to claim 1, characterized in that, The grating driving signal includes: The grating driving signal is a multi-channel voltage waveform signal, which includes a first voltage waveform sub-signal and a second voltage waveform sub-signal. The first voltage waveform sub-signal is loaded onto multiple electrically controlled liquid crystal half-wave plate layers, and the second voltage waveform sub-signal is loaded onto multiple liquid crystal polarization grating (LCPG) layers. When updating the status code, the first voltage waveform sub-signal and the second voltage waveform sub-signal sequentially include a pre-emphasis voltage segment, a steady-state voltage segment, and a reverse pre-emphasis voltage segment. The voltage amplitude of the pre-emphasis voltage segment is greater than that of the steady-state voltage segment, and the voltage amplitude of the reverse pre-emphasis voltage segment is greater than that of the steady-state voltage segment.

9. The space laser communication method based on a cascaded liquid crystal polarization grating device according to claim 1, characterized in that, The status codes are encoded using Gray code, including a bit flip of 1 between adjacent status codes.

10. A space laser communication system based on cascaded liquid crystal polarization grating devices, characterized in that, The space laser communication method based on a cascaded liquid crystal polarization grating device according to any one of claims 1-9 includes: an optical antenna, a beam-shrinking module, a cascaded liquid crystal polarization grating module, a first beam-splitting module, a coarse tracking detector, a fine tracking deflection module, a second beam-splitting module, a fine tracking detector, a control module, and a pointing monitoring module. An optical antenna, a beam-shrinking module, a cascaded liquid crystal polarization grating module, and a fine tracking deflection module are sequentially connected along the main optical path; a first beam-splitting module is located between the output optical path of the cascaded liquid crystal polarization grating module and the incident optical path of the fine tracking deflection module, and a second beam-splitting module is located in the output optical path of the fine tracking deflection module. The coarse tracking detector is used to output a coarse tracking error signal to the control module based on the coarse sampled beam obtained by the first beam splitting module, and the fine tracking detector is used to output a fine tracking error signal to the control module and the pointing monitoring module based on the fine sampled beam obtained by the second beam splitting module. The control module is used to store the status code mapping table. The control module is used to generate status codes based on the coarse tracking error signal and perform table lookup output. The table lookup output is to look up the status code in the status code mapping table and output the grating drive signal to the cascaded liquid crystal polarization grating module. The control module is used to calculate the continuous compensation angle based on the fine tracking error signal, calculate the absolute value of the continuous compensation angle, and output the fast-reflection mirror drive signal to the fine tracking deflection module. When the absolute value of the continuous compensation angle reaches the upper limit of the compensation angle of the fine tracking deflection module, the control module is used to calculate the status code update amount based on the continuous compensation angle, update the status code, reset the continuous compensation angle to 0 angle, output the fast-reflection mirror drive signal to the fine tracking deflection module, and perform table lookup output based on the updated status code. The pointing monitoring module is used to calculate the pointing error amplitude based on the fine tracking error signal. When the pointing error amplitude is greater than the pointing error threshold, it triggers the control module to calculate the status code update amount based on the pointing error amplitude, update the status code, reset the continuous compensation angle to 0 angle, and output the fast-reflection mirror drive signal to the fine tracking deflection module. It also performs a table lookup output based on the updated status code.

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