A testing device and testing method for a coherent detection laser communication terminal

Abstract

The application provides a kind of testing device and testing method of coherent detection laser communication terminal, for solving the technical problem that the performance of coherent detection laser communication terminal cannot be accurately tested by using existing IM / DD laser communication terminal test system.The testing device comprises a turntable, an optical platform and an optical system, the turntable is located outside the optical platform and is used to carry the laser communication terminal to be tested;The optical system comprises a beam shaping unit, a galvanometer, a 1 / 4 wave plate, a first beam splitter and an optical test system arranged in turn along the outgoing light path of the laser communication terminal to be tested, and a light source system;The light source system is used to provide light source for the laser communication terminal to be tested;The optical test system is used to test the performance of the laser communication terminal to be tested.The testing method can accurately test the emission function, tracking function and communication function of the laser communication terminal to be tested, and the coaxiality of the emission system and tracking system of the laser communication terminal to be tested.

Description

Technical Field

[0001] This invention relates to a laser communication terminal testing method, specifically to a coherent detection laser communication terminal testing device and testing method. Background Technology

[0002] Laser communication is a communication method that uses lasers to transmit information. It has the advantages of large communication capacity, high transmission rate, good confidentiality, small size, light weight and low power consumption. It is currently widely used in various aerospace fields such as remote sensing, navigation, communication, deep space exploration and space stations. It is a powerful communication method for long-distance, high-speed and secure information communication in the future.

[0003] Currently, intensity modulation / direct detection (IM / DD) laser communication terminals are the primary type of laser communication system. This type of communication system is simple in structure, low in cost, and easy to modulate and demodulate. However, its limited modulation method restricts its information carrying capacity. Coherent detection laser communication terminals, due to their high sensitivity, ease of miniaturization, and good filtering performance, have become a research hotspot in space laser communication technology in recent years. However, there is currently no ground-based testing system for these laser communication terminals. Using existing IM / DD laser communication terminal testing systems results in low sensitivity and large measurement errors, making it impossible to accurately test the performance of these detection laser communication terminals. Summary of the Invention

[0004] This invention provides a testing device and method for coherent detection laser communication terminals, which solves the technical problem that existing IM / DD laser communication terminal testing systems cannot accurately test the performance of coherent detection laser communication terminals.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] A test device for a coherent detection laser communication terminal, characterized in that:

[0007] This includes a turntable, an optical platform, and an optical system mounted on the optical platform;

[0008] The turntable is located outside the optical platform and is used to mount the laser communication terminal under test.

[0009] The optical system includes a beam shaping unit, a galvanometer, a quarter-wave plate, a first beam splitter, and an optical testing system arranged sequentially along the output optical path of the laser communication terminal under test, as well as a light source system. The light source system is used to provide a light source for the laser communication terminal under test, and the first beam splitter, quarter-wave plate, galvanometer, beam shaping unit, and laser communication terminal under test are located sequentially on the output optical path of the light source system.

[0010] The beam shaping unit includes a primary mirror and a secondary mirror, with the primary mirror having a larger aperture than the secondary mirror; along the output optical path of the laser communication terminal under test, the primary mirror and the secondary mirror form a beam-shrinking system; along the output optical path of the light source system, the secondary mirror and the primary mirror form a beam-expanding system.

[0011] The galvanometer is used to simulate the vibration of a satellite platform and to change the path of the outgoing light reaching its mirror surface.

[0012] In the output light path of the laser communication terminal under test, the quarter-wave plate is used to ensure that the spot of the output light remains unchanged; the first beam splitter splits the output light through the quarter-wave plate into two beams, one of which enters the optical testing system, which is used to test the performance of the laser communication terminal under test.

[0013] In the output light path of the light source system, the 1 / 4 wave plate is used to make the output light circularly polarized or elliptically polarized.

[0014] Furthermore, the quarter-wave plate is mounted on an optical platform via a single-axis turntable, which is used to adjust the mounting angle of the quarter-wave plate.

[0015] Furthermore, the light source system includes a laser and a first optical lens, and the laser is connected to the first optical lens via a single-mode polarization-maintaining fiber; the laser is used to generate a linearly polarized beam. The laser emits laser light, which enters a quarter-wave plate after passing through the first optical lens and the first beam splitter. The quarter-wave plate generates circularly polarized light or elliptically polarized light, which enters the laser communication terminal after passing through a galvanometer and a beam-shrinking system, providing a light source for the laser communication terminal under test.

[0016] Furthermore, the optical testing system includes a first testing system and a second testing system;

[0017] The first testing system includes a second beam splitter, a second optical lens, and a spot analyzer;

[0018] The second test system includes a reflector, a third optical lens, and a power meter;

[0019] One of the two beams formed by the first beam splitter is split into two again by the second beam splitter. One of the beams passes through the second optical lens and enters the spot analyzer, which is located at the focal plane of the second optical lens. The spot analyzer is used to analyze the spot information and obtain the divergence angle of the laser communication terminal under test. The other beam passes through the mirror and then through the third optical lens to enter the power meter, which is located at the focal plane of the third optical lens. The power meter is used to measure the received spot energy.

[0020] This invention also provides a testing method for a coherent detection laser communication terminal, characterized in that it employs the testing apparatus for the coherent detection laser communication terminal described in this invention, and includes the following steps:

[0021] [1] Install the laser communication terminal to be tested on the turntable;

[0022] [2] Start the laser communication terminal under test, and test the performance of the laser communication terminal under test under the condition that the turntable and galvanometer are working; the performance includes the divergence angle, real-time emission power, equivalent omnidirectional radiation power, tracking function, communication function, and coaxiality of the emission system and tracking system of the laser communication terminal under test.

[0023] Furthermore, in step [2], the test method for the divergence angle and real-time transmission power of the laser communication terminal under test is as follows:

[0024] 1) The signal light emitted by the laser communication terminal under test passes through the beam shrinking system, galvanometer, quarter wave plate and first beam splitter in sequence and is split into two beams. One beam is split into two beams again by the second beam splitter. One beam enters the spot analyzer and the other enters the power meter.

[0025] 2) Obtain the divergence angle θ of the laser communication terminal under test using a spot analyzer;

[0026] The expression for the divergence angle θ of the laser communication terminal under test is: θ=2arctan(d / 2f), where d is the diameter of the beam received by the beam analyzer, f is the focal length of the receiving branch of the optical system, and f=f1×β, where f1 is the focal length of the second optical lens and β is the magnification of the beam shrinking system.

[0027] 3) Obtain the real-time transmission power of the laser communication terminal under test through a power meter.

[0028] Furthermore, in step [2], the method for testing the equivalent isotropic radiated power of the laser communication terminal under test is as follows:

[0029] Connect the power meter to the transmitting system of the laser communication terminal under test, obtain the maximum power P of the transmitting system, and obtain the equivalent isotropic radiation power EIRP of the laser communication terminal under test based on the divergence angle θ of the laser communication terminal under test; the expression for the equivalent isotropic radiation power EIRP is:

[0030]

[0031] Furthermore, in step [2], the test method for the laser communication terminal tracking system under test is as follows:

[0032] 1) Turn on the laser of the light source system. The emitted light from the laser is split into two paths after passing through the first optical lens and the first beam splitter. One path enters the optical testing system, and the other path is received by the laser communication terminal under test after passing through the quarter wave plate, galvanometer and beam expander system.

[0033] 2) Change the orientation angle of the turntable so that the outgoing light entering the laser communication terminal under test reaches the two edge fields of view of its tracking system, thereby obtaining the entire field of view that the laser communication terminal under test can capture and track.

[0034] Furthermore, in step [2], the test method for the communication function of the laser communication terminal under test is as follows:

[0035] The laser is turned off. The communication device is connected to the first optical lens via a single-mode polarization-maintaining fiber. A laser communication link is established between the ground testing equipment and the receiving system of the laser communication terminal under test. The communication device emits signal light, which is coupled into the single-mode polarization-maintaining fiber. The signal light then passes sequentially through the first optical lens, the first beam splitter, the quarter-wave plate, the galvanometer, and the beam expander before entering the receiving system of the laser communication terminal under test. The ground testing equipment demodulates the signal light received by the receiving system of the laser communication terminal under test and compares it with the signal loaded by the communication device. If the bit error rate is less than the bit error rate required by the laser communication terminal under test, it means that the communication function of the laser communication terminal under test is good; otherwise, it means that the communication function of the laser communication terminal under test is poor.

[0036] Furthermore, in step [2], the method for testing the coaxiality of the transmitting system and the tracking system of the laser communication terminal under test is as follows:

[0037] 1) Turn on the laser and rotate the turntable so that the light spot received by the laser communication terminal under test is located at the center of its tracking system.

[0038] 2) Turn on the transmitting system of the laser communication terminal under test, and use a spot analyzer to calculate the centroid position (x, y) of the received spot on the spot analyzer. Obtain the coaxiality of the transmitting system and the tracking system of the laser communication terminal under test. coaxiality The calculation formula is: In the formula: f is the focal length of the receiving branch of the optical system, f = f1 × β1, where f1 is the focal length of the second optical lens and β1 is the magnification of the beam expander system.

[0039] Compared with the prior art, the advantages of the present invention are:

[0040] 1. The test is accurate and highly adaptable.

[0041] The apparatus of this invention is a matching test device designed for testing coherent probe laser communication terminals. It includes a turntable, an optical platform, and an optical system. In the optical system, a first beam splitter and a quarter-wave plate are combined to ensure the beam spot remains unchanged in the output optical path of the laser communication terminal under test. In the output optical path of the light source system, they are used to generate circularly or elliptically polarized light from the linearly polarized laser, which is then received by the laser communication terminal under test, thereby enabling comprehensive performance testing of the laser communication terminal under test. This apparatus can accurately test not only the performance of coherent probe laser communication terminals but also that of direct probe laser communication terminals. Therefore, various single-end parameters of different types of laser communication terminals can be accurately verified during the ground verification phase.

[0042] 2. The methods are clear and comprehensive.

[0043] The test method of this invention comprehensively describes the test methods for the divergence angle, equivalent omnidirectional radiation power, acquisition and tracking field of view, communication function and coaxiality of laser communication terminals. Based on this method, various single-end indicators of various laser communication terminals can be fully verified on the ground. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of a test device embodiment for a coherent detection laser communication terminal according to the present invention.

[0045] The attached figures are labeled as follows:

[0046] 1-Turntable; 2-Laser communication terminal under test; 3-Optical platform; 4-Primary mirror; 5-Secondary mirror; 6-Galvanometer; 7-Single-axis turntable; 8-1 / 4 wave plate; 9-First beam splitter; 10-Light source system; 101-Laser; 102-First optical lens; 103-Single-mode polarization-maintaining fiber; 11-Optical testing system; 111-Second beam splitter; 112-Second optical lens; 113-Spot analyzer; 114-Reflector; 115-Third optical lens; 116-Power meter. Detailed Implementation

[0047] Currently, coherent laser communication systems have become a research hotspot in space laser communication technology in recent years due to their 10-20 dB higher detection sensitivity compared to IM / DD under the same link distance, code rate, and bit error rate. However, existing IM / DD laser communication terminal testing platforms cannot meet the testing and dual-end connection testing requirements of coherent laser communication terminals. Therefore, this embodiment establishes a ground-based testing device for coherent detection laser communication terminals and a testing method based on this device. This allows for precise testing before actual application, thereby improving the accuracy of data exploration and other functions of coherent detection laser communication terminals during actual use.

[0048] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the terms "first," "second," "third," etc., are used for descriptive purposes only and do not imply their relative importance.

[0049] like Figure 1 As shown, a test device for a coherent detection laser communication terminal includes a turntable 1, an optical platform 3, and an optical system mounted on the optical platform 3.

[0050] Turntable 1 is located outside optical platform 3 and is used to mount laser communication terminal 2 under test. Turntable 1 can be controlled by ground inspection equipment.

[0051] The optical system includes a beam shaping unit, a galvanometer 6, a quarter-wave plate 8, a first beam splitter 9, an optical testing system 11, and a light source system 10, arranged sequentially along the output optical path of the laser communication terminal 2 under test. The light source system 10 provides a light source for the laser communication terminal 2 under test. The first beam splitter 9, the quarter-wave plate 8, the galvanometer 6, the beam shaping unit, and the laser communication terminal 2 under test are located sequentially along the output optical path of the light source system 10.

[0052] The beam shaping unit includes a primary mirror 4 and a secondary mirror 5, with the aperture of the primary mirror 4 being larger than that of the secondary mirror 5. Along the output optical path of the laser communication terminal 2 under test, the primary mirror 4 and the secondary mirror 5 form a beam-shrinking system. Along the output optical path of the light source system 10, the secondary mirror 5 and the primary mirror 4 form a beam-expanding system.

[0053] Along the outgoing light path of the laser communication terminal 2 under test, the galvanometer 6 is located on the reflected light path of the secondary mirror 5 to simulate the vibration of the satellite platform. Generally, the mirror surface of the galvanometer 6 forms a 45° angle with the central axis of the secondary mirror 5, which can reflect the outgoing light reflected by the secondary mirror 5 back to the quarter-wave plate 8. The first beam splitter 9 is a polarizing beam splitter, which is located behind the quarter-wave plate 8 and is used to split the outgoing light through the quarter-wave plate 8 into two paths. One of the beams enters the optical testing system 11, which is used to test the performance of the laser communication terminal 2 under test.

[0054] In this embodiment, the quarter-wave plate 8 serves as a polarization maintainer, ensuring that the path and spot quality of the emitted light from the laser communication terminal 2 under test remain unchanged. In the emitted light path of the light source system 10, it generates circularly or elliptically polarized light, which can then be received by the laser communication terminal 2 under test, thereby improving the testing accuracy of the laser communication terminal 2.

[0055] In this embodiment, the quarter-wave plate 8 is mounted on the optical platform 3 via a single-axis turntable 7. The single-axis turntable 7 is used to adjust the mounting angle of the quarter-wave plate 8 so that the emitted beam reaches the corresponding degree of polarization. Generally, during the debugging stage before mounting the quarter-wave plate 8, the single-axis turntable 7 has been adjusted to the specific angle according to the installation requirements of the test device. There are two types of angles: one angle will cause the quarter-wave plate 8 to produce left-handed circularly polarized light, and the other angle will cause the quarter-wave plate 8 to produce right-handed circularly polarized light. During the use stage, the mounting angle of the single-axis turntable 7 is selected according to the need for right-handed or right-handed polarization.

[0056] The light source system 10 includes a laser 101 and a first optical lens 102. The laser 101 and the first optical lens 102 are connected by a single-mode polarization-maintaining fiber 103. The single-mode polarization-maintaining fiber 103 has a small core diameter, which can meet the conditions for far-field transmission, and has strong anti-interference ability, high reliability, and long transmission distance. The laser 101 is used to generate a linearly polarized beam. The laser 101 emits linearly polarized light, which enters a quarter-wave plate 8 after passing through the first optical lens 102 and the first beam splitter 9. The quarter-wave plate 8 generates circularly polarized light or elliptically polarized light. The circularly polarized light or elliptically polarized light enters the laser communication terminal 2 after passing through the galvanometer 6 and the beam-shrinking system, thereby providing a light source for the laser communication terminal 2 under test.

[0057] The optical testing system 11 is used to test the performance of the laser communication terminal 2 under test. The optical testing system 11 includes a first testing system and a second testing system.

[0058] The first test system includes a second beam splitter 111, a second optical lens 112, and a spot analyzer 113.

[0059] The second test system includes a reflector 114, a third optical lens 115, and a power meter 116.

[0060] One of the two beams formed by the first beam splitter 9 is split into two again by the second beam splitter 111. One of the beams passes through the second optical lens 112 and enters the spot analyzer 113. The spot analyzer 113 is located at the focal plane of the second optical lens 112 and is used to analyze the spot information and obtain the divergence angle of the laser communication terminal 2 under test. The other beam passes through the reflector 114 and then through the third optical lens 115 and enters the power meter 116. The power meter 116 is located at the focal plane of the third optical lens 115 and is used to measure the received spot energy.

[0061] After calibration, the testing device in this embodiment clarifies various parameters of the optical system, and can clearly analyze the test errors of each index during the testing of the laser communication terminal 2 under test, thereby improving the test accuracy.

[0062] Furthermore, this embodiment also provides a testing method for a coherent detection laser communication terminal. Using the coherent detection laser communication terminal testing device described in this embodiment, before testing, the position and angle of the single-axis turntable 7 and the quarter-wave plate 8 are adjusted in advance according to the installation position of the laser communication terminal 2 under test. The specific testing method includes the following steps:

[0063] Step [1] Install the laser communication terminal 2 under test on the turntable 1 so that the aperture 2 of the laser communication terminal 2 under test is aligned with the center of the aperture of the main mirror 4.

[0064] Step [2] Start the laser communication terminal 2 under test. Under the condition that the turntable 1 and the galvanometer 6 are working, the performance of the laser communication terminal 2 under test is tested.

[0065] This embodiment mainly tests the transmission function, tracking function, communication function of the laser communication terminal 2 under test, as well as the coaxiality of the transmission system and tracking system of the laser communication terminal 2 under test. The transmission function includes divergence angle, real-time transmission power, equivalent isotropic radiation power, etc.

[0066] The following describes the specific test methods for various performance characteristics of the laser communication terminal 2 under test:

[0067] The testing of the divergence angle and real-time transmission power of the laser communication terminal 2 under test includes the following steps:

[0068] 1) The laser communication terminal 2 under test emits a signal light. The signal light passes through the beam shrinking system, the galvanometer 6, the quarter-wave plate 8, and the first beam splitter 9 in sequence and is then split into two paths. One of the beams is split into two paths again by the second beam splitter 111. One path enters the spot analyzer 113, and the other path enters the power meter 116. During this process, the laser (101) is in the off state.

[0069] 2) Obtain the divergence angle θ of the laser communication terminal 2 under test through the spot analyzer 113.

[0070] The expression for the divergence angle θ of the laser communication terminal 2 under test is: θ = 2arctan(d / 2f), where d is the diameter of the beam received by the beam analyzer 113, and the gray value of the beam is equal to the maximum value 1 / e. 2 The contour lines (e is a constant), f is the focal length of the receiving branch of the optical system, and f = f1 × β, where f1 is the focal length of the second optical lens 112, and β is the magnification of the beam-shrinking system.

[0071] 3) Obtain the real-time transmission power of the laser communication terminal 2 under test through power meter 116.

[0072] II. Test method for the equivalent isotropic radiated power (EIRP) of the laser communication terminal under test 2:

[0073] Connect power meter 116 to the transmitting system of the laser communication terminal 2 under test, obtain the maximum power P of the transmitting system of the laser communication terminal 2 under test through power meter 116, and obtain the equivalent isotropic radiation power EIRP of the laser communication terminal 2 under test based on the divergence angle θ of the laser communication terminal 2 under test; the expression of the equivalent isotropic radiation power EIRP is:

[0074] III. The testing of the tracking function of the laser communication terminal 2 tracking system under test includes the following steps;

[0075] 1) Turn on the laser 101 of the light source system 10. The emitted light from the laser 101 is split into two paths after passing through the first optical lens 102 and the first beam splitter 9. One path enters the optical test system 11, and the other path is received by the laser communication terminal 2 under test after passing through the quarter wave plate 8, the galvanometer 6 and the beam expander system.

[0076] 2) Change the azimuth angle of turntable 1 so that the emitted light beam entering the laser communication terminal 2 under test is at the edge of the field of view on one side of the tracking system of the laser communication terminal 2 under test. Reset the azimuth angle of turntable 1 to zero, and rotate the azimuth angle of turntable 1 again so that the emitted light beam entering the laser communication terminal 2 under test is at the edge of the field of view on the other side of its tracking system. The rotation angle of turntable 1 is the capture and tracking field of view of the laser communication terminal 2 under test, thereby obtaining the entire field of view that the laser communication terminal 2 under test can capture and track.

[0077] IV. The specific testing of the communication function of the laser communication terminal 2 under test is as follows:

[0078] The laser 101 is turned off. The communication device is connected to the first optical lens 102 via a single-mode polarization-maintaining fiber 103. A laser communication link is established between the ground testing equipment and the receiving system of the laser communication terminal 2 under test. An existing communication device can be selected, and the corresponding test signal can be applied to it.

[0079] The communication unit is activated, emitting signal light which is coupled into a single-mode polarization-maintaining fiber. The signal light sequentially passes through the first optical lens 102, the first beam splitter 9, the quarter-wave plate 8, the galvanometer 6, and the beam expander before entering the receiving system of the laser communication terminal 2 under test. The energy of the signal light loaded by the communication unit is W, and the communication rate of the loaded laser is S. The expression for the loaded energy W is:

[0080]

[0081] In the expression, P out1. Power of the laser communication terminal 2 under test during communication, in W; 2. Aperture of the optical antenna of the laser communication terminal 2 under test, in mm; 3. Communication distance of the laser communication terminal 2 under test, in km; 4. Divergence angle of the laser communication terminal 2 under test, in rad; 5. Transmittance of the transmission branch of the laser communication terminal 2 under test (i.e., the branch through which the signal light passes during the test).

[0082] The ground testing equipment demodulates the signal light received by the receiving system of the laser communication terminal 2 under test, and compares it with the signal loaded by the communication device. If the bit error rate between the received signal and the loaded signal is less than the bit error rate required by the laser communication terminal 2 under test (in this embodiment, the bit error rate requirement for the laser communication terminal 2 under test is 1*10), the test is successful. -7 If the signal is positive, it indicates that the communication function of the laser communication terminal 2 under test is good; otherwise, it indicates that the communication function of the laser communication terminal 2 under test is poor.

[0083] V. The specific test of the coaxiality of the transmitting system and tracking system of the laser communication terminal under test is as follows:

[0084] 1) Turn off the communication device, turn on the laser 101 of the light source system 10, and rotate the turntable 1 so that the light spot received by the laser communication terminal 2 under test is located at the center of its tracking system.

[0085] 2) Turn on the transmitting system of the laser communication terminal 2 under test, and use the spot analyzer 113 to calculate the centroid position (x, y) of the received spot on the spot analyzer 113, and obtain the coaxiality of the transmitting system and the tracking system of the laser communication terminal 2 under test. coaxiality The calculation formula is: In the formula: f is the focal length of the receiving branch of the optical system, f = f1 × β1, where f1 is the focal length of the second optical lens 112, and β1 is the magnification of the beam expander system (same as the β value).

[0086] In summary, the test method of this embodiment can comprehensively test the divergence angle, actual transmission power, equivalent isotropic radiation power, acquisition and tracking field of view, communication function and coaxiality of the coherent detection laser communication terminal 2. Based on this method, various single-end indicators of various laser communication terminals can also be comprehensively verified on the ground.

Claims

1. A testing device for a coherent detection laser communication terminal, characterized in that: It includes a turntable (1), an optical platform (3), and an optical system mounted on the optical platform (3); The turntable (1) is located outside the optical platform (3) and is used to mount the laser communication terminal (2) under test; The optical system includes a beam shaping unit, a galvanometer (6), a quarter-wave plate (8), a first beam splitter (9), and an optical testing system (11) arranged sequentially along the output optical path of the laser communication terminal (2) under test, as well as a light source system (10); the light source system (10) is used to provide a light source for the laser communication terminal (2) under test, and the first beam splitter (9), the quarter-wave plate (8), the galvanometer (6), the beam shaping unit, and the laser communication terminal (2) under test are located sequentially on the output optical path of the light source system (10); The beam shaping unit includes a primary mirror (4) and a secondary mirror (5), and the aperture of the primary mirror (4) is larger than that of the secondary mirror (5); along the output optical path of the laser communication terminal (2) under test, the primary mirror (4) and the secondary mirror (5) form a beam shrinking system; along the output optical path of the light source system (10), the secondary mirror (5) and the primary mirror (4) form a beam expanding system. The galvanometer (6) is used to simulate the vibration of the satellite platform and change the path of the outgoing light reaching its mirror surface; In the output light path of the laser communication terminal (2) under test, the quarter-wave plate (8) is used to ensure that the spot of the output light remains unchanged; the first beam splitter (9) splits the output light through the quarter-wave plate (8) into two beams, one of which enters the optical testing system (11), and the optical testing system (11) is used to test the performance of the laser communication terminal (2) under test. In the outgoing light path of the light source system (10), the 1 / 4 wave plate (8) is used to make the outgoing light generate circularly polarized light or elliptically polarized light.

2. The testing apparatus for a coherent detection laser communication terminal according to claim 1, characterized in that: The quarter-wave plate (8) is mounted on the optical platform (3) via a single-axis turntable (7), which is used to adjust the mounting angle of the quarter-wave plate (8).

3. The testing apparatus for a coherent detection laser communication terminal according to claim 2, characterized in that: The light source system (10) includes a laser (101) and a first optical lens (102). The laser (101) is connected to the first optical lens (102) through a single-mode polarization-maintaining fiber (103). The laser (101) is used to generate a linearly polarized beam. The laser (101) emits laser light, which enters a quarter-wave plate (8) after passing through the first optical lens (102) and the first beam splitter (9). The quarter-wave plate (8) generates circularly polarized light or elliptically polarized light. The circularly polarized light or elliptically polarized light enters the laser communication terminal (2) after passing through a galvanometer (6) and a beam-shrinking system, providing a light source for the laser communication terminal (2) under test.

4. The testing apparatus for a coherent detection laser communication terminal according to claim 3, characterized in that: The optical testing system (11) includes a first testing system and a second testing system; The first testing system includes a second beam splitter (111), a second optical lens (112), and a spot analyzer (113); The second test system includes a reflector (114), a third optical lens (115), and a power meter (116); One of the two beams formed by the first beam splitter (9) is split into two again by the second beam splitter (111). One of the beams passes through the second optical lens (112) and enters the spot analyzer (113). The spot analyzer (113) is located at the focal plane of the second optical lens (112) and is used to analyze the spot information and obtain the divergence angle of the laser communication terminal (2) under test. The other beam passes through the reflector (114) and then through the third optical lens (115) and enters the power meter (116). The power meter (116) is located at the focal plane of the third optical lens (115) and is used to measure the received spot energy.

5. A test method for a coherent detection laser communication terminal, characterized in that, The test apparatus for the coherent detection laser communication terminal according to any one of claims 1-4 includes the following steps: 【1】The laser communication terminal (2) to be tested is mounted on the turntable (1); [2] Start the laser communication terminal under test (2), and under the condition that the turntable (1) and galvanometer (6) are working, the performance of the laser communication terminal under test (2) is tested; the performance includes the divergence angle, real-time emission power, equivalent omnidirectional radiation power, tracking function, communication function and the coaxiality of the emission system and the tracking system of the laser communication terminal under test (2).

6. The test method for a coherent detection laser communication terminal according to claim 5, characterized in that, In step [2], the test method for the divergence angle and real-time transmission power of the laser communication terminal (2) under test is as follows: 1) The signal light emitted by the laser communication terminal under test (2) passes through the beam shrinking system, galvanometer (6), quarter wave plate (8), and first beam splitter (9) in sequence and is split into two beams. One beam is split into two again by the second beam splitter (111). One beam enters the spot analyzer (113) and the other enters the power meter (116). 2) Obtain the divergence angle θ of the laser communication terminal (2) under test using a spot analyzer (113); The expression for the divergence angle θ of the laser communication terminal (2) under test is: θ=2arctan(d / 2f), where d is the beam diameter received by the beam analyzer (113), f is the focal length of the receiving branch of the optical system, and f=f1×β, where f1 is the focal length of the second optical lens (112), and β is the magnification of the beam shrinking system. 3) Obtain the real-time transmission power of the laser communication terminal (2) under test through a power meter (116).

7. The test method for a coherent detection laser communication terminal according to claim 6, characterized in that, In step [2], the test method for the equivalent isotropic radiated power of the laser communication terminal (2) under test is as follows: Connect the power meter (116) to the transmitting system of the laser communication terminal (2) under test, obtain the maximum power P of the transmitting system of the laser communication terminal (2) under test, and obtain the equivalent isotropic radiation power EIRP of the laser communication terminal (2) under test based on the divergence angle θ of the laser communication terminal (2) under test; the expression of the equivalent isotropic radiation power EIRP is:

8. The test method for a coherent detection laser communication terminal according to claim 5, characterized in that, In step [2], the test method for the tracking system of the laser communication terminal (2) under test is as follows: 1) Turn on the laser (101). The outgoing light emitted by the laser (101) is split into two paths after passing through the first optical lens (102) and the first beam splitter (9). One path enters the optical test system (11), and the other path is received by the laser communication terminal under test (2) after passing through the 1 / 4 wave plate (8), the galvanometer (6) and the beam expander system. 2) Change the orientation angle of the turntable (1) so that the outgoing light entering the laser communication terminal (2) under test reaches the two edge fields of view of its tracking system, thereby obtaining the entire field of view that the laser communication terminal (2) under test can capture and track.

9. The test method for a coherent detection laser communication terminal according to claim 5, characterized in that, In step [2], the test method for the communication function of the laser communication terminal (2) under test is as follows: The laser (101) is turned off. The communication device is connected to the first optical lens (102) through a single-mode polarization-maintaining fiber (103). The ground testing equipment is then connected to the receiving system of the laser communication terminal (2) under test. The communication device emits signal light and couples it into the single-mode polarization-maintaining fiber (103). The signal light then passes through the first optical lens (102), the first beam splitter (9), the quarter-wave plate (8), the galvanometer (6), and the beam expander in sequence before entering the receiving system of the laser communication terminal (2) under test. The ground testing equipment demodulates the signal light received by the receiving system of the laser communication terminal (2) under test and compares it with the signal loaded by the communication device. If the bit error rate is less than the bit error rate required by the laser communication terminal (2) under test, it means that the communication function of the laser communication terminal (2) under test is good; otherwise, it means that the communication function of the laser communication terminal (2) under test is poor.

10. The test method for a coherent detection laser communication terminal according to claim 5, characterized in that, In step [2], the test method for the coaxiality of the transmitting system and the tracking system of the laser communication terminal (2) under test is as follows: 1) Turn on the laser (101) and rotate the turntable (1) so that the light spot received by the laser communication terminal under test (2) is located at the center of its tracking system; 2) Turn on the transmitting system of the laser communication terminal (2) under test, and use the spot analyzer (113) to calculate the centroid position (x, y) of the received spot on the spot analyzer (113), and obtain the coaxiality of the transmitting system and the tracking system of the laser communication terminal (2) under test. coaxiality The calculation formula is: In the formula: f is the focal length of the receiving branch of the optical system, f = f1 × β1, where f1 is the focal length of the second optical lens (112) and β1 is the magnification of the beam expander system.

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