Laser link tracking stability experiment system and test method

Abstract

The invention relates to the technical field of space-air-ground laser communication, in particular to a laser link tracking stability experiment system and a test method.The laser link tracking stability experiment system comprises a light beam emitting module, a light spot receiving module and a light modulation module, and the light beam emitting module comprises a laser, a beam expander, an aperture diaphragm and a first polaroid; a light beam emitted by a laser is expanded through a beam expander, the spot diameter of the expanded light beam is controlled by an aperture diaphragm, and the light beam enters a spatial light modulator SLM in a light modulation module after the polarization direction of the light beam is adjusted through a first polaroid; a light spot receiving module is arranged between the light beam emitting module and the light modulation module, light with the polarization direction adjusted through the first polaroid is subjected to beam splitting through the beam splitter, the polarization direction of the light is adjusted through the second polaroid, and then the light is amplified through the lens and enters the CCD detector. The visual management and guidance of the laser link tracking process are realized to find the loss of the real environment caused by the abnormal link.

Description

Technical Field

[0001] The present invention relates to the technical field of air-to-ground laser communication, and in particular to a laser link tracking stability experimental system and a testing method. Background Art

[0002] With the continuous development of space laser communication technology, it can be widely used in various fields as an emergency communication means, such as earthquake relief, emergencies, anti-evil, public security and confidential communications. The laser communication technologies used in these applications can be classified into three categories, including point-to-point laser communication technology, networked optical communication technology and missile-borne laser communication technology. In early research, space laser communication mainly adopted point-to-point mode due to the small beam divergence and good directivity of the micro-light. The satellite laser communication system is an extension of laser communication technology in the space field, but the satellite laser communication system is not equivalent to the direct migration of the ground laser communication system to the satellite platform. The satellite laser communication system is a high-precision optomechanical integration system working under space environment conditions. The design of its optical system must fully consider the space application background, and the hardware implementation is required to have the characteristics of light weight, small size, low power consumption, simple structure, high transmission efficiency and high reliability, and the performance changes in the space environment need to be considered. Considering the reliability of laser communication, it is necessary to conduct a detailed analysis of the laser communication link and perform link tracking and optimization; by adding virtual reality information to the real production scene, visual management and guidance of the laser link tracking process can be achieved to discover the losses in the real environment caused by abnormal links. Summary of the invention

[0003] The purpose of the present invention is to provide a laser link tracking stability experimental system and a testing method to solve the technical problems existing in the above-mentioned background technology.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A laser link tracking stability experimental system comprises: a beam emitting module, a light spot receiving module and a light modulation module, wherein the beam emitting module comprises: a laser, a beam expander, an aperture diaphragm and a polarizer 1, the beam emitted by the laser is expanded by the beam expander, the spot diameter of the expanded beam is controlled by the aperture diaphragm, the polarization direction of the expanded beam is adjusted by the polarizer 1 and incident on the spatial light modulator SLM in the light modulation module; the light modulation module further comprises: a PC, the spatial light modulator SLM and the PC are electrically connected, a light spot receiving module is arranged between the beam emitting module and the light modulation module, the light spot receiving module comprises: a beam splitter, a polarizer 2, a lens and a CCD detector; the light whose polarization direction is adjusted by the polarizer 1 is split by the beam splitter and the polarization direction is adjusted by the polarizer 2, then amplified by the lens and incident on the CCD detector.

[0006] Furthermore, the first polarizer and the second polarizer are both linear polarizers.

[0007] A laser link tracking stability test method, using the above-mentioned laser link tracking stability experimental system, specifically includes the following steps:

[0008] S1. Construct a verification system for the correlation effect of the far-field dynamic characteristics of the beam;

[0009] S2, using simulation technology combined with VR to build a virtual link tracking experimental system;

[0010] S3. Use Unity to build AR application scenarios to complete visualization;

[0011] S4, publish the constructed application scenario to the Android system and install the application;

[0012] S5. In the virtual reality link tracking stability experimental system, the on-orbit tracking stability optimization method is used for simulation verification.

[0013] Furthermore, the virtual link tracking experimental system constructed in S2 has a virtual learning process, specifically:

[0014] S21, feature information database is established;

[0015] S22, positioning feature information matching.

[0016] Furthermore, the feature information library in S21 is established as follows: first, the 3D coordinates of the positioning management node in the network are obtained, and then the three-dimensional coordinates of the point of interest are transformed using the KL standard basis according to the minimum mean square error criterion to obtain two-dimensional feature information, and finally the two-dimensional coordinate values ​​are mapped to the 0-1 interval to obtain the corresponding feature parameter vector, and stored in the feature information library.

[0017] Furthermore, the positioning feature information matching in S22 is specifically as follows:

[0018] S221, divide the network area composed of the management node itself and each associated node into a category w i ,i=1,2,3,···, the device in the network area is a sample in this category;

[0019] S222, calculate the distance between the real-time positioning coordinates p of the mobile object and each sample in category m, and find the minimum distance G i (p), the distance is defined as the distance between the real-time positioning coordinates and the category w, G i (x) = min||pp k ||, k = 1, 2, 3, · · ·, N;

[0020] S223. Find the minimum distance g between the positioning coordinates and category a i (p), Ng i (p) = min g(p);

[0021] S224, confirm: g i (p)≤l, if the distance is less than the specified distance, the positioning coordinate x is classified into this category and the match is successful; otherwise, the decision is rejected.

[0022] Furthermore, the design of the application scenario in S3 is specifically as follows: when the production personnel are within a certain range of the device DMC-80H centered on the associated node, the indoor positioning system is used to obtain the indoor positioning coordinate information of the mobile device, and the positioning information is used as the positioning coordinate information of the mobile device camera; the camera positioning information is transmitted to the system server to match the positioning feature information of the device; if the match is successful, the virtual monitoring information of the device is pushed and displayed in integration with the device based on the camera posture estimation of the mobile device.

[0023] Furthermore, after the application in S4 is opened, the home page has two selection buttons, corresponding to the basic data of the device and the operation data of the device respectively.

[0024] Furthermore, the simulation verification of the on-orbit tracking stability optimization method in S5 specifically includes: light beam far-field equivalence analysis, far-field spot simulation and simulation verification process to track and optimize each communication link of the laser link.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] By adding virtual reality information to the real production scene, visual management and guidance of the laser link tracking process can be achieved to discover the losses in the real environment caused by abnormal links. First, a verification system is built for the influence of the correlation of the far-field dynamic characteristics of the light beam. Secondly, a virtual link tracking experimental system is built using simulation technology combined with VR. Then, the AR application scenario is built through Unity to complete the visualization. Finally, in the virtual reality link tracking stability experimental system, the on-orbit tracking stability optimization method is used for simulation verification, including the far-field equivalence analysis of the light beam, the far-field spot simulation and the simulation verification process to track and optimize the various communication links of the laser link. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of the laser link tracking stability experimental system in the present invention;

[0028] Figure 2 is a flow chart of the laser link tracking stability testing method in the present invention;

[0029] Figure 3 is a flow chart of the nearest neighbor algorithm with rejection decision in the present invention;

[0030] Figure 4 This is a simulation diagram of the far-field light spot in the present invention;

[0031] Figure 5 It is a statistical diagram of changes in correlation factors of far-field dynamic characteristics of the initial light beam of beacon light during the entire link stability maintenance process of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0033] See also Figures 1 to 4 As shown, a laser link tracking stability experimental system includes: a beam emitting module, a spot receiving module and a light modulation module, the beam emitting module includes: a laser, a beam expander, an aperture diaphragm and a polarizer 1, the beam emitted by the laser is expanded by the beam expander, the spot diameter of the expanded beam is controlled by the aperture diaphragm, the polarization direction of the expanded beam is adjusted by the polarizer 1 and is incident on the spatial light modulator SLM in the light modulation module; the light modulation module also includes: a PC, the spatial light modulator SLM and the PC are electrically connected, a spot receiving module is arranged between the beam emitting module and the light modulation module, the spot receiving module includes: a beam splitter, a polarizer 2, a lens and a CCD detector; the light whose polarization direction is adjusted by the polarizer 1 is split by the beam splitter and the polarization direction is adjusted by the polarizer 2, then amplified by the lens and incident on the CCD detector.

[0034] Both polarizer 1 and polarizer 2 are linear polarizers.

[0035] A laser link tracking stability testing method specifically comprises the following steps:

[0036] S1. Construct a verification system for the correlation effect of the far-field dynamic characteristics of the beam;

[0037] S2, using simulation technology combined with VR to build a virtual link tracking experimental system;

[0038] The virtual link tracking experimental system constructed in S2 has a virtual learning process, specifically:

[0039] S21, establishing a feature information database; the feature information database in S21 is established as follows: first, the 3D coordinates of the positioning management node in the network are obtained, and then the three-dimensional coordinates of the interest point are transformed using the KL standard basis according to the minimum mean square error criterion to obtain two-dimensional feature information, and finally the two-dimensional coordinate values ​​are mapped to the 0-1 interval to obtain the corresponding feature parameter vector, and store it in the feature information database;

[0040] S22, positioning feature information matching, the positioning feature information matching in S22 is specifically:

[0041] S221, divide the network area composed of the management node itself and each associated node into a category w i ,i=1,2,3,···, the device in the network area is a sample in this category;

[0042] S222, calculate the distance between the real-time positioning coordinates p of the mobile object and each sample in category m, and find the minimum distance G i (p), the distance is defined as the distance between the real-time positioning coordinates and the category w, G i (x) = min||pp k ||, k = 1, 2, 3, · · ·, N;

[0043] S223. Find the minimum distance g between the positioning coordinates and category a i (p), Ng i (p) = min g(p);

[0044] S224, confirm: g i (p)≤l, if the distance is less than the specified distance, the positioning coordinate x is classified into this category and the match is successful; otherwise, the decision is rejected;

[0045] S3, build an AR application scenario through Unity to complete visualization; the design of the application scenario in S3 is specifically as follows: when the production personnel are within a certain range of the device DMC-80H centered on the associated node, the indoor positioning system is used to obtain the indoor positioning coordinate information of the mobile device, and the positioning information is used as the positioning coordinate information of the mobile device camera; the camera positioning information is transmitted to the system server to match the positioning feature information of the device; if the match is successful, according to the camera posture estimation of the mobile device, the virtual monitoring information of the device is pushed and displayed in fusion with the device;

[0046] S4, publish the constructed application scenario to the Android system and install the application; after the application in S4 is opened, there are two selection buttons on the homepage, corresponding to the basic data of the device and the running data of the device respectively;

[0047] S5. In the virtual reality link tracking stability experimental system, the on-orbit tracking stability optimization method is used for simulation and verification. The on-orbit tracking stability optimization method simulation and verification in S5 specifically includes: light beam far-field equivalence analysis, far-field spot simulation and simulation verification process to track and optimize each communication link of the laser link.

[0048] The far-field equivalence analysis of the beam is as follows:

[0049] The distribution of the far-field characteristics of the light beam is of great significance to the stable tracking of the platform laser link, and the measurement of the far-field light spot centroid of the light beam is very necessary. The distribution of the far-field light spot centroid of the light beam in the detector's receiving field of view will affect the calculation of the tracking angle deviation of the tracking control system, and directly reflect the stability performance of the tracking system. Under normal circumstances, the distance between the satellite and the ground laser link is greater than 1000km, and it is not realistic to directly measure the far-field light spot of the light beam. The ground far-field distance simulation experiment is usually less than 50k. The light intensity received at the receiving end is difficult to meet the distribution of the far-field light intensity of the light beam, and the measurement results still need to be evaluated. Based on this, the equivalent distribution of the far-field light spot centroid of the light beam can be simulated by simulation methods to verify the correctness of the link tracking stability optimization method.

[0050] The far-field spot simulation is as follows:

[0051] The atmospheric turbulence effect causes the link beam to drift, expand, and fluctuate in intensity. At the same time, there is a wave phase difference in the link beam itself, so the distribution of the beam's far-field spot is relatively complex. The present invention tracks the instantaneous distribution of the far-field dynamic characteristics of the beacon beam, simulates the far-field dynamic characteristics of the link beam in the Monte Carlo method, and simulates the instantaneous spot centroid distribution of the spot. The instantaneous spot size in the far field of the beam is caused by the combined effects of beam drift and expansion, so it can be known that the mathematical expression of the instantaneous spot radius is: In the above formula, ρ is the atmospheric coherence length.

[0052] The spot size of the far-field long exposure of the beam is based on the instantaneous spot radius, taking into account the influence of the divergence angle, wave phase difference, beam drift and expansion of the emitted beam itself. Therefore, the radius size of the link beam far-field long exposure spot is: In the above formula, σ 2 is the tracking angle error caused by the wave phase difference. Ideally, according to the law of conservation of energy, the peak value of the far-field light intensity of a plane wave transmitted in the atmospheric full flow is: In the above formula, τ represents the transmittance of the atmosphere, I(0) represents the peak light intensity under ideal conditions, w is the beam angular radius, Z is the transmission distance, and the tracking beam emission system is a Cassegrain structure beam. Therefore, the power density function of its peak value is: I M =(1-ε) 2 I0, the expression of the far-field spot intensity of the far-field light of the link beam on the far-field detector is: The far-field spot of the link beam is divided into an instantaneous spot and a long exposure spot. The instantaneous spot will drift relative to the center of the target plate, and the probability of the two-dimensional tracking beam drift follows the Rayleigh distribution. According to the idea of ​​Monte Carlo, a random normal distribution sequence is generated to simulate the distribution of the instantaneous center of mass of the far-field spot relative to the center of the target plate.

[0053] Under the simulation conditions of tracking beam wavelength of 808nm, tracking accuracy of 5urad, transmitting antenna aperture of 250mm, tracking beam divergence angle of 50urad, central obstruction ratio of 1 / 3 and transmission distance of 10km, the far-field spot centroid and spot image of the link beam are numerically simulated.

[0054] When the atmospheric scintillation frequency is 50 Hz, 50 spot centroids are simulated per second, and the detector target spot centroid is simulated as follows: Figure 4 As shown;

[0055] The angular radius of the red solid circle in the figure is 5urad. Figure 4 (a) is the distribution diagram of the centroid of the light spot when the light emission time is 10s. Figure 4 (b) is the distribution diagram of the centroid of the light spot when the light emission time is 15s. According to the calculated probability that the centroid of the far-field light spot of the link beam is within the circular area during the light emission time, it is 45.4% (light emission 10s) and 45.94% (light emission 15s), respectively. The simulation probability is 45%, 21% and 45.87%; therefore, the simulation results are in good agreement with the theoretical calculation results, and the longer the light emission time, the higher the probability that the centroid is distributed within the circular area. The optical power received by the two terminals at time t will be affected by the opposite terminal t d The impact of the tracking error angle before seconds (t d = is the delay of long-distance transmission of light. Therefore, according to the two-terminal tracking coupling equation, the distribution of the far-field spot is related to the divergence angle of the beam and the wavefront distortion degree k. Bidirectional tracking beam, tracking beam wavelength is 808nm, tracking accuracy is 5urad, tracking beam divergence angle is 5urad, transmitting antenna aperture is 250mm, center obstruction ratio is 1 / 3, transmission distance is 10km, and light drift variance is σ1 2 =0.0128m 2 , 2 Guangdong expansion variance is σ2 2 =0.027m 2 , the light emission time is 20s, and the far-field light spot synthetic image is used for numerical simulation.

[0056] The simulation verification process is as follows:

[0057] The whole tracking simulation experimental device includes: two sets of optical communication terminals A and B, which have the same basic structure. The coarse tracking device of the optical system is mainly composed of a drive system and a universal turntable. The universal turntable includes a pitch axis and an azimuth axis. The deflection angle range of the pitch axis is ±180°, and the angle deflection range of the azimuth axis is 360°. The optical terminal fine tracking device is mainly composed of a piezoelectric drive system and an FMS reflector.

[0058] The optical terminal has two transmitting antennas and two receiving image detectors. The transmitting and receiving are coaxial, and the distance between the transmitting antennas of the two wavelengths is 30cm. A 50mm focusing imaging lens and a narrowband filter are placed on the detector to improve the detection accuracy of the tracking deviation angle. The central wavelength of the narrowband filter is 808nm. During the simulation process, the terminal must be adjusted first to ensure that the beacon light of the two terminals is incident on the center of the CCD detector of the other terminal. Assume that the precise tracking directions of terminal A and terminal B are A and B respectively. Taking the precise tracking process of terminal A as an example, the angle between the initial tracking angle direction of terminal A and Ao is adjusted to change the tracking direction.

[0059] Adjust the initial tracking angle direction of terminal B and The angle between them can change the size of the tracking angle offset, and the change of the variance of the correlation factor of the far-field dynamic characteristics of the light beam during the tracking and holding process can be analyzed by numerical simulation.

[0060] The whole link stability maintenance process tracks the statistical changes in the correlation factors of the far-field dynamic characteristics of the initial beam of the beacon light. Figure 5 shown.

[0061] The normalized optical power threshold is set as P d =80%, there is an optimal initial correlation factor variance σ k0 2 , so that the tracking and keeping ratio is maximized. The simulation results of the link stability keeping simulation system and the curve derived from the theory fit well, verifying the correctness of the theoretical derivation of the link tracking stability optimization method.

[0062] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A laser link tracking stability experimental system, characterized in that: include: A light beam emitting module, a light spot receiving module and a light modulation module, wherein the light beam emitting module comprises: a laser, a beam expander, an aperture diaphragm and a polarizer 1, wherein the light beam emitted by the laser is expanded by a beam expander, the spot diameter of the expanded light beam is controlled by the aperture diaphragm, the polarization direction of the expanded light beam is adjusted by the polarizer 1 and then incident on the spatial light modulator SLM in the light modulation module; the light modulation module further comprises: a PC, the spatial light modulator SLM and the PC are electrically connected, a light spot receiving module is arranged between the light beam emitting module and the light modulation module, and the light spot receiving module comprises: a beam splitter, a polarizer 2, a lens and a CCD detector; the light whose polarization direction is adjusted by the polarizer 1 is split by a beam splitter and the polarization direction is adjusted by the polarizer 2, then amplified by a lens and incident on the CCD detector.

2. A laser link tracking stability experimental system according to claim 1, characterized in that: The first polarizer and the second polarizer are both linear polarizers.

3. A laser link tracking stability test method, using the laser link tracking stability test system according to claim 2, characterized in that: The specific steps include: S1. Construct a verification system for the correlation effect of the far-field dynamic characteristics of the beam; S2, using simulation technology combined with VR to build a virtual link tracking experimental system; S3. Use Unity to build AR application scenarios to complete visualization; S4, publish the constructed application scenario to the Android system and install the application; S5. In the virtual reality link tracking stability experimental system, the on-orbit tracking stability optimization method is used for simulation verification.

4. A laser link tracking stability testing method according to claim 3, characterized in that: The virtual link tracking experimental system constructed in S2 has a virtual learning process, specifically: S21, feature information database is established; S22, positioning feature information matching.

5. A laser link tracking stability testing method according to claim 4, characterized in that: The feature information library in S21 is established specifically as follows: first, the 3D coordinates of the positioning management node in the network are obtained, and then the three-dimensional coordinates of the interest point are transformed using the KL standard basis according to the minimum mean square error criterion to obtain two-dimensional feature information, and finally the two-dimensional coordinate values ​​are mapped to the 0-1 interval to obtain the corresponding feature parameter vector, and store it in the feature information library.

6. A laser link tracking stability testing method according to claim 5, characterized in that: The positioning feature information matching in S22 is specifically as follows: S221, divide the network area composed of the management node itself and each associated node into a category w i ,i=1,2,3,···, the device in the network area is a sample in this category; S222, calculate the distance between the real-time positioning coordinates p of the mobile object and each sample in category m, and find the minimum distance G i (p), the distance is defined as the distance between the real-time positioning coordinates and the category w, G i (x) = min||pp k ||, k = 1, 2, 3, · · ·, N; S223. Find the minimum distance g between the positioning coordinates and category a i (p), Ng i (p) = ming(p); S224, confirm: g i (p)≤l, if the distance is less than the specified distance, the positioning coordinate x is classified into this category and the match is successful; otherwise, the decision is rejected.

7. A laser link tracking stability testing method according to claim 6, characterized in that: The application scenario in S3 is specifically designed as follows: when the production personnel are within a certain range of the device DMC-80H centered on the associated node, the indoor positioning system is used to obtain the indoor positioning coordinate information of the mobile device, and the positioning information is used as the positioning coordinate information of the camera of the mobile device; The camera's positioning information is transmitted to the system server and matched with the device's positioning feature information; if the match is successful, the device's virtual monitoring information is pushed and displayed in fusion with the device based on the camera's position estimation of the mobile device.

8. A laser link tracking stability testing method according to claim 7, characterized in that: The home page of the application in S4 after opening has two selection buttons corresponding to the basic data of the device and the operation data of the device respectively.

9. A laser link tracking stability testing method according to claim 8, characterized in that: The simulation verification of the on-orbit tracking stability optimization method in S5 specifically includes: light beam far-field equivalence analysis, far-field spot simulation and simulation verification process to track and optimize each communication link of the laser link.

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