Underwater large-range searching and tracking duplex laser communication device and method

Abstract

The invention relates to an underwater laser communication device and method, in particular to an underwater large-range searching and tracking duplex laser communication device and method, and solves the technical problem that rapid orientation and establishment of an optical communication link between underwater random motion platforms are difficult. The two-dimensional turntable is matched with the photoelectric detector and the image detector to respectively perform primary large-range scanning and secondary fine tracking scanning, so that a large scanning range is ensured, the method has the characteristics of high speed and high precision, and aiming at an underwater non-cooperative target scene, an uncertain area can be quickly reduced, initial pointing can be completed, and the accuracy of the underwater non-cooperative target scene is improved. The underwater random motion platform is found and captured, an optical communication link can be quickly established, meanwhile, the communication distance and the communication rate are effectively improved, the overall layout of equipment is compact and miniaturized, and engineering application is easy.

Description

Technical Field

[0001] The invention relates to an underwater laser communication device and method, and in particular to an underwater large-range search and tracking duplex laser communication device and method. Background Art

[0002] Compared with traditional underwater acoustic communication, underwater wireless optical communication has the advantages of large bandwidth, high speed, low power consumption, high anti-interference and good confidentiality, and has attracted widespread attention in recent years. In underwater wireless optical communication, compared with optical communication equipment using LED light sources, the use of laser light sources can effectively improve the communication rate and distance, but due to the narrow laser beam and strong directivity, it is necessary to achieve strong alignment of the underwater optical path, and it is very difficult to establish a communication link and maintain it stably.

[0003] Capturing, aiming and tracking (APT) of laser communication beams is one of the prerequisites for underwater laser communication. First of all, although the APT system for space laser communication is mature, the aperture of optical equipment in the space environment is large, and special environmental requirements such as huge underwater pressure and sealing are not considered, so it is difficult to directly apply it to underwater laser communication. At present, underwater laser communication often uses a fixed frame to achieve ballistic beam alignment, and uses an underwater dynamic sealed pan-tilt or swing mirror for target search. However, the fixed frame is difficult to meet the complex practical application requirements. The underwater dynamic sealed pan-tilt has a slow response speed and low precision. The equipment size and weight are large and the carrying capacity is limited; and the swing mirror has a small rotation range, which makes it difficult to achieve a large-scale target search.

[0004] Secondly, common space laser communication equipment uses the platform as the cooperation target. For example, the satellite platform can calculate the initial position through the ephemeris, and can quickly establish an optical communication link in a small uncertainty area. However, underwater laser communication equipment is generally carried on mobile platforms such as manned submersibles, AUVs (autonomous underwater vehicles) or ROVs (remotely controlled unmanned submersibles). The mobile platform moves randomly. If the acoustic communication is used, the positioning accuracy is not high, and the positioning information is easily exposed, making it difficult for the underwater communication target to obtain the initial direction.

[0005] Therefore, underwater laser communication equipment needs to be able to scan and capture over a large spatial range in order to establish an optical communication link. Summary of the invention

[0006] The purpose of the present invention is to solve the technical problem that it is difficult to quickly orient and establish optical communication links between underwater randomly moving platforms, and to provide an underwater large-scale search and tracking duplex laser communication device and method.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] An underwater large-scale search and tracking duplex laser communication device comprises two optical communication machines with the same structure, which are respectively installed on a local device and a remote device. The optical communication machine comprises a sealed cabin composed of a fixed seat and a transparent optical window, a two-dimensional turntable and a main control unit arranged in the sealed cabin, and a transceiver off-axis optical system arranged on the two-dimensional turntable;

[0009] The off-axis transmitting and receiving optical system is arranged close to the transparent optical window, and comprises a transmitting branch and a receiving branch which are parallel to each other;

[0010] The transmitting branch includes a laser for emitting beacon light and / or communication light, and a laser collimator and a first zoom lens sequentially arranged along the laser transmission direction;

[0011] The receiving branch includes a second zoom lens and a beam splitter prism arranged in sequence along the light beam transmission direction, a first-level large-range scanning and communication unit and a second-level precision tracking scanning unit are respectively arranged on the transmission light path and the reflection light path of the beam splitter prism, the first-level large-range scanning and communication unit includes a collimating and focusing unit and a photoelectric detector arranged in sequence along the light beam propagation direction, and the second-level precision tracking scanning unit includes a reflector, a focusing unit and an image detector arranged in sequence along the light beam propagation direction;

[0012] The main control unit is electrically connected to the two-dimensional turntable, the laser, the photoelectric detector, and the image detector respectively, and is used to control the two-dimensional turntable, modulate the laser output by the laser, and filter and demodulate the laser signals received by the photoelectric detector and the image detector.

[0013] Further, the laser includes a beacon laser and a communication laser, the wavelength of the light beams emitted by the beacon laser and the communication laser is the same, the communication laser is used to emit communication light, and the beacon laser is used to emit beacon light and enhance the power of the communication light;

[0014] The rear ends of the beacon laser and the communication laser are sequentially provided with a laser collimator and a first zoom lens along the laser transmission direction.

[0015] Furthermore, the detection fields of the photoelectric detector and the image detector are both ≥10°;

[0016] The photoelectric detector adopts a PMT detector, and the image detector adopts a CCD camera;

[0017] The transparent optical window is a large-aperture transparent optical window of a cylindrical segment plus a hemisphere, and an anti-reflection coating is provided on the inner surface thereof;

[0018] The two-dimensional turntable adopts an L-shaped layout, the azimuth rotation and the pitch rotation are driven by a servo motor, and the angle measuring element adopts a small time-grating encoder;

[0019] The splitting ratio of the beam splitter prism is 1:4.

[0020] Further, the collimating and focusing unit comprises a first focusing lens, a variable iris, a shaping lens, a narrowband filter and a second focusing lens which are sequentially arranged along the propagation direction of the light beam, and the variable iris is electrically connected to the main control unit;

[0021] The focusing unit includes a third focusing lens.

[0022] Furthermore, it also includes a tracking processing board, which is electrically connected to the laser, the photodetector, and the image detector respectively, and is wirelessly connected to the main control unit, and is used to receive the modulated electrical signal sent by the main control unit and send it to the laser, and amplify the output signal of the photodetector, analyze the output signal of the image detector, and send it to the main control unit;

[0023] Alternatively, it also includes an external synchronous rotating frame with two ends respectively mounted on the two-dimensional turntable and the off-axis transmitting and receiving optical system, and the electrical connections between the main control unit and the two-dimensional turntable, laser, photoelectric detector, and image detector are fixed on the external synchronous rotating frame.

[0024] The present invention also provides an underwater large-scale search and tracking duplex laser communication method, which uses the above-mentioned underwater large-scale search and tracking duplex laser communication device, and its special feature is that it includes the following steps:

[0025] Step 1: The local main control unit controls the laser to emit beacon light, and the opposite main control unit controls the two-dimensional turntable to drive the photoelectric detector to perform a first-level large-range scan and the image detector to perform a second-level precision tracking scan, so that the beacon light spot emitted by the local laser is at the center of the target surface of the opposite image detector;

[0026] Step 2: According to the method of step 1, the beacon light spot emitted by the laser at the other end is placed at the center of the target surface of the image detector at the local end, thereby establishing a communication link;

[0027] Step 3, respectively adjust the positions of the second zoom lenses of the local end and the opposite end to reduce the receiving field angle, and then the main control units of the local end and the opposite end respectively control the corresponding lasers to emit communication light;

[0028] Step 4: The communication light of the local end and the opposite end is divided into a tracking beam and a communication beam after passing through the second zoom lens and the beam splitter prism of the opposite end in turn. The tracking beam is focused by the focusing unit and then received by the image detector and transmitted to the main control unit. The communication beam is shaped and focused by the collimating and focusing unit and then received by the photoelectric detector and transmitted to the main control unit.

[0029] Step 5. The main control units of this end and the other end respectively process the output signals of the corresponding image detectors in real time, calculate the centroid position of the communication light spot, and adjust the two-dimensional turntable so that the communication light spot is always in the center of the target surface of the image detector; the main control units of this end and the other end respectively process the output signals of the corresponding photoelectric detectors in real time, obtain communication information, and complete underwater large-scale search and tracking duplex laser communication.

[0030] Furthermore, the step 1 is specifically as follows:

[0031] Step 1.1, setting the adjustment time interval and position of the first zoom lens at the local end, the main control unit controls the laser to emit beacon light, and then uses a polling method to adjust the position of the first zoom lens according to the set adjustment interval and position, thereby adjusting the beam divergence angle of the beacon light at the local end;

[0032] Step 1.2, the opposite two-dimensional turntable is powered on and returns to zero to enter a waiting state, and then the second zoom lens is adjusted to maximize the receiving field angle of the opposite end, and the predetermined scanning track and step distance of the two-dimensional turntable in the first-level large-range scanning and second-level precise tracking scanning states, as well as the output threshold of the photoelectric detector are set through the main control unit;

[0033] Step 1.3, turn on the opposite photoelectric detector and the image detector, and the main control unit determines whether it receives the light spot according to the output signal of the image detector. If the light spot is received, execute step 1.8; otherwise, execute step 1.4;

[0034] Step 1.4, the opposite end main control unit controls the two-dimensional turntable to perform a first-level large-range scan according to a predetermined scanning trajectory and step length, and records the output signal of the photodetector until the scanning of the entire spatial range is completed;

[0035] Step 1.5, the opposite end main control unit analyzes the output signal of the photodetector. If the output signal of the photodetector is greater than the output threshold, the spatial area corresponding to the maximum light intensity peak interval of the photodetector output signal is extracted and determined as the suspected target area, and then step 1.6 is executed;

[0036] Otherwise, reduce the predetermined step length of the first-level large-range scanning of the other end, reduce the beam divergence angle of the beacon light of the local end, and then return to step 1.4;

[0037] Step 1.6, the opposite end main control unit controls the two-dimensional turntable to perform secondary precision tracking scanning on the suspected target area according to the predetermined scanning trajectory and step length, and records the output signal of the image detector;

[0038] Step 1.7, the opposite end main control unit performs real-time analysis on the output signal of the image detector. If the opposite end image detector receives the light spot, execute step 1.8; otherwise, reduce the predetermined step length of the secondary fine tracking scan and return to step 1.6;

[0039] Step 1.8, the opposite end main control unit calculates the spot centroid position of the image detector output signal, and then adjusts the two-dimensional turntable according to the spot centroid position so that the beacon light spot emitted by the local laser is at the center of the target surface of the opposite end image detector 24.

[0040] Furthermore, in step 1.2, the output threshold of the photodetector is obtained by the following method:

[0041] Use a photodetector to record background noise, calculate the average output voltage of the background noise, and then take the average output voltage plus 3 times the standard deviation as the output threshold of the photodetector;

[0042] Alternatively, a photodetector is used to record background noise, the average rate of change of the background noise is calculated, and the average rate of change of the background noise plus 3 times the standard deviation is used as the output threshold of the photodetector.

[0043] Furthermore, in step 1.1, the beam divergence angle of the local beacon light satisfies: the diameter of the beam emitted through the transparent optical window at least covers the optical communication device at the opposite end.

[0044] Furthermore, in step 1.2, the predetermined scanning trajectory and step length of the two-dimensional turntable in the first-level large-range scanning and second-level fine tracking scanning states are specifically:

[0045] The predetermined scanning trajectory of the first-level large-range scanning is a serpentine scan or a rectangular scan, and the step distance is 80% to 85% of the field of view of the photodetector;

[0046] The predetermined scanning trajectory of the secondary fine tracking scanning is spiral scanning, and the step distance is 80% to 85% of the divergence angle of the laser beam.

[0047] Compared with the prior art, the present invention has the following beneficial technical effects:

[0048] 1. The present invention provides an underwater large-scale search and tracking duplex laser communication device, which uses a photoelectric detector in conjunction with a two-dimensional turntable for a first-level large-scale scan, and an image detector in conjunction with a two-dimensional turntable for a second-level precision tracking scan, which not only ensures a large scanning range, but also has the characteristics of high speed and high precision. For underwater non-cooperative target scenes, the uncertain area can be quickly narrowed, the initial pointing can be completed, and then the laser spot centroid position can be obtained to locate and track it, thereby realizing the discovery and capture of underwater random motion platforms, and quickly establishing optical communication links, while effectively improving the communication distance and communication rate. The overall layout of the equipment is compact and miniaturized, and it is easy for engineering applications.

[0049] 2. In the underwater large-scale search and tracking duplex laser communication device provided by the present invention, the transmitting branch is parallel to the receiving branch, which can ensure that no interference occurs between the transmitting and receiving signals during the communication process;

[0050] 3. In an underwater large-scale search and tracking duplex laser communication device provided by the present invention, a reflector is arranged on the reflected light path of the beam splitter prism, so that the image detector branch and the photoelectric detector branch are arranged in parallel, which can reduce the system volume and meet the size constraints of the system;

[0051] 4. In an underwater large-scale search and tracking duplex laser communication device provided by the present invention, two laser emission paths are set, and the wavelengths of the light beams emitted by the two lasers are the same. One of them is used to emit a beacon light, which is used for tracking and scanning of the device on the one hand, and is used to enhance the communication light power when the communication light power is insufficient on the other hand;

[0052] 5. In the underwater large-scale search and tracking duplex laser communication device provided by the present invention, a PMT detector is used, which has a large field of view, high sensitivity, and fast data processing speed. For underwater non-cooperative target scenes, the uncertain area can be quickly reduced;

[0053] 6. In an underwater large-scale search and tracking duplex laser communication device provided by the present invention, a two-dimensional turntable adopts a servo motor and a small time-grating encoder, which avoids a large friction torque of a dynamic seal and has fast response and high-precision performance;

[0054] 7. In an underwater large-scale search and tracking duplex laser communication device provided by the present invention, the sealed cabin adopts a transparent optical window and a fixing seat, which can protect the device from the underwater environment without interfering with light transmission, and the anti-reflection coating on the inner surface of the transparent optical window can enable the transparent optical window to maintain excellent optical transmittance;

[0055] 8. In an underwater large-scale search and tracking duplex laser communication device provided by the present invention, an external synchronous rotating frame is used to fix the electrical wiring to keep the connecting wire relatively still, avoiding the axis alignment of the two-dimensional turntable, or a tracking processing board is used to perform preliminary processing on the data before wirelessly transmitting it to the main control unit, which solves the problem of winding and twisting of the connecting wire during rotation under the constraints of a compact layout;

[0056] 9. In an underwater large-scale search and tracking duplex laser communication device provided by the present invention, a variable iris is included, and the main control unit can adjust the size of the variable iris in real time according to the noise count in the bit time slot to reduce the interference of the background light signal;

[0057] 10. The present invention provides an underwater large-scale search and tracking duplex laser communication method, which first uses a photoelectric detector to scan the entire space range, establishes a suspected target area according to the peak mutation of its output signal in the search period, and then uses an image detector to perform precise tracking scanning of the suspected target area. The two-dimensional turntable is adjusted according to the centroid position of the light spot calculated according to the output signal of the image detector, so that the centroid position of the light spot is at the center of the target surface of the image detector, thereby realizing the discovery and capture of random moving underwater targets;

[0058] 11. In an underwater large-scale search and tracking duplex laser communication method provided by the present invention, when the device is in a staring scanning state, the receiving branch is in a large field of view state, capturing the receiving light beam of the other end in a large range; when the alignment, capture, and tracking states are completed and the communication link is established, the receiving branch is in a small field of view state to avoid background light deteriorating the communication quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A schematic diagram of the structure of an optical communication device in an embodiment of the present invention;

[0060] Figure 2 It is a structural schematic diagram of an off-axis optical system for transmitting and receiving in an embodiment of the present invention;

[0061] Figure 3 is a schematic diagram of an optical communication device according to an embodiment of the present invention;

[0062] Figure 4 It is a flow chart of a method for underwater large-scale search and tracking duplex laser communication according to an embodiment of the present invention;

[0063] The following are the descriptions of the reference numerals:

[0064] 1-sealed cabin, 2-two-dimensional turntable, 3-off-axis optical system for transmitting and receiving, 4-main control unit, 5-transparent optical window, 6-fixed seat, 7-sealing pad, 8-sealing ring, 9-transmitting branch, 10-receiving branch;

[0065] 11-laser, 12-laser collimator, 13-first zoom lens; 14-second zoom lens, 15-beam splitter, 16-first focusing lens, 17-variable aperture, 18-shaping lens, 19-narrowband filter, 20-second focusing lens, 21-photodetector; 22-reflector, 23-third focusing lens, 24-image detector. DETAILED DESCRIPTION

[0066] The following is a further detailed description of an underwater large-scale search and tracking duplex laser communication device and method proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0067] An underwater large-scale search and tracking duplex laser communication device comprises two optical communication machines with the same structure, the two optical communication machines are respectively installed on a local device and a peer device, such as Figure 1 As shown, the optical communication device includes a sealed cabin 1, a two-dimensional turntable 2 and a main control unit 4 arranged in the sealed cabin 1, and a transceiver off-axis optical system 3 arranged on the two-dimensional turntable 2.

[0068] The sealed cabin 1 is composed of a fixed seat 6 and a transparent optical window 5. The fixed seat 6 and the transparent optical window 5 are sealed by a sealing gasket 7 and a sealing ring 8. The transparent optical window 5 is a large-diameter transparent optical window of a cylindrical segment plus a hemisphere, and an anti-reflection coating is provided on its inner surface. The sealed cabin 1 has a large-range light-transmitting window and provides a large-range rotation space for the two-dimensional turntable 2. It can protect the equipment from the underwater environment without interfering with the light transmission. On the one hand, it has good high-pressure resistance and sealing performance, which can ensure that the interior of the optical communication machine is completely isolated from the external environment and prevent the intrusion of water, dust, gas, etc.; on the other hand, the anti-reflection coating combined with the transparent optical window 5 can maintain excellent optical transmittance, especially in a specific spectral range.

[0069] The two-dimensional turntable 2 adopts an L-shaped layout. The azimuth rotation and pitch rotation are driven by servo motors. The angle measuring element adopts a small time-grating encoder. The response time of the control command is less than 20ms.

[0070] like Figure 2 As shown, the off-axis optical system 3 for transmitting and receiving is arranged near the transparent optical window 5, and includes a transmitting branch 9 and a receiving branch 10 which are parallel to each other. The transmitting branch is parallel to the receiving branch, and the weight of the whole optical system is ≤200g, which can reduce the driving torque of the servo motor and realize a compact layout.

[0071] like Figure 3As shown, the transmitting branch 9 includes a laser 11 for emitting beacon light and / or communication light, and a laser collimator 12 and a first zoom lens 13 arranged in sequence along the laser transmission direction. In other embodiments, there may be two lasers 11, and a laser collimator 12 and a first zoom lens 13 are arranged in sequence at the rear end of each laser along the laser transmission direction. The wavelengths of the light beams emitted by the two lasers are the same, one of which is used to emit beacon light, which is used for tracking and scanning of the device on the one hand, and for enhancing the transmission light power when the communication light power is insufficient on the other hand. On the one hand, the transmitting branch can emit continuous laser light with a variable light beam divergence angle for scanning the opposite communication terminal, and this process is assisted by the first zoom lens 13; on the other hand, after the two optical communication machines complete the alignment, capture and tracking of the light beams, the signal is modulated onto the optical carrier to emit the communication light.

[0072] The receiving branch 10 includes a second zoom lens 14 and a beam splitter prism 15 arranged in sequence along the direction of light beam transmission. The transmission light path of the beam splitter prism 15 is provided with a first focusing lens 16, a variable aperture 17, a shaping lens 18, a narrowband filter 19, a second focusing lens 20 and a photodetector 21 in sequence along the direction of light beam propagation. The reflection light path is provided with a reflector 22, a third focusing lens 23 and an image detector 24 in sequence along the direction of light beam propagation. The narrowband filter 19 enhances the quality of the received signal by filtering out non-target light wavelengths. The variable aperture 17 is electrically connected to the main control unit 4. The beam splitter prism 5 is used to split the received light beam into a tracking light beam and a communication light beam, and the splitting ratio is 1:4. In other embodiments, the splitting ratio can be adjusted. The tracking light beam enters the image detector 24 for fine tracking and alignment, and the communication light beam enters the photodetector 21 for coarse tracking and communication. The photodetector 21 and the image detector 24 can be interchanged according to structural requirements.

[0073] The photodetector 21 uses a PMT detector to perform a first-level large-range scan. It has the characteristics of high sensitivity, fast response, and a large field of view, so that the two-dimensional turntable 2 can perform a large-range search. According to the peak mutation of the PMT detector response signal within the search range, a suspected target area is established to achieve rough initial pointing. The image detector 24 uses a CCD camera to perform a second-level precision tracking scan. It starts scanning in the suspected target area according to spiral, rectangular, and other trajectories, and captures the target light spot, thereby entering the tracking state, so that the light beams at both ends of the communication are aligned. The detection fields of the photodetector 21 and the image detector 24 are similar, and both are ≥10°. The target surfaces of the PMT detector and the CCD camera are comparable, and the size difference between the two is plus or minus 2mm.

[0074] The main control unit 4 adopts FPGA and is electrically connected to the two-dimensional turntable 2, the laser 11, the photodetector 21, and the image detector 24 respectively. It is used to control the two-dimensional turntable 2, modulate the laser output by the laser 11, and filter and demodulate the laser signals received by the photodetector 21 and the image detector 22.

[0075] There are optical fibers and electrical connections between the off-axis transceiver optical system 3, the two-dimensional turntable 2 and the main control unit 4. Under the constraints of a compact layout, two methods can be used to solve the problem of winding and twisting of the connecting wires during rotation. One is to adopt an external wiring solution, install an external synchronous rotating frame on the two-dimensional turntable 2 and the off-axis transceiver optical system 3, and fix the optical fiber and electrical connections of the off-axis transceiver optical system 3 through the external synchronous rotating frame to keep the connecting wires relatively still. The second is to use a tracking processing board, electrically connect the tracking processing board to the laser 11, the photodetector 21, and the optical detector 24, and use a wireless connection with the main control unit 4, use the tracking processing board to amplify the output signal of the photodetector 21, and analyze the output signal of the image detector 24, and then use high-speed WIFI to interact with the main control unit 4 for wireless data, and the data delay does not exceed 10ms.

[0076] When the device starts working, the system is in the staring scanning state, and the zoom optical system is in a large field of view state, capturing the receiving light beam of the opposite end in a large range; when the alignment, capture, and tracking states are completed and the communication link is established, the zoom optical system is in a small field of view state to prevent background light from deteriorating the communication quality. The 1:4 beam splitter prism 5 is placed in parallel to the zoom optical system to split the incident light, of which 20% of the light energy is split and enters the image detector 24 for beam precision tracking and real-time follow-up. 80% of the light energy is used for communication. The first focusing lens 16, the variable aperture 17, the shaping lens 18 and the second focusing lens 20 collimate and focus the light beam, the narrowband filter 19 filters the signal light, and the photodetector 21 is placed at the focal plane of the focusing lens to convert the received light signal into an electrical signal. The main control unit 4 synchronizes, filters and demodulates the optical signal output by the photodetector 21, and adjusts the size of the variable aperture 17 in real time according to the noise count in the bit time slot to reduce the interference of the background light signal.

[0077] This embodiment also provides an underwater large-scale search and tracking duplex laser communication method, using the above-mentioned underwater large-scale search and tracking duplex laser communication device, such as Figure 4 As shown, the following steps are included:

[0078] Step 1: The local main control unit 4 controls the laser 11 to emit beacon light, and the opposite main control unit 4 controls the two-dimensional turntable 2 to drive the photoelectric detector 21 to perform a first-level large-range scan and the image detector 24 to perform a second-level precision tracking scan, so that the beacon light spot emitted by the local laser 11 is at the center of the target surface of the opposite image detector 24. Specifically:

[0079] Step 1.1, set the adjustment time interval and position of the first zoom lens 13 at the local end, the main control unit 4 controls the laser 11 to emit beacon light, the local main control unit 4 modulates to generate a modulated electrical signal, the electrical signal is amplified by the amplifier and then driven by the driver to emit beacon light, after being transmitted through the pigtail, it is emitted by the laser collimator 12, and then the position of the first zoom lens 13 is adjusted according to the set adjustment interval and position in a polling manner, so as to adjust the beam divergence angle of the beacon light at the local end. The beam divergence angle of the beacon light should meet the following requirements: the diameter of the beam emitted through the transparent optical window 5 at least covers the optical communication machine at the opposite end.

[0080] Step 1.2, the two-dimensional turntable 2 at the opposite end is powered on and returns to zero to enter the waiting state, the photodetector 21 is in the staring state, and then the second zoom lens 14 is adjusted to maximize the receiving field of view of the opposite end, and the predetermined scanning trajectory and step length of the two-dimensional turntable 2 in the first-level large-range scanning and second-level fine tracking scanning states, as well as the output threshold of the photodetector 21 are set through the main control unit 4. Among them, the predetermined scanning trajectory of the first-level large-range scanning is serpentine scanning or rectangular scanning, and the step length is determined according to the field of view size of the photodetector 21. In this embodiment, 80% of the field of view of the photodetector 21 is taken; the predetermined scanning trajectory of the second-level fine tracking scanning is spiral scanning, and the step length is determined according to the beam divergence angle of the laser 11. In this embodiment, 80% of the beam divergence angle of the laser 11 is taken. The output threshold of the photodetector 21 is obtained by the following method:

[0081] The photodetector 21 is used to record the background noise, the output voltage average value of the background noise is calculated, and then the output voltage average value plus 3 times the standard deviation is taken as the output threshold value of the photodetector 21;

[0082] Alternatively, the photodetector 21 is used to record the background noise, the average value of the change rate of the background noise is calculated, and the average change rate of the background noise plus 3 times the standard deviation is used as the output threshold of the photodetector 21 .

[0083] Step 1.3, turn on the opposite end photoelectric detector 21 and the image detector 24, and the main control unit 4 determines whether it receives the light spot according to the output signal of the image detector 24. If the light spot is received, execute step 1.8; otherwise, execute step 1.4.

[0084] Step 1.4, the opposite end main control unit 4 controls the two-dimensional turntable 2 to perform a first-level large-scale scan according to the predetermined scanning trajectory and step length, and records the output signal of the photodetector 21 until the entire spatial range (azimuth ±180°, pitch ±90°) is scanned. The first-level large-scale scanning sampling grid search method divides the entire field of view of the optical window (azimuth ±180°, pitch ±90°) into 16 rectangular grids, each grid size is equivalent to the detection field of view of the photodetector 21, and a serpentine traversal search order is adopted.

[0085] Step 1.5, the opposite end main control unit 4 analyzes the output signal of the photodetector 21. If the output signal of the photodetector 21 is greater than the output threshold, the spatial area corresponding to the maximum light intensity peak interval of the output signal of the photodetector 21 is extracted and determined as the suspected target area, and then step 1.6 is executed;

[0086] Otherwise, reduce the predetermined step length of the first-level large-range scanning at the other end, reduce the beam divergence angle of the beacon light at this end, and then return to step 1.4.

[0087] Step 1.6: The opposite end main control unit 4 controls the two-dimensional turntable 2 to perform secondary fine tracking scanning on the suspected target area according to the predetermined scanning trajectory and step length, and records the output signal of the image detector 24. The specific method of the secondary fine tracking scanning is to perform spiral scanning with the center of the suspected target area as the starting position.

[0088] Step 1.7, the opposite main control unit 4 performs real-time analysis on the output signal of the image detector 24. If the opposite image detector 24 receives a light spot, execute step 1.8; otherwise, reduce the predetermined step length of the secondary fine tracking scan and return to step 1.6.

[0089] Step 1.8, the opposite end main control unit 4 calculates the spot centroid position of the output signal of the image detector 24, and then adjusts the two-dimensional turntable 2 according to the spot centroid position so that the beacon light spot emitted by the local laser 11 is at the center of the target surface of the opposite end image detector 24.

[0090] Step 2: According to the method of step 1, the beacon light spot emitted by the laser 11 at the other end is placed at the center of the target surface of the image detector 24 at the local end, thereby establishing a communication link.

[0091] Step 3: respectively adjust the positions of the second zoom lenses 14 at the local end and the opposite end to reduce the receiving field angle, and then the main control units 4 at the local end and the opposite end respectively control the corresponding lasers 11 to emit communication light.

[0092] Step 4, the communication light of this end and the other end passes through the second zoom lens 14 and the splitter prism 15 of the other end in turn and is divided into a tracking beam and a communication beam. The tracking beam is focused by the focusing unit, received by the image detector 24 and transmitted to the main control unit 4, and the communication beam is shaped and focused by the collimating and focusing unit, received by the photodetector 21 and transmitted to the main control unit 4.

[0093] Step 5, the main control units 4 at this end and the other end respectively process the output signals of the corresponding image detectors 24 in real time, calculate the centroid position of the communication light spot, and adjust the two-dimensional turntable 2 so that the communication light spot is always at the center of the target surface of the image detector 24; the main control units 4 at this end and the other end respectively process the output signals of the corresponding photoelectric detectors 21 in real time, obtain the communication information, and complete the underwater large-scale search and tracking duplex laser communication.

[0094] During the entire process of establishing the capture and tracking link, the communication sensitivity of the optical communication link should not be higher than the saturated optical power of the photodetector 21 and the image detector 24 .

Claims

1. An underwater large-scale search and tracking duplex laser communication device, comprising two optical communication devices of the same structure, the two optical communication devices being respectively installed on a local device and a peer device, characterized in that: The optical communication device comprises a sealed cabin (1) composed of a fixing seat (6) and a transparent optical window (5), a two-dimensional turntable (2) and a main control unit (4) arranged in the sealed cabin (1), and a transceiver off-axis optical system (3) arranged on the two-dimensional turntable (2); The off-axis transmitting and receiving optical system (3) is arranged close to the transparent optical window (5), and comprises a transmitting branch (9) and a receiving branch (10) which are parallel to each other; The transmitting branch (9) comprises a laser (11) for emitting beacon light and / or communication light, and a laser collimator (12) and a first zoom lens (13) arranged in sequence along the laser transmission direction; The receiving branch (10) comprises a second zoom lens (14) and a beam splitter prism (15) arranged in sequence along the light beam transmission direction; a first-level large-range scanning and communication unit and a second-level precision tracking scanning unit are respectively arranged on the transmission light path and the reflection light path of the beam splitter prism (15); the first-level large-range scanning and communication unit comprises a collimating and focusing unit and a photoelectric detector (21) arranged in sequence along the light beam propagation direction; and the second-level precision tracking scanning unit comprises a reflector (22), a focusing unit and an image detector (24) arranged in sequence along the light beam propagation direction; The main control unit (4) is electrically connected to the two-dimensional turntable (2), the laser (11), the photodetector (21), and the image detector (24) respectively, and is used to control the two-dimensional turntable (2), modulate the laser output by the laser (11), and filter and demodulate the laser signals received by the photodetector (21) and the image detector (22).

2. According to claim 1, an underwater large-scale search and tracking duplex laser communication device is characterized in that: The laser (11) comprises a beacon laser and a communication laser. The wavelengths of the light beams emitted by the beacon laser and the communication laser are the same. The communication laser is used to emit communication light, and the beacon laser is used to emit beacon light and enhance the power of the communication light. The laser collimator (12) and the first zoom lens (13) are sequentially arranged at the rear ends of the beacon laser and the communication laser along the laser transmission direction.

3. An underwater large-scale search and tracking duplex laser communication device according to claim 1 or 2, characterized in that: The detection fields of the photoelectric detector (21) and the image detector (24) are both ≥10°; The photoelectric detector (21) is a PMT detector, and the image detector (24) is a CCD camera; The transparent optical window (5) is a large-aperture transparent optical window in the form of a cylindrical segment plus a hemisphere, and an anti-reflection coating is provided on the inner surface thereof; The two-dimensional turntable (2) adopts an L-shaped layout, the azimuth rotation and the pitch rotation are driven by a servo motor, and the angle measuring element adopts a small time-grating encoder; The light splitting ratio of the light splitting prism (15) is 1:

4.

4. The underwater large-scale search and tracking duplex laser communication device according to claim 3, characterized in that: The collimating and focusing unit comprises a first focusing lens (16), a variable iris (17), a shaping lens (18), a narrowband filter (19) and a second focusing lens (20) which are sequentially arranged along the propagation direction of the light beam, and the variable iris (17) is electrically connected to the main control unit (4); The focusing unit comprises a third focusing lens (23).

5. The underwater large-scale search and tracking duplex laser communication device according to claim 4, characterized in that: The device also includes a tracking processing board, which is electrically connected to the laser (11), the photodetector (21), and the image detector (24), and is wirelessly connected to the main control unit (4), and is used to receive a modulated electrical signal sent by the main control unit (4), and send it to the laser (11), and to amplify the output signal of the photodetector (21), analyze the output signal of the image detector (24), and send it to the main control unit (4); Alternatively, it also includes an external synchronous rotating frame with two ends respectively mounted on the two-dimensional turntable (2) and the off-axis transceiver optical system (3), and the electrical connections between the main control unit (4) and the two-dimensional turntable (2), the laser (11), the photoelectric detector (21), and the image detector (24) are fixed on the external synchronous rotating frame.

6. An underwater large-scale search and tracking duplex laser communication method, using an underwater large-scale search and tracking duplex laser communication device according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, the local main control unit (4) controls the laser (11) to emit beacon light, and the opposite main control unit (4) controls the two-dimensional turntable (2) to drive the photoelectric detector (21) to perform a first-level large-range scan and the image detector (24) to perform a second-level precision tracking scan, so that the beacon light spot emitted by the local laser (11) is located at the center of the target surface of the opposite image detector (24); Step 2: According to the method of step 1, the beacon light spot emitted by the opposite end laser (11) is placed at the center of the target surface of the local end image detector (24), thereby establishing a communication link; Step 3, respectively adjusting the positions of the second zoom lenses (14) at the local end and the opposite end to reduce the receiving field angle, and then the main control units (4) at the local end and the opposite end respectively control the corresponding lasers (11) to emit communication light; Step 4, the communication light of the local end and the opposite end passes through the second zoom lens (14) and the beam splitter prism (15) of the opposite end in sequence, and is then divided into a tracking light beam and a communication light beam. The tracking light beam is focused by the focusing unit, received by the image detector (24), and transmitted to the main control unit (4). The communication light beam is shaped and focused by the collimating and focusing unit, received by the photoelectric detector (21), and transmitted to the main control unit (4). Step 5, the main control units (4) at this end and the other end respectively process the output signals of the corresponding image detectors (24) in real time, calculate the centroid position of the communication light spot, and adjust the two-dimensional turntable (2) so that the communication light spot is always at the center of the target surface of the image detector (24); the main control units (4) at this end and the other end respectively process the output signals of the corresponding photoelectric detectors (21) in real time, obtain communication information, and complete underwater large-scale search and tracking duplex laser communication.

7. The underwater large-scale search and tracking duplex laser communication method according to claim 6, characterized in that: The step 1 is specifically as follows: Step 1.1, setting the adjustment time interval and position of the first zoom lens (13) at the local end, the main control unit (4) controls the laser (11) to emit beacon light, and then uses a polling method to adjust the position of the first zoom lens (13) according to the set adjustment interval and position, thereby adjusting the beam divergence angle of the beacon light at the local end; Step 1.2, the opposite two-dimensional turntable (2) is powered on and returns to zero to enter a waiting state, and then the second zoom lens (14) is adjusted to maximize the receiving field angle of the opposite end, and the predetermined scanning trajectory and step distance of the two-dimensional turntable (2) in the first-level large-range scanning and second-level precise tracking scanning states, as well as the output threshold of the photoelectric detector (21) are set through the main control unit (4); Step 1.3, turning on the opposite end photoelectric detector (21) and the image detector (24), the main control unit (4) determines whether it receives the light spot according to the output signal of the image detector (24), if the light spot is received, executing step 1.8; otherwise, executing step 1.4; Step 1.4, the opposite end main control unit (4) controls the two-dimensional turntable (2) to perform a first-level large-range scan according to a predetermined scanning trajectory and step length, and records the output signal of the photodetector (21) until the scanning of the entire spatial range is completed; Step 1.5, the opposite end main control unit (4) analyzes the output signal of the photodetector (21), and if the output signal of the photodetector (21) is greater than the output threshold, extracts the spatial area corresponding to the maximum light intensity peak interval of the output signal of the photodetector (21), determines it as the suspected target area, and then executes step 1.6; Otherwise, reduce the predetermined step length of the first-level large-range scanning of the other end, reduce the beam divergence angle of the beacon light of the local end, and then return to step 1.4; Step 1.6, the opposite end main control unit (4) controls the two-dimensional turntable (2) to perform a secondary precision tracking scan on the suspected target area according to a predetermined scanning trajectory and step length and records the output signal of the image detector (24); Step 1.7, the opposite end main control unit (4) performs real-time analysis on the output signal of the image detector (24), and if the opposite end image detector (24) receives the light spot, execute step 1.8; otherwise, reduce the predetermined step length of the secondary fine tracking scan, and return to step 1.6; Step 1.8, the opposite end main control unit (4) calculates the spot mass center position of the image detector (24) output signal, and then adjusts the two-dimensional turntable (2) according to the spot mass center position, so that the beacon light spot emitted by the local laser (11) is at the center of the target surface of the opposite end image detector (24).

8. The underwater large-scale search and tracking duplex laser communication method according to claim 7, characterized in that: In step 1.2, the output threshold of the photodetector (21) is obtained by the following method: Using a photodetector (21) to record background noise, calculating an output voltage average of the background noise, and then taking the output voltage average plus 3 times the standard deviation as an output threshold of the photodetector (21); Alternatively, the photoelectric detector (21) is used to record the background noise, the average value of the change rate of the background noise is calculated, and the average change rate of the background noise plus 3 times the standard deviation is used as the output threshold of the photoelectric detector (21).

9. The underwater large-scale search and tracking duplex laser communication method according to claim 8, characterized in that: In step 1.1, the beam divergence angle of the local beacon light satisfies: the diameter of the beam emitted through the transparent optical window (5) at least covers the optical communication device at the opposite end.

10. The underwater large-scale search and tracking duplex laser communication method according to claim 9, characterized in that: In step 1.2, the predetermined scanning trajectory and step length of the two-dimensional turntable (2) in the first-level large-range scanning and second-level fine tracking scanning states are specifically: The predetermined scanning trajectory of the first-level large-range scanning is a serpentine scan or a rectangular scan, and the step distance is 80% to 85% of the field of view of the photoelectric detector (21); The predetermined scanning track of the secondary fine tracking scanning is spiral scanning, and the step distance is 80% to 85% of the divergence angle of the laser beam (11).

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