A laser communication optical transceiver suitable for UAV platforms with limited load capacity

Abstract

The invention discloses a laser communication optical terminal suitable for an unmanned aerial vehicle platform with limited carrying capacity, belonging to the technical field of optical communication; the laser communication optical terminal comprises a laser emitting unit, a MEMS reflector scanning unit, and a tracking and receiving communication unit; the MEMS reflector scanning unit uses a two-axis quasi-static MEMS reflector to replace a mechanical structure for light beam scanning, and is composed of a Galileo telescope composed of a MEMS reflector and a positive and negative lens group; the tracking and receiving unit is mainly composed of a photoelectric detection unit, a servo tracking unit, and a communication demodulation unit, and completes the communication and tracking functions respectively through electronic processing means mainly based on addition circuits and subtraction circuits; the invention uses a MEMS reflector as a servo mechanism, an inverted zoom Galileo telescopic optical system as an antenna, and CMOS and QD as coarse and fine tracking detectors respectively, and realizes rapid scanning and capturing by zooming, and has a reasonable design and a novel method, and has a prospect of application in a fixed environment.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a laser communication optical terminal suitable for an unmanned aerial vehicle platform with limited carrying capacity. Background Art

[0002] Compared with radio frequency microwave communication technology, wireless laser communication technology has attracted widespread attention due to its fast communication rate and strong applicability in denied environments. At present, a variety of products have been developed at home and abroad, including ground-based, satellite-based, airborne, ship-based, underwater and single-soldier products, covering mobile and non-mobile platforms in multiple fields such as air, space, land and sea. With the development of technology, wireless laser communication is rapidly iterating in the direction of miniaturization and generalization.

[0003] The miniaturization design of wireless laser communication terminals can be achieved with the help of MEMS (Micro-Electro-Mechanical) devices, such as MEMS actuators, MEMS reflectors, etc. The volume and weight advantages of these devices can ensure the stable capture, tracking and aiming of the servo mechanism on the basis of miniaturization. Among them, the MEMS reflector is generally in the form of a chip, integrating a millimeter-level circular or rectangular reflective surface, and the mechanical deflection angle is generally within ±5°.

[0004] The satellite-borne wireless laser communication terminal has a long communication distance, and a telescopic optical system can be added in front of the MEMS reflector to increase the receiving aperture and obtain a greater receiving gain. The telescopic system will also cause the optical deflection range to be compressed, but the satellite-borne terminal can use star sensitivity to control the initial pointing within the range of ±1°, so the entire system can fully meet the long-distance capture, tracking and aiming requirements between satellites.

[0005] The biggest technical difficulty for individual or handheld miniaturized wireless optical communication terminals is that they cannot be accurately guided for auxiliary alignment, and their ATP function is completely dependent on the terminal itself. Therefore, there are defects such as small scanning range and difficulty in link establishment. Summary of the invention

[0006] The present invention proposes a laser communication optical terminal suitable for UAV platforms with limited carrying capacity; it uses a MEMS reflector as a servo mechanism, an inverted zoom Galileo telescopic optical system as an antenna, CMOS and QD (Quadrantphoto-detector) as coarse and fine tracking detectors respectively, and realizes rapid scanning and capturing by zooming. It has a reasonable design and a novel method, and has the prospect of application in a fixed environment.

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

[0008] A laser communication optical terminal suitable for an unmanned aerial vehicle platform with limited carrying capacity, comprising a laser transmitting unit, a MEMS reflector scanning unit, and a tracking and receiving communication unit;

[0009] The MEMS reflector scanning unit uses a two-axis quasi-static MEMS reflector to replace the mechanical structure for light beam scanning, and is composed of a Galilean telescope consisting of a MEMS reflector and a positive and negative lens group;

[0010] The tracking and receiving unit is mainly composed of a photoelectric detection unit, a servo tracking unit, and a communication demodulation unit, and completes the communication and tracking functions respectively through electronic processing means mainly based on addition circuits and subtraction circuits;

[0011] The dual optical terminals use beacon lights with a large beam divergence angle to scan each other in the uncertain area to reduce the uncertainty area; then the communication light is used to complete the capture and tracking. The specific process is as follows:

[0012] Step 1: The A-end and B-end are initialized, the angle of the MEMS reflector is reset to zero, and the zoom optical antenna is reset;

[0013] Step 2: The pointing adjustment range of the A-end and the B-end is 40°×60°. The A-end uses a CMOS detector with a zoom optical antenna to maintain staring, that is, the diagonal full field of view of the CMOS effective area is about 70°; the B-end uses a large-beam divergence beacon light to scan the entire pointing adjustment range in a spiral scanning manner; after the A-end detects the beacon light of the B-end, it adjusts the optical axis to point to the B-end;

[0014] Step 3: After the B-end machine completes the scanning, it returns to the center zero position. The A-end machine uses a large-beam divergence beacon light to scan a small range around the direction of the B-end machine. After the B-end machine detects the beacon light of the A-end machine, it adjusts the optical axis to point to the A-end machine.

[0015] Step 4: After the A and B terminals complete scanning respectively, the uncertain area is obtained. At this time, the optical antenna needs to complete zooming, switch the large-beam divergence beacon light to the small-beam divergence signal light, and enter the secondary capture and tracking; the size of the uncertain area depends on the segmentation capability of the CMOS detector and the centroid extraction algorithm. The detector field of view in the secondary capture and tracking optical path is larger than the uncertain area to ensure that the secondary detector can receive the optical signal;

[0016] Step 5: In the second-level capture and tracking, a four-quadrant detector is used to further adjust the direction of the optical axis and realize the integration of tracking and communication.

[0017] Furthermore, the MEMS mirror scanning unit is a transmit-receive common-aperture multiplexing unit composed of a MEMS mirror and a Galilean telescope. The Galilean telescope includes a Keplerian telescope system and a Galilean telescope system. The MEMS mirror includes a two-axis quasi-static MEMS mirror, a two-axis resonant MEMS mirror and an x-axis quasi-static MEMS mirror.

[0018] Furthermore, the laser emitting unit uses a laser to generate laser light of the required frequency and energy, utilizes a random number generation module to simulate the data transmitted by laser communication, and uses RS encoding and decoding technology to enhance the anti-interference capability of the system.

[0019] Furthermore, the tracking and receiving unit adopts a large target hollow four-quadrant detector to resolve the contradiction between the target size, communication bandwidth and communication rate, thereby ensuring the laser communication rate while achieving high-precision target position solution.

[0020] Furthermore, the Galilean telescope is composed of a positive lens group and a negative lens group, and can greatly expand the scanning aperture according to the focal lengths of the two lens groups; the angular magnification capability of the Galilean telescope system is determined by the focal length multiples of the two lens groups.

[0021] The beneficial effects of the above technical solution of the present invention are:

[0022] The present invention can greatly expand the optical deflection angle range of the MEMS galvanometer through the inverted Galileo optical telescope system, and the combination of positive and negative lenses makes the overall structure shorter, which is conducive to the miniaturization design of the system; on this basis, the light source beam divergence angle is changed by switching the zoom to realize the design of switching between the transmitted signal light and the beacon light, which greatly simplifies the ATP servo structure and is more conducive to system integration and lightweight design. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the principle of an embodiment of the present invention.

[0024] Figure 2 Schematic diagram of the scanning range expansion principle of an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] In view of the problems in the background technology, this embodiment integrates a small MEMS reflector and considers using the telescopic optical system invertedly, maintaining the mechanical deflection angle of the MEMS reflector while expanding the optical deflection angle. Based on this idea, a solution that does not require guidance and can search, track, and communicate over a large range is proposed. The MEMS reflector is used as a servo mechanism, the inverted zoom Galileo telescopic optical system is used as an antenna, and CMOS and QD (Quadrant photodetector) are used as coarse and fine tracking detectors respectively. Rapid scanning and capture are achieved through zooming, which greatly expands the scanning and search range and improves the efficiency of link establishment at the communication end.

[0028] Reference Figure 1 , the principle block diagram of the wireless optical communication terminal proposed in this embodiment, the designed communication distance is not less than 250m. The capture and tracking consists of two stages, and the two stages share the same MEMS reflector as the actuator. Terminal A and terminal B use continuous lasers with wavelengths of 808nm and 850nm respectively. Only one laser is used in each terminal, which emits beacon light before zooming and signal light after zooming. Visible light CMOS detectors and silicon-based four-quadrant detectors are used in the first-level capture and tracking and the second-level capture and tracking respectively. The response range of these two detectors is between 400 and 1100nm, which can realize the detection and positioning of 808nm and 850nm lasers.

[0029] The wireless optical communication terminal mainly includes a laser transmitting module, an optical antenna module, a servo tracking module, a communication baseband module, and a power module. In the present invention, a single terminal laser transmitting module integrates only one laser light source, and relies on a zoom optical antenna to realize the switching between signal light and beacon light. The servo tracking module scans and step-tracks the incident light signal through a MEMS galvanometer according to the feedback signal of the detector. After establishing an effective optical link connection, the communication baseband module is responsible for the encoding and modulation of the outgoing light signal and the demodulation of the received signal. The power module provides a stable constant voltage output for other modules.

[0030] The technical solution provided in this embodiment provides a method for designing optical antennas for laser communication terminals suitable for satellite-borne, UAV, individual soldier and other platforms, so as to solve technical problems such as large field of view scanning capture, pointing range limitation, and excessive full-field distortion in lightweight and miniaturized wireless optical communication terminals.

[0031] The design uses MEMS mirrors as servo control devices for antenna pointing control. MEMS mirrors have the advantages of high precision, small size and low power consumption. Mirrorcle's MEMS mirrors can support two-axis rotation, with a mechanical deflection angle of up to ±5°, a resolution of 14bit, a target size of up to 5mm, and an optical deflection adjustment range of up to ±10° for parallel light incident at 45°. The design uses an inverted optical telescope system to expand this optical deflection range to 70°. The Galilean telescope using a combination of positive and negative lenses can reduce the total length of the system while maintaining the same angular magnification capability, which is conducive to miniaturized structural design. The principle of its scanning range expansion is as follows: Figure 2 shown.

[0032] On this basis, the antenna zoom function is added, and the telescope system is improved by switching zoom. The front group is a switchable positive doublet lens, and the rear group is a negative doublet lens. The angular magnification is kept at 3 by designing the focal length multiple of the lens group, and the simulation is performed after optimization using the AMAG operand. When the collimated laser is incident on the MEMS galvanometer and enters the zoom system after one reflection, the divergence angle is 50mrad before switching; after switching, while keeping the angular magnification unchanged, the divergence angle can be controlled at 1mrad, which is close to the diffraction limit. This design uses even-order aspheric surfaces for distortion correction, and the first and last surfaces of the rear group of doublet lenses are both even-order aspheric surfaces. The simulation results show the correction effect before zooming, and it is found that both before and after zooming are barrel distortion, and the field of view reaches the maximum when the difference is 0.9 and is less than 0.10%.

[0033] In this design, the laser emission and reception adopt the common aperture mechanism. The receiving optical path can be obtained by inverting the above emission optical path. In the signal receiving optical path, the actual aperture diaphragm is a MEMS reflector, and the MEMS reflector is placed at an angle of 45°. If its aperture is D MEMS , then the maximum aperture D of the signal light emitted from the MEMS reflector signal for:

[0034]

[0035] A single positive lens is used in front of the CMOS to simply converge the received beacon light. At 50lp / mm, the MTF value of each field of view is greater than 0.5. Using a detector with a pixel size less than 10um, the angular resolution of the beacon light detection system is better than 2.5mrad. Considering the maximum distortion difference of 0.5mrad before and after zooming, the field of view of the four-quadrant detector in the precision tracking system should be greater than 5mrad. When the four-quadrant detector directly receives the reflected light of the MEMS reflector without using a converging lens, in order to achieve a better detection effect of the four-quadrant detector, its target surface diameter D QD for:

[0036] D QD≈2D signal

[0037] In the precision tracking system, the maximum image field angle of the four-quadrant detector is 5mrad. If the distance between the center of the MEMS reflector and the center of the four-quadrant detector is L1, then:

[0038]

[0039] In wireless laser communication, the system's laser divergence angle, ATP field of view, uncertain area and other areas are different. Therefore, capture alignment can be roughly divided into three modes: stare-stare, stare-scan, and jump-scan. In order to simplify the structure of the terminal and reduce complexity, this implementation uses a composite method of beacon light and signal light to achieve the purpose of switching through a zoom antenna. The core idea is: the dual-optical terminal uses beacon light with a larger beam divergence angle to scan each other in the uncertain area to reduce the uncertain area; then use the communication light to complete the capture and tracking. The specific steps are as follows:

[0040] (1) The A and B terminals are initialized, the angle of the MEMS mirror is returned to zero, and the zoom optical antenna is reset.

[0041] (2) The pointing adjustment range of both end machines is 40°×60°, and there is no precise guidance means in the environment. Therefore, the A end machine uses a CMOS detector with a zoom optical antenna to maintain gaze, that is, the diagonal full field of view of the CMOS effective area is about 70°. The B end machine uses a large beam divergence beacon light to scan the entire pointing adjustment range in a spiral scanning manner. After the A end machine detects the beacon light of the B end machine, it adjusts the optical axis to point to the B end machine.

[0042] (3) After the B-end machine completes the scan, it returns to the center zero position. The A-end machine uses a large-beam divergence beacon light to scan a small range around the direction of the B-end machine. After the B-end machine detects the beacon light of the A-end machine, it adjusts the optical axis to point to the A-end machine.

[0043] (4) After the A and B terminals complete scanning, the uncertainty area is obtained. At this time, the optical antenna needs to complete zooming, switch the large-beam divergence beacon light to the small-beam divergence signal light, and enter the secondary capture and tracking. The size of the uncertainty area depends on the segmentation capability of the CMOS detector and the centroid extraction algorithm. The detector field of view in the secondary capture and tracking optical path is larger than the uncertainty area to ensure that the secondary detector can receive the optical signal.

[0044] (5) In the second-level capture and tracking, a four-quadrant detector is used to further adjust the direction of the optical axis and realize the integration of tracking and communication.

Claims

1. A laser communication optical terminal suitable for an unmanned aerial vehicle platform with limited carrying capacity, characterized in that: It includes a laser emitting unit, a MEMS reflector scanning unit, and a tracking and receiving communication unit; The MEMS reflector scanning unit uses a two-axis quasi-static MEMS reflector to replace the mechanical structure for light beam scanning, and is composed of a Galilean telescope consisting of a MEMS reflector and a positive and negative lens group; The tracking and receiving unit is mainly composed of a photoelectric detection unit, a servo tracking unit, and a communication demodulation unit, and completes the communication and tracking functions respectively through electronic processing means mainly based on addition circuits and subtraction circuits; The dual optical terminals use beacon lights with a large beam divergence angle to scan each other in the uncertain area to reduce the uncertainty area; then the communication light is used to complete the capture and tracking. The specific process is as follows: Step 1: The A-end and B-end are initialized, the angle of the MEMS reflector is reset to zero, and the zoom optical antenna is reset; Step 2: The pointing adjustment range of the A-end and the B-end is 40°×60°. The A-end uses a CMOS detector with a zoom optical antenna to maintain staring, that is, the diagonal full field of view of the CMOS effective area is about 70°; the B-end uses a large-beam divergence beacon light to scan the entire pointing adjustment range in a spiral scanning manner; after the A-end detects the beacon light of the B-end, it adjusts the optical axis to point to the B-end; Step 3: After the B-end machine completes the scanning, it returns to the center zero position. The A-end machine uses a large-beam divergence beacon light to scan a small range around the direction of the B-end machine. After the B-end machine detects the beacon light of the A-end machine, it adjusts the optical axis to point to the A-end machine. Step 4: After the A and B terminals complete scanning respectively, the uncertain area is obtained. At this time, the optical antenna needs to complete zooming, switch the large-beam divergence beacon light to the small-beam divergence signal light, and enter the secondary capture and tracking; the size of the uncertain area depends on the segmentation capability of the CMOS detector and the centroid extraction algorithm. The detector field of view in the secondary capture and tracking optical path is larger than the uncertain area to ensure that the secondary detector can receive the optical signal; Step 5: In the second-level capture and tracking, a four-quadrant detector is used to further adjust the direction of the optical axis and realize the integration of tracking and communication.

2. According to claim 1, a laser communication optical terminal suitable for an unmanned aerial vehicle platform with limited carrying capacity is characterized in that: The MEMS reflector scanning unit is a transmit-receive common aperture multiplexing unit composed of a MEMS reflector and a Galilean telescope. The Galilean telescope includes a Keplerian telescope system and a Galilean telescope system. The MEMS reflector includes a two-axis quasi-static MEMS reflector, a two-axis resonant MEMS reflector and an x-axis quasi-static MEMS reflector.

3. According to claim 1, a laser communication optical terminal suitable for an unmanned aerial vehicle platform with limited carrying capacity, characterized in that: The laser emitting unit uses a laser to generate laser light of the required frequency and energy, utilizes a random number generation module to simulate the data transmitted by laser communication, and uses RS encoding and decoding technology to enhance the anti-interference capability of the system.

4. According to claim 1, a laser communication optical terminal suitable for an unmanned aerial vehicle platform with limited carrying capacity is characterized in that: The tracking and receiving unit adopts a large target hollow four-quadrant detector to solve the contradiction between target size, communication bandwidth and communication rate, and ensures the laser communication rate while achieving high-precision target position solution.

5. According to claim 2, a laser communication optical terminal suitable for an unmanned aerial vehicle platform with limited carrying capacity is characterized in that: The Galilean telescope is composed of a positive lens group and a negative lens group, and can greatly expand the scanning aperture according to the focal lengths of the two lens groups; the angular magnification capability of the Galilean telescope system is determined by the focal length multiples of the two lens groups.

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