Space laser communication terminal and communication method thereof

Abstract

The application provides a space laser communication terminal and a communication method thereof, and relates to the technical field of space information, the terminal comprising a double-wedge structure coaxially arranged at the beam-expanding end of an optical antenna, the double-wedge structure comprising a wedge group and a rotating device, the wedge group being composed of two wedges arranged coaxially and oppositely, and the rotating device being used for rotating the wedges. Through the terminal, real-time tracking of a target satellite can be realized, and a signal transmission task can be efficiently completed, and the overall structure is simple and compact, the optical path requirement is short, and the occupied space is small.

Description

Technical Field

[0001] This invention relates to the field of space information technology, and in particular to a space laser communication terminal and its communication method. Background Technology

[0002] Space information networks are network systems that use space platforms (such as satellites, stratospheric balloons, or aircraft) as carriers and interconnect through integrated networking to acquire, transmit, and process space information in real time. Laser communication has advantages such as strong anti-interference capabilities, high security, fast transmission speed, and large information capacity, making it an ideal choice for building space information networks.

[0003] Currently, space laser communication terminals generally employ servo mechanisms for beam acquisition, tracking, and aiming. Coarse tracking between communication terminals can also be achieved through satellite attitude adjustments. The former method requires at least a two-dimensional servo mechanism to adjust the pitch and yaw angles of the optical lens to achieve mutual alignment of the laser communication terminals. This method necessitates the coordination of multiple servo axes, resulting in a large structure and low space utilization. While the second method has a simpler structure, it suffers from low alignment accuracy, a small field of view, and requires satellite attitude control for acquisition and tracking. Even a slight change in satellite attitude can cause a communication link interruption, paralyzing the entire communication system. Therefore, a novel technical solution is urgently needed to address these problems. Summary of the Invention

[0004] The purpose of this invention is to provide a space laser communication terminal and its communication method to solve at least one of the above-mentioned technical problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides a space laser communication terminal, including a dual optical wedge structure. The dual optical wedge structure is coaxially disposed at the beam expander end of the optical antenna and connected to the optical antenna to form an optical path. The dual optical wedge structure includes a plurality of optical wedge groups and a rotating device. The optical wedge group is composed of two optical wedges with vertical planes facing each other and placed coaxially. The rotating device is used to rotate the optical wedges.

[0006] According to the principle of light refraction, when the inclined surfaces of the two light wedges in the light wedge assembly are not parallel, the light will be deflected after passing through the two wedges. Adjusting the relative rotation angle of the two light wedges can control the deflection angle of the light. By synchronously rotating the two light wedges through the rotating device, light scanning can be achieved; by asynchronously rotating the two light wedges, the deflection angle of the light can be adjusted.

[0007] Therefore, the dual-wedge structure enables the laser communication terminal to scan and track target satellites. Compared with the space laser communication terminal using a servo mechanism in the prior art, the structure is simpler and the optical path is shorter, thereby reducing the requirement for equipment size.

[0008] Furthermore, the optical antenna is a transmission telescope head used to expand the emitted beam, shrink the received beam, and correct the optical distortion caused by the double-wedge structure. The beam expansion refers to increasing the diameter of the beam, and the beam shrinking refers to reducing the diameter of the beam.

[0009] Preferably, the optical antenna is a Galilean beam expander lens, which is a prior art technology and consists of a positive lens and a negative lens. Therefore, it has no internal focus and does not require internal focusing, thereby avoiding wavefront error.

[0010] Furthermore, it also includes a fast reflector, which is disposed at the beam-contraction end of the optical antenna and connected to the optical antenna to form an optical path.

[0011] The fast-reflecting mirror includes a motor and can finely adjust the deflection angle of the reflective lens to stabilize the optical system's line of sight and adjust the beam direction.

[0012] Furthermore, it also includes a tracking communication composite unit, which comprises a filter, a focusing unit, and a combined detector arranged sequentially.

[0013] The filter section is used to filter out stray light and allow signal light and beacon light to be transmitted to the focusing section. The filter section can be a filter or other filter components known in the art.

[0014] The focusing unit is used to converge the signal light and the beacon light onto the combined detector. The focusing unit can be a focusing lens or other focusing components known in the art.

[0015] The combined detector is used to detect the position of the beacon light and receive the signal light to complete information transmission. The position of the beacon light is used to adjust the deflection angle of the fast-reflecting mirror to maintain tracking of the target satellite.

[0016] The signal light is used to transmit information.

[0017] The tracking and communication composite unit can simultaneously complete both tracking and communication tasks using a single optical path, reducing the number of split optical paths and simplifying the system structure.

[0018] Preferably, the combined detector is a four-quadrant and avalanche photodetector combination detector, wherein the four-quadrant detector is used to provide feedback on the position of the beacon light; and the avalanche photodetector is used to receive the signal light.

[0019] The four-quadrant detector adjusts the deflection angle of the fast-reflecting mirror by the position of the feedback beacon light spot on the target surface, keeping the light spot within the center range of the target surface, thereby completing the tracking task.

[0020] The avalanche photodetector detects and identifies signal light to complete the communication task.

[0021] Furthermore, it also includes a second tracking unit, which is disposed on the same incident surface as the dual-wedge structure. The second tracking unit includes a lens and an image sensor. The lens is used to receive beacon light and transmit it to the image sensor. The image sensor is used to provide feedback on the position of the beacon light. The position of the beacon light is used to adjust the dual-wedge structure to maintain tracking of the target satellite.

[0022] The beacon light is used to locate and track target satellites.

[0023] Preferably, the image sensor is a CCD image sensor, i.e., a charge-coupled device image sensor, used to convert optical signals into digital signals.

[0024] Of course, other image sensors known in the field, such as CMOS image sensors, can also be used to achieve the same technical effect.

[0025] Furthermore, it also includes a dichroic mirror, which is used to reflect or transmit light according to wavelength differences.

[0026] Specifically, when emitted light and received light, signal light and beacon light appear simultaneously in the same optical path, in order to avoid crosstalk, they are often distinguished by wavelength differences. The method of using the dichroic mirror to project the mixed light into different receiving devices according to different wavelengths makes it easier to identify emitted light and received light, and to distinguish signal light and beacon light, thereby ensuring normal transmission and reception.

[0027] Furthermore, it also includes a beam splitter, which is used to split a beam of light into two beams according to a power ratio, for reflection and transmission respectively.

[0028] The beam splitter is used to divide the optical path into two, thereby enabling different optical path functions.

[0029] Furthermore, it also includes a third tracking unit, which comprises a filter, a focusing unit, and a detector:

[0030] The filter section receives reflected light from the beam splitter, filters out signal light, and allows beacon light to pass through and be transmitted to the focusing section.

[0031] The filtering part can be a filter or other filtering component known in the art;

[0032] The focusing unit is used to focus the beacon light onto the detector;

[0033] The focusing part can be a focusing lens or other focusing components known in the art;

[0034] The detector is used to detect the position of the beacon light, and the position of the beacon light is used to adjust the dual optical wedge structure to maintain tracking of the target satellite.

[0035] The third tracking unit is used to improve the tracking accuracy of the beacon light.

[0036] In addition, this application also provides a communication method using the above-mentioned space laser communication terminal, comprising:

[0037] The ephemeris is consulted to calculate the position of the target satellite. Based on the position of the target satellite, the double optical wedge structure is adjusted to capture the target satellite, and multiple sets of beacon light and signal light of different wavelengths are emitted to the target satellite.

[0038] After receiving the beacon light and the signal light, the target satellite feeds back another set of response beacon light and response signal light of different wavelengths along the original optical path;

[0039] The second tracking unit receives the response beacon light and provides feedback on the position of the response beacon light spot on the image sensor target surface. It then adjusts the dual-wedge structure to coarsely track the target satellite and keep the light spot within the center range of the target surface.

[0040] The third tracking unit receives the transponder beacon light after spectral processing and feeds back the position of the transponder beacon light spot on the detector target surface. It further adjusts the dual-wedge structure to precisely track the target satellite and keep the light spot within the center range of the target surface.

[0041] By tracking the communication composite unit, the system receives the response signal light and the response beacon light, and provides feedback on the position of the response beacon light spot on the target surface of the combined detector. It then adjusts the deflection angle of the fast-reflecting mirror to track the target satellite more precisely, keeping the light spot within the center range of the target surface, and receives the response signal light to complete signal transmission.

[0042] By adopting the above technical solution, the present invention has the following beneficial effects:

[0043] The present invention provides a space laser communication terminal and its communication method, which utilizes a dual-wedge structure, a four-quadrant and avalanche photoelectric combined detector and a multi-level tracking method to achieve real-time and accurate tracking of target satellites. It can efficiently complete signal transmission tasks, and the overall structure is simple and compact with a small footprint. Attached Figure Description

[0044] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of a space laser communication terminal system provided in an embodiment of the present invention;

[0046] Figure 2 Schematic diagram for use with a single optical wedge;

[0047] Figure 3 This is a schematic diagram illustrating the usage principle of the double optical wedge structure provided in an embodiment of the present invention.

[0048] Figure 4 This is a schematic diagram of the optical path of the first dichroic mirror provided in an embodiment of the present invention.

[0049] Figure 5 A schematic diagram of the target surface of the four-quadrant and avalanche photoelectric combined detector provided in an embodiment of the present invention;

[0050] Figure 6 Optical path diagram of a four-quadrant and avalanche photoelectric combined detector provided in an embodiment of the present invention;

[0051] Figure 7 A schematic diagram of a four-quadrant and avalanche photoelectric combined detector provided in an embodiment of the present invention;

[0052] Figure 8 A signal amplification circuit diagram of the APD photodetector provided in an embodiment of the present invention;

[0053] Figure 9 This is a signal amplification circuit diagram of a QD detector provided in an embodiment of the present invention;

[0054] Figure 10 This is a schematic diagram of the optical path of the second dichroic mirror provided in an embodiment of the present invention;

[0055] Figure label:

[0056] 1-Double beam wedge structure; 2-Galilean beam expander lens; 3-Quick reversal mirror; 4-First dichroic mirror;

[0057] 5- Beam splitter; 6- Third tracking unit; 7- Tracking and communication composite unit; 8- Second dichroic mirror;

[0058] 9-Signal light transmitting unit; 10-Beacon light transmitting unit; 11-Second tracking unit. Detailed Implementation

[0059] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0061] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0062] The present invention will be further explained below with reference to specific embodiments.

[0063] like Figure 1 As shown, the space laser communication terminal provided in this embodiment mainly includes a double-wedge structure 1, a Galilean beam expander lens 2, a fast-reflecting mirror 3, a first dichroic mirror 4, a beam splitter 5, a third tracking unit 6, a tracking-communication composite unit 7, a second dichroic mirror 8, a signal light emitting unit 9, a beacon light emitting unit 10, and a second tracking unit 11.

[0064] The dual optical wedge structure 1 is coaxially disposed at the beam-expanding end of the Galilean beam expander lens 2. The dual optical wedge structure 1 includes a set of optical wedges and a rotating device. The optical wedges are composed of two optical wedges of the same shape, with their vertical surfaces facing each other and placed coaxially. The rotating device includes a motor for making the optical wedges rotate synchronously or asynchronously around the axis.

[0065] According to the principle of light refraction, light rays will be deflected when passing through a single optical wedge, and the light path will be as follows: Figure 2As shown, let the refractive index of the light wedge be n and the wedge angle be α. Then, in a vacuum environment, the deflection angle of the light is β = (n-1)*α. If the light wedge is rotated one revolution, a circular trajectory will be formed on the receiving surface.

[0066] like Figure 3 As shown, when an identical optical wedge is placed behind the first optical wedge, the deflection angle of the light is greatest when the angle between the inclined surfaces of the two optical wedges is at its maximum. At this time, the angle γ between the outgoing and incoming light rays is 2(n-1)*α. If the relative rotation angle of the two optical wedges remains unchanged and they rotate synchronously for one revolution, a larger circular trajectory is formed on the receiving surface. Specifically, when the inclined surfaces of the two optical wedges are parallel, the incident light rays propagate in their original direction after two refractions, and γ = 0°. According to the principle of the reversibility of light, the field of view that the double optical wedge structure 1 can scan is 0 to γ.

[0067] The optical wedge material can be, for example, optical glass of model H-ZF7LA, with a wedge angle of 12.5°, which enables optical scanning and reception with a viewing angle greater than 20°.

[0068] Of course, the material and wedge angle of the optical wedge can also be adjusted according to actual needs to achieve different viewing angles.

[0069] The dual-wedge structure 1 can be used to scan and track target satellites by a space laser communication terminal. Compared with a space laser communication terminal using a servo mechanism, it has a simpler structure, shorter optical path, smaller size, and lower power consumption.

[0070] The Galilean beam expander 2 consists of a convex lens and a concave lens, with one end of the convex lens serving as the beam expander and the other end of the concave lens serving as the beam reducer. The Galilean beam expander 2 is used to expand and reduce the signal light and the beacon light, and can also correct the optical distortion caused by the double-wedge structure. The Galilean beam expander 2 has no internal focus and does not require internal focusing, thus avoiding wavefront error.

[0071] The fast reflector 3 is located at the beam-contraction end of the Galilean beam expander 2 and is connected to the Galilean beam expander 2 to form an optical path. The fast reflector 3 includes a motor, which can slightly adjust the deflection angle of the reflector to stabilize the optical system and adjust the direction of the beam, thereby completing the precise tracking of the target satellite.

[0072] The first dichroic mirror 4 is disposed on the reflected light path of the fast reflector 3 and is used to reflect or transmit light according to wavelength differences.

[0073] For example, if the space laser communication terminal emits signal light with a wavelength of λ11 (1542nm) and beacon light with a wavelength of λ21 (790nm), such as... Figure 4 The arrows point from left to right; they receive the response signal light at wavelength λ12 (1561nm) and the response beacon light at wavelength λ22 (810nm), such as... Figure 4 The arrow points downwards from the top. Therefore, the first dichroic mirror 4 reflects signal light with a wavelength of λ11 (1542nm) and beacon light with a wavelength of λ21 (790nm), as shown above. Figure 4 The arrow points from bottom to top; it transmits the response signal light at wavelength λ12 (1561nm) and the response beacon light at wavelength λ22 (810nm), such as... Figure 4 The arrow pointing downwards is shown below.

[0074] If the space laser communication terminal emits signal light with a wavelength of λ12 (1561nm) and beacon light with a wavelength of λ22 (810nm), then... Figure 4 The arrows point from left to right; they receive the response signal light at wavelength λ11 (1542nm) and the response beacon light at wavelength λ21 (790nm), such as... Figure 4 The arrow points downwards from the top. Therefore, the first dichroic mirror 4 reflects signal light with a wavelength of λ12 (1561nm) and beacon light with a wavelength of λ22 (810nm), as shown above. Figure 4 The arrow points from bottom to top; it transmits the response signal light at wavelength λ11 (1542nm) and the response beacon light at wavelength λ21 (790nm), such as... Figure 4 The arrow below points in the direction of downwards.

[0075] The wavelength of light is selected from the C-band and L-band light waves commonly used in space laser communication. Of course, other wavelengths can also be selected as needed to meet the requirements.

[0076] The beam splitter 5 is located at the end of the first dichroic mirror 4 away from the fast-reflecting mirror 3, and is used to split a beam of light into two beams of light with a power ratio of 1:9, wherein the ratio 1 is used for transmission and the ratio 9 is used for reflection.

[0077] The third tracking unit 6 is disposed on the reflected light path of the beam splitter 5 and includes a filter, a focusing lens and a detector arranged in sequence; the filter receives the reflected light from the beam splitter 5, filters out the signal light, and allows the beacon light to pass through and be transmitted to the focusing lens.

[0078] The focusing lens is used to converge the beacon light onto the target surface of the detector and correct the optical aberrations generated by the Galilean beam expander 2; the detector is used to detect and provide feedback on the position of the beacon light spot on the target surface, and to keep the beacon light spot within the center range of the target surface by adjusting the rotation device of the double wedge structure 1, thereby tracking the target satellite.

[0079] The tracking communication composite unit 7 is disposed on the transmission light path of the beam splitter 5, and includes a filter, a focusing lens, and a four-quadrant and avalanche photodetector arranged sequentially. The filter receives the transmitted light from the beam splitter 5, filters out stray light, and allows the signal light and beacon light to be transmitted to the focusing lens. The focusing lens is used to converge the signal light onto the target surface of the four-quadrant and avalanche photodetector. The four-quadrant and avalanche photodetector, which can be simply referred to as a QD-APD combined detector, combines a four-quadrant detector (QD detector) with an avalanche photodetector (APD photodetector). The target surface structure of the four-quadrant and avalanche photodetector is as follows... Figure 5 As shown, the target surface of the four-quadrant detector is composed of four identical silicon-based photodetectors arranged in the four quadrants of a Cartesian coordinate system, dividing the target surface into four regions: A, B, C, and D. There is a 0.03mm gap between the four regions. The four-quadrant detector can detect light wavelengths in the range of 350nm-1100nm and is used to detect beacon light. The target surface of the avalanche photodetector is located at the origin of the Cartesian coordinate system and is connected to the silicon-based photodetector via bonding. The target surface of the avalanche photodetector can be an indium gallium arsenide (InGaAs) detector, detecting wavelengths in the range of 1100nm-1700nm, and is used to collect and receive signal light.

[0080] The optical path trajectory of the four-quadrant and avalanche photoelectric combined detector is as follows: Figure 6 As shown in the diagram, the solid line represents the signal light, and the dashed line represents the beacon light. The signal light and beacon light are incident on the focusing lens in an approximately parallel manner. Since the wavelength of the signal light is longer than that of the beacon light, the focal point of the signal light is farther from the focusing lens than the focal point of the beacon light. Let the diameter of the target surface of the four-quadrant detector be D1, and the diameter of the target surface of the avalanche photodetector be D2, with the target surface located at the focal point of the focusing lens. Then, the diameter of the defocused beacon light spot displayed on the target surface is D1 / 2. Due to the photosensitivity of the avalanche photodetector, this will not affect the signal light received by the avalanche photodetector. The position of the beacon light spot is determined by the light intensity received by the four silicon-based photodetectors A, B, C, and D on the target surface. After position calculation, the position deviation is obtained. Based on the position deviation, the deflection angle of the fast-reflecting mirror 3 is adjusted to control the light spot to be located at the center of the detector. At this time, the focal point of the signal light is located on the target surface of the avalanche photodetector, which receives the signal light and demodulates the signal, thus completing signal reception.

[0081] A schematic diagram of the QD-APD combined detector, as shown below. Figure 7As shown, the system includes a QD detector, an APD photodetector, a transimpedance amplifier, a narrowband filter circuit, a gain amplifier circuit, and a bias voltage circuit. The working principle is as follows: The input optical signal is converted to four quadrants by the QD detector, resulting in four current signals, which are then sequentially transmitted to the transimpedance amplifier, narrowband filter, and gain amplifier circuit for signal amplification. Based on the transimpedance amplifier, the DC noise of the photodiode is limited through AC coupling, the leakage current of the photodiode is compensated by the forward resistor of the operational amplifier, and the thermal noise of the resistor is reduced by the capacitor, thereby improving the signal-to-noise ratio. The narrowband filter circuit then filters out unnecessary frequency noise during signal transmission. Finally, based on the gain amplifier circuit, a wideband adjustable gain amplifier amplifies the signal power, and the amplification factor can be determined through a feedback network, ultimately achieving high gain and high bandwidth.

[0082] like Figure 8 As shown, one signal amplification circuit layout of the APD photodetector includes a transimpedance amplifier composed of a photodiode APD, resistors R1, R2, and Rf, capacitors Ci, CI, C3, and Cf, and an operational amplifier OPA657. The bias voltage of the APD photodetector is input to the positive terminal of the photodiode APD. The negative terminal of the photodiode APD is connected to one end of each of the resistors R1, Ci, and CI. The other end of the capacitor CI is connected to the negative input terminal of the operational amplifier OPA657. The other ends of the resistors R1 and Ci are grounded. One end of the parallel connection of the resistors R2 and C3 is connected to the positive input terminal of the operational amplifier OPA657, and the other end is grounded. The parallel connection of the resistors Rf and Cf is connected to the negative input terminal and the output terminal of the operational amplifier OPA657. The output terminal of the operational amplifier OPA657 is connected to a voltage amplification circuit.

[0083] The circuit layout described above can be used to amplify the signal from the photodiode (APD).

[0084] like Figure 9As shown, one signal amplification circuit layout of the QD detector mainly includes a gain amplifier AD603, resistors R46, R47, R54, R55, capacitors C71, C73, C74, C80, C82, C84, and C83. Capacitors C71 and C73 form a positive 5V power input filter circuit, with C71 having a capacitance of 1uF and C73 having a capacitance of 100nF, effectively filtering out high-frequency noise in the positive 5V power supply circuit. Capacitors C82 and C84 form a negative 5V power input filter circuit, with C84 having a capacitance of 1uF and C82 having a capacitance of 100nF, effectively filtering out high-frequency noise in the positive 5V power supply circuit. The capacitor C80 effectively filters out high-frequency noise in the negative 5V power supply circuit and filters out DC interference signals in the signal channel. The capacitor C80 and the resistor R54 form a low-pass filter circuit to filter out noise signals outside the target signal frequency band. The resistors R47 and R48 form a voltage divider circuit on the second pin of the gain amplifier AD603. The resistor R46 is used as a pull-down resistor, and the capacitor C74 is used as a filter capacitor. The voltage difference between the first and second pins of the gain amplifier AD603 is controlled by the external microcontroller's digital-to-analog converter pin to adjust the signal power amplification factor. The connection ratio of the resistor R55 and the capacitor C83 can change the operating mode of the gain amplifier AD603.

[0085] The circuit layout described above enables the amplification of the signal from the QD detector.

[0086] The second dichroic mirror 8 is disposed on the reflected light path of the first dichroic mirror 4, and forms a 45° angle with the optical axis of the reflected light path, and is used to reflect or transmit light according to wavelength differences.

[0087] For example, if the space laser communication terminal emits signal light with a wavelength of λ11 (1542nm), such as Figure 10 The arrow points from bottom to top; it emits beacon light with a wavelength of λ21 (790nm), such as... Figure 10 The arrow on the left side of the middle point points to the direction from left to right. Therefore, the second dichroic mirror 8 reflects beacon light with a wavelength of λ21 (790nm), such as... Figure 10 The arrow on the right side of the middle point points in the direction from left to right; it transmits signal light with a wavelength of λ11 (1542nm), as shown... Figure 10 The direction of the arrow from left to right on the right side of the middle;

[0088] If the space laser communication terminal emits signal light with a wavelength of λ12 (1561nm), such as Figure 10 The arrow points upwards; it emits beacon light with a wavelength of λ22 (810nm), such as... Figure 10 The arrow on the left side of the middle point points to the direction from left to right. Therefore, the second dichroic mirror 8 reflects signal light with a wavelength of λ12 (1561nm), as shown below. Figure 10 The arrow on the right side of the middle point points in the direction from left to right; it transmits beacon light with a wavelength of λ22 (810nm), as shown... Figure 10 The arrow on the right side of the middle point points in the direction from left to right.

[0089] The signal light emitting unit 9 is disposed on the reflected light path of the second dichroic mirror 8, and includes an emitting optical fiber and a beam collimation structure, for emitting the emitted beam in the form of parallel light. It can emit signal light with wavelengths such as λ11 (1542nm) or λ12 (1561nm), and the range of the wavelengths can be set as needed.

[0090] The beacon light emitting unit 10 is disposed on the transmission light path of the second dichroic mirror 8, and includes an emitting optical fiber and a beam collimation structure, for emitting the emitted beam in the form of parallel light. It can emit beacon light with wavelengths such as λ21 (790nm) or λ22 (810nm), and the range of the wavelengths can be set as needed.

[0091] The second tracking unit 11 is arranged with the dual-wedge structure 1 on the same incident surface to ensure that the incident parallel light enters the second tracking unit 11 and the dual-wedge structure 1 at the same angle. The second tracking unit 11 includes a lens and a CCD image sensor. The lens is a receiving lens with a field of view of 40°, but it can be replaced with a receiving lens with other field of view angles as needed. The lens receives beacon light transmitted to the target surface of the CCD image sensor. When the incident angle is less than 40°, a light spot can be displayed on the target surface of the CCD image sensor. Based on the field of view of the dual-wedge structure 1, a central range is set on the CCD image sensor, and by adjusting the relative angle of the dual-wedge structure 1, the light spot is controlled to remain within the central range, thereby completing coarse tracking of the target satellite.

[0092] The specific working process of this embodiment is briefly described as follows:

[0093] The target satellite's position is calculated based on the ephemeris. The relative rotation angle of the dual-wedge structure 1 is adjusted, and signal light with a wavelength of λ11 (e.g., 1542nm) is emitted from the signal light emitting unit 9, while beacon light with a wavelength of λ21 (e.g., 790nm) is emitted from the beacon light emitting unit 10. The signal light is reflected by the second dichroic mirror 8 and projected onto the first dichroic mirror 4. The beacon light is also transmitted through the second dichroic mirror 8 and projected onto the first dichroic mirror 4. The first dichroic mirror 4 reflects the mixed beam composed of the signal light and the beacon light and projects it onto the fast-reflecting mirror 3. The fast-reflecting mirror 3 reflects the mixed beam onto the Galilean beam expander lens 2. The Galilean beam expander lens 2 performs optical gain and beam expansion before projecting the mixed beam onto the dual-wedge structure 1. The dual-wedge structure 1 directs the mixed beam toward the target satellite, completing the first-stage tracking with a tracking accuracy of 50 rad.

[0094] After receiving the mixed beam, the target satellite feeds back a response signal light with a wavelength of λ12 (e.g., 1561nm) and a response beacon light with a wavelength of λ22 (e.g., 810nm). The response signal light and the response beacon light are combined to form a mixed response light, which is projected in parallel onto the dual-wedge structure 1 and the second tracking unit 11. The second tracking unit 11 calculates the incident angle θ of the mixed response light by feeding back the position of the light spot on the CCD image sensor. When θ is less than the maximum scanning angle of 20° of the dual-wedge structure 1, the two wedges are asynchronously rotated by a rotating device to change the relative rotation angle and keep the light spot within the center range of the CCD image sensor. At this time, the second-level tracking is completed, and the tracking accuracy can reach 10 μrad.

[0095] The response mixed light is projected onto the Galilean beam expander 2 via the dual-wedge structure 1, then projected onto the fast-reflecting mirror 3 after beam contraction by the Galilean beam expander 2, reflected by the fast-reflecting mirror 3, and then projected onto the first dichroic mirror 4. After transmission through the first dichroic mirror 4, it is projected onto the beam splitter 5. The beam splitter 5 splits the response mixed light into two parts at a power ratio of 1:9. 90% of the response mixed light is reflected onto the third tracking unit 6, and 10% of the response mixed light is transmitted onto the tracking-communication composite unit 7. The third tracking unit 6 filters out the response signal light, provides feedback on the position of the response beacon light spot, and adjusts the dual-wedge structure 1 to keep the light spot within the center range of the detector target surface of the third tracking unit 6. At this point, three-stage tracking is completed, and the tracking accuracy can reach 1 urad.

[0096] After the three-stage tracking, the response mixed light can be accurately transmitted to the target surface of the QD-APD combined detector of the tracking communication composite unit 7. The QD detector identifies and reports the position of the response beacon light spot, and the deflection angle of the fast reflector 3 is adjusted to ensure that the light spot of the response mixed light is located at the center of the target surface of the QD detector, thus completing the four-stage tracking with a tracking accuracy of 0.5 μA. At the same time, the APD photodetector located at the center of the QD detector target surface can collect and receive the response signal light, completing the signal transmission.

[0097] This invention replaces the traditional servo structure with a specially designed dual-wedge structure, reducing the size of the laser communication terminal while ensuring the required scanning angle. This invention uses a four-stage tracking method, which greatly improves the alignment and reception accuracy of inter-satellite communication. This invention adopts a QD-APD combined detector, which combines the fourth-stage tracking optical path with the optical path required for communication, simplifying the optical path, reducing the difficulty of optical assembly and adjustment, and reducing the cost of terminal equipment.

[0098] On the other hand, embodiments of the present invention also provide a communication method for a space laser communication terminal, the process of which is as follows:

[0099] Step 1: Query the ephemeris to calculate the target satellite's position, adjust the dual-wedge structure to capture the target satellite based on the target satellite's position, and emit multiple sets of beacon light and signal light of different wavelengths to the target satellite to complete the first-level tracking;

[0100] Step 2: After receiving the beacon light and the signal light, the target satellite feeds back another set of response beacon light and response signal light of different wavelengths along the original optical path;

[0101] Step 3: The second tracking unit receives the response beacon light and provides feedback on the position of the response beacon light spot on the target surface of the image sensor. The dual-wedge structure is adjusted to coarsely track the target satellite, keeping the light spot within the center range of the target surface, thus completing the secondary tracking.

[0102] Step 4: The third tracking unit receives the response beacon light after beam splitting and feeds back the position of the response beacon light spot on the detector target surface. The dual optical wedge structure is then adjusted to precisely track the target satellite and keep the light spot within the center range of the target surface, thus completing the three-stage tracking.

[0103] Step 5: Through the tracking communication composite unit, receive the response signal light and the response beacon light, and provide feedback on the position of the response beacon light spot on the target surface of the combined detector. Adjust the deflection angle of the fast reflector to track the target satellite more precisely, keep the light spot within the center range of the target surface, complete the fourth-level tracking, and receive the response signal light to complete the signal transmission.

[0104] Using the above method, a four-level tracking approach is adopted to achieve precise tracking of the target satellite and efficiently complete the signal transmission task.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A space laser communication terminal, characterized by, The device comprises a double-wedge structure, a Galilean beam expander, a fast mirror, a first dichroic mirror, a beam splitter, a third tracking unit, a tracking and communication composite unit, a second dichroic mirror, a signal light emitting unit, a beacon light emitting unit and a second tracking unit. The double-wedge structure is coaxially arranged at the beam expanding end of the Galilean beam expander, and comprises a wedge group and a rotating device. The fast mirror is arranged at the beam shrinking end of the Galilean beam expander, and comprises a motor for adjusting the deflection angle of the mirror of the fast mirror. The first dichroic mirror is arranged on the reflection light path of the fast mirror, and is used for reflecting and transmitting light according to wavelength difference. The beam splitter is arranged at the end of the first dichroic mirror away from the fast mirror, and is used for splitting light into transmitted light and reflected light according to power ratio. The third tracking unit is arranged on the reflection light path of the beam splitter, and comprises a first filter, a first focusing lens and a detector arranged in sequence. The first filter receives reflected light from the beam splitter, filters out signal light, and transmits beacon light to the focusing lens. The first focusing lens is used for converging beacon light to the target surface of the detector. The detector is used for detecting and feeding back the position of the beacon light spot on the target surface, and keeping the beacon light spot within the central range of the target surface by adjusting the rotating device of the double-wedge structure. The tracking and communication composite unit is arranged on the transmission light path of the beam splitter, and comprises a second filter, a second focusing lens and a QD-APD combined detector arranged in sequence. The second filter is used for receiving transmitted light from the beam splitter, filtering out stray light, and transmitting signal light and beacon light to the focusing lens. The second focusing lens is used for converging signal light to the target surface of the combined detector. The QD-APD combined detector identifies and feeds back the position of the beacon light spot by the QD detector, adjusts the deflection angle of the fast mirror, and at the same time, the APD photodetector at the center of the target surface of the QD detector collects the signal of the received response signal light, to complete signal transmission. The second dichroic mirror is arranged on the reflection light path of the first dichroic mirror, and forms a 45° angle with the optical axis of the reflection light path, and is used for reflecting and transmitting light according to wavelength difference. The signal light emitting unit is arranged on the reflection light path of the second dichroic mirror, and comprises an emitting optical fiber and a beam collimation structure, and is used for emitting the outgoing signal light beam in the form of parallel light. The beacon light emitting unit is arranged on the transmission light path of the second dichroic mirror, and comprises an emitting optical fiber and a beam collimation structure, and is used for emitting the outgoing beacon light beam in the form of parallel light. The second tracking unit is arranged on the common incidence plane of the double-wedge structure, and includes a lens and a CCD image sensor; the lens is used to receive beacon light and transmit the beacon light to the target surface of the CCD image sensor; and the CCD image sensor is used to feed back the position of the beacon light, and the position of the beacon light is used to adjust the double-wedge structure.

2. The space laser communication terminal according to claim 1, characterized in that, The combined detector is a detector composed of a four-quadrant detector and an avalanche photodetector; the four-quadrant detector is used to detect the position of beacon light; and the avalanche photodetector is used to receive signal light.

3. A communication method using the space laser communication terminal according to any one of claims 1 to 2, characterized by, The method comprises the following steps: querying ephemeris to calculate the position of a target satellite, adjusting the double-wedge structure to capture the target satellite according to the position of the target satellite, and emitting a plurality of groups of beacon light and signal light with different wavelengths to the target satellite; after the target satellite receives the beacon light and the signal light, the target satellite feeds back another group of response beacon light and response signal light along the original light path; through a second tracking unit, the response beacon light is received, and the position of the response beacon light spot on the target surface of an image sensor is fed back, the double-wedge structure is adjusted, and the light spot is kept within the central range of the target surface; through a third tracking unit, the response beacon light after light splitting is received, and the position of the response beacon light spot on the target surface of a detector is fed back, the double-wedge structure is adjusted, and the light spot is kept within the central range of the target surface; through a tracking communication composite unit, the response beacon light and the response signal light are received, the position of the response beacon light spot on the target surface of a combined detector is fed back, the angle of a fast-response mirror is adjusted, the light spot is kept within the central range of the target surface, and the response signal light is received to complete signal transmission.

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