Laser radar system for detecting space debris and method for detecting space debris

Abstract

The present application relates to the technical field of laser radar detection, and particularly relates to a laser radar system for detecting space debris and a space debris detection method. The system comprises a laser emission module, a rotating mirror assembly, a common optical path, a return wave receiving module and a control subsystem. The laser emission module is used for emitting polarized light of a corresponding wavelength. The rotating mirror assembly is arranged between the laser emission module, the return wave receiving module and the common optical path. In a transmitting state, the rotating mirror assembly is moved to a first target position to make the polarized light emitted by the laser emission module directly emit to the common optical path. In a receiving state, the rotating mirror assembly is moved to a second target position to reflect the target return wave received by the common optical path to the return wave receiving module, so as to realize optical path switching. The control subsystem realizes distance measurement of a long-distance target space debris according to the receiving time of the target return wave and the emitting time of the polarized light, and identifies the material of the target space debris according to the return wave intensity of the target return wave in different polarization states.

Description

Technical Field

[0001] This invention relates to the field of lidar detection technology, and in particular to a lidar system and method for detecting space debris. Background Technology

[0002] As humanity explores space, more and more space debris, such as malfunctioning spacecraft, rocket wreckage, operational debris, and disintegration debris, remains in space, gradually beginning to threaten and affect human space activities.

[0003] Existing lidar systems for detecting space debris mostly use laser pulses. However, laser pulses are mainly used for ranging. When faced with atmospheric interference at extremely long distances, the detection accuracy needs to be improved, and it is also difficult to identify space debris. Therefore, existing lidar systems for detecting space debris cannot meet the detection requirements.

[0004] Therefore, there is an urgent need for a new lidar system for detecting space debris. Summary of the Invention

[0005] To address the problem that existing lidar systems for detecting space debris cannot meet the requirements for space debris detection, this invention provides a lidar system and a space debris detection method for detecting space debris.

[0006] In a first aspect, embodiments of the present invention provide a lidar system for detecting space debris, comprising: a laser emitting module, a rotating mirror assembly, a common optical path, an echo receiving module, and a control subsystem;

[0007] The laser emitting module is disposed at the first end of the rotating mirror assembly. The laser emitting module is used to emit polarized light of different polarization directions and polarization states of a first wavelength or polarized light of different polarization directions and polarization states of a second wavelength; wherein the second wavelength is smaller than the first wavelength.

[0008] The rotating mirror assembly is disposed between the laser emitting module, the echo receiving module, and the common optical path. In the emitting state, the rotating mirror assembly is used to move to a first target position so that the polarized light emitted by the laser emitting module is directly emitted to the common optical path. In the receiving state, the rotating mirror assembly moves to a second target position to reflect the target echo received by the common optical path to the echo receiving module, thereby realizing the optical path switching for the transition between the transmitting and receiving states.

[0009] The common optical path is disposed at the second end of the rotating mirror assembly. The common optical path is used to emit the polarized light to the target space debris in the emission state and to receive the target echo reflected by the target space debris in the receiving state.

[0010] The echo receiving module is disposed at the third end of the rotating mirror assembly. The echo receiving module is used to receive the target echo and detect the echo intensity of the target echo under different polarization states.

[0011] The control subsystem is electrically connected to the laser emitting module, the rotating mirror assembly, the common optical path, and the echo receiving module, respectively. The control subsystem is used to control the working state of the laser emitting module, the rotating mirror assembly, the common optical path, and the echo receiving module, and to receive the echo intensity of the target echo under different polarization states detected by the echo receiving module, so as to determine the distance of the target space debris based on the reception time of the target echo and the emission time of the polarized light, and to identify the material of the target space debris based on the echo intensity of the target echo under different polarization states.

[0012] Secondly, embodiments of the present invention also provide a space debris detection method based on the system described in any embodiment of this specification, comprising:

[0013] When the rotating mirror assembly moves to the first target position, the control subsystem controls the laser emission module to emit polarized light with different polarization directions and polarization states corresponding to the wavelength;

[0014] A dual-point high-reflectivity mirror of the corresponding wavelength directly reflects the polarized light to a common optical path, so as to use the common optical path to emit the polarized light to the target space debris;

[0015] The target echo reflected by the target space debris is received using the shared optical path; wherein the wavelength of the target echo is the same as the wavelength of the polarized light.

[0016] The rotating mirror assembly moves to the second target position to reflect the target echo received by the shared optical path to the echo receiving module;

[0017] The echo receiving module is used to detect the echo intensity of the target echo under different polarization states, and the detection results are sent to the control subsystem.

[0018] The control subsystem determines the distance to the target space debris based on the reception time of the target echo and the emission time of the polarized light, and identifies the material of the target space debris based on the echo intensity of the target echo under different polarization states.

[0019] This invention provides a lidar system and method for detecting space debris. The system includes a laser emitting module, a rotating mirror assembly, a common optical path, an echo receiving module, and a control subsystem. In the emitting state, the laser emitting module emits polarized light with different polarization directions and states corresponding to the wavelength. The rotating mirror assembly moves to a first target position so that the polarized light emitted by the laser emitting module is directly emitted to the common optical path, which then emits the polarized light to the target space debris. When the target space debris is present, it reflects the polarized light, generating a target echo that is reflected back to the common optical path. At this time, the system is in the receiving state. The rotating mirror assembly moves to a second target position and reflects the target echo received by the common optical path to the echo receiving module. The echo receiving module detects the echo intensity of the target echo under different polarization states and sends it to the control subsystem. The control subsystem uses the reception time of the target echo under different polarization states and the emission time of the polarized light to achieve long-distance target space debris ranging. Furthermore, based on the echo intensity of the target echo under different polarization states, the material of the target space debris can be identified. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the 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 based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the composition of a lidar system for detecting space debris according to an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the optical path in the transmission state of a lidar system for detecting space debris, provided in an embodiment of the present invention.

[0023] Figure 3 This is a schematic diagram of the receiving optical path of a lidar system for detecting space debris according to an embodiment of the present invention;

[0024] Figure 4 This is a front view of a lens provided in an embodiment of the present invention;

[0025] Figure 5 This is a flowchart of a space debris detection method provided in an embodiment of the present invention.

[0026] Figure label:

[0027] 1. Laser emitting module; 11. Dual-wavelength laser device; 12. Polarizing assembly; 121. First displacement platform; 122. First rotating waveplate group; 123. Second rotating waveplate group;

[0028] 2. Mirror rotation assembly; a. First target position; b. Second target position;

[0029] 3. Shared optical path; 31. Adjusting the optical path; 311. First negative lens; 312. Second negative lens; 313. Second displacement platform; 314. Positive lens; 32. Beam splitter; 33. Telescope;

[0030] 4. Echo receiving module; 41. Third displacement platform; 411. Second reflector; 42. First reflector; 43. First echo receiving box; 431. First focusing lens; 432. First pinhole aperture; 433. First collimating lens; 434. First wavelength quarter-wave plate; 435. Glan laser polarizer; 436. Fiber optic coupling lens; 437. First single-photon detector; 44. Second echo receiving box; 441. Second focusing lens; 442. Second pinhole aperture; 443. Second collimating lens; 444. Second wavelength quarter-wave plate; 445. Polarizer; 446. Second single-photon detector;

[0031] 5. Double-point high-reflectivity mirror. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] As mentioned earlier, most existing lidar systems for detecting space debris use laser pulses. However, laser pulses are mainly used for ranging. Faced with atmospheric interference at extremely long distances, the detection accuracy needs to be improved, and it is also difficult to identify space debris. Therefore, existing lidar systems for detecting space debris cannot meet the detection requirements for space debris.

[0034] To address the aforementioned technical issues, the inventors could consider utilizing polarization state information to identify the material of space debris. Furthermore, emitting polarized light with different directions and polarization states can improve the detection range. Therefore, a laser emitting module emits polarized light of different wavelengths, polarization directions, and polarization states. In the emitting state, by moving the rotating mirror assembly to the first target position, the polarized light emitted by the laser emitting module is directly emitted into a common optical path, which then transmits the polarized light to the target space debris. When the target space debris is present, it reflects the polarized light, generating a target echo that is reflected back into the common optical path. The system then switches to a receiving state, moving the rotating mirror assembly to the second target position to reflect the target echo received by the common optical path to the echo receiving module. The echo receiving module detects the echo intensity of the target echo under different polarization states and sends it to the control subsystem. The control subsystem uses the reception time of the target echo under different polarization states and the emission time of the polarized light to achieve long-distance target space debris ranging. Furthermore, based on the echo intensity of the target echo under different polarization states, the material of the target space debris can be identified. Therefore, this solution can not only improve the detection range and the accuracy of space debris distance detection, but also identify the material of space debris.

[0035] The following describes the specific implementation of the above concept.

[0036] Please refer to Figure 1 This invention provides a lidar system for detecting space debris, comprising: a laser emitting module 1, a rotating mirror assembly 2, a common optical path 3, an echo receiving module 4, and a control subsystem;

[0037] A laser emitting module 1 is disposed at the first end of the rotating mirror assembly 2. The laser emitting module 1 is used to emit polarized light of different polarization directions and polarization states of a first wavelength or polarized light of different polarization directions and polarization states of a second wavelength; wherein the second wavelength is shorter than the first wavelength.

[0038] The rotating mirror assembly 2 is disposed between the laser emitting module 1, the echo receiving module 4 and the common optical path 3. The rotating mirror assembly 2 is used to move to the first target position a in the emitting state so that the polarized light emitted by the laser emitting module 1 is directly emitted to the common optical path 3. In the receiving state, the rotating mirror assembly 2 moves to the second target position so as to reflect the target echo received by the common optical path 3 to the echo receiving module 4, so as to realize the optical path switching of the transmitting and receiving state.

[0039] The common optical path 3 is set at the second end of the rotating mirror assembly 2. The common optical path 3 is used to emit polarized light to the target space debris in the emission state and to receive the target echo reflected by the target space debris in the receiving state.

[0040] The echo receiving module 4 is located at the third end of the rotating mirror assembly 2. The echo receiving module 4 is used to receive the target echo and detect the echo intensity of the target echo under different polarization states.

[0041] The control subsystem is electrically connected to the laser emitting module 1, the rotating mirror assembly 2, the common optical path 3, and the echo receiving module 4, respectively. The control subsystem is used to control the working status of the laser emitting module 1, the rotating mirror assembly 2, the common optical path 3, and the echo receiving module 4, and to receive the echo intensity of the target echo under different polarization states detected by the echo receiving module 4. The control subsystem is used to determine the distance of the target space debris based on the reception time of the target echo and the emission time of the polarized light, and to identify the material of the target space debris based on the echo intensity of the target echo under different polarization states.

[0042] In this embodiment of the invention, during the emission state, the laser emission module 1 emits polarized light with different polarization directions and polarization states corresponding to the wavelength. The rotating mirror assembly 2 moves to the first target position a so that the polarized light emitted by the laser emission module 1 is directly emitted to the common optical path 3. The common optical path 3 emits the polarized light to the target space debris. When the target space debris is present, the target space debris will reflect the polarized light, generating a target echo that is reflected back to the common optical path 3. At this time, the system is in the receiving state. The rotating mirror assembly 2 moves to the second target position b and reflects the target echo received by the common optical path to the echo receiving module 4. The echo receiving module 4 detects the echo intensity of the target echo under different polarization states and sends it to the control subsystem. The control subsystem realizes long-distance target space debris ranging based on the reception time of the target echo under different polarization states and the emission time of the polarized light. Based on the echo intensity of the target echo under different polarization states, the material of the target space debris can be identified.

[0043] refer to Figure 2 In some embodiments, the laser emitting module 1 includes a dual-wavelength laser device 11 and a polarization assembly 12; the dual-wavelength laser device 11 is used to emit linearly polarized light of a corresponding wavelength according to the instructions of the control subsystem.

[0044] The dual-wavelength laser device 11 includes a first laser, a second laser, a reflector group, and a frequency doubling crystal. The first laser and the second laser are arranged side by side, and the emission end of the second laser is on the same straight line as the laser emission end of the dual-wavelength laser device 11. The wavelength of the linearly polarized light emitted by the first laser and the second laser is the first wavelength.

[0045] The reflector group is set at the output end of the first laser and is used to reflect the linearly polarized light of the first wavelength emitted by the first laser to the laser output end of the dual-wavelength laser device 11.

[0046] A frequency doubling chip is placed at the output end of the second laser to convert linearly polarized light of the first wavelength emitted by the second laser into linearly polarized light of the second wavelength.

[0047] The polarization component 12 is disposed at the laser emission end of the dual-wavelength laser device 11. The polarization component 12 is used to modulate linearly polarized light of the first wavelength or the second wavelength into polarized light with different polarization directions and polarization states.

[0048] In this embodiment, the dual-wavelength laser device 11 is used to achieve single-channel 1064nm polarized light emission or single-channel 532nm polarized light emission, where 1064nm is the first wavelength and 532nm is the second wavelength. By inserting the reflector, the laser emitting end of the dual-wavelength laser device 11 emits linearly polarized light of the first wavelength emitted by the first laser; by removing the reflector, the dual-wavelength laser device 11 emits linearly polarized light of the second wavelength. In this embodiment, all reflectors are 45-degree reflectors. By inserting and removing the reflector, the switching between 532nm and 1064nm lasers is achieved. By setting a polarizing component 12 at the laser emitting end of the dual-wavelength laser device 11, the linearly polarized light of the first or second wavelength is modulated into polarized light with different polarization directions and polarization states.

[0049] Continue to refer to Figure 2 In some embodiments, the polarization assembly 12 includes: a first displacement platform 121, a first rotating waveplate group 122, and a second rotating waveplate group 123; wherein the first rotating waveplate group 122 and the second rotating waveplate group 123 are respectively adapted to a first wavelength and a second wavelength; the first rotating waveplate group 122 includes a quarter-wave plate and a half-wave plate for the first wavelength, and the second rotating waveplate group 123 includes a quarter-wave plate and a half-wave plate for the second wavelength;

[0050] The first rotating waveplate group 122 and the second rotating waveplate group 123 are disposed on the first displacement platform 121. By moving the first displacement platform 121, the linearly polarized light emitted by the dual-wavelength laser device 11 passes through the first rotating waveplate group 122 or the second rotating waveplate group 123.

[0051] The first displacement platform 121 is used to move according to the wavelength of the linearly polarized light emitted by the dual-wavelength laser device 11, so that the rotating waveplate group of the corresponding wavelength is moved to the laser emission direction of the dual-wavelength laser device 11, so as to use the rotating waveplate group of the corresponding wavelength to modulate the linearly polarized light of the corresponding wavelength into polarized light with different polarization directions and polarization states.

[0052] In this embodiment, the first rotating waveplate group 122 includes a 1064nm quarter-wave plate and a 1064nm half-wave plate, and the second rotating waveplate group 123 includes a 532nm quarter-wave plate and a 532nm half-wave plate, as shown below. Figure 2As shown, when the wavelength of the linearly polarized light emitted by the dual-wavelength laser device 11 is 532nm, the first displacement platform 121 moves the second rotating waveplate group 123 to the laser emission direction of the dual-wavelength laser device 11, so that the 532nm linearly polarized light emitted by the dual-wavelength laser device 11 passes through the rotating 532nm half-waveplate and the rotating 532nm quarter-waveplate in sequence, and is modulated into polarized light with different polarization directions and polarization states. The same applies when the wavelength is 1064nm.

[0053] refer to Figure 2 and Figure 3 In some embodiments, the common optical path 3 includes: an adjustment optical path 31, a beam splitter 32, and a telescope 33;

[0054] The adjustment optical path 31 is set at the second end of the rotating mirror assembly 2, which is used to expand the polarized light emitted by the laser emitting module 1 into collimated light in the emission state, and to reduce the beam of the target echo in the receiving state.

[0055] The beam splitter 32 is a plane mirror, which is set at the other end of the adjustment optical path 31. It is used to reflect the expanded polarized light to the telescope 33 and to reflect the target echo to the adjustment optical path 31.

[0056] Telescope 33 is located at the other end of beam splitter 32 and is used to emit expanded polarized light toward the target space debris and to receive the target echo reflected by the target space debris.

[0057] In this embodiment, as Figure 2 As shown, in the transmitting state, the polarized light emitted by the laser emitting module 1 is reflected by the double high-point reflector 5 to the rotating mirror assembly 2. Since it is in the transmitting state, the rotating mirror assembly 2 does not reflect the polarized light; the polarized light directly enters the adjustment optical path 31 of the common optical path 3. The adjustment optical path 31 expands the polarized light into collimated light and directs it to the beam splitter 32. The beam splitter 32 reflects the expanded collimated light to the telescope 33, thus directing the expanded polarized light towards the target space debris. In the receiving state, as... Figure 3 As shown, the telescope 33 receives the target echo reflected by the target space debris, the beam splitter 32 reflects the target echo to the adjustment optical path 31, the adjustment optical path 31 reduces the beam of the target echo, and the reduced target echo is directed to the rotating mirror assembly 2.

[0058] In this embodiment, the telescope 33 has a diameter of 1.2m to achieve ranging and identification of distant space debris. The beam splitter 32 is a plane mirror, its function being to reflect the expanded laser beam into the telescope 33 for outward emission and to reflect the returning target echo into the adjustment optical path 31. Furthermore, starlight from the telescope 33 must pass through this mirror to form an image. To maintain good optical performance and the ability to reflect target echoes and transmit starlight, the surface shape PV of the front and rear surfaces of the beam splitter 32 is better than 0.25λ. The front surface is coated with a high-reflection film with 45° incident wavelength and 532nm and 1064nm, while the rear surface is coated with an anti-reflection film with 45° incident wavelength and 400-800nm.

[0059] Continue to refer to Figure 2 and Figure 3 In some embodiments, the adjustment optical path 31 includes: a first negative lens 311, a second negative lens 312, a second displacement platform 313, and a positive lens 314;

[0060] The applicable wavelengths of the first negative lens 311 and the second negative lens 312 are the first wavelength and the second wavelength, respectively. The first negative lens 311 and the second negative lens 312 are disposed on the second displacement platform 313. By moving the second displacement platform 313, polarized light or target echo can pass through the first negative lens 311 or the second negative lens 312.

[0061] Positive lens 314 is located at one end of beam splitter 312.

[0062] In this embodiment, to accommodate laser beams of various wavelengths, a second displacement platform 313 is set in the optical path 31, such as... Figure 2 and Figure 3 Taking the second wavelength of 532nm as an example, in the transmitting state, the second displacement platform 313 moves the second negative lens 312 into the optical path, so that the second negative lens 312 and the positive lens 314 form a beam-expanding optical path, which expands the polarized light into collimated light; in the receiving state, the positive lens 314 and the second negative lens 312 form a beam-contracting optical path, and the target echo passes through the positive lens 314 and the second negative lens 312 to reduce the beam size.

[0063] refer to Figure 3 In some embodiments, the echo receiving module 4 includes: a third displacement platform 41, a first reflector 42, a first echo receiving box 43, and a second echo receiving box 44;

[0064] The second echo receiver box 44 is located at the third end of the rotating mirror assembly 2, and a third displacement platform 41 is provided at the upper end of the second echo receiver box 44; the second echo receiver box 44 is used to receive the target echo of the second wavelength.

[0065] The first echo receiver box 43 and the second echo receiver box 44 are arranged in parallel, and the first reflector 42 is provided at the upper end of the first echo receiver box 43; the first echo receiver box 43 is used to receive the target echo of the first wavelength.

[0066] The third displacement platform 41 is equipped with a second reflector 411. When the target echo is of the second wavelength, the third displacement platform 41 moves out of the upper end of the second echo receiving box 44 so that the target echo is reflected to the second echo receiving box 44 via the rotating mirror assembly 2. When the target echo is of the first wavelength, the third displacement platform 41 moves the second reflector 411 to the upper end of the second echo receiving box 44 so that the target echo reflected by the rotating mirror assembly 2 is reflected by the second reflector 411 to the first reflector 42, and then the target echo is reflected to the first echo receiving box 43 by the first reflector 42.

[0067] In this embodiment, as Figure 3 As shown, when the wavelength of the target echo is 532nm, the third displacement platform 41 moves to the right, moving the second reflecting mirror 411 to... Figure 3 The position shown is such that the target echo is reflected by the rotating mirror assembly 2 to the second echo receiving box 44; when the wavelength of the target echo is 1064nm, the third displacement platform 41 moves to the left, moving the second reflector 411 to the position shown. Figure 3 The position marked by the dashed line is used to reflect the target echo reflected by the rotating mirror assembly 2 to the first reflector 42 using the second reflector 411, and then to reflect the target echo to the first echo receiving box 43 using the first reflector 42.

[0068] refer to Figure 3 In some embodiments, the first echo receiver box 43 includes: a first focusing lens 431, a first pinhole aperture 432, a first collimating lens 433, a quarter-wave plate of the first wavelength 434, a Glan laser polarizer 435, an optical fiber coupling lens 436, and a first single-photon detector 437.

[0069] The second echo receiver box 44 includes: a second focusing lens 441, a second pinhole aperture 442, a second collimating lens 443, a quarter-wave plate of the second wavelength 444, a polarizer 445, and a second single-photon detector 446.

[0070] In this embodiment, the first focusing lens 431 and the first collimating lens 433 in the first echo receiving box 43 are combined to reduce the target echo beam. The reduced beam is incident on the 1064nm quarter-wave plate 434 and the Glan laser polarizer 435 to modulate the polarization direction of the 1064nm target echo. The SNSPD photon detector 437 is used to detect the echo intensity of the 1064nm target echo under different polarization states.

[0071] The second focusing lens 441 and the second collimating lens 443 in the second echo receiver box 44 are combined to match the target echo beam with the detector. A second pinhole aperture 442 is set at the focal point of the second focusing lens 441 to reduce the receiving field of view and filter out noise light that is different from the direction of the target echo. The second single-photon detector 446 at the 532nm receiver end is an HQE-SPAD detector, which uses a single-photon avalanche diode as a photodetector.

[0072] It should be noted that this embodiment provides two different movement modes for the rotating mirror assembly 2.

[0073] Method 1: For example Figure 1 As shown, the first type of motion involves translating between the first target position a and the second target position b to achieve optical path switching between transmitting and receiving states. It can be understood that the rotating mirror assembly 2 in this first type of motion includes a translation platform for driving the lens to translate.

[0074] Method 2: A lens with a light-passing slot rotates around the central axis in the optical path. In the transmitting state, the light-passing slot rotates to the third target position (i.e., facing the optical path). The optical path switching between transmitting and receiving states is achieved through the rotation of the light-passing slot.

[0075] The rotating mirror component 2 of method two will be explained in detail below.

[0076] Combination Figure 2 , Figure 3 and Figure 4 In some embodiments, the rotating mirror assembly 2 may include: a circular lens, a mirror chamber, a transmission mechanism, a motor, a control drive device, and a synchronization signal generator;

[0077] The edge of the lens is provided with a light-passing groove. The light-passing groove is used to allow the polarized light emitted by the laser emitting module 1 to pass through and be directly emitted to the common optical path 3 when the laser is emitting. When the laser is receiving, the target echo is emitted from the common optical path 3 to the lens so that the lens can reflect the target echo to the echo receiving module 4.

[0078] The mirror chamber is used to install the lenses, and the center of the mirror chamber is connected to the transmission mechanism;

[0079] The other end of the transmission mechanism is connected to the motor, which is electrically connected to the control drive device. The control drive device is used to control the rotation speed of the motor to drive the transmission mechanism, mirror chamber and lens to rotate.

[0080] The synchronization signal generator is used to detect the rotation of the lens. When the lens rotates to the set position, the synchronization signal generator generates a pulse signal to the control subsystem to control the laser emission module 1 to emit polarized light of the corresponding wavelength, and the light-transmitting slot rotates to the third target position so that the polarized light passes through the light-transmitting slot and is emitted to the common optical path 3.

[0081] In this embodiment, the rotating mirror assembly 2 is disposed in the optical path, such as... Figure 4 As shown, a light-passing groove is provided on the edge of the lens. When the lens rotates to the set position, the synchronization signal generator generates a pulse signal to the control subsystem to control the laser emission module 1 to emit polarized light of the corresponding wavelength. The light-passing groove rotates to the third target position, allowing the polarized light to pass through and be emitted into the common optical path 3. The rotation of the light-passing groove enables the rotating mirror assembly 2 to switch between the light-receiving and receiving paths. The lens rotation speed is controlled by a control drive device. The lens rotation speed is set to 10±1 R / S, which is close to the operating frequency of the laser in the dual-wavelength laser device 11. The optimal rotation speed is 10 R / S. The rotation speed is slightly increased or decreased depending on the arrival time of the echo to avoid overlap between the echo arrival time and the laser emission time.

[0082] The synchronization signal generator consists of a photodiode, a 650nm laser, and auxiliary circuitry. To improve control accuracy, a high-speed photodiode with a response time of less than 50ns is selected, ensuring that the jitter at the leading edge of the main control signal is less than 10μs. Furthermore, filtering measures are implemented to prevent parasitic pulses from causing accidental laser emission, thus guaranteeing that the polarized laser beam accurately passes through the light-transmitting slot of the lens each time it is emitted.

[0083] In addition, the timing of the pulse signal generated by the synchronization signal generator can be used to record the emission time of polarized light for ranging of target space debris.

[0084] In some embodiments, it also includes: a polarization detection device;

[0085] The polarization detection device is used to detect the polarization state of the polarized light emitted by the laser emitting module 1, so that after the control subsystem receives the echo intensity of the target echo detected by the echo receiving module 4 under different polarization states, it can identify the material of the target space debris based on the polarization state of the polarized light emitted by the laser emitting module 1 and the echo intensity of the target echo under different polarization states.

[0086] In this embodiment, the polarization state of the polarized light emitted by the laser emitting module 1 is detected by a polarization detection device. After each detection of the polarization state of the polarized light, the polarization detection device can be disconnected.

[0087] In this embodiment, the material of the target space debris can be identified using the following formula:

[0088] S out =M target ·S in

[0089] In the formula, S out S represents the echo intensity of the target echo under different polarization states. in M represents the polarization state of the emitted polarized light. targetThe polarization characteristics of the target space debris.

[0090] By analyzing the polarization characteristics M of the target space debris target The calculation determines the material of the target space fragment.

[0091] The principles and methods for identifying the material of target space fragments are explained below.

[0092] When light is reflected from a target surface, the polarization state of the light changes due to different incident angles, the surface roughness of the target, and the properties of the material itself. Therefore, the reflection process carries over characteristic information about the target object's properties. Each object's reflected light wave has its own unique polarization information, and different targets or different states of the same target will also produce different polarization information. Typically, the characteristic polarization of a target contains various information about it, and by detecting the echo intensity of different polarization states of the target's echo, one can, to a certain extent, determine the target's characteristics.

[0093] The polarized light emitted by the laser emitting module 1 with different polarization directions and polarization states can be described by the Stokes vector. The Stokes vector can describe polarized light with arbitrary polarization states. The polarization detection device can be used to measure the four parameters of each polarization state of the polarized light emitted by the laser emitting module 1.

[0094] The Stokes vector of a monochromatic plane wave is:

[0095]

[0096] Where I represents radiation intensity, E x E y Let δ be the amplitude of the two transverse components on the vibration plane, and δ be the phase difference between the two transverse amplitude components.

[0097] For fully polarized light, the four Stokes components have an identity relationship:

[0098] I 2 =Q 2 +U 2 +V 2

[0099] Where I represents radiation intensity.

[0100] The Stokes vectors corresponding to commonly used polarization states are shown in Table 1 below.

[0101] Table 1

[0102] polarization state Stokes vector polarization state Stokes vector Horizontal polarized light <![CDATA[[1 1 0 0] T ]]> Left-handed circular polarization <![CDATA[[1 0 0 -1] T ]]> Vertical polarized light <![CDATA[[1 -1 0 0] T ]]> Right-handed circular polarization <![CDATA[[1 0 0 1] T ]]> +45° linear polarization <![CDATA[[1 0 1 0] T ]]> -45° linear polarization <![CDATA[[1 0 -1 0] T ]]>

[0103] During transmission, polarized light is affected by external factors such as the transmission medium, reflection and scattering at interfaces, and passing through optical devices or systems. As a result, the polarization state of the original polarized light changes, leading to a decrease in the degree of polarization of the original polarized light. This phenomenon is called depolarization.

[0104] The polarization characteristics of the target echo are described by the Mueller matrix, which represents the change in polarization state of the polarized light (i.e., the Stokes vector) by the scattering medium, namely:

[0105] S out =M target ·S in

[0106] The Mueller matrix takes the following form:

[0107]

[0108] In the formula, the physical meanings described by each Meuller matrix component are as follows:

[0109] M 11 The change in the total intensity of light waves before and after incidence can directly reflect the overall information about the size of the scattering particles;

[0110] M 12 The depolarization rate of linearly polarized light parallel and perpendicular to the scattering plane, the value of which is related to the size, shape and complex refractive index of the scatterer;

[0111] -M 12 / M 11 The degree of linear polarization of the scatterer;

[0112] M 13 Depolarization rate of linearly polarized light at ±45°;

[0113] M 14 Depolarization rate of circularly polarized light;

[0114] M 21 : Describes the variation of incident light with ±90° linear polarization with respect to scattered light with ±90° linear polarization, M 22 Deviation from M 11 It is an important criterion for revealing that a scatterer is non-spherical;

[0115] M 44 : Describes the variation of incident light with ±45° linear polarization with respect to scattered light with ±45° linear polarization, M 44 Deviation from M 33 This indicates that the scatterer is non-spherically symmetric.

[0116] M 34: Describes the variation of circularly polarized incident light with respect to ±45° linearly polarized scattered light, reflecting the size and complex refractive index of the scatterer.

[0117] Understanding the role of each Mueller component in the polarization state of light and the information it contains allows us to fabricate corresponding optical devices to change the polarization state of light, which is beneficial for analyzing the polarization information in statistical echoes.

[0118] In this embodiment, it is necessary to predetermine all possible materials of the space debris and determine the Mueller matrix of each material through simulation experiments.

[0119] For example, when the target surface is a Lambertian body, its Mueller matrix can be expressed as:

[0120]

[0121] Where ρ is the reflectivity of the target, the Mueller matrix of the target clearly retains only the I component of the incident wave, so it can be called a completely deflected target.

[0122] For a perfectly bias-preserving objective, its Mueller matrix can be expressed as:

[0123]

[0124] The Mueller matrix of a painted metal sheet can be represented as:

[0125]

[0126] Therefore, by determining the Mueller matrix of the target space debris based on the polarization state of the polarized light emitted by the laser emitting module 1 and the echo intensity of the target echo under different polarization states, the material of the target space debris can be further identified based on the Mueller matrix of the target space debris.

[0127] like Figure 5 As shown, this invention also provides a space debris detection method based on any embodiment of the system described in this specification, the method comprising:

[0128] Step 500: When the rotating mirror assembly 2 moves to the first target position a, the control subsystem controls the laser emission module 1 to emit polarized light with different polarization directions and polarization states corresponding to the wavelength.

[0129] Step 502: The dual-point high-reflectivity mirror 5 of the corresponding wavelength directly reflects the polarized light to the common optical path 3, so as to use the common optical path 3 to emit the polarized light to the target space debris.

[0130] Step 504: Receive the target echo reflected by the target space debris using the shared optical path 3; wherein the wavelength of the target echo is the same as the wavelength of the polarized light.

[0131] Step 506: The rotating mirror assembly 2 moves to the second target position b to reflect the target echo received by the common optical path 3 to the echo receiving module 4.

[0132] Step 508: Use echo receiving module 4 to detect the echo intensity of the target echo under different polarization states, and send the detection results to the control subsystem;

[0133] Step 510: The control subsystem determines the distance of the target space debris based on the reception time of the target echo and the emission time of the polarized light, and identifies the material of the target space debris based on the echo intensity of the target echo under different polarization states.

[0134] Since the above method is based on the same concept as the system embodiment of the present invention, the specific details can be found in the description of the system embodiment of the present invention, and will not be repeated here.

[0135] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0136] 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lidar system for detecting space debris, characterized in that, include: The system includes a laser emitting module (1), a rotating mirror assembly (2), a common optical path (3), an echo receiving module (4), and a control subsystem. The laser emitting module (1) is disposed at the first end of the rotating mirror assembly (2). The laser emitting module (1) is used to emit polarized light with different polarization directions and polarization states of a first wavelength or polarized light with different polarization directions and polarization states of a second wavelength; wherein the second wavelength is smaller than the first wavelength. The rotating mirror assembly (2) is disposed between the laser emitting module (1), the echo receiving module (4) and the common optical path (3). The rotating mirror assembly (2) is used to move to the first target position (a) in the emitting state so that the polarized light emitted by the laser emitting module (1) is directly emitted to the common optical path (3). In the receiving state, the rotating mirror assembly (2) moves to the second target position so as to reflect the target echo received by the common optical path (3) to the echo receiving module (4) to realize the optical path switching of the transmitting and receiving state. The common optical path (3) is set at the second end of the rotating mirror assembly (2). The common optical path (3) is used to emit the polarized light to the target space debris in the emission state and to receive the target echo reflected by the target space debris in the receiving state. The echo receiving module (4) is disposed at the third end of the rotating mirror assembly (2). The echo receiving module (4) is used to receive the target echo and detect the echo intensity of the target echo under different polarization states. The control subsystem is electrically connected to the laser emitting module (1), the rotating mirror assembly (2), the common optical path (3), and the echo receiving module (4), respectively. The control subsystem is used to control the working status of the laser emitting module (1), the rotating mirror assembly (2), the common optical path (3), and the echo receiving module (4), and to receive the echo intensity of the target echo under different polarization states detected by the echo receiving module (4), so as to determine the distance of the target space debris according to the reception time of the target echo and the emission time of the polarized light, and to identify the material of the target space debris according to the echo intensity of the target echo under different polarization states. The echo receiving module (4) includes: a third displacement platform (41), a first reflector (42), a first echo receiving box (43), and a second echo receiving box (44). The second echo receiving box (44) is disposed at the third end of the rotating mirror assembly (2), and the third displacement platform (41) is disposed at the upper end of the second echo receiving box (44); the second echo receiving box (44) is used to receive the target echo of the second wavelength; The first echo receiving box (43) and the second echo receiving box (44) are arranged in parallel, and the first reflector (42) is provided at the upper end of the first echo receiving box (43); the first echo receiving box (43) is used to receive the target echo of the first wavelength; The third displacement platform (41) is equipped with a second reflector (411). When the target echo is of the second wavelength, the third displacement platform (41) moves out of the upper end of the second echo receiving box (44) so ​​that the target echo is reflected to the second echo receiving box (44) via the rotating mirror assembly (2). When the target echo is of the first wavelength, the third displacement platform (41) moves the second reflector (411) to the upper end of the second echo receiving box (44) so ​​that the second reflector (411) can reflect the target echo reflected by the rotating mirror assembly (2) to the first reflector (42), and then the first reflector (42) can reflect the target echo to the first echo receiving box (43).

2. The system according to claim 1, characterized in that, The laser emitting module (1) includes: a dual-wavelength laser device (11) and a polarization assembly (12); the dual-wavelength laser device (11) is used to emit linearly polarized light of a corresponding wavelength according to the instructions of the control subsystem; The dual-wavelength laser device (11) includes a first laser, a second laser, a reflector group, and a frequency doubling crystal. The first laser and the second laser are arranged side by side, and the emitting end of the second laser is on the same straight line as the laser emitting end of the dual-wavelength laser device (11). The wavelength of the linearly polarized light emitted by the first laser and the second laser is the first wavelength. The reflector group is disposed at the output end of the first laser and is used to reflect the linearly polarized light of the first wavelength emitted by the first laser to the laser output end of the dual-wavelength laser device (11). The frequency doubling chip is disposed at the output end of the second laser and is used to convert the linearly polarized light of the first wavelength emitted by the second laser into linearly polarized light of the second wavelength. The polarization component (12) is disposed at the laser emission end of the dual-wavelength laser device (11). The polarization component (12) is used to modulate the linearly polarized light of the first wavelength or the second wavelength into polarized light with different polarization directions and polarization states.

3. The system according to claim 2, characterized in that, The polarization assembly (12) includes: a first displacement platform (121), a first rotating waveplate group (122), and a second rotating waveplate group (123); wherein the first rotating waveplate group (122) and the second rotating waveplate group (123) are respectively adapted to a first wavelength and a second wavelength; the first rotating waveplate group (122) includes a quarter-wave plate and a half-wave plate for the first wavelength, and the second rotating waveplate group (123) includes a quarter-wave plate and a half-wave plate for the second wavelength; The first rotating waveplate group (122) and the second rotating waveplate group (123) are disposed on the first displacement platform (121). By moving the first displacement platform (121), the linearly polarized light emitted by the dual-wavelength laser device (11) passes through the first rotating waveplate group (122) or the second rotating waveplate group (123). The first displacement platform (121) is used to move according to the wavelength of the linearly polarized light emitted by the dual-wavelength laser device (11) so that the rotating waveplate group of the corresponding wavelength moves to the laser emission direction of the dual-wavelength laser device (11) so as to use the rotating waveplate group of the corresponding wavelength to modulate the linearly polarized light of the corresponding wavelength into polarized light with different polarization directions and polarization states.

4. The system according to claim 1, characterized in that, The rotating mirror assembly (2) includes: a circular lens, a mirror chamber, a transmission mechanism, a motor, a control drive device, and a synchronization signal generator; The edge of the lens is provided with a light-passing groove. The light-passing groove is used to allow the polarized light emitted by the laser emitting module (1) to pass through and be directly emitted to the common optical path (3) when the laser is emitting. When the laser is receiving, the target echo is emitted from the common optical path (3) to the lens so that the lens can reflect the target echo to the echo receiving module (4). The mirror chamber is used to install the lens, and the center of the mirror chamber is connected to the transmission mechanism; The other end of the transmission mechanism is connected to the motor, and the motor is electrically connected to the control drive device. The control drive device is used to control the rotation speed of the motor so as to drive the transmission mechanism, the mirror chamber and the lens to rotate. The synchronization signal generator is used to detect the rotation of the lens. When the lens rotates to a set position, the synchronization signal generator generates a pulse signal to the control subsystem to control the laser emission module (1) to emit polarized light of the corresponding wavelength, and the light-passing slot rotates to the third target position so that the polarized light passes through the light-passing slot and is emitted to the common optical path (3).

5. The system according to claim 1, characterized in that, The common optical path (3) includes: an adjustment optical path (31), a beam splitter (32), and a telescope (33); The adjustment optical path (31) is set at the second end of the rotating mirror assembly (2) and is used to expand the polarized light emitted by the laser emission module (1) into collimated light in the emission state and to reduce the beam of the target echo in the receiving state. The beam splitter (32) is a plane mirror and is located at the other end of the adjustment optical path (31) to reflect the expanded polarized light to the telescope (33) and to reflect the target echo to the adjustment optical path (31). The telescope (33) is located at the other end of the beam splitter (32) and is used to emit expanded polarized light toward the target space debris and to receive the target echo reflected by the target space debris.

6. The system according to claim 5, characterized in that, The adjustment optical path (31) includes: a first negative lens (311), a second negative lens (312), a second displacement platform (313), and a positive lens (314). The applicable wavelengths of the first negative lens (311) and the second negative lens (312) are the first wavelength and the second wavelength, respectively. The first negative lens (311) and the second negative lens (312) are disposed on the second displacement platform (313). By moving the second displacement platform (313), the polarized light or the target echo passes through the first negative lens (31) or the second negative lens (312). The positive lens (314) is disposed at one end of the beam splitter (312).

7. The system according to claim 1, characterized in that, The first echo receiver box (43) includes: a first focusing lens (431), a first pinhole aperture (432), a first collimating lens (433), a quarter-wave plate of the first wavelength (434), a Glan laser polarizer (435), an optical fiber coupling lens (436), and a first single-photon detector (437). The second echo receiver box (44) includes: a second focusing lens (441), a second pinhole aperture (442), a second collimating lens (443), a quarter-wave plate of the second wavelength (444), a polarizer (445), and a second single-photon detector (446).

8. The system according to any one of claims 1-6, characterized in that, Also includes: Polarization detection device; The polarization detection device is used to detect the polarization state of the polarized light emitted by the laser emitting module (1), so that after the control subsystem receives the echo intensity of the target echo under different polarization states detected by the echo receiving module (4), it can identify the material of the target space debris based on the polarization state of the polarized light emitted by the laser emitting module (1) and the echo intensity of the target echo under different polarization states.

9. A space debris detection method based on the system described in any one of claims 1-8, characterized in that, include: When the rotating mirror assembly (2) moves to the first target position (a), the control subsystem controls the laser emission module (1) to emit polarized light with different polarization directions and polarization states corresponding to the wavelength; The dual-point high-reflectivity mirror (5) of the corresponding wavelength directly reflects the polarized light to the common optical path (3), so as to use the common optical path (3) to emit the polarized light to the target space debris; The target echo reflected by the target space debris is received using the shared optical path (3); wherein the wavelength of the target echo is the same as the wavelength of the polarized light. The rotating mirror assembly (2) moves to the second target position (b) to reflect the target echo received by the common optical path (3) to the echo receiving module (4). The echo receiving module (4) is used to detect the echo intensity of the target echo under different polarization states, and the detection results are sent to the control subsystem. The control subsystem determines the distance to the target space debris based on the reception time of the target echo and the emission time of the polarized light, and identifies the material of the target space debris based on the echo intensity of the target echo under different polarization states.

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