A coherent lidar system

Abstract

The utility model discloses a kind of coherent laser radar systems, including laser transceiver assembly for emitting n laser beams, telescope component, it includes super surface module, it at least includes two super surface mirrors, it is used to reflect and focus after n laser beams, or after reflection, focusing and adjusting phase or polarization characteristics and emit to detection space with different pointing angles, n laser beams encounter aerosol in detection space, backward scattering occurs, form n-way back light signal, super surface module receives n-way back light signal, and coupled into laser transceiver assembly, laser transceiver assembly detects detection space based on back light signal, n laser beams are n different wavelength laser beams, n is positive integer.Further, the present scheme can realize multiple channels to detection space detection, by the setting of super surface mirror, make telescope simple structure, small, light in weight, be conducive to satisfying the miniaturization development demand of radar.

Description

Technical Field

[0001] This utility model relates to the field of wind measurement lidar technology, and in particular to a coherent lidar system. Background Technology

[0002] Coherent wind lidar is a non-contact telemetry lidar based on the principle of coherent Doppler velocities. Its optical path principle is as follows: Figure 1 As shown, a narrow-linewidth continuous laser generated by a seed source is split by a beam splitter. One beam is modulated into a pulsed laser by a modulator, then amplified and passed through a circulator before being emitted into the air to be measured via a telescope (i.e., an optical antenna). There, it interacts with aerosols, generating a backscattered echo signal containing atmospheric information. This echo signal contains information about the aerosol's radial velocity along the laser beam (i.e., radial wind speed). This signal is received by the optical antenna, transmitted by the circulator to the coupler, and beats with another reference beam split from the seed source in the coupler. The beat signal is detected by a detector, and after processing by a signal processing unit, the wind speed and direction information in the specified detection space can be retrieved. The main principle is that the optical Doppler effect allows the aerosol's velocity to be converted into a frequency change in the laser signal. Coherent wind-measuring lidar can detect this frequency change and thus calculate the radial wind speed. A single laser beam can only detect the one-dimensional wind speed component in the direction of laser propagation, and cannot directly obtain the three-dimensional vector information of the wind field. Therefore, in practical coherent wind lidar, multiple laser beams with multiple azimuth angles are usually emitted to obtain the one-dimensional wind speed components in multiple independent directions. Subsequently, the three-dimensional wind field is inverted through vector synthesis algorithms to ensure the comprehensiveness and accuracy of wind field detection.

[0003] To ensure the emission of multiple laser beams at multiple azimuth angles, existing coherent wind lidar typically uses multi-channel telescopes or monocular telescopes with beam scanning mechanisms (such as mechanical motors combined with wedge mirrors, or galvanometers, fast-reflecting mirrors, etc.) to achieve beam switching or scanning mechanisms, thereby enabling time-division multiplexing of radial wind speed measurement and vector synthesis. However, both methods result in telescopes that are long, bulky, and heavy. In particular, with the development of emerging industries such as the low-altitude economy (especially involving high-density, high-frequency, and high-risk low-altitude flight activities), the demands for real-time, convenient, and precise remote sensing monitoring of wind speed and direction are increasing, directly driving the trend towards miniaturization of coherent wind lidar. However, the current long, bulky, and heavy telescope design of coherent wind lidar hinders overall miniaturization, thus limiting its application in emerging scenarios, and therefore urgently needs improvement. Utility Model Content

[0004] This invention provides a coherent lidar system to solve the problems of long telescope length, large size, and heavy weight in related technologies.

[0005] According to one aspect of the present invention, a coherent lidar system is provided, comprising: a laser transceiver assembly and a telescope assembly;

[0006] The laser transceiver assembly is used to emit n laser beams. The telescope assembly includes a metasurface module, which includes at least two metasurface mirrors. The metasurface module is used to reflect and focus the n laser beams, or to reflect, focus, and adjust their phase or polarization characteristics before emitting them at different pointing angles into the detection space. Aerosols in the detection space backscatter the n laser beams to form a backlight signal. The metasurface module receives the backlight signal and couples it into the laser transceiver assembly. The laser transceiver assembly detects the detection space based on the backlight signal. The n laser beams are n laser beams of different wavelengths, where n is a positive integer.

[0007] Optionally, the metasurface module includes a first metasurface mirror and a second metasurface mirror. The first metasurface mirror is used to receive the n laser beams emitted by the laser transceiver component and to reflect the n laser beams according to wavelength to the second metasurface mirror. The second metasurface mirror is used to focus the n laser beams and emit them into the detection space at different pointing angles.

[0008] Optionally, the first metasurface or the second metasurface mirror is also used to adjust the phase or polarization characteristics to generate a vortex beam or a vector beam.

[0009] Optionally, the metasurface module includes k metasurface mirrors, where k is greater than 2. The first k-2 metasurface mirrors are used to reflect the n laser beams and adjust the beam waist of the n laser beams to the required focusing position. The (k-1)th metasurface mirror is used to adjust the phase of the n laser beams. The kth metasurface mirror is used to deflect the n laser beams to different pointing angles and emit them into the detection space.

[0010] Optionally, the (k-1)th metasurface mirror is used to generate a vortex beam or a vector beam.

[0011] Optionally, the laser transceiver assembly includes a seed source, a beam splitter, a modulator, an amplifier, a circulator, a coupler, and a detector;

[0012] The seed source is used to output the n laser beams, and the beam splitter is used to split the n laser beams into a reference beam and a probe beam. The probe beam passes sequentially through the modulator, the amplifier, and the circulator before being incident on the telescope assembly. After receiving the return light signal, the telescope assembly is coupled to the coupler through the circulator. The reference beam is coupled to the coupler. The return light signal interferes with the reference beam to form a coherent beam. The detector probes the detection space based on the coherent beam.

[0013] Optionally, the laser transceiver assembly further includes a metasurface compensator located between the beam splitter and the coupler, for adjusting the phase of the reference beam in real time.

[0014] Optionally, the focal length of the telescope assembly satisfies the formula: ;

[0015] Where S'max is the focusing position of the telescope assembly in the atmosphere, f is the effective focal length of the telescope assembly, and Zr is the Rayleigh distance of the lidar emitted beam;

[0016] The effective radius of the spot of the n laser beams at the telescope assembly The effective focal length f at the telescope assembly satisfies:

[0017] ;

[0018] Wherein, NA is the numerical aperture of the optical fiber connecting the laser transceiver assembly and the telescope assembly.

[0019] The actual radius of the telescope assembly The effective radius of the spot of the n laser beams at the telescope assembly The relationship is given by the following formula:

[0020] ;

[0021] in, This is the cutoff ratio, and its value ranges from (0,1).

[0022] Optionally, the radius of the kth metasurface mirror The overall equivalent focal length provided by all the aforementioned metamirrors and the divergence angle of the laser The following relationship must be satisfied: ;

[0023] Where NA is the numerical aperture of the optical fiber connecting the laser transceiver assembly and the telescope assembly. This is the cutoff ratio, and its value ranges from (0,1).

[0024] Optionally, for the i-th wavelength channel corresponding to the i-th time moment, the measured beat spectrum of the coherent beam satisfies: ,in, The center frequency of the modulator. Let be the center frequency of the beat frequency corresponding to the i-th wavelength channel. The frequency independent variable of the beat spectrum is... Let i be the signal amplitude corresponding to the i-th wavelength channel; The discrete impulse function is defined as follows: when the independent variable of the discrete impulse function is equal to 0, the function value is 1; otherwise, it is 0. i is a positive integer, and i is less than or equal to n.

[0025] The coherent lidar system provided by this utility model includes: a laser transceiver assembly and a telescope assembly. The laser transceiver assembly emits n laser beams, and the telescope assembly includes a metasurface module. The metasurface module includes at least two metasurface mirrors. The metasurface module reflects and focuses the n laser beams, or adjusts their phase or polarization characteristics, reflects and focuses them, and then emits them at different pointing angles into the detection space. When the n laser beams encounter aerosols in the detection space, they undergo backscattering, forming n return signals. The metasurface module receives these n return signals and couples them into the laser transceiver assembly. The laser transceiver assembly detects the detection space based on the return signals. The n laser beams are n laser beams of different wavelengths, where n is a positive integer. Furthermore, by setting the metasurface mirrors, the n laser beams can be adjusted to emit them into the detection space at different pointing angles, achieving multi-channel detection of the detection space. Compared to traditional telescopes, this solution makes full use of the metasurface mirrors. Since metasurface mirrors can perform multiple functions and emit n laser beams with different pointing angles, the need for multi-channel telescope setups or beam scanning mechanisms in related technologies can be eliminated, making the telescope structure simple, small in size, and light in weight, which is conducive to meeting the miniaturization development needs of radar.

[0026] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this utility model, nor is it intended to limit the scope of this utility model. Other features of this utility model will become readily apparent from the following description. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the structure of a coherent lidar system provided in related technologies;

[0029] Figure 2 This is a schematic diagram of the coherent lidar system provided in this embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the structure of a coherent lidar system provided in one embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the structure of a coherent lidar system provided in another embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of the structure of a coherent lidar system provided in a specific embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of the structure of a coherent lidar system provided in another specific embodiment of this utility model. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0035] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this utility model are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this utility model described herein can be implemented in sequences other than those illustrated or described herein.

[0036] Figure 2 This is a schematic diagram of the coherent lidar system provided in an embodiment of this utility model. Figure 2 As shown, the system includes: a laser transceiver assembly 100 and a telescope assembly 200;

[0037] The laser transceiver assembly 100 is used to emit n laser beams. The telescope assembly 200 includes a metasurface module 201, which includes at least two metasurface mirrors. The metasurface module 201 is used to reflect and focus the n laser beams, or to reflect, focus, adjust the phase or polarization characteristics, and emit them to the detection space 300 at different pointing angles. The aerosol in the detection space 300 backscatters the n laser beams to form a backlight signal. The metasurface module 201 receives the backlight signal and couples it into the laser transceiver assembly 100. The laser transceiver assembly 100 detects the detection space 300 based on the backlight signal. The n laser beams are n laser beams of different wavelengths, where n is a positive integer.

[0038] It is understandable that the n laser beams are n laser beams of different wavelengths. The n laser beams of different wavelengths can be deflected by the metasurface module 201 at different pointing angles to generate n probe sub-beams with different pointing angles, which will produce backscattering at the probe space 300.

[0039] Specifically, n laser beams can be generated using an ITLA (Integrated Tunable Laser Assembly); that is, the seed source in the laser transceiver assembly 100 can be an ITLA. An ITLA is a high-performance optical communication component, mainly found in fiber optic communication systems, used for signal transmission and modulation. Internally, it includes components such as a laser, modulator, and optical amplifier. Through electrical modulation, thermal modulation, and other methods, an ITLA can time-division multiplexedly scan and output a series of lasers of different wavelengths, covering an operating band of 1530-1625 nm, with a linewidth as narrow as 50 kHz. Therefore, it is suitable as a narrow-linewidth seed source in the coherent wind-measuring lidar involved in this invention. Besides ITLA, other types of multi-wavelength laser sources can also be used, such as frequency-modulated continuous wave sources or optical frequency combs, to output narrow-linewidth, highly coherent lasers within a certain wavelength range. The metasurface module 201 includes at least two metasurface mirrors. The metasurface module 201 is used to reflect and focus n laser beams and emit them to the detection space 300 at different pointing angles. Specifically, the metasurface module 201 modulates the n laser beams to achieve reflection, focusing, and emission at different pointing angles. Alternatively, the metasurface module 201 modulates the n laser beams to achieve reflection, focusing, adjustment of phase or polarization characteristics, and emission at different pointing angles. This process can be performed using two or more metasurface mirrors. The shape, period, duty cycle, and arrangement rules of the metasurface microstructures on the metasurface mirrors can be designed according to the detection distance requirements of the detection space 300 and the expected functions of the metasurface module 201. It is understood that in a metasurface module with phase or polarization adjustment functions, this function can be implemented by a single metasurface mirror or superimposed on a metasurface mirror with other functions; for example, phase or polarization adjustment can be achieved simultaneously with reflection, or phase or polarization adjustment can be achieved simultaneously with focusing, or different pointing angles can be achieved simultaneously with focusing, etc. In the functions implemented by the metasurface module described above, reflection, focusing, and emission at different angles follow a specific order. Adjusting the phase or polarization characteristics can occur at any point before the function of achieving different angle emission. When the aerosol in the detection space 300 backscatters the emitted laser beam and forms a return signal, the return signal can return to the laser transceiver assembly 100 along the emitted optical path. In other words, the return signal can return to the laser transceiver assembly 100 after passing through the metasurface module 201. Because the metasurface mirror can integrate multiple functions on the same surface, enabling multi-channel laser emission, compared to the original lens-based telescope, the scanning method can be simplified, scanning elements reduced, and the telescope size decreased, facilitating radar miniaturization.

[0040] It should be noted that the core of the time-division multiplexing multi-channel wind speed demodulation scheme in this coherent lidar system relies on the laser transceiver module and the metasurface module to achieve time-division processing of multi-channel signals through timing control, without the need for additional hardware components, thus avoiding increased system complexity. Specifically, the laser transceiver module generates n laser beams of different wavelengths in a fixed time sequence, with each laser beam corresponding to a detection channel (pointing angle), and outputs them sequentially in different time segments; after receiving the laser beams of each wavelength, the metasurface module accurately emits light waves of specific wavelengths to specific directions in the detection space, ensuring that only one laser beam of a specific wavelength points to the target detection area in each time segment.

[0041] In terms of timing planning, the maximum time required for the laser to travel to and from the target detection distance in the detection space is calculated, and a dedicated transmit-receive time window is determined for each channel. This ensures that the return signal formed by the laser from the previous channel being scattered by the target is fully received before the laser transmission and reception of the next channel (wavelength) is started, avoiding signal superposition and interference between different channels. During reception, the metasurface module couples the return signal returning from a specific direction back to the laser transceiver component. This return signal beats with the reference beam of the corresponding wavelength within the laser transceiver component. The Doppler frequency shift carried by the return signal of this channel is extracted using existing coherent detection hardware and algorithms. Simultaneously, the detector only starts working within the time window of the current channel, and the binding of the return signal to the corresponding channel is completed through timing matching.

[0042] In the wind speed demodulation stage, after all the signal acquisitions of n channels are completed within a complete cycle, the wind speed component in the propagation direction of each laser is calculated by combining the specific directional angles pre-calibrated when the laser of each channel is emitted through the metasurface. The three-dimensional actual wind speed and wind direction of the detection area are obtained through vector synthesis. The entire process reuses the radar's signal processing module without the need for additional hardware equipment. This maintains the advantages of radar miniaturization and achieves accurate demodulation of multi-channel wind speed and wind direction.

[0043] In one embodiment, n can be 2, 3, 4, etc., and the specific value can be determined according to the actual situation.

[0044] Furthermore, in this embodiment, multiple laser beams can be emitted using only one telescope assembly. Compared to the traditional method of emitting multiple laser beams, which requires the use of a multi-channel telescope or a beam scanning mechanism such as a mechanical motor and a wedge mirror, the telescope assembly in this embodiment is smaller and more compact.

[0045] Optionally, Figure 3 This is a schematic diagram of the structure of a coherent lidar system provided in one embodiment of this utility model. Figure 3As shown, the metasurface module 201 includes a first metasurface mirror 2011 and a second metasurface mirror 2012. The first metasurface mirror 2011 is used to receive n laser beams emitted by the laser transceiver assembly 100 and to reflect the n laser beams according to wavelength to the second metasurface mirror 2012. The second metasurface mirror 2012 is used to focus the n laser beams and emit them to the detection space 300 at different pointing angles.

[0046] The pointing angle refers to the acute angle between the emitted beam and the telescope axis, which can be decomposed into the horizontal and vertical pointing angles. Figure 3 In this diagram, α and β represent the lateral and longitudinal pointing angles, respectively, and λ is the wavelength of the corresponding laser beam. It can be understood that after the first metamirror 2011 receives n laser beams emitted from the laser transceiver assembly 100, it can reflect these n beams to a specific area of ​​the second metamirror 2012. The second metamirror 2012 can deflect the n laser beams at different angles according to their wavelengths and focus them on a specific area in the detection space, generating n detection sub-beams with different pointing angles, resulting in backscattering at the detection space 300. The backlight signals at different angles are received by the second metamirror 2012 and then coupled backlight signals at different angles into the laser transceiver assembly 100 via the first metamirror 2011.

[0047] It should be noted that the first metamirror 2011 modulates the incident light through a Pancharatnam-Berry (PB) phase modulation mechanism to directionally control the incident light to reach a specific region of the second metamirror 2012. By setting the geometric parameters (duty cycle, shape, period, etc.) of the microstructures on the first metamirror 2011 according to wavelength division, light of different wavelengths is divided into zones. The second metamirror 2012 can also perform zone modulation of different incident light according to a resonant phase modulation mechanism, that is, it can also set microstructures of different sizes in zones. Microstructures of different sizes resonate with light of different wavelengths, thereby realizing the zone modulation of light of different wavelengths and their emission into the detection space 300 at different angles.

[0048] The first metasurface mirror 2011 deflects the beam's transmission direction, while the second metasurface mirror 2012 divides the beam into wavelength zones. This process avoids the use of dynamic components such as optical switches. Furthermore, the second metasurface mirror 2012 modulates and deflects the beam for different wavelengths, further reducing the telescope's size. The two-piece metasurface module 201, through focusing and reflection functions, can replace traditional telescopes. Compared to lenses, it can significantly reduce thickness, enabling optical path folding and thus compressing the telescope's size, ensuring high magnification and a compact structure.

[0049] In one embodiment, the total length of the telescope formed by the two metasurface mirrors can be calculated as follows:

[0050] The required focal length of the telescope assembly 200 is determined based on the required detection distance and beam pointing angle of the detection space 300. The aperture of the second metasurface mirror 2012 f / 2 The focal length of the first metasurface mirror 2011 is... satisfy, .

[0051] The optical path distance between the first metasurface mirror 2011 and the second metasurface mirror 2012 is taken as Telescope magnification: .

[0052] Second metasurface mirror 2012 focal length satisfy: , .

[0053] The actual total length of the telescope assembly 200 is equal to the distance L from the first metasurface mirror 2011 to the focal plane, which satisfies the following condition. .

[0054] In this embodiment, the total length L of the telescope assembly 200 in the transmission optical path is approximately the focal length f of the telescope, i.e., L=f. Compared with the transmission telescope assembly 200, the compressible length of the telescope assembly in this embodiment is approximately 300-99.8=200.2mm.

[0055] Therefore, forming the telescope assembly 200 using the metasurface module 201 can shorten the overall length of the telescope and help reduce the overall size of the radar system.

[0056] Optionally, the first metasurface mirror 2011 or the second metasurface mirror 2012 is also used to adjust the phase or polarization characteristics to generate a vortex beam or a vector beam. This utilizes the anti-turbulence advantages of the vortex beam or vector beam to improve the radar's detection accuracy and signal-to-noise ratio in the detection space 300.

[0057] It should be noted that the core characteristic of a vortex beam is its helical phase distribution, whose phase satisfies φ(r,θ)=Iθ (where I is the topological charge, θ is the azimuth angle, and r is the radial coordinate). This phase distribution causes the beam to rotate in a helical shape, with a phase singularity at the center, i.e., a dark spot with zero light intensity. When incident light (such as a plane wave) irradiates the metamirror, each structure on the metamirror will reflect and modulate the light according to a preset phase, ultimately superimposing to form a helical vortex beam. Specifically, the first metamirror 2011 or the second metamirror 2012 can be modulated with corresponding phases to generate a vortex beam after the laser beam passes through the metamirror module 201.

[0058] Vector beams are a special type of beam with a spatially non-uniformly distributed polarization state. Their core characteristic is the regular variation in polarization direction (or polarization state) at different positions on the beam's cross-section. They must be described simultaneously by the spatial distribution of amplitude, phase, and polarization state, and can carry physical quantities such as orbital angular momentum. This aligns well with the requirements of wind field detection for anti-interference capabilities, spatial resolution, multi-dimensional information acquisition, and transmission stability. For example, when wind fields exhibit abrupt changes or eddies, high spatial resolution is needed to capture details, and the non-uniform intensity distribution of vector beams can improve detection accuracy. Specifically, the first metasurface mirror 2011 or the second metasurface mirror 2012 can modulate the amplitude, phase, and polarization state of the laser beam to generate a vector beam after passing through the metasurface module 201.

[0059] Optionally, Figure 4 This is a schematic diagram of the structure of a coherent lidar system provided in another embodiment of this utility model. (See diagram below.) Figure 4 As shown, the metasurface module 201 includes k metasurface mirrors, where k is greater than 2. The first k-2 metasurface mirrors are used to reflect n laser beams and adjust the beam waist of the n laser beams to the required focusing position. The (k-1)th metasurface mirror is used to adjust the phase of the n laser beams. The kth metasurface mirror is used to deflect the n laser beams to different pointing angles and emit them into the detection space 300.

[0060] It should be noted that the laser transceiver 100 emits n beams of light with different wavelengths. These beams are adjusted to the desired focusing position by the first k-2 metasurface mirrors in the metasurface module 201. Then, the (k-1)th metasurface mirror adjusts the phase of the beam, and the kth metasurface mirror deflects the n beams at different pointing angles according to their wavelengths, generating n probe sub-beams with different pointing angles, which are then backscattered into the probe space 300. The atmospheric backlight signals at different angles are then received by the metasurface module 201 and sequentially pass through the kth metasurface mirror, the (k-1)th metasurface mirror, the (k-2)th metasurface mirror, and finally back to the laser transceiver 100 via the first metasurface mirror.

[0061] Since k-2 metasurface mirrors reflect the light beam, similar to a catadioptric telescope, the entire optical path can be compressed accordingly, reducing the size and weight of the entire telescope assembly 200. Furthermore, the k-th metasurface mirror can deflect the light beam at different angles according to different wavelengths, thus projecting it to different positions in the detection space 300. In this way, multi-channel laser emission can be achieved using the k-th metasurface mirror, eliminating the need for scanning or rotating components as in traditional telescope assemblies, thereby further reducing the size of the telescope assembly 200.

[0062] It is understandable that the microstructure of each metasurface mirror in the metasurface module 201 can be set according to the detection distance of the detection space 300 and the pointing angle of the laser.

[0063] Optionally, the (k-1)th metasurface mirror is used to generate a vortex beam or a vector beam.

[0064] The core feature of the vortex beam is its spiral phase distribution, which satisfies φ(r,θ)=Iθ (where I is the topological charge, θ is the azimuth angle, and r is the radial coordinate). This phase distribution causes the beam to rotate in a spiral shape, with a phase singularity at the center, i.e., a dark spot with zero light intensity. When incident light (such as a plane wave) irradiates the metasurface mirror, each structure on the metasurface mirror will reflect and modulate the light according to the preset phase, and finally superimpose to form a spiral vortex beam.

[0065] Similarly, vector beams are a special type of beam with a spatially non-uniformly distributed polarization state. Their core characteristic is the regular variation in polarization direction (or polarization state) at different positions on the beam's cross-section. This requires simultaneous description using the spatial distribution of amplitude, phase, and polarization state, and they can carry physical quantities such as orbital angular momentum. This aligns well with the requirements of wind field detection for anti-interference capabilities, spatial resolution, multi-dimensional information acquisition, and transmission stability. For example, when wind fields exhibit abrupt changes or eddies, high spatial resolution is needed to capture details, and the non-uniform intensity distribution of vector beams can improve detection accuracy. Specifically, the (k-1)th metasurface mirror can modulate the amplitude, phase, and polarization state of the laser beam, causing it to generate a vector beam after passing through it, thus improving the detection accuracy within the 300° detection space.

[0066] Optionally, Figure 5 This is a schematic diagram of the structure of a coherent lidar system provided in a specific embodiment of this utility model. For example... Figure 5 As shown, the laser transceiver assembly 100 includes a seed source 101, a beam splitter 102, a modulator 103, an amplifier 104, a circulator 105, a coupler 106, and a detector 107.

[0067] The seed source 101 is used to output n laser beams, and the beam splitter 102 is used to split the n laser beams to form a reference beam and a probe beam. The probe beam passes through the modulator 103, amplifier 104, and circulator 105 in sequence before being incident on the telescope assembly 200. After receiving the return light signal, the telescope assembly 200 is coupled to the coupler 106 through the circulator 105. The reference beam is coupled to the coupler 106. The return light signal and the reference beam interfere to form a coherent beam. The detector 107 detects the detection space 300 based on the coherent beam.

[0068] In this design, seed source 101 can be an ITLA (In-The-Layer Array), beam splitter 102 can be a fiber optic beam splitter, modulator 103 can be an optical modulator, and amplifier 104 can be an optical signal amplifier. Modulator 103 and amplifier 104 can optimize the time-domain waveform of laser beam 301. Circulator 105 can be a fiber optic circulator with three fiber optic ports: one connected to amplifier 104, one connected to telescope assembly 200, and one connected to coupler 106. Coupler 106 has two inputs and one output. The first input is connected to beam splitter 102, the second input is connected to circulator 105, and the output is connected to detector 107.

[0069] Thus, the laser beam output from seed source 101 is split into a probe beam and a reference beam by beam splitter 102. The reference beam is directly input to coupler 106, while the probe beam passes sequentially through modulator 103, amplifier 104, and circulator 105 before being emitted into probe space 300 via telescope assembly 200. Aerosols in probe space 300 backscatter the probe beam, forming a backscatter signal. This backscatter signal passes through circulator 105 and enters coupler 106. In coupler 106, the backscatter signal and the reference beam form a coherent beam, and detector 107 detects the beat frequency signal carried by the coherent beam. Performing a Fourier transform on this beat frequency signal yields a beat spectrum reflecting the velocity of the aerosols along the beam's direction, with frequency on the horizontal axis and amplitude on the vertical axis.

[0070] It should be noted that, for the i-th wavelength channel corresponding to the i-th time moment, the measured beat spectrum of the coherent beam satisfies: ,in, The center frequency of the modulator. Let be the center frequency of the beat frequency corresponding to the i-th wavelength channel. The frequency independent variable of the beat spectrum is... Let i be the signal amplitude corresponding to the i-th wavelength channel; It is a discrete impulse function. When its independent variable is equal to 0, the function value is 1, otherwise it is 0.

[0071] The beat spectrum is related to the wind direction in the detection space. That is, the position of the horizontal axis where the non-zero amplitude is located on the beat spectrum is related to the radial wind speed and wind direction in the detection space, and can be used to calculate the radial wind speed and wind direction in the detection space. The beat spectrum of multiple wavelength channels corresponds to the radial wind speed and wind direction in multiple directions. Through vector synthesis algorithm, the wind field can be inverted using the wind speed components in these directions.

[0072] Optionally, Figure 6 This is a schematic diagram of the structure of a coherent lidar system provided in another specific embodiment of this utility model. For example... Figure 6As shown, the laser transceiver assembly 100 also includes a metasurface compensator 108, which is located between the beam splitter 102 and the coupler 106 and is used to adjust the phase of the reference beam in real time.

[0073] In other words, the metasurface compensator 108 can adjust the phase of the reference beam in real time, which is beneficial to improving the detection signal-to-noise ratio and the accuracy of subsequent beat frequency signal processing. Specifically, there is a time difference between the time it takes for the laser beam emitted from the seed source 101 to reach the detection space 300 and the time it takes for the return signal to reach the coupler 106 for coherence. During this time, the optical field of the reference beam input to the coupler 106 may have changed. Therefore, placing the metasurface compensator 108 between the beam splitter 102 and the coupler 106 can compensate the current optical field of the reference beam to be in phase with the optical field of the laser beam emitted from the seed source 101 when it reaches the detection space 300, thus improving the coherence between the reference beam and the return signal. The metasurface compensator 108 can be set up through calibration.

[0074] The following describes the relationship between the focal length of the telescope assembly 200 and the output numerical aperture of the laser transceiver assembly 100, and how the effective radius of the light spot is determined by the telescope assembly 200, thereby determining the overall size of the telescope assembly 200 and the size of the microstructure.

[0075] Optionally, the focal length of the telescope assembly 200 satisfies the formula: Where S'max is the focusing position of the telescope assembly 200 in the atmosphere, f is the effective focal length of the telescope assembly 200, Zr is the Rayleigh distance of the laser radar emitted beam, and n laser beams have an effective spot radius at the telescope assembly 200. The effective focal length f at 200 of the telescope assembly satisfies: Where NA is the numerical aperture of the optical fiber connecting the laser transceiver assembly 100 and the telescope assembly 200; and the actual radius of the telescope assembly 200 is... The effective radius of the spot of the n laser beams at the telescope assembly The relationship is given by the following formula: ;in, This is the cutoff ratio, and its value ranges from (0, 1).

[0076] Therefore, once the detection distance of the detection space 300 and the pointing angle of the laser are determined, the Rayleigh distance of the laser radar beam and the focusing position of the telescope assembly 200 in the atmosphere can be determined, thereby determining the effective focal length of the telescope assembly 200. Then, the effective radius of the light spot of the telescope assembly 200 can be determined according to the numerical aperture of the optical fiber. Then, the actual radius of the telescope assembly 200 can be determined, so that the corresponding microstructure design can be carried out within the effective radius of the light spot on the substrate of the actual radius.

[0077] When the metasurface module 201 includes k metasurface mirrors, optionally, the radius of the kth metasurface mirror is... The overall equivalent focal length provided by all the metasurface mirrors and the divergence angle of the laser The following relationship must be satisfied: ;

[0078] Where NA is the numerical aperture of the optical fiber connecting the laser transceiver assembly 100 and the telescope assembly 200. This is the cutoff ratio, and its value ranges from (0, 1).

[0079] By analogy, when the metasurface module 201 includes two metasurface mirrors, the radius of the second metasurface mirror, the overall equivalent focal length provided by the first metasurface mirror 2011 and the second metasurface mirror 2012, and the divergence angle of the laser can also satisfy the above relationship.

[0080] It should be noted that metasurface mirrors, as two-dimensional optical components, achieve the manipulation of laser phase, amplitude, polarization state, and beam direction based on subwavelength microstructures, thereby enabling precise control of the light field and even generating light fields different from the traditional Gaussian distribution, such as vortex beams and vector beams. Compared with traditional lenses, the use of metasurface mirrors increases the freedom of optical design. In addition, metasurface mirrors have advantages such as small size and light weight. By using two or more (k) metasurface mirrors to deflect the optical path, the total length of the telescope can be compressed, and the volume of the transceiver components can be reduced. By using wavelength differentiation to achieve multi-channel beam emission, radar can avoid the use of dynamic components such as optical switches, mechanical motors with wedge mirrors, galvanometers, and fast-reflecting mirrors, reducing device redundancy. Metasurface mirrors can also generate vortex beams or vector beams, and utilize the anti-turbulence advantages of vortex beams or vector beams to improve the detection accuracy and signal-to-noise ratio of radar. A metasurface compensator can be added before the reference beam enters the detector to adjust the phase of the reference beam in real time, so that it is consistent with the phase of the light field of the laser beam emitted into the detection space, thereby improving the coherence between the reference beam and the return signal, and thus improving the detection accuracy and signal-to-noise ratio of radar.

[0081] In summary, the coherent lidar system provided by this invention includes a laser transceiver assembly and a telescope assembly. The laser transceiver assembly emits n laser beams, and the telescope assembly includes a metasurface module. The metasurface module includes at least two metasurface mirrors. The metasurface module reflects and focuses the n laser beams, or reflects, focuses, and adjusts their phase or polarization characteristics before emitting them at different pointing angles into the detection space. When the n laser beams encounter aerosols in the detection space, they undergo backscattering, forming n return signals. The metasurface module receives these n return signals and couples them into the laser transceiver assembly. The laser transceiver assembly detects the detection space based on the return signals. The n laser beams are n lasers of different wavelengths, where n is a positive integer. Furthermore, by using the metasurface mirrors, the n laser beams can be adjusted to emit them into the detection space at different pointing angles, enabling multi-channel detection of the detection space. Compared to traditional telescopes, this solution, through the use of metasurface mirrors, simplifies the telescope structure, reduces its size and weight, and is beneficial for meeting the miniaturization requirements of radar.

[0082] The specific embodiments described above do not constitute a limitation on the scope of protection of this utility model. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A coherent lidar system, characterized in that, include: Laser transceiver assembly and telescope assembly; The laser transceiver assembly is used to emit n laser beams. The telescope assembly includes a metasurface module, which includes at least two metasurface mirrors. The metasurface module is used to reflect and focus the n laser beams, or to reflect, focus, adjust the phase or polarization characteristics, and emit them to the detection space at different pointing angles. Aerosols in the detection space backscatter the n laser beams to form a backlight signal. The metasurface module receives the backlight signal and couples it into the laser transceiver assembly. The laser transceiver assembly detects the detection space based on the backlight signal. The n laser beams are n laser beams of different wavelengths, where n is a positive integer.

2. The coherent lidar system according to claim 1, characterized in that, The metasurface module includes a first metasurface mirror and a second metasurface mirror. The first metasurface mirror is used to receive the n laser beams emitted by the laser transceiver assembly and to reflect the n laser beams according to wavelength to the second metasurface mirror. The second metasurface mirror is used to focus the n laser beams and emit them into the detection space at different pointing angles.

3. The coherent lidar system according to claim 2, characterized in that, The first metasurface mirror or the second metasurface mirror is also used to adjust the phase or polarization characteristics to generate a vortex beam or a vector beam.

4. The coherent lidar system according to claim 1, characterized in that, The metasurface module includes k metasurface mirrors, where k is greater than 2. The first k-2 metasurface mirrors are used to reflect the n laser beams and adjust the beam waist of the n laser beams to the required focusing position. The (k-1)th metasurface mirror is used to adjust the phase of the n laser beams. The kth metasurface mirror is used to deflect the n laser beams to different pointing angles and emit them into the detection space.

5. The coherent lidar system according to claim 4, characterized in that, The (k-1)th metasurface mirror is used to generate a vortex beam or a vector beam.

6. The coherent lidar system according to claim 1, characterized in that, The laser transceiver assembly includes a seed source, a beam splitter, a modulator, an amplifier, a circulator, a coupler, and a detector; The seed source is used to output the n laser beams, and the beam splitter is used to split the n laser beams into a reference beam and a probe beam. The probe beam passes sequentially through the modulator, the amplifier, and the circulator before being incident on the telescope assembly. After receiving the return light signal, the telescope assembly is coupled to the coupler through the circulator. The reference beam is coupled to the coupler. The return light signal interferes with the reference beam to form a coherent beam. The detector probes the detection space based on the coherent beam.

7. The coherent lidar system according to claim 6, characterized in that, The laser transceiver assembly also includes a metasurface compensator located between the beam splitter and the coupler, which is used to adjust the phase of the reference beam in real time.

8. The coherent lidar system according to claim 1, characterized in that, The focal length of the telescope assembly satisfies the formula: ; Where S'max is the focusing position of the telescope assembly in the atmosphere, f is the effective focal length of the telescope assembly, and Zr is the Rayleigh distance of the lidar emitted beam; The effective radius of the spot of the n laser beams at the telescope assembly The effective focal length f at the telescope assembly satisfies: ； Wherein, NA is the numerical aperture of the optical fiber connecting the laser transceiver assembly and the telescope assembly. The actual radius of the telescope assembly The effective radius of the spot of the n laser beams at the telescope assembly The relationship is given by the following formula: ； in, This is the cutoff ratio, and its value ranges from (0,1).

9. The coherent lidar system according to claim 4, characterized in that, Wherein the radius of the kth metasurface mirror The overall equivalent focal length provided by all the metasurface mirrors and the divergence angle of the laser The following relationship must be satisfied: ; Where NA is the numerical aperture of the optical fiber connecting the laser transceiver assembly and the telescope assembly. This is the cutoff ratio, and its value ranges from (0,1).

10. The coherent lidar system according to claim 6 or 7, characterized in that, For the i-th wavelength channel corresponding to the i-th time moment, the measured beat spectrum of the coherent beam satisfies: ,in, The center frequency of the modulator. Let be the center frequency of the beat frequency corresponding to the i-th wavelength channel. The frequency independent variable of the beat spectrum is... Let i be the signal amplitude corresponding to the i-th wavelength channel; Let i be a discrete impulse function. When the independent variable of the discrete impulse function is equal to 0, the function value is 1, otherwise it is 0. i is a positive integer, i is less than or equal to n.

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