Zero-blind-area noise-reduction atmosphere laser radar system and detection method thereof

Abstract

The invention relates to a laser radar system, in particular to a zero-blind-area noise-reducing atmosphere laser radar system and a detection method thereof. A zero-blind-area noise-reducing atmosphere laser radar system comprises a transmitting system which comprises a laser and a metasurface array connected with the laser, and the metasurface array is used for generating a perfect vortex beam with a micro-radian-level small divergence angle and a radial size not changing along with topological charge; the receiving system is used for receiving back scattering signals excited by the laser beams of the transmitting system, realizing optical signal collection through convergence and realizing optical signal extraction through a light splitting module at the rear end; and the photoelectric converter signal processing system is used for processing the optical signal of the receiving system and presenting the aerosol distribution condition of the whole atmosphere on a laser path. According to the system, zero-blind-area and high-signal-to-noise-ratio detection performance of the laser radar is realized based on a perfect vortex light source; the metasurface micro-nano photonic device is adopted, the size is small, the integration degree is high, and miniaturization of the laser radar can be achieved.

Description

Technical Field

[0001] The present invention relates to a laser radar system, in particular to an atmospheric laser radar system with zero blind zone and noise reduction and a detection method thereof. Background Art

[0002] Atmospheric LiDAR is an active remote sensing device that can conduct continuous atmospheric observations with a spatial resolution of meters. It is usually divided into Mie scattering atmospheric LiDAR, Raman atmospheric LiDAR, differential absorption atmospheric LiDAR, etc. according to the detection principle. The working environment of atmospheric LiDAR is diverse, and it can be selected to work in the LiDAR cabin or outdoors according to the detection needs. Existing atmospheric LiDAR systems usually use traditional Gaussian distribution laser light sources combined with common lenses to control the light beam, that is, to achieve functions such as light source shaping, coupled spectroscopy, filtering, and focusing. The traditional Gaussian light source used in LiDAR has a divergence angle of millirads, and based on the existing structure and the bottleneck of traditional lens design, whether in coaxial or off-axis structures, a single telescope LiDAR system will have a blind area of ​​tens of meters or even hundreds of meters, and it is impossible to obtain the atmospheric state in the blind area. In addition, traditional lenses have a single function, and multiple lens matching designs are required to achieve focusing, collimation, aberration correction and other functions in the system, resulting in a complex optical path structure, a large volume, and difficulties in system integration, debugging and miniaturization.

[0003] The existing solution uses a multi-telescope solution combined with structural optimization design to suppress blind spots. The entire system is extremely large and cannot meet the needs of miniaturization, portability, and multi-scenario applications of lidar. Summary of the invention

[0004] In order to solve the above problems, the present invention provides an atmospheric laser radar system with zero blind zone and noise reduction, and the specific technical solution is as follows: A zero-blind-zone and noise-reducible atmospheric lidar system comprises: a transmitting system, comprising a laser and a metasurface array arranged opposite to the laser, wherein the metasurface array is used to generate a perfect vortex light beam with a small divergence angle at a micro-radian level and a radial size that does not change with topological charge; a receiving system, used to receive a backscattered signal excited by the laser beam of the transmitting system, collect light signals by converging, and extract light signals by a back-end spectroscopic module; and a photoelectric conversion and signal processing system, used to process the light signals of the receiving system and present the aerosol distribution of the entire atmosphere on the laser path.

[0005] Preferably, the laser is used to generate an original emission linearly polarized Gaussian beam.

[0006] Preferably, the metasurface array comprises a silicon dioxide substrate and gold nanorods disposed on the silicon dioxide substrate, the metasurface composed of the metal nanorod array is an array element, and the array elements constitute a centimeter-scale metasurface array.

[0007] Furthermore, the phase design formula of the metasurface is as follows: ; Where: is the cylindrical coordinate system parameter, l is the topological charge, is the wavelength, is the focal length of the lens, NA is the numerical aperture, a is the horizontal normalization factor, and b is the vertical normalization factor.

[0008] Preferably, the receiving system includes an optical receiving unit, a Casselling-type reflective telescope system, a signal processing unit, a collimation module, an optical microlens array module, a spectroscopic module, and a signal separation module, which are arranged in sequence.

[0009] Preferably, the photoelectric conversion and signal processing system includes an acquisition module and a processing module which are arranged in sequence.

[0010] A detection method for an atmospheric laser radar with zero blind zone and noise reduction is used for an atmospheric laser radar system with zero blind zone and noise reduction. A laser generates a linearly polarized fundamental mode Gaussian beam, which is shaped into a perfectly homogenized vortex beam after being phase modulated by a metasurface array; the shaped beam emitted by a transmitting system is emitted into the atmosphere and generates a backscattered photon signal, which is received by a receiving system; the backscattered photon signal is transmitted to a signal processing unit after passing through a Cassegrain telescope, and the processed light signal is further collimated and transmitted to an optical microlens array module for signal-noise spectroscopic operation, and signal-noise separation is performed through a light blocking device to obtain a high-purity signal; the high-purity light signal is further transmitted to a photoelectric conversion and signal processing system, and an effective echo signal is obtained after being received by a detector, processed by a high-speed acquisition card, and processed by a computer.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The zero-blind-zone and noise-reducing atmospheric lidar system provided by the present invention is based on a perfect vortex light source and can solve the problems of large divergence angle of traditional vortex light, difficulty in blind-zone compression and low resolution, thereby achieving zero-blind-zone and high signal-to-noise ratio detection performance of the lidar. It adopts ultra-surface micro-nano photonic devices with small size and high integration, thereby realizing miniaturization of the lidar. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a structural diagram of this application; Figure 2 It is a schematic diagram of the structure of the metasurface array. DETAILED DESCRIPTION

[0013] The present invention will be further described with reference to the accompanying drawings.

[0014] At present, atmospheric laser radar has technical difficulties such as large blind spots and high noise. The large blind spots make it impossible to capture the near-field state during detection, and the high noise leads to low signal-to-noise ratio and poor detection performance. The present invention solves these two technical difficulties based on optical principles, thereby achieving zero blind spot and high signal-to-noise ratio detection, and the system has high integration and can be miniaturized.

[0015] As a vortex light source that does not change with the topological charge, the perfect vortex beam is naturally resistant to the atmospheric diffusion effect. In the transition zone of the radar signal, it can maintain the stability of the light intensity distribution and improve the accuracy of the signal.

[0016] A zero-blind-zone and noise-reducing atmospheric lidar system based on a perfect vortex light source can solve the problems of large divergence angle of traditional vortex light, difficult blind-zone compression and low resolution, and achieve lidar detection performance with zero blind zone and high signal-to-noise ratio; it uses ultra-surface micro-nano photonic devices with small size and high integration, which can realize miniaturization of lidar.

[0017] A zero-blind-zone and noise-reducible atmospheric lidar system comprises: a transmitting system, comprising a laser and a metasurface array arranged opposite to the laser, wherein the metasurface array is used to generate a perfect vortex light beam with a small divergence angle at a micro-radian level and a radial size that does not change with topological charge; a receiving system, used to receive a backscattered signal excited by the laser beam of the transmitting system, collect light signals by converging, and extract light signals by a back-end spectroscopic module; and a photoelectric conversion and signal processing system, used to process the light signals of the receiving system and present the aerosol distribution of the entire atmosphere on the laser path.

[0018] A zero-blind-zone and noise-reducing atmospheric lidar system realizes the integration of perfect vortex light source and metasurface in the atmospheric lidar system. By using a perfect vortex light source at the transmitting end of the radar system, the divergence angle in free space can be suppressed, and combined with the optimized design of the optical path of the transmitting and receiving structure, the lidar detection zero blind zone can be achieved; in addition, the radial scale of the traditional vortex light beam will increase with the increase of the topological charge. With the perfect vortex light source, the radial scale of the light spot basically does not change with the topological charge, and the anti-turbulence ability of the vortex light will be enhanced, which is conducive to system integration and miniaturization; in the spectroscopic system, the filtering, collimation, focusing and other functional modules use metasurfaces, which can achieve an order of magnitude compression of the external dimensions, from tens of centimeters to millimeters; the subsequent optical path system uses a metasurface array to take into account the reception of far-field and near-field light, and realize the system zero blind zone; in addition, the metasurface can break through the diffraction limit, optimize the system imaging quality, and improve the optical resolution of the imaging system. In the combination mode of perfect vortex light source, metasurface and microlens array, the background light separation ability can be effectively improved, and the system signal-to-noise ratio and detection performance can be improved.

[0019] The perfect vortex light source atmospheric lidar system based on metasurface array consists of a transmitting system, a receiving system, and a photoelectric conversion and information processing system. The main modules of these three systems include the perfect vortex light source generation module, the receiving module, the signal-noise separation module, the subsequent spectroscopic module, and the data acquisition control processing module.

[0020] The principle of the laser radar system, the system composition of each module and the cascade relationship are as follows: The laser emits a linearly polarized Gaussian light source, which is modulated by a metasurface array to generate a perfect vortex beam. The perfect vortex beam has a phase singularity, which makes it feasible to separate background noise and effective signals. At the same time, the radial size of the perfect vortex beam does not change with the change of topological charge. Increasing the topological charge within a certain range can enhance the anti-turbulence ability of the perfect vortex, maintain a high beam quality before scattering, and prevent optical turbulence phenomena such as drift and jitter. The perfect vortex beam also has the characteristic of a small divergence angle. The perfect vortex beam is emitted into the atmosphere and is received by the telescope after backscattering by particles or atmospheric molecules in the atmosphere. The telescope system transmits the received light signal to the microlens array module and the light blocking device for signal-to-noise separation. The separated effective signal enters the spectroscopic module composed of the metasurface array for spectroscopic, collimation, focusing and other operations, and is finally detected by the detector. The converted electrical signal is processed by the acquisition card and enters the computer system for analysis and processing.

[0021] The light emitted by the laser is vertically linearly polarized light with a high polarization ratio. A quarter-wave plate is placed at the rear end of the laser so that the fast axis of the wave plate is at a 45° angle to the vertical direction. Then the light emitted from the wave plate is left-handed circularly polarized light. The obtained left-handed circularly polarized light is then incident on the metasurface array to obtain a perfectly homogenized vortex beam.

[0022] At present, atmospheric laser radar has technical difficulties such as large blind spots and high noise. The large blind spots make it impossible to capture the near-field state during detection, and the high noise leads to low signal-to-noise ratio and poor detection performance. The present invention solves these two technical difficulties based on optical principles, thereby achieving zero blind spot and high signal-to-noise ratio detection, and the system has high integration and can be miniaturized.

[0023] The transmitting system transmits a laser beam of a specific wavelength to realize the backscattering signal of atmospheric aerosol and air molecules so that it can be received by the receiving system. The transmitting system mainly includes lasers and metasurface arrays. The modules are described as follows: Laser: The excitation source of the entire lidar system, used to generate the original emission linearly polarized Gaussian beam, generally a solid-state laser; Metasurface array: used to generate perfect vortex beams with small divergence angles at the micro-radian level and radial dimensions that do not vary with topological charge.

[0024] The normalized intensity of the perfect vortex beam is: ; in, is the input Gaussian beam waist, is the beam waist at the rear focal plane, and R is the perfect vortex beam ring size.

[0025] The phase design formula of the metasurface that generates a perfect vortex beam is as follows: in is the cylindrical coordinate system parameter, l is the topological charge, is the wavelength, is the focal length of the lens, NA is the numerical aperture, a is the horizontal normalization factor, and b is the vertical normalization factor.

[0026] The receiving system is used to receive the backscattered signal excited by the laser beam of the transmitting system, collect the optical signal through convergence, and extract the specific optical signal through the back-end spectrometer module.

[0027] The receiving system generally uses a reflective or transmissive telescope to implement its functions. The present invention uses a reflective telescope system to receive the emitted photon echo signal. Compared with the conventional transmissive Kepler telescope system, it has smaller aberrations, better imaging quality, and a more compact spatial structure, which is convenient for integrated application. The noisy signal received by the telescope is separated from the signal by a microlens array, the background noise is concentrated in the phase singularity region of the perfect vortex, the signal light is concentrated on the perfect vortex ring belt, and the light blocking device is used to block the noise, so that the effective signal and the noise signal can be separated.

[0028] The subsequent spectroscopic module using the metasurface array can be highly integrated, and can realize filtering, splitting, collimation, and focusing functions in an extremely small volume. It can also take into account the reception of far-field and near-field optical signals to achieve zero blind spots in the system.

[0029] The photoelectric conversion and signal processing system receives the optical signal of the receiving system, and converts the optical signal into a processable electrical signal through a photoelectric detector, and then records the original data text through a series of electrical signal data processing such as filtering, amplification, and high-speed acquisition. Finally, the computer extracts the original data text and forms a specific data product output through specific algorithm processing calculation to present the aerosol distribution of the entire atmosphere on the laser path. The system is generally composed of a photoelectric detector, a circuit processing board, a high-speed acquisition card, and a computer.

[0030] Based on the principle of micro-nano optics, a homogenized perfect vortex light source with stable atmospheric transmission is generated. The device has a small size, good beam quality and a small divergence angle. The system achieves zero blind zone in hardware, optimizes near-field detection of atmospheric lidar, and is easy to package, highly integrated, and can be miniaturized.

[0031] As a vortex light source that does not change with the topological charge, the perfect vortex beam is naturally resistant to the atmospheric diffusion effect. In the transition zone of the radar signal, it can maintain the stability of the light intensity distribution and enhance the system's ability to detect weak signals.

[0032] The laser emits a linearly polarized Gaussian light source, which is modulated by a metasurface array to generate a perfect vortex beam. The perfect vortex beam has a phase singularity, which makes it feasible to separate background noise and effective signals. At the same time, the radial size of the perfect vortex beam does not change with the change of topological charge. Increasing the topological charge within a certain range can enhance the anti-turbulence ability of the perfect vortex, maintain a high beam quality before scattering, and prevent optical turbulence phenomena such as drift and jitter. The perfect vortex beam also has the characteristic of a small divergence angle. The perfect vortex beam is emitted into the atmosphere and is received by the telescope after backscattering by particles or atmospheric molecules in the atmosphere. The telescope system transmits the received light signal to the microlens array module and the light blocking device for signal-to-noise separation. The separated effective signal enters the spectroscopic module composed of the metasurface array for spectroscopic, collimation, focusing and other operations, and is finally detected by the detector. The converted electrical signal is processed by the acquisition card and enters the computer system for analysis and processing.

[0033] The present invention uses a metasurface composed of a silicon dioxide substrate and a gold nanocolumn array as an array element to form a centimeter-level metasurface array to achieve system miniaturization; at the same time, a linearly polarized fundamental mode Gaussian beam is used as an input source to obtain a perfect vortex beam at the rear end of the metasurface array, compress the divergence angle, and is received by a telescope after being backscattered by the atmosphere. A microlens array is arranged at the rear end of the telescope to separate background and signal light, and the background light is removed by a light blocking device to achieve effective signal extraction, thereby improving the system signal-to-noise ratio and detection performance. At the same time, a subsequent module adds a metasurface array that takes into account both far-field and near-field reception, which can simultaneously detect near-field signals and far-field signals, thereby achieving a miniaturized, low-noise, zero-blind-zone lidar system.

[0034] A detection method for an atmospheric laser radar with zero blind zone and noise reduction is used for an atmospheric laser radar system with zero blind zone and noise reduction. A laser generates a linearly polarized fundamental mode Gaussian beam, which is shaped into a perfectly homogenized vortex beam after being phase modulated by a metasurface array; the shaped beam emitted by a transmitting system is emitted into the atmosphere and generates a backscattered photon signal, which is received by a receiving system; the backscattered photon signal is transmitted to a signal processing unit after passing through a Cassegrain telescope, and the processed light signal is further collimated and transmitted to an optical microlens array module for signal-noise spectroscopic operation, and signal-noise separation is performed through a light blocking device to obtain a high-purity signal; the high-purity light signal is further transmitted to a photoelectric conversion and signal processing system, and an effective echo signal is obtained after being received by a detector, processed by a high-speed acquisition card, and processed by a computer.

[0035] The laser generates a linearly polarized fundamental mode Gaussian beam, which is shaped into a perfectly homogenized vortex beam after phase modulation by the metasurface array. The metasurface array here is equivalent to the perfectly homogenized vortex beam generating unit. The perfectly homogenized vortex beam is used as the emission beam. The homogenization feature can reduce the blind area or even achieve zero blind area. The perfect vortex feature can effectively separate the signal from the noise and effectively improve the detection distance and signal-to-noise ratio. The shaped light beam emitted by the transmitting system enters the atmosphere and generates a backscattered photon signal, which is received by the receiving system; The receiving system consists of a Cassegrain telescope and a subsequent optical path. The backscattered photon signal is received by the Cassegrain telescope (optical receiving unit) and then transmitted to the subsequent optical path system (signal processing unit). The processed optical signal is further collimated and transmitted to the optical microlens array for signal-noise spectroscopic operation. The signal-noise separation is performed through a light blocking device to obtain a high-purity signal (zero blind spot focusing spot). The high-purity optical signal is further transmitted to the photoelectric conversion and signal processing system, and after being received by the detector, processed by the high-speed acquisition card, and processed by the computer, an effective echo signal is obtained.

[0036] The technical principle of the present invention is described above in conjunction with specific embodiments. These descriptions are only for explaining the principle of the present invention and cannot be interpreted as limiting the protection scope of the present invention in any way. Based on the explanations herein, those skilled in the art can associate other specific implementations of the present invention without paying creative labor, and these methods will fall within the protection scope of the claims of the present invention.

Claims

1. A zero-blind-zone and noise-reducible atmospheric laser radar system, characterized in that: include: A transmitting system, comprising a laser and a metasurface array arranged opposite to the laser, wherein the metasurface array is used to generate a perfect vortex beam with a small divergence angle at a micro-radian level and a radial size that does not change with topological charge; The receiving system is used to receive the backscattered signal excited by the laser beam of the transmitting system, collect the optical signal by converging it, and extract the optical signal by the back-end spectrometer module; The photoelectric conversion and signal processing system is used to process the optical signal of the receiving system and present the aerosol distribution of the entire atmosphere along the laser path.

2. The zero-blind-zone and noise-reducible atmospheric laser radar system according to claim 1, characterized in that: The laser is used to generate an original emission linearly polarized Gaussian beam.

3. The zero-blind-zone and noise-reducible atmospheric laser radar system according to claim 1, characterized in that: The metasurface array comprises a silicon dioxide substrate and gold nanorods arranged on the silicon dioxide substrate. The metasurface composed of the metal nanorod array is an array element, and the array elements constitute a centimeter-level metasurface array.

4. The zero-blind-zone and noise-reducible atmospheric laser radar system according to claim 3, characterized in that: The phase design formula of the metasurface is as follows: ； Where: is the cylindrical coordinate system parameter, l is the topological charge, is the wavelength, is the focal length of the lens, NA is the numerical aperture, a is the horizontal normalization factor, and b is the vertical normalization factor.

5. The zero-blind-zone and noise-reducible atmospheric laser radar system according to claim 1, characterized in that: The receiving system comprises an optical receiving unit, a Casselling-type reflective telescope system, a signal processing unit, a collimating module, an optical microlens array module, a light splitting module and a signal separation module which are arranged in sequence.

6. The zero-blind-zone and noise-reducible atmospheric laser radar system according to claim 1, characterized in that: The photoelectric conversion and signal processing system comprises a collection module and a processing module which are arranged in sequence.

7. A detection method of an atmospheric laser radar with zero blind zone and noise reduction, used in the atmospheric laser radar system with zero blind zone and noise reduction according to claim 1, characterized in that: The laser generates a linearly polarized fundamental mode Gaussian beam, which is then phase modulated by the metasurface array and shaped into a perfectly homogenized vortex beam. The shaped light beam emitted by the transmitting system enters the atmosphere and generates a backscattered photon signal, which is received by the receiving system; The backscattered photon signal is transmitted to the signal processing unit after passing through the Cassegrain telescope. The processed optical signal is further collimated and transmitted to the optical microlens array module for signal-noise splitting operation. The signal-noise separation is performed through the light blocking device to obtain a high-purity signal. The high-purity optical signal is further transmitted to the photoelectric conversion and signal processing system, and after being received by the detector, processed by the high-speed acquisition card, and processed by the computer, an effective echo signal is obtained.

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