Near-infrared rotational raman polarization lidar spectrometer and method

Abstract

The present application belongs to the technical field of laser atmospheric remote sensing, and discloses a near-infrared rotational Raman polarization laser radar spectrometer and method. The received echo signals are divided into first and second echo signals, the first echo signals are filtered to obtain near-infrared rotational Raman signals with a first target wavelength, and the near-infrared rotational Raman signals with the first target wavelength are detected; the second echo signals are filtered, and the filtered near-infrared signals with a second target wavelength are divided into vertical and horizontal polarization signals; the vertical polarization signals are divided into vertical polarization high and low altitude signals, and the vertical polarization high and low altitude signals are detected respectively; and the horizontal polarization signals are divided into horizontal polarization high and low altitude signals, and the horizontal polarization high and low altitude signals are detected respectively. The present application can realize signal large dynamic range measurement and effective measurement of weak near-infrared band nitrogen-oxygen Raman scattering echo signals.

Description

Technical Field

[0001] This invention belongs to the field of laser atmospheric remote sensing technology, and more specifically, relates to a near-infrared rotating Raman polarization lidar beam splitting device and method. Background Technology

[0002] Atmospheric particle extinction coefficients, polarization, and scattering optical properties are key parameters describing the impact of clouds and aerosols on the environment, weather, and climate processes, and are also crucial for obtaining the microphysical properties of clouds and aerosols. Lidar is the only active optical remote sensing device capable of acquiring particle extinction coefficient profiles. It works by having a laser emitter interact with atmospheric particles, receiving backscattered echo signals through a telescope, and then splitting the received backscattered echo signals according to different detection requirements. A photodetector then converts the optical signals into electrical signals, and finally, a data acquisition system collects and stores the signals, ultimately measuring the particle properties. The splitting device is the core of the entire lidar system design and is key to meeting the diverse detection needs of lidar.

[0003] Raman polarization lidar, as a conventional and reliable ground-based method for measuring the optical properties of particles, primarily works by splitting the Mie scattering polarization and weak nitrogen-oxygen Raman scattering echoes in the echo signal to meet more detection needs and achieve precise measurements of particle optical properties. Due to the maturity of photodetector technology in the ultraviolet and visible light bands, this technology has already been developed and applied in these bands. The near-infrared band has high atmospheric vertical transmittance, making lidar in this band the best tool for detecting upper-level cirrus clouds, stratospheric plumes, and volcanic ash. However, existing near-infrared detection methods often suffer from two problems: first, the detection efficiency of photodetectors is generally low, and when faced with strong low-altitude scattering signals, the Mie scattering polarization receiving channel often experiences low-altitude signal saturation, preventing the measurement of a large dynamic range. Second, the nitrogen-oxygen Raman scattering echo signal in the near-infrared band is weak, making it difficult to effectively measure this weak signal. Summary of the Invention

[0004] This invention provides a near-infrared rotating Raman polarization lidar beam splitting device and method, which solves the problems of low detection efficiency of lidar in the near-infrared band and difficulty in effectively measuring weak nitrogen and oxygen Raman scattering echo signals in the prior art.

[0005] This invention provides a near-infrared rotating Raman polarization lidar beam splitting device, comprising: a first beam splitter, a Raman beam splitting optical path, a polarization beam splitting optical path, and a high- and low-altitude signal beam splitting optical path;

[0006] The first beam splitter is used to divide the received echo signal into a first echo signal and a second echo signal according to a preset first ratio.

[0007] The Raman beam splitting optical path includes a first interference filter and a first detection component arranged sequentially along the optical path; the first interference filter is used to filter the first echo signal to obtain a near-infrared rotating Raman signal with a first target wavelength; the first detection component is used to detect the near-infrared rotating Raman signal.

[0008] The polarization beam splitter includes a second interference filter and a first polarization beam splitter arranged sequentially along the optical path; the second interference filter is used to filter the second echo signal, and the first polarization beam splitter is used to divide the filtered near-infrared signal with the second target wavelength into a vertically polarized signal and a horizontally polarized signal.

[0009] The high- and low-altitude signal splitting optical path includes a second beam splitter, a second detection component, a third detection component, a third beam splitter, a fourth detection component, and a fifth detection component. The second beam splitter is used to split the vertically polarized signal into a vertically polarized high-altitude signal and a vertically polarized low-altitude signal according to a preset second ratio. The second detection component is used to detect the vertically polarized high-altitude signal, and the third detection component is used to detect the vertically polarized low-altitude signal. The third beam splitter is used to split the horizontally polarized signal into a horizontally polarized high-altitude signal and a horizontally polarized low-altitude signal according to a preset third ratio. The fourth detection component is used to detect the horizontally polarized low-altitude signal, and the fifth detection component is used to detect the horizontally polarized high-altitude signal.

[0010] Preferably, the near-infrared rotating Raman polarization lidar beam splitter further includes a first switching component disposed on the incident light path of the first beam splitter; the first switching component includes a first servo motor and a plurality of optical elements with different functions; the first servo motor is used to switch the optical elements with target functions into the incident light path of the first beam splitter according to the detection requirements, or the first servo motor is used to switch all optical elements in the first switching component out of the incident light path of the first beam splitter according to the detection requirements.

[0011] Preferably, the plurality of optical elements with different functions in the first switching assembly include a depolarizer and a first neutral density filter; the depolarizer is used to convert the received echo signal from polarized light to unpolarized light; the first neutral density filter is used to attenuate the received echo signal.

[0012] Preferably, the near-infrared rotating Raman polarization lidar beam splitter further includes a second switching assembly disposed between the first beam splitter and the second interference filter; the second switching assembly includes a second servo motor and a plurality of optical elements with different functions; the second servo motor is used to cut the optical elements with target functions into the optical path between the first beam splitter and the second interference filter according to the detection requirements, or the second servo motor is used to cut all the optical elements in the second switching assembly out of the optical path between the first beam splitter and the second interference filter according to the detection requirements.

[0013] Preferably, the second switching assembly includes a second neutral density filter and a third neutral density filter, which are used to attenuate the second echo signal to different degrees.

[0014] Preferably, a fourth neutral density filter is further disposed between the first polarizing beam splitter and the second beam splitter; the fourth neutral density filter is used to attenuate the vertically polarized signal.

[0015] A second polarizing beam splitter and a fifth neutral density filter are also disposed between the first polarizing beam splitter and the third polarizing beam splitter; the second polarizing beam splitter is used to improve the polarization purity of the horizontally polarized signal; the fifth neutral density filter is used to attenuate the horizontally polarized signal.

[0016] Preferably, the first detection component includes a first fiber collimator and a first fiber; the first fiber collimator is used to focus the near-infrared rotating Raman signal onto the collimated first fiber, and the first fiber is used to transmit the near-infrared rotating Raman signal to a first photodetector;

[0017] The second detection component includes a second fiber collimator and a second fiber; the second fiber collimator is used to focus the vertically polarized high-altitude signal onto the collimated second fiber, and the second fiber is used to transmit the vertically polarized high-altitude signal to a second photodetector;

[0018] The third detection component includes a third fiber collimator and a third fiber; the third fiber collimator is used to focus the vertically polarized low-altitude signal onto the collimated third fiber, and the third fiber is used to transmit the vertically polarized low-altitude signal to a third photodetector.

[0019] The fourth detection component includes a fourth fiber collimator and a fourth fiber; the fourth fiber collimator is used to focus the horizontally polarized low-altitude signal onto the collimated fourth fiber, and the fourth fiber is used to transmit the horizontally polarized low-altitude signal to the fourth photodetector.

[0020] The fifth detection component includes a fifth fiber collimator and a fifth fiber; the fifth fiber collimator is used to focus the horizontally polarized high-altitude signal onto the collimated fifth fiber, and the fifth fiber is used to transmit the horizontally polarized high-altitude signal to the fifth photodetector.

[0021] Preferably, the near-infrared rotating Raman polarization lidar beam splitter further includes: a beam splitter housing; the beam splitter housing is used for integrating and encapsulating the beam splitter.

[0022] The fifth detection component also includes a total reflection mirror disposed between the third beam splitter and the fifth fiber collimator, the total reflection mirror being used to change the propagation direction of the horizontally polarized high-altitude signal.

[0023] Preferably, the first ratio is 7:3, the second ratio is 9:1, and the third ratio is 9:1; the first target wavelength is 1056nm, the center wavelength of the first interference filter is 1056nm, the bandwidth is 1-12nm, and the transmittance is 30%-70%; the second target wavelength is 1064nm, the center wavelength of the second interference filter is 1064nm, the bandwidth is 0.1-2nm, and the transmittance is greater than 70%.

[0024] On the other hand, the present invention provides a near-infrared rotating Raman polarization lidar beam splitting method, which uses the above-mentioned near-infrared rotating Raman polarization lidar beam splitting device for beam splitting.

[0025] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0026] (1) On the one hand, the detection efficiency of near-infrared band detectors is low. When faced with strong low-altitude scattering signals, there is often a problem of low-altitude signal saturation in the Mie scattering polarization receiving channel. This invention uses a beam splitter to split the signal at high and low altitudes (more of the light is used for high-altitude measurement, for example, the energy is split at a ratio of 1:9, 10% of the light is used for low-altitude measurement, which can avoid exceeding the detection threshold of the detector, and 90% of the light is used for high-altitude measurement, so that the high-altitude signal will generally not be saturated and the signal-to-noise ratio of the high-altitude signal can be preserved). This ensures the quality of the high-altitude signal and avoids the problem of low-altitude signal saturation. In this way, it can realize the large dynamic range detection of vertical and horizontal polarization signals in the Mie scattering detection target band (e.g., 1064nm). On the other hand, addressing the weakness of nitrogen-oxygen Raman scattering echo signals in the near-infrared band and the difficulty in effectively measuring these signals, this invention focuses on enhancing the Raman echo signal intensity during its design. First, a beam splitter is used to disperse the atmospheric echo signal, with a designed proportion (a higher proportion, e.g., 70%) of the echo signal reflected into the Raman channel. Then, a corresponding interference filter (e.g., an interference filter with a center wavelength of 1056 nm, a bandwidth of 6 nm, and a transmittance of 70%) is used to extract the Raman signal. This design significantly improves the Raman echo signal intensity, thereby enabling the measurement of weak nitrogen-oxygen Raman signals. Combining these two aspects, this invention achieves measurement of a large dynamic range and effective measurement of weak near-infrared nitrogen-oxygen Raman scattering echo signals, which is beneficial for lidar to provide more reliable characterization of the optical and microphysical properties of aerosols.

[0027] (2) In view of the problem that stray light and the instability of optical components can affect the detection performance of lidar, the present invention adopts an integrated design of beam splitter box, which can effectively ensure the sealing. In addition, during the design of beam splitter box, installation positions are reserved for each device and medium isolation is set between each channel, thereby effectively ensuring the compactness and stability of the system structure. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a near-infrared rotating Raman polarization lidar beam splitter provided in Embodiment 1 of the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of a near-infrared rotating Raman polarization lidar beam splitter provided in Embodiment 1 of the present invention, showing the first servo motor controlling the switching of the depolarizer and the first neutral density filter.

[0030] Figure 3This is a schematic diagram of the structure of a near-infrared rotating Raman polarization lidar beam splitter provided in Embodiment 1 of the present invention, in which a second servo motor controls the switching of a second neutral density filter and a third neutral density filter.

[0031] Among them, 1001 is the first servo motor, and 1002 is the second servo motor.

[0032] 200-Depolarizer;

[0033] 301 - First neutral density filter, 302 - Second neutral density filter, 303 - Third neutral density filter, 304 - Fourth neutral density filter, 305 - Fifth neutral density filter;

[0034] 401 - First beam splitter, 402 - Second beam splitter, 403 - Third beam splitter;

[0035] 501 - First interference filter, 502 - Second interference filter;

[0036] 601-First fiber optic collimator, 602-Second fiber optic collimator, 603-Third fiber optic collimator, 604-Fourth fiber optic collimator, 605-Fifth fiber optic collimator;

[0037] 701 - First optical fiber, 702 - Second optical fiber, 703 - Third optical fiber, 704 - Fourth optical fiber, 705 - Fifth optical fiber;

[0038] 801 - First polarizing beam splitter, 802 - Second polarizing beam splitter;

[0039] 900-Total Reflection Mirror. Detailed Implementation

[0040] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0041] Example 1:

[0042] Example 1 provides a near-infrared rotating Raman polarization lidar beam splitter device, see [link to example]. Figures 1 to 3 It includes: a first beam splitter 401, a Raman beam splitter, a polarization beam splitter, and a high and low altitude signal beam splitter.

[0043] The first beam splitter 401 is used to divide the received echo signal into a first echo signal and a second echo signal according to a preset first ratio. For example, the first ratio is 7:3, that is, it is divided into 70% first echo signal and 30% second echo signal.

[0044] The Raman beam splitting optical path includes a first interference filter 501 and a first detection component arranged sequentially along the optical path. The first interference filter 501 is used to filter the first echo signal to obtain a near-infrared rotating Raman signal with a first target wavelength. The first detection component is used to detect the near-infrared rotating Raman signal. For example, the first target wavelength is 1056 nm, the center wavelength of the first interference filter is 1056 nm, the bandwidth is 1–12 nm, and the transmittance is 30%–70%.

[0045] The polarization beam splitter includes a second interference filter 502 and a first polarization beam splitter 801 arranged sequentially along the optical path. The second interference filter 502 is used to filter the second echo signal, and the first polarization beam splitter 801 is used to separate the filtered near-infrared signal with the second target wavelength into a vertically polarized signal and a horizontally polarized signal. For example, the second target wavelength is 1064 nm, the center wavelength of the second interference filter is 1064 nm, the bandwidth is 0.1-2 nm, and the transmittance is greater than 70%.

[0046] The high- and low-altitude signal splitting optical path includes a second beam splitter 402, a second detection component, a third detection component, a third beam splitter 403, a fourth detection component, and a fifth detection component. The second beam splitter 402 splits the vertically polarized signal into a vertically polarized high-altitude signal and a vertically polarized low-altitude signal according to a preset second ratio. The second detection component detects the vertically polarized high-altitude signal, and the third detection component detects the vertically polarized low-altitude signal. The third beam splitter 403 splits the horizontally polarized signal into a horizontally polarized high-altitude signal and a horizontally polarized low-altitude signal according to a preset third ratio. The fourth detection component detects the horizontally polarized low-altitude signal, and the fifth detection component detects the horizontally polarized high-altitude signal. For example, the second ratio is 9:1, meaning it is split into 90% vertically polarized high-altitude signal and one layer of vertically polarized low-altitude signal; the third ratio is 9:1, meaning it is split into 90% horizontally polarized high-altitude signal and one layer of horizontally polarized low-altitude signal.

[0047] The first detection component includes a first fiber collimator 601 and a first fiber 701. The first fiber collimator 601 focuses the near-infrared rotating Raman signal onto the collimated first fiber 701, and the first fiber 701 transmits the near-infrared rotating Raman signal to a first photodetector. The second detection component includes a second fiber collimator 602 and a second fiber 702. The second fiber collimator 602 focuses the vertically polarized high-altitude signal onto the collimated second fiber 702, and the second fiber 702 transmits the vertically polarized high-altitude signal to a second photodetector. The third detection component includes a third fiber collimator 603 and a third fiber 703. The third fiber collimator 603 focuses the vertically polarized low-altitude signal onto the collimated third fiber 703, and the third fiber 703 transmits the vertically polarized low-altitude signal to a third photodetector. The fourth detection component includes a fourth fiber collimator 604 and a fourth fiber 704; the fourth fiber collimator 604 is used to focus the horizontally polarized low-altitude signal onto the collimated fourth fiber 704, and the fourth fiber 704 is used to transmit the horizontally polarized low-altitude signal to a fourth photodetector. The fifth detection component includes a fifth fiber collimator 605 and a fifth fiber 705; the fifth fiber collimator 605 is used to focus the horizontally polarized high-altitude signal onto the collimated fifth fiber 705, and the fifth fiber 705 is used to transmit the horizontally polarized high-altitude signal to a fifth photodetector.

[0048] To ensure structural compactness, the fifth detection component may further include a total reflection mirror 900 disposed between the third beam splitter 403 and the fifth fiber collimator 605. The total reflection mirror 900 is used to change the propagation direction of the horizontally polarized high-altitude signal, for example, to change the propagation direction by 90 degrees.

[0049] Furthermore, the near-infrared rotating Raman polarization lidar beam splitter may also include a first switching component disposed on the incident light path of the first beam splitter 401; the first switching component includes a first servo motor 1001 and a plurality of optical elements with different functions; the first servo motor 1001 is used to cut the optical element with target function into the incident light path of the first beam splitter 401 according to the detection requirements, or the first servo motor 1001 is used to cut all the optical elements in the first switching component out of the incident light path of the first beam splitter 401 according to the detection requirements. For example, the plurality of optical elements with different functions in the first switching component include a depolarizer 200 and a first neutral density filter 301; the depolarizer 200 is used to change the received echo signal from polarized light to unpolarized light; the first neutral density filter 301 is used to attenuate the received echo signal.

[0050] The near-infrared rotating Raman polarization lidar beam splitter may further include a second switching assembly disposed between the first beam splitter 401 and the second interference filter 502. The second switching assembly includes a second servo motor 1002 and multiple optical elements with different functions. The second servo motor 1002 is used to insert the optical element with target function into the optical path between the first beam splitter 401 and the second interference filter 502 according to the detection requirements; alternatively, the second servo motor 1002 is used to cut all optical elements in the second switching assembly out of the optical path between the first beam splitter 401 and the second interference filter 502 according to the detection requirements. For example, the multiple optical elements with different functions in the second switching assembly include a second neutral density filter 302 and a third neutral density filter 303; the second neutral density filter 302 and the third neutral density filter 303 are used to attenuate the second echo signal to different degrees.

[0051] The first switching component and the second switching component can be used to switch between different configured optical lenses to meet different detection requirements.

[0052] A fourth neutral density filter 304 may be disposed between the first polarizing beam splitter 801 and the second beam splitter 402; the fourth neutral density filter 304 is used to attenuate the vertically polarized signal. A second polarizing beam splitter 802 and a fifth neutral density filter 305 may also be disposed between the first polarizing beam splitter 801 and the third beam splitter 403; the second polarizing beam splitter 802 is used to improve the polarization purity of the horizontally polarized signal; the fifth neutral density filter 305 is used to attenuate the horizontally polarized signal.

[0053] By using multiple optical devices to attenuate the light energy, the energy received by the detector can be reduced, ensuring that it does not exceed the detection threshold and thus ensuring that the signal does not saturate.

[0054] The near-infrared rotating Raman polarization lidar beam splitter may further include: a beam splitter housing; the beam splitter housing is used to integrate and encapsulate the beam splitter.

[0055] The present invention will be further described below with reference to specific parameters.

[0056] Depolarizer 200: Switched by the first servo motor 1001 according to usage requirements, its function is to change the polarized light received by the telescope into unpolarized light and then transmit it.

[0057] Neutral density filter: used to attenuate the transmitted echo signal, wherein the first neutral density filter 301 (OD1, where OD stands for optical density) is switched by the first servo motor 1001, the second neutral density filter 302 (OD1.3) and the third neutral density filter 302 (OD0.5) are switched by the second servo motor 1002, and the fourth neutral density filter 304 (OD0.6) and the fifth neutral density filter 305 (OD0.6) are used in a fixed beam splitting path.

[0058] Beam splitters: Depending on the requirements of different receiving channels, they reflect and transmit the echo signal according to different beam splitting ratios. Specifically, the first beam splitter 401 reflects 70% of the received echo signal and transmits 30% of the echo signal, while the second beam splitter 402 and the third beam splitter 403 reflect a portion of the received echo signal and transmit a portion of the echo signal.

[0059] Interference filters: Taking 1056nm and 1064nm interference filters as examples, the relevant parameters of the first interference filter 501 are as follows: center wavelength of 1056nm, bandwidth of 1-12nm, preferably 6nm, and transmittance of 30%-70%; the relevant parameters of the second interference filter 502 are as follows: center wavelength of 1064nm, bandwidth of 0.1-2nm, preferably 1nm, and transmittance greater than 70%. These parameters were determined through continuous selection and optimization in the early stages of research, resulting in better beam splitting performance.

[0060] Polarizing beam splitter: used to split the received echo signal into vertically polarized light and horizontally polarized light, wherein the first polarizing beam splitter 801 splits the received echo signal into a 1064nm vertically polarized echo signal and a 1064nm horizontally polarized echo signal; the second polarizing beam splitter 802 further improves the purity of the received 1064nm horizontally polarized echo signal.

[0061] Fiber optic collimators: used to focus the received echo signal onto a collimated fiber, specifically including the first fiber optic collimator 601, the second fiber optic collimator 602, the third fiber optic collimator 603, the fourth fiber optic collimator 604, and the fifth fiber optic collimator 605.

[0062] Optical fiber: used to transmit the echo signal focused by the optical fiber collimator to the photodetector. The connector is FC / APC, and the optical window size is 150 micrometers-250 micrometers. Specifically, it includes the first optical fiber 701, the second optical fiber 702, the third optical fiber 703, the fourth optical fiber 704, and the fifth optical fiber 705.

[0063] Servo motor: Used to switch different optical elements to meet the detection requirements of near-infrared rotating Raman polarization lidar. The optical elements controlled by the first servo motor 1001 include the depolarizer 200 and the first neutral density filter 301. (See also...) Figure 2 The optical elements controlled by the second servo motor 1002 include the second neutral density filter 302 and the third neutral density filter 303, see [link / reference]. Figure 3 .

[0064] Total reflection mirror: The total reflection mirror 900 is used to change the direction of signal transmission.

[0065] The working principle of this invention is as follows:

[0066] Depending on the different detection requirements, the first servo motor 1001 can control the switching of one of the elements of the depolarizer 200 and the first neutral density filter 301 onto the beam splitter path to perform depolarization, attenuation, or transmission processing on the echo signal received by the telescope. The processed beam is then incident on the first beam splitter 401. Alternatively, the depolarizer 200 and the first neutral density filter 301 may not be switched onto the beam splitter path. In this case, the echo signal received by the telescope is directly incident on the first beam splitter 401.

[0067] The first beam splitter 401 reflects and transmits the transmitted echo signal or the directly incident echo signal according to a preset first ratio (e.g., a 7:3 ratio). The echo signal reflected by the first beam splitter 401 (i.e., 70% of the reflected echo signal) is filtered by the first interference filter 501 (e.g., a 1056nm interference filter) to remove echo signals of other wavelengths. Then, it is focused by the first fiber collimator 601 onto the collimated first fiber 701, and received by the first fiber 701 and transmitted to the first photodetector to detect the weak nitrogen-oxygen Raman signal in the first target wavelength (i.e., 1056nm) band.

[0068] Depending on the different detection requirements, the second servo motor 1002 can control the switching of one of the elements of the second neutral density filter 302 and the third neutral density filter 303 to attenuate the echo signal (i.e., the 30% transmitted echo signal) projected by the first beam splitter 401 to different degrees. The echo signal attenuated by the second neutral density filter 302 or the third neutral density filter 303 is filtered by the second interference filter 502 (e.g., a 1064nm interference filter), allowing the echo signal of the second target wavelength (i.e., 1064nm) to pass through. The 1064nm echo signal after passing through is polarized by the first polarizing beam splitter 801 and divided into a 1064nm vertically polarized echo signal and a 1064nm horizontally polarized echo signal, which are then transmitted and reflected, respectively.

[0069] The 1064nm vertically polarized echo signal transmitted through the first polarizing beam splitter 801 is attenuated by the fourth neutral density filter 304 and then reflected and transmitted by the second beam splitter 402 according to a preset second ratio (e.g., a 9:1 ratio). The echo signal reflected by the second beam splitter 402 (i.e., 90% of the reflected echo signal) is focused by the second fiber collimator 602 onto the collimated second fiber 702, and then received by the second fiber 702 and transmitted to the second photodetector for 1064nm vertically polarized high-altitude detection. The echo signal transmitted by the second beam splitter 402 (i.e., 10% of the transmitted echo signal) is focused by the third fiber collimator 603 onto the collimated third fiber 703, and then received by the third fiber 703 and transmitted to the third photodetector for 1064nm vertically polarized low-altitude detection. In addition, during the above process, it can be determined whether the fourth neutral density filter 304 needs to be installed based on the intensity of the vertically polarized echo signal. If signal attenuation is required, the fourth neutral density filter 304 can be placed between the first polarizing beam splitter 801 and the second beam splitter 402.

[0070] The 1064nm horizontally polarized echo signal reflected by the first polarizing beam splitter 801 is purified by the second polarizing beam splitter 802. After attenuation by the fifth neutral density filter 305, the purified 1064nm horizontally polarized echo signal is reflected and transmitted by the third beam splitter 403 at a preset third ratio (e.g., 1:9). One-tenth of the echo signal reflected by the third beam splitter 403 is focused by the fourth fiber collimator 604 onto the collimated fourth fiber 704, and then transmitted by the fourth fiber 704 to the fourth photodetector for low-altitude detection with 1064nm horizontal polarization. Nine-tenths of the echo signal transmitted by the third beam splitter 403 is reflected by the total reflection mirror 900. The echo signal reflected by the total reflection mirror 900 is focused by the fifth fiber collimator 605 onto the collimated fifth fiber 705, and then transmitted by the fifth fiber 705 to the fifth photodetector for high-altitude detection with 1064nm horizontal polarization.

[0071] As can be seen from the above-described spectral separation steps, the present invention can complete the high and low altitude detection of vertically and horizontally polarized signals in the second target wavelength (e.g., 1064 nm) band, as well as the detection of weak nitrogen-oxygen Raman signals in the first target wavelength (e.g., 1056 nm) band.

[0072] It should be noted that this invention is not limited to Mie scattering detection in the 1064nm band, but can also achieve measurements in other bands, such as the 355nm and 532nm bands. Similarly, this invention is not limited to Raman detection in the 1056nm band, but can also achieve Raman detection in other bands; the only difference is that the corresponding filter needs to be replaced and the beam splitter's beam splitting ratio adjusted as needed.

[0073] Example 2:

[0074] Example 2 provides a near-infrared rotating Raman polarization lidar beam splitting method, which uses the near-infrared rotating Raman polarization lidar beam splitting device as described in Example 1.

[0075] Example 2 provides a near-infrared rotating Raman polarization lidar beam splitting method. A first beam splitter splits the received echo signal into a first echo signal and a second echo signal according to a preset first ratio. A first interference filter in the Raman beam splitting optical path filters the first echo signal to obtain a near-infrared rotating Raman signal with a first target wavelength. A first detection component detects the near-infrared rotating Raman signal. A second interference filter in the polarization beam splitting optical path filters the second echo signal. A first polarization beam splitter splits the filtered near-infrared signal with the second target wavelength into a vertically polarized signal and a water-polarized signal. The vertically polarized signal is divided into a vertically polarized high-altitude signal and a vertically polarized low-altitude signal according to a preset second ratio using a second beam splitter in the high- and low-altitude signal splitting optical path. The vertically polarized high-altitude signal is detected using a second detection component, and the vertically polarized low-altitude signal is detected using a third detection component. The horizontally polarized signal is then divided into a horizontally polarized high-altitude signal and a horizontally polarized low-altitude signal according to a preset third ratio using a third beam splitter. The horizontally polarized low-altitude signal is detected using a fourth detection component, and the horizontally polarized high-altitude signal is detected using a fifth detection component.

[0076] Example 2 is capable of detecting vertically and horizontally polarized signals of the second target wavelength band at both high and low altitudes, as well as detecting weak nitrogen-oxygen Raman signals of the first target wavelength band. The method provided in Example 2 corresponds to the functions of each device in the apparatus provided in Example 1, and therefore can be understood by referring to the description in Example 1, which will not be repeated here.

[0077] In summary, this invention provides a near-infrared rotating Raman polarization lidar beam splitting device and method, which is beneficial for lidar to achieve beam splitting measurement of weak nitrogen-oxygen Raman scattering echoes and Mie scattering echoes with a large dynamic range in the infrared band.

[0078] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A near-infrared rotating Raman polarization lidar beam splitter, characterized in that, include: First beam splitter, Raman beam splitter, polarization beam splitter, and high and low altitude signal beam splitter; The first beam splitter is used to divide the received echo signal into a first echo signal and a second echo signal according to a preset first ratio. The Raman beam splitting optical path includes a first interference filter and a first detection component arranged sequentially along the optical path; the first interference filter is used to filter the first echo signal to obtain a near-infrared rotating Raman signal with a first target wavelength; the first detection component is used to detect the near-infrared rotating Raman signal. The polarization beam splitter includes a second interference filter and a first polarization beam splitter arranged sequentially along the optical path; the second interference filter is used to filter the second echo signal, and the first polarization beam splitter is used to divide the filtered near-infrared signal with the second target wavelength into a vertically polarized signal and a horizontally polarized signal. The high- and low-altitude signal splitting optical path includes a second beam splitter, a second detection component, a third detection component, a third beam splitter, a fourth detection component, and a fifth detection component. The second beam splitter is used to split the vertically polarized signal into a vertically polarized high-altitude signal and a vertically polarized low-altitude signal according to a preset second ratio. The second detection component is used to detect the vertically polarized high-altitude signal, and the third detection component is used to detect the vertically polarized low-altitude signal. The third beam splitter is used to split the horizontally polarized signal into a horizontally polarized high-altitude signal and a horizontally polarized low-altitude signal according to a preset third ratio. The fourth detection component is used to detect the horizontally polarized low-altitude signal, and the fifth detection component is used to detect the horizontally polarized high-altitude signal.

2. The near-infrared rotating Raman polarization lidar beam splitter according to claim 1, characterized in that, It also includes a first switching component disposed on the incident light path of the first beam splitter; the first switching component includes a first servo motor and a plurality of optical elements with different functions; the first servo motor is used to cut the optical element with the target function into the incident light path of the first beam splitter according to the detection requirements, or the first servo motor is used to cut all the optical elements in the first switching component out of the incident light path of the first beam splitter according to the detection requirements.

3. The near-infrared rotating Raman polarization lidar beam splitter according to claim 2, characterized in that, The first switching assembly includes multiple optical elements with different functions, including a depolarizer and a first neutral density filter; the depolarizer is used to convert the received echo signal from polarized light to unpolarized light; the first neutral density filter is used to attenuate the received echo signal.

4. The near-infrared rotating Raman polarization lidar beam splitter according to claim 1, characterized in that, It also includes a second switching assembly disposed between the first beam splitter and the second interference filter; the second switching assembly includes a second servo motor and a plurality of optical elements with different functions; the second servo motor is used to cut the optical element with the target function into the optical path between the first beam splitter and the second interference filter according to the detection requirements, or the second servo motor is used to cut all the optical elements in the second switching assembly out of the optical path between the first beam splitter and the second interference filter according to the detection requirements.

5. The near-infrared rotating Raman polarization lidar beam splitter according to claim 4, characterized in that, The second switching assembly includes multiple optical elements with different functions, including a second neutral density filter and a third neutral density filter; the second neutral density filter and the third neutral density filter are used to attenuate the second echo signal to different degrees.

6. The near-infrared rotating Raman polarization lidar beam splitter according to claim 1, characterized in that, A fourth neutral density filter is further disposed between the first polarizing beam splitter and the second beam splitter; the fourth neutral density filter is used to attenuate the vertically polarized signal. A second polarizing beam splitter and a fifth neutral density filter are also disposed between the first polarizing beam splitter and the third polarizing beam splitter; the second polarizing beam splitter is used to improve the polarization purity of the horizontally polarized signal; the fifth neutral density filter is used to attenuate the horizontally polarized signal.

7. The near-infrared rotating Raman polarization lidar beam splitter according to claim 1, characterized in that, The first detection component includes a first fiber collimator and a first fiber; the first fiber collimator is used to focus the near-infrared rotating Raman signal onto the collimated first fiber, and the first fiber is used to transmit the near-infrared rotating Raman signal to a first photodetector; The second detection component includes a second fiber collimator and a second fiber; the second fiber collimator is used to focus the vertically polarized high-altitude signal onto the collimated second fiber, and the second fiber is used to transmit the vertically polarized high-altitude signal to a second photodetector; The third detection component includes a third fiber collimator and a third fiber; the third fiber collimator is used to focus the vertically polarized low-altitude signal onto the collimated third fiber, and the third fiber is used to transmit the vertically polarized low-altitude signal to a third photodetector. The fourth detection component includes a fourth fiber collimator and a fourth fiber; the fourth fiber collimator is used to focus the horizontally polarized low-altitude signal onto the collimated fourth fiber, and the fourth fiber is used to transmit the horizontally polarized low-altitude signal to the fourth photodetector. The fifth detection component includes a fifth fiber collimator and a fifth fiber; The fifth fiber collimator is used to focus the horizontally polarized high-altitude signal onto the collimated fifth fiber, and the fifth fiber is used to transmit the horizontally polarized high-altitude signal to the fifth photodetector.

8. The near-infrared rotating Raman polarization lidar beam splitter according to claim 7, characterized in that, It also includes: a beam splitter housing; the beam splitter housing is used for integrating and encapsulating the beam splitting device; The fifth detection component also includes a total reflection mirror disposed between the third beam splitter and the fifth fiber collimator, the total reflection mirror being used to change the propagation direction of the horizontally polarized high-altitude signal.

9. The near-infrared rotating Raman polarization lidar beam splitter according to claim 1, characterized in that, The first ratio is 7:3, the second ratio is 9:1, and the third ratio is 9:1; the first target wavelength is 1056nm, the center wavelength of the first interference filter is 1056nm, the bandwidth is 1-12nm, and the transmittance is 30%-70%; the second target wavelength is 1064nm, the center wavelength of the second interference filter is 1064nm, the bandwidth is 0.1-2nm, and the transmittance is greater than 70%.

10. A near-infrared rotating Raman polarization lidar beam splitting method, characterized in that, The beam splitting is performed using the near-infrared rotating Raman polarization lidar beam splitter as described in any one of claims 1-9.

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