Dual-band multi-wavelength laser radar and coaxial transmitting and receiving method thereof

Abstract

The invention discloses a dual-band multi-wavelength laser radar and a coaxial transmitting and receiving method thereof, and belongs to the technical field of laser radars, the laser radar comprises an industrial personal computer, a laser, a transmitting light path, a receiving telescope, a collimating lens, a first detector, a second detector and a data acquisition module; a laser is controlled by an industrial personal computer to output laser of two wave bands, the laser of the two wave bands is adjusted and expanded in an emission light path and then is emitted into the atmosphere at the same time, the laser interacts with molecules and aerosol in the atmosphere, and an atmosphere back scattering echo signal is collected by a receiving telescope; after being collimated by the collimating lens and split by the spectroscope, two wavebands are respectively received by the two detectors and are input into the industrial personal computer for data processing and result display; the lasers of the two wave bands are detected simultaneously through the wavelength division multiplexing technology, and the lasers of different wavelengths in the same wave band are subjected to time division switching detection through the time division multiplexing technology. According to the invention, the multi-target gas profile detection capability of a single laser radar system can be improved.

Description

Technical Field

[0001] This invention belongs to the field of lidar technology, specifically relating to a dual-band multi-wavelength lidar and its coaxial transmission and reception method. Background Technology

[0002] Differential absorption lidar is an effective tool for measuring the spatiotemporal distribution and changes of trace gases in the atmosphere, and it has significant application value for studying various physical processes in the atmosphere. A single lidar system capable of simultaneously detecting multiple gases helps researchers quickly understand the spatiotemporal distribution and changes of various gases. However, due to the fingerprint characteristics of laser spectra, different gases interact with lasers at different wavelengths and with different spectral characteristics. Multi-factor lidar typically requires multiple laser sources to emit lasers of various frequencies into the atmosphere through multiple channels. However, multi-channel emission makes it difficult to ensure that the lasers in each channel are emitted coaxially. Non-coaxial emission from multiple sources results in some long-distance signals not being effectively recovered and detected, limiting the effective detection range of multi-atmospheric factor lidar. Furthermore, under the requirements of system miniaturization and cost control, such a large and complex multi-axis emission radar detection system is difficult to meet practical needs.

[0003] This invention addresses the technical challenges of coaxial transmission and reception in multi-atmospheric factor detection and dual-band multi-wavelength lidar systems. For applications involving the detection of multiple atmospheric factors over long distances, the spectral characteristics of each factor differ, and gas absorption spectra are narrow. Therefore, lidar systems for multi-atmospheric factor detection typically require multiple narrow-linewidth, high-frequency stable light sources of various wavelengths. Furthermore, detecting atmospheric backscattered signals places high energy demands on the laser source. Based on the requirements of system miniaturization and low cost, a single laser needs to be able to simultaneously emit multiple wavelengths, with each wavelength meeting the requirements of high energy, narrow linewidth, and high-frequency stability. Existing bulky multi-axis transmitting lidar systems are insufficient to meet these practical needs. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A dual-band multi-wavelength lidar includes: an industrial control computer, a laser, a transmitting optical path, a receiving telescope, a collimating lens, a first detector, a second detector, and a data acquisition module. The industrial control computer controls the laser to output laser light in two bands. After adjustment and beam expansion in the transmitting optical path, the two laser bands are simultaneously emitted into the atmosphere. The lasers interact with molecules and aerosols in the atmosphere, and the atmospheric backscattered echo signals are collected by the receiving telescope. After collimation by the collimating lens and beam splitting by the beam splitter, the two bands are received by the first and second detectors, respectively. The signals received by the first and second detectors are acquired by the data acquisition module and input to the industrial control computer for data processing and result display. The two laser bands are simultaneously detected using wavelength division multiplexing (WDM) technology, and lasers of different wavelengths within the same band are detected using time division multiplexing (TDM) technology.

[0006] A coaxial transmission and reception method for a dual-band multi-wavelength lidar, used in the dual-band multi-wavelength lidar, includes:

[0007] Step 1: Select the wavelength combination for the target gas to be detected. The selection criterion is to select the wavelength combination of the target gas to be tested in two bands with an interval of more than 10 nm.

[0008] Step 2: Design the laser amplification cavity for each of the two selected wavelength bands, and design the seed light for each wavelength according to the spectrum of each gas to be tested, so as to realize the design and implementation of the dual-band multi-wavelength laser.

[0009] Step 3: Place the dual-band multi-wavelength laser into the lidar system, select appropriate beam splitter groups and detectors for the two bands, and perform overall hardware design and software algorithm programming for the lidar system to ultimately achieve high spatiotemporal resolution detection of various atmospheric factors.

[0010] The present invention has the following beneficial effects:

[0011] This invention precisely selects a combination of closely spaced multi-atmospheric factor detection wavelengths across two bands, combines this with a specialized lidar light source design, and employs seed injection locking technology to achieve dual-band, multi-wavelength laser signal output from a single laser. This invention enhances the multi-target gas profile detection capability of a single lidar system and promotes the comprehensive application of lidar for multi-atmospheric factor detection. Attached Figure Description

[0012] Figure 1 A schematic diagram of a lidar for detecting multiple atmospheric factors;

[0013] Figure 2 This is a timing diagram for dual-band, multi-wavelength differential absorption lidar detection.

[0014] Figure 3Absorption coefficient diagrams of carbon dioxide (CO2), methane (CH4), water vapor (H2O), and nitrous oxide (N2O) obtained from database queries are shown. (a) is the absorption coefficient diagram of the first band CO2 and N2O detection wavelength combination, and (b) is the absorption coefficient diagram of the second band H2O and CH4 detection wavelength combination.

[0015] Figure 4 This is a schematic diagram of a dual-band multi-wavelength laser, where 1 is a beam splitter and a combination mirror for adjusting the optical path, and 2 is a combination of a combination mirror for adjusting the optical path and a beam combiner. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0017] This invention proposes a dual-band multi-wavelength lidar, comprising: an industrial control computer (PC), a laser, a transmitting optical path, a receiving telescope, a collimating lens, a first detector, a second detector, and a data acquisition module. The PC controls the laser to output laser light in two bands. After adjustment and beam expansion in the transmitting optical path, the two laser bands are simultaneously emitted into the atmosphere. The lasers interact with molecules and aerosols in the atmosphere, and the atmospheric backscattered echo signals are collected by the receiving telescope. After collimation by the collimating lens and splitting by the beam splitter, the two bands are received by the first and second detectors, respectively. The signals received by the first and second detectors are acquired by the data acquisition module and input to the PC for data processing and result display. The two laser bands are simultaneously detected using wavelength division multiplexing (WDM) technology, and lasers of different wavelengths within the same band are detected using time division multiplexing (TDM) technology. The two laser bands are simultaneously transmitted and received, and the two bands are simultaneously received by the first and second detectors, respectively. Lasers of different wavelengths within the same band are transmitted and received alternately in a time-division multiplexing manner. The beam splitter is coated with a 1.65μm reflective film and a 4.47μm antireflective film. The laser is a dual-band, multi-wavelength, high-energy laser. The dual-band, multi-wavelength, high-energy laser includes a pump source, a first optical parametric oscillator (OPO) amplification cavity, a second OPO amplification cavity, a first tunable laser, and a second tunable laser. The pump light emitted from the pump source is sent to the first and second OPOs for nonlinear laser frequency conversion, forcing the first and second OPOs to preferentially amplify the selected wavelength and suppress other frequency outputs. The first and second tunable lasers are connected to the first and second OPOs respectively via optical fibers. Two tunable, frequency-stabilized seed beams are used for seed injection locking to ensure that the laser output frequency is consistent with the seed beams. Multiple wavelengths of laser light in the two bands are switched and output by changing the seed beam frequency.

[0018] This invention further proposes a coaxial transmission and reception method for a dual-band multi-wavelength lidar, comprising:

[0019] Based on differential absorption lidar atmospheric factor detection technology, for each atmospheric factor, a strong absorption position (i.e., wavelength on) and a near-non-absorption position (i.e., wavelength off) are selected on its absorption spectrum. The concentration is calculated based on the gas absorption law using the absorption difference between the two wavelengths, and a distance-informed concentration distribution profile of the gas is obtained based on the radar equation. This is achieved by rationally selecting the spectral lines of each atmospheric factor, ensuring that all spectral lines are distributed across two bands and that the detection wavelengths within each band are close in distance. A dual-band, multi-wavelength laser is then used as the laser emitting device.

[0020] Figure 1A schematic diagram of a lidar system for detecting various atmospheric factors is presented. Taking a dual-band system detecting two gases each as an example, the system detects four gases: carbon dioxide (CO2), methane (CH4), water vapor (H2O), and nitrous oxide (N2O). The laser is controlled by an industrial PC to output laser light in two bands. After adjustment and beam expansion in the emission optical path, the two laser bands are simultaneously emitted into the atmosphere. The lasers interact with molecules and aerosols in the atmosphere, and the atmospheric backscattered echo signals are collected by a receiving telescope. After collimation by a collimating lens and splitting by a beam splitter (coated with a 1.65μm reflective film and a 4.47μm antireflective film), the two bands are received by two detectors, such as an APD (Avalanche Photodiode) and a second APD (Avalanche Photodiode). The signals received by the first and second detectors are acquired by a data acquisition module and input to the industrial PC for data processing and result display. Two-band lasers can be detected simultaneously using wavelength division multiplexing (WDM) technology, while lasers of different wavelengths within the same band can be detected by time division multiplexing (TDM) technology. The emission timing of dual-band multi-wavelength lasers is as follows: Figure 2 As shown, lasers in two bands are simultaneously emitted and received. The two bands are simultaneously received by the first detector (APD) and the second detector (APD), respectively. Lasers of different wavelengths within the same band are emitted and received alternately in a time-division multiplexing manner. Assume that wavelengths 1 and 3 in the first band are the detection wavelength combination on1 and off1 for nitrous oxide, and wavelengths 1 and 3 in the second band are the detection wavelength combination on3 and off3 for methane; wavelengths 2 and 4 in the first band are the detection wavelength combination on2 and off2 for carbon dioxide, and wavelengths 2 and 4 in the second band are the detection wavelength combination on4 and off4 for water vapor. If there are more gases to be detected in a band during actual use, after detecting wavelengths 1 and 2, wavelengths 3 and 4 in each band, wavelengths 5 and 6 are then detected, and this process is repeated cyclically.

[0021] Step 1: Select the wavelength combination for the target gas. The selection criteria are to choose the wavelength combination of the target gas from two relatively far apart wavelength bands (the wavelength interval should be greater than 10 nm for convenient subsequent spectral dispersion). Multiple wavelengths within the same band should be relatively close (usually < 1 nm) so that they can be amplified by the same laser amplification cavity. Assume the greenhouse gases to be measured are: carbon dioxide (CO2), methane (CH4), water vapor (H2O), and nitrous oxide (N2O). Wavelength selection can be performed using HITRAN (High Resolution Transmission Molecular Absorption Database), such as... Figure 3The diagram shows several differential absorption wavelength combinations. For N2O and CO2, the selected wavelength combinations are on1: 4.47328 μm and on2: 4.474406 μm, respectively. N2O and CO2 can share the off wavelength, with off1 and off2 wavelengths being 4.47366 μm. For CH4 and H2O, the selected wavelength combinations are on3: 1.65095 μm and on4: 1.65202 μm, respectively. H2O and CH4 can share the off wavelength, with off3 and off4 wavelengths being 1.65157 μm. When selecting multiple wavelengths within the same wavelength band, the wavelength difference should be less than 1 nm to ensure that multiple wavelengths within the same band can be amplified through the same laser amplification cavity. Figure 3 The database retrieves the absorption coefficient diagrams for carbon dioxide (CO2), methane (CH4), water vapor (H2O), and nitrous oxide (N2O). Figure 3 (a) is the absorption coefficient diagram of the combination of CO2 and N2O detection wavelengths in the first band. Figure 3 (b) is the absorption coefficient diagram of the H2O and CH4 detection wavelength combination in the second band.

[0022] Step 2: Design the laser amplification cavity for each of the two selected dual-band lasers, and design the seed light for each wavelength according to the spectrum of each gas to be tested, so as to realize the design and implementation of the dual-band multi-wavelength laser.

[0023] Step 3: Place the dual-band multi-wavelength laser into the lidar system, select appropriate beam splitter groups and detectors for the two bands, and perform overall hardware design and software algorithm programming for the lidar system to ultimately achieve high spatiotemporal resolution detection of various atmospheric factors.

[0024] To address the requirements for high-energy, dual-band, multi-wavelength, narrow-linewidth, and high-frequency stable laser output, this invention designs a dual-band, multi-wavelength, high-energy laser structure as follows: Figure 4 As shown, the pump source typically employs a high-power Nd:YAG (neodymium-doped yttrium aluminum garnet laser, a type of solid-state laser; its core lies in the use of trivalent neodymium ions Nd...) 3+ Yttrium aluminum garnet (Y3Al5O3) was incorporated as an activating ion. 12A laser (using YAG crystal as the laser gain medium) uses pump light sent to a first optical parametric oscillator (OPO) and a second OPO for nonlinear frequency conversion. Seed light is then injected into the OPOs, forcing them to preferentially amplify the selected wavelength and suppress other frequencies. The first and second tunable lasers can be connected to the OPOs via optical fibers, respectively. A seed injection locking technique using two tunable, frequency-stabilized seed lights ensures the laser output frequency matches the seed light, achieving narrow linewidth, high-frequency, and stable laser output. Multiple wavelengths within the two bands can be switched by changing the seed light frequency.

[0025] Beam splitter and optical path adjustment combination mirror 1 ( Figure 4 The dashed box on the left is used to ensure that both pump beams can be adjusted independently; the frequencies of the two beams after passing through the first and second optical parametric oscillators are consistent with the first and second tunable lasers, respectively. The two wavelengths of light output from the first and second optical parametric oscillators are adjusted by the combination of the combining mirror and the beam combiner 2 ( Figure 4 (The dashed box on the right) is used to combine the beams, ensuring that both laser beams can be individually adjusted to be completely overlapped before output.

[0026] The above description is merely an embodiment of the present invention and does not limit the scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related system fields, are similarly included within the protection scope of the present invention.

[0027] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A dual-band multi-wavelength lidar, characterized in that, include: Industrial control computer, laser, transmitting optical path, receiving telescope, collimating lens, first detector, second detector and data acquisition module; The industrial control computer controls the laser to output laser light in two bands. After adjustment and beam expansion in the emission optical path, the two laser bands are emitted simultaneously into the atmosphere. The laser interacts with molecules and aerosols in the atmosphere, and the atmospheric backscattered echo signal is collected by the receiving telescope. After collimation by the collimating lens and splitting by the beam splitter, the two bands are received by the first detector and the second detector, respectively. The signals received by the first detector and the second detector are collected by the data acquisition module and input to the industrial control computer for data processing and result display. The two laser bands are detected simultaneously using wavelength division multiplexing technology, and lasers of different wavelengths in the same band are detected by time division multiplexing technology.

2. The dual-band multi-wavelength lidar according to claim 1, characterized in that, Lasers in two bands are transmitted and received simultaneously, and the two bands are received simultaneously by the first detector and the second detector, respectively.

3. The dual-band multi-wavelength lidar according to claim 1, characterized in that, Lasers of different wavelengths within the same band are transmitted and received in turn via time-division switching.

4. The dual-band multi-wavelength lidar according to claim 1, characterized in that, The beam splitter is coated with a 1.65μm reflective film and a 4.47μm antireflective film.

5. The dual-band multi-wavelength lidar according to claim 1, characterized in that, The laser is a dual-band, multi-wavelength, high-energy laser.

6. The dual-band multi-wavelength lidar according to claim 5, characterized in that, The dual-band multi-wavelength high-energy laser includes a pump source, a first optical parametric oscillator amplification cavity, a second optical parametric oscillator amplification cavity, a first tunable laser, and a second tunable laser. The pump light emitted from the pump source is sent to the first and second optical parametric oscillators for nonlinear laser frequency conversion, forcing the first and second optical parametric oscillators to preferentially amplify the selected wavelength and suppress the output of other frequency light. The first tunable laser and the second tunable laser are connected to the first optical parametric oscillator and the second optical parametric oscillator respectively via optical fiber; two tunable frequency-stabilized seed lights are used for seed injection locking to ensure that the laser output light frequency is consistent with the seed light, and multiple wavelength lasers in the two bands can be switched and output by changing the seed light frequency.

7. The dual-band multi-wavelength lidar according to claim 6, characterized in that, The pump source is a high-power Nd:YAG laser.

8. The dual-band multi-wavelength lidar according to claim 6, characterized in that, The dual-band multi-wavelength high-energy laser further includes: a beam splitter and an optical path adjustment combination mirror, and a combination of the optical path adjustment combination mirror and a beam combiner; the beam splitter and the optical path adjustment combination mirror are disposed between the pump source and the combination of the first optical parametric oscillator amplification cavity and the second optical parametric oscillator amplification cavity; the optical path adjustment combination mirror and the beam combiner are disposed after the combination of the first optical parametric oscillator amplification cavity and the second optical parametric oscillator amplification cavity.

9. A coaxial transmission and reception method for a dual-band multi-wavelength lidar, used in the dual-band multi-wavelength lidar as described in any one of claims 1 to 8, characterized in that, include: Step 1: Select the wavelength combination for the target gas to be detected. The selection criterion is to select the wavelength combination of the target gas to be tested in two bands with an interval of more than 10 nm. Step 2: Design the laser amplification cavity for each of the two selected wavelength bands, and design the seed light for each wavelength according to the spectrum of each gas to be tested, so as to realize the design and implementation of the dual-band multi-wavelength laser. Step 3: Place the dual-band multi-wavelength laser into the lidar system, select appropriate beam splitter groups and detectors for the two bands, and perform overall hardware design and software algorithm programming for the lidar system to ultimately achieve high spatiotemporal resolution detection of various atmospheric factors.

10. The coaxial transmission and reception method for a dual-band multi-wavelength lidar according to claim 9, characterized in that, In step 1, when selecting multiple wavelengths within the same wavelength band, the wavelength difference should be less than 1 nm, so that multiple wavelengths within the same wavelength band can be amplified through the same laser amplification cavity.

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