CN117949934A - Coherent wind lidar echo signal calibration system and design method - Google Patents
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Abstract
The invention discloses a coherent wind lidar echo signal calibration system and a design method, wherein the system comprises the following components: the device comprises a seed laser, an acousto-optic modulator, an optical fiber amplifier, an optical transceiver telescope, a beam splitter, a single-mode optical fiber coupler, a multimode optical fiber coupler, a first filter, a second filter, a first detector, a second detector, a first acquisition card and a second acquisition card; the method for calibrating the coherent Doppler wind lidar echo signal has the advantages of high precision by measuring the intensity of the single-mode fiber echo signal and the intensity of the multimode fiber echo signal simultaneously based on the equivalent relation between the coherent efficiency and the single-mode fiber coupling efficiency to obtain the coupling efficiency, thereby realizing the measurement of the coherent efficiency and the calibration of the coherent Doppler wind lidar echo signal.
Description
Technical Field
The invention relates to the technical field of laser radars, in particular to a coherent wind lidar echo signal calibration system and a design method.
Background
Coherent doppler lidar can provide accurate atmospheric motion velocity detection at high temporal and spatial resolution by detecting doppler shift of echo signals of moving objects (e.g., atmospheric aerosols, clouds, hard objects, etc.). The method is widely used in the fields of aviation safety guarantee, wind power generation, air pollution monitoring and forecasting and the like.
The coherent Doppler laser radar adopts aerosol as a tracer for wind speed detection, so that an echo signal of the coherent Doppler laser radar can be used for inverting the optical parameters of the aerosol. In order to accurately invert the aerosol optical parameters, the coherence efficiency of the coherence Doppler laser radar needs to be accurately calibrated. The coherence efficiency is essentially the degree of matching of the local oscillator light and the backscattered light mode field, and is related to system parameters such as laser beam, caliber, etc., and is therefore a function of distance. Currently, most theoretical analytical expressions are based on an ideal gaussian beam, which is not always applicable. There are researchers that acquire coherence efficiency curves by some indirect methods, such as using coherent lidar echoes to the same target at different distances, inversion of level detection data based on the assumption of uniform distribution of aerosol levels, comparison with other aerosol lidar echo curves, etc. These methods are based on the assumption that the coherence efficiency is not directly measured, and the influence of atmospheric turbulence on the coherence efficiency is ignored, so that the accuracy of the result is low.
Disclosure of Invention
The invention aims to: the invention aims to provide a coherent wind lidar echo signal calibration system and a design method, which are beneficial to inverting aerosol optical parameters more accurately and researching and analyzing the influence of parameters such as atmospheric turbulence, system caliber, focal length and the like on the aerosol optical parameters through direct measurement of a coherent Doppler wind lidar coherent efficiency curve.
The technical scheme is as follows: the invention relates to a coherent wind lidar echo signal calibration system, which comprises: the device comprises a seed laser, an acousto-optic modulator, an optical fiber amplifier, an optical transceiver telescope, a beam splitter, a single-mode optical fiber coupler, a multimode optical fiber coupler, a first filter, a second filter, a first detector, a second detector, a first acquisition card and a second acquisition card;
The output end of the seed laser is connected with the input end of the acousto-optic modulator, the output end of the acousto-optic modulator is connected with the input end of the optical fiber amplifier, the output end of the optical fiber amplifier is connected with the transmitting end of the optical transceiver telescope, the receiving end of the optical transceiver telescope is connected with the input end of the beam splitter, the output end A of the beam splitter is connected with the single-mode fiber coupler, the output end of the single-mode fiber coupler is connected with the first filter, the first filter is connected with the first detector, and the first detector is connected with the first acquisition card; the output end B of the beam splitter, the multimode fiber coupler, the second filter, the second detector and the second acquisition card are sequentially connected.
Further, the laser wavelength emitted by the seed laser is 1550nm.
Further, the beam splitter is a 3dB beam splitter, and the echo signals are equally divided into two beams of 50:50.
Further, the fiber core diameter of the single mode fiber coupler is 8-10 microns.
Further, the multimode fiber coupler has a core diameter of 50-62.5 microns.
Further, the first detector and the second detector are dual-channel single photon detectors.
Further, the first filter and the second filter are interference filters, and the bandwidth is 0.1nm.
Further, the acousto-optic modulator modulates continuous laser into pulse light, the pulse width is 100 ns-800 ns, and the pulse light has 80MHz frequency shift.
The invention relates to a design method of a coherent wind lidar echo signal calibration system, which comprises the following steps:
S1, outputting continuous laser by a seed laser, modulating the continuous laser into pulse light by an acousto-optic modulator, amplifying the pulse light by an optical fiber amplifier, and finally emitting the pulse light to the atmosphere by an emitting end of an optical receiving and transmitting telescope;
S2, after the atmospheric echo signals at different distances are received through the receiving end of the optical receiving and transmitting telescope, the atmospheric echo signals are split into two beams through the beam splitter, the two beams are respectively coupled into single-mode/multi-mode optical fibers through the single-mode/multi-mode coupler, background light noise is filtered through the filter, photoelectric conversion is carried out by the detector, and electric signals are acquired by the acquisition card;
S3, carrying out cumulative average on echo signals of a large number of pulses to respectively obtain average atmospheric echo signal intensities of a single-mode fiber channel and a multi-mode fiber channel, and respectively marking the average atmospheric echo signal intensities as And/>；
S4, calculating the ratio of single-mode/multi-mode optical fiber echo signalsObtaining the coupling efficiency of the single-mode fiber according to the coherent efficiency/>Coupling efficiency with Single mode fiber/>Equivalent relation/>Obtaining a change curve/>, of coherent laser radar coherence efficiency along with distance。
Further, in the step S4, according to the pulse laser radar equation, the single-mode/multimode fiber channel echo signal equation is as follows:
；
Wherein, Representing a single mode/multimode fibre channel,/>Is the effective receiving area,/>Is the energy of the transmitted pulse and,Is a geometrical overlap factor,/>Is the optical fiber coupling efficiency,/>Is the quantum efficiency,/>Is the back scattering coefficient of the aerosol volume,/>Is the transmission rate of the back and forth atmosphere, h is the Planck constant, v is the optical frequency, and c is the optical speed;
the fiber coupling efficiency is the ratio of the average power coupled into the receiving fiber to the average power in the coupler aperture plane, and according to the multimode fiber receiving signal having an area greater than that of a single mode fiber, the coupling efficiency is: the obtained single mode fiber coupling efficiency formula is as follows:
；
according to the theoretical calculation formula of single-mode fiber coupling efficiency and coherence efficiency, the method proves that:
；
a change curve of the coherence efficiency with distance is obtained:
。
The beneficial effects are that: compared with the prior art, the invention has the following remarkable advantages: based on the equivalent relation between the coherent efficiency and the single-mode fiber coupling efficiency, the coupling efficiency is obtained by measuring the single-mode fiber echo signal intensity and the multi-mode fiber echo signal intensity at the same time, and then the coherent efficiency measurement and the coherent Doppler wind lidar echo signal calibration method are realized, so that the method has the advantage of high precision.
Drawings
FIG. 1 is a schematic diagram of a system architecture of the present invention;
FIG. 2 is an exemplary plot of an atmospheric echo signal curve for a single mode/multimode fiber channel of the present invention;
FIG. 3 is an exemplary graph of a coherent efficiency curve for different turbulence intensity conditions of the present invention.
Detailed Description
The technical scheme of the invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, an embodiment of the present invention provides a coherent wind lidar echo signal calibration system, including: the device comprises a seed laser 1, an acousto-optic modulator 2, an optical fiber amplifier 3, an optical transceiver 4, a beam splitter 5, a single-mode optical fiber coupler 6, a multi-mode optical fiber coupler 7, a first filter 8, a second filter 9, a first detector 10, a second detector 11, a first acquisition card 12 and a second acquisition card 13;
The output end of the seed laser 1 is connected with the input end of the acousto-optic modulator 2, the output end of the acousto-optic modulator 2 is connected with the input end of the optical fiber amplifier 3, the output end of the optical fiber amplifier 3 is connected with the transmitting end of the optical transceiver telescope 4, the receiving end of the optical transceiver telescope 4 is connected with the input end of the beam splitter 5, the output end A of the beam splitter 5 is connected with the single-mode fiber coupler 6, the output end of the single-mode fiber coupler 6 is connected with the first filter 8, the first filter 8 is connected with the first detector 10, and the first detector 10 is connected with the first acquisition card 12; the output end B of the beam splitter 5, the multimode fiber coupler 7, the second filter 9, the second detector 11 and the second acquisition card 13 are sequentially connected.
The laser wavelength emitted by the seed laser 1 is 1550nm; the acousto-optic modulator 2 modulates continuous laser into pulse light, the pulse width is 100 ns-800 ns, and the pulse light has 80MHz frequency shift; the beam splitter 5 is a 3dB beam splitter, equally dividing the echo signal into two beams of 50:50. The fiber core diameter of the single-mode fiber coupler 6 is 8-10 microns, and the fiber core diameter of the multimode fiber coupler 7 is 50-62.5 microns. The first detector 10 and the second detector 11 are dual-channel single photon detectors. The first filter 8 and the second filter 9 are interference filters, and the bandwidth is 0.1nm.
Working principle: the seed laser 1 outputs 1550nm continuous laser, the continuous laser is modulated into pulse light through the acousto-optic modulator 2, the pulse light is amplified by the optical fiber amplifier 3, and finally the pulse light is emitted to the atmosphere through the emitting end of the optical transceiver telescope 4.
Amplified by an optical fiber amplifier 3, the energy of the laser pulse is 100-300 microjoules so as to ensure the detection distance; and the light passes through the transmitting end of the optical receiving and transmitting telescope 4 and exits to the atmosphere.
The atmospheric echo signals at different distances are received by the receiving end of the optical receiving and transmitting telescope 4, are equally divided into two beams by the 3dB beam splitter 5, are respectively coupled into a single-mode/multi-mode optical fiber by a single-mode/multi-mode coupler, are filtered by a 0.1nm bandwidth narrow-band interference filter, are subjected to photoelectric conversion by a single-photon detector, and are collected by a collecting card.
Because the atmospheric echo signals are very weak, the single pulse detection echo signal strength is very weak, so that the echo signals of a large number of pulses need to be accumulated and averaged to improve the signal to noise ratio, and finally, the average atmospheric echo signal strengths of the single-mode fiber channel and the multi-mode fiber channel are respectively obtained.
As shown in fig. 2, the embodiment of the invention further provides a design method of a coherent wind lidar echo signal calibration system, which comprises the following steps:
S1, outputting continuous laser by a seed laser, modulating the continuous laser into pulse light by an acousto-optic modulator, amplifying the pulse light by an optical fiber amplifier, and finally emitting the pulse light to the atmosphere by an emitting end of an optical receiving and transmitting telescope;
S2, after the atmospheric echo signals at different distances are received through the receiving end of the optical receiving and transmitting telescope, the atmospheric echo signals are split into two beams through the beam splitter, the two beams are respectively coupled into single-mode/multi-mode optical fibers through the single-mode/multi-mode coupler, background light noise is filtered through the filter, photoelectric conversion is carried out by the detector, and electric signals are acquired by the acquisition card;
S3, carrying out cumulative average on echo signals of a large number of pulses to respectively obtain average atmospheric echo signal intensities of a single-mode fiber channel and a multi-mode fiber channel, and respectively marking the average atmospheric echo signal intensities as And/>；
S4, calculating the ratio of single-mode/multi-mode optical fiber echo signalsObtaining the coupling efficiency of the single-mode fiber according to the coherent efficiency/>Coupling efficiency with Single mode fiber/>Equivalent relation/>Obtaining a change curve/>, of coherent laser radar coherence efficiency along with distance. The method comprises the following steps: according to the pulse laser radar equation, the single-mode/multimode fiber channel echo signal equation is as follows:
；
Wherein, Representing a single mode/multimode fibre channel,/>Is the effective receiving area,/>Is the energy of the transmitted pulse and,Is a geometrical overlap factor,/>Is the optical fiber coupling efficiency,/>Is the quantum efficiency,/>Is the back scattering coefficient of the aerosol volume,/>Is the transmission rate of the back and forth atmosphere, h is the Planck constant, v is the optical frequency, and c is the optical speed;
the fiber coupling efficiency is the ratio of the average power coupled into the receiving fiber to the average power in the coupler aperture plane, and according to the multimode fiber receiving signal having an area greater than that of a single mode fiber, the coupling efficiency is: the obtained single mode fiber coupling efficiency formula is as follows:
；
according to the theoretical calculation formula of single-mode fiber coupling efficiency and coherence efficiency, the method proves that:
；
a change curve of the coherence efficiency with distance is obtained:
。
FIG. 3 shows an exemplary plot of the coherence efficiency curve for different turbulence intensity conditions. It can be seen that the lower the coherence efficiency decreases with increasing turbulent refractive index constant.
Claims (10)
1. A coherent wind lidar echo signal calibration system is characterized by comprising: the device comprises a seed laser (1), an acousto-optic modulator (2), an optical fiber amplifier (3), an optical transceiver telescope (4), a beam splitter (5), a single-mode optical fiber coupler (6), a multimode optical fiber coupler (7), a first filter (8), a second filter (9), a first detector (10), a second detector (11), a first acquisition card (12) and a second acquisition card (13);
The seed laser device comprises a seed laser device (1), an acousto-optic modulator (2), an optical fiber amplifier (3), a beam splitter (5), a single-mode fiber coupler (6), a first filter (8), a first detector (10) and a first acquisition card (12), wherein the output end of the seed laser device (1) is connected with the input end of the acousto-optic modulator (2), the output end of the acousto-optic modulator (2) is connected with the input end of the optical fiber amplifier (3), the output end of the optical fiber amplifier (3) is connected with the transmitting end of the optical transceiver (4), the receiving end of the optical transceiver (4) is connected with the input end of the beam splitter (5), the output end A of the beam splitter (5) is connected with the single-mode fiber coupler (6), the output end of the single-mode fiber coupler (6) is connected with the first filter (8), the first filter (8) is connected with the first detector (10); the output end B of the beam splitter (5), the multimode fiber coupler (7), the second filter (9), the second detector (11) and the second acquisition card (13) are sequentially connected.
2. A coherent wind lidar echo signal calibration system according to claim 1, characterized in that the seed laser (1) emits laser light with a wavelength of 1550nm.
3. A coherent wind lidar echo signal calibration system according to claim 1, characterized in that the beam splitter (5) is a 3dB beam splitter, dividing the echo signal equally into two beams of 50:50.
4. A coherent wind lidar echo signal calibration system according to claim 1, characterized in that the fiber core diameter of the single-mode fiber coupler (6) is 8-10 μm.
5. A coherent wind lidar echo signal calibration system according to claim 1, wherein the multimode fiber coupler (7) has a core diameter of 50-62.5 μm.
6. A coherent wind lidar echo signal calibration system according to claim 1, characterized in that the first detector (10) and the second detector (11) are two-channel single photon detectors.
7. The coherent wind lidar echo signal calibration system according to claim 1, wherein the first filter (8) and the second filter (9) are interference filters with a bandwidth of 0.1nm.
8. The coherent wind lidar echo signal calibration system according to claim 1, wherein the acousto-optic modulator (2) modulates continuous laser light into pulse light with a pulse width of 100 ns-800 ns and a frequency shift of 80 MHz.
9. A design method of a coherent wind lidar echo signal calibration system is characterized by comprising the following steps:
S1, outputting continuous laser by a seed laser, modulating the continuous laser into pulse light by an acousto-optic modulator, amplifying the pulse light by an optical fiber amplifier, and finally emitting the pulse light to the atmosphere by an emitting end of an optical receiving and transmitting telescope;
S2, after the atmospheric echo signals at different distances are received through the receiving end of the optical receiving and transmitting telescope, the atmospheric echo signals are split into two beams through the beam splitter, the two beams are respectively coupled into single-mode/multi-mode optical fibers through the single-mode/multi-mode coupler, background light noise is filtered through the filter, photoelectric conversion is carried out by the detector, and electric signals are acquired by the acquisition card;
S3, carrying out cumulative average on echo signals of a large number of pulses to respectively obtain average atmospheric echo signal intensities of a single-mode fiber channel and a multi-mode fiber channel, and respectively marking the average atmospheric echo signal intensities as And/>；
S4, calculating the ratio of single-mode/multi-mode optical fiber echo signalsObtaining the coupling efficiency of the single-mode fiber according to the coherent efficiency/>Coupling efficiency with Single mode fiber/>Equivalent relation/>Obtaining a change curve/>, of coherent laser radar coherence efficiency along with distance。
10. The method for designing a coherent wind lidar echo signal calibration system according to claim 9, wherein in the step S4, according to the pulse lidar equation, a single-mode/multimode fiber channel echo signal equation is as follows:
；
Wherein, Representing a single mode/multimode fibre channel,/>Is the effective receiving area,/>Is the transmitted pulse energy,/>Is a geometrical overlap factor,/>Is the optical fiber coupling efficiency,/>Is the quantum efficiency,/>Is the back-scattering coefficient of the volume of the aerosol,Is the transmission rate of the back and forth atmosphere, h is the Planck constant, v is the optical frequency, and c is the optical speed;
the fiber coupling efficiency is the ratio of the average power coupled into the receiving fiber to the average power in the coupler aperture plane, and according to the multimode fiber receiving signal having an area greater than that of a single mode fiber, the coupling efficiency is: the obtained single mode fiber coupling efficiency formula is as follows:
；
according to the theoretical calculation formula of single-mode fiber coupling efficiency and coherence efficiency, the method proves that:
；
a change curve of the coherence efficiency with distance is obtained:
。
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Citations (5)
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|---|---|---|---|---|
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| US20140209798A1 (en) * | 2013-01-29 | 2014-07-31 | Tt Government Solutions, Inc. | Devices and methods for multimode light detection |
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| CN116953671A (en) * | 2023-07-17 | 2023-10-27 | 中国科学院上海光学精密机械研究所 | Coherent wind-finding laser radar optical axis monitoring and self-adaptive correction device |
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|---|---|---|---|---|
| US4902127A (en) * | 1988-03-22 | 1990-02-20 | Board Of Trustees Of Leland Stanford, Jr. University | Eye-safe coherent laser radar |
| JP2003307567A (en) * | 2002-04-16 | 2003-10-31 | Mitsubishi Electric Corp | Coherent laser radar device |
| US20140209798A1 (en) * | 2013-01-29 | 2014-07-31 | Tt Government Solutions, Inc. | Devices and methods for multimode light detection |
| CN104133202A (en) * | 2014-05-27 | 2014-11-05 | 北京空间机电研究所 | 2mum coherent wind lidar polarization state matching and correcting system |
| CN116953671A (en) * | 2023-07-17 | 2023-10-27 | 中国科学院上海光学精密机械研究所 | Coherent wind-finding laser radar optical axis monitoring and self-adaptive correction device |
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