Atmospheric laser radar based on Add-Drop filter

Abstract

An atmosphere laser radar based on an Add-Drop type filter comprises a narrow linewidth laser, a laser frequency stabilization system, an optical emission system, an optical receiving system, the cascaded Add-Drop type filter, a multi-channel photoelectric detection system and a data acquisition and processing system. The atmospheric laser radar based on the Add-Drop filter can directly measure the scattering intensity of atmospheric aerosol and atmospheric molecules, obtains high-precision optical parameters of atmospheric aerosol and molecules, and can measure an atmospheric wind field by simultaneously utilizing Mie scattering and Rayleigh scattering of the atmosphere.

Description

Technical Field

[0001] The present invention relates to an atmospheric laser radar based on an Add-Drop filter, and more specifically to an atmospheric laser radar using an Add-Drop filter as a high spectral resolution optical filter. Background Art

[0002] Atmospheric lidar uses high spectral resolution optical filters to directly separate atmospheric aerosol scattering and atmospheric molecular scattering, thereby obtaining high-precision optical parameters of atmospheric aerosols and molecules.

[0003] The high spectral resolution optical filter in the atmospheric lidar can convert the Doppler frequency shift in the atmospheric laser echo into a change in transmittance, and then invert the laser Doppler frequency shift based on the change in transmittance to obtain the atmospheric wind speed and direction.

[0004] The high spectral resolution optical filters currently used in atmospheric lidar include Fabry–Pérot interferometer, molecular (atomic) filter, Fizeau interferometer, etc.

[0005] The Add-Drop filter consists of three parts: Bus waveguide, Dropping waveguide, and coupling unit between Bus waveguide and Dropping waveguide. Light is input from the input port of Bus waveguide, and most of the light is output from the output port of Bus waveguide with almost no attenuation. When the wavelength of light meets the resonance wavelength of the coupling unit, the light of this wavelength is coupled from Bus waveguide to Dropping waveguide and output from the forward or backward port of Dropping waveguide. Therefore, the output of Bus waveguide is equivalent to optical band-stop filter, and the output of Dropping waveguide is equivalent to optical bandpass filter.

[0006] Add-Drop filters are currently mainly used in optical communications, biosensors and other fields. Summary of the invention

[0007] The object of the present invention is to provide an atmospheric laser radar based on an Add-Drop filter, wherein the Add-Drop filter serves as a high spectral resolution optical filter.

[0008] The invention comprises a narrow line width laser, a laser frequency stabilization system, an optical transmitting system, an optical receiving system, a cascaded Add-Drop filter, a multi-channel photoelectric detection system, and a data acquisition and processing system.

[0009] The output wavelength of the narrow linewidth laser is locked to the spectrum of the selected Add-Drop filter by using a laser frequency stabilization system. The stabilized laser is emitted into the atmosphere by using an optical emission system, and then the atmospheric echo is received by an optical receiving system and coupled into the cascaded Add-Drop filter.

[0010] The Add-Drop filter locked with the laser wavelength can filter out some Mie scattering and Rayleigh scattering in the atmospheric echo; the Add-Drop filters on both sides of the laser wavelength can filter out some Rayleigh scattering in the atmospheric echo. The filtered Mie scattering and Rayleigh scattering are converted into electrical signals by using a multi-channel photoelectric detection system and imported into the data acquisition and processing system.

[0011] When the atmospheric wind field can be ignored, because the atmospheric Mie scattering and Rayleigh scattering models are accurately known, the Mie scattering signal and multi-path Rayleigh scattering signal filtered out by the cascaded Add-Drop filter can be used to invert the atmospheric Mie scattering and Rayleigh scattering intensities, and then derive the corresponding optical parameters of atmospheric aerosols and molecules.

[0012] When the atmospheric wind field cannot be ignored, different atmospheric wind fields will produce different laser Doppler frequency shifts, which will cause the intensity changes of the filtered Mie scattering signal and the multi-path Rayleigh scattering signal. Based on the above intensity changes, the atmospheric wind field can be inverted.

[0013] The line width of the narrow line width laser is smaller than the spectral width of the Add-Drop filter. The free spectral range of the Add-Drop filter is larger than the atmospheric Rayleigh scattering spectral width. Two times the spectral interval between two adjacent Add-Drop filters in the cascaded Add-Drop filter is smaller than the atmospheric Rayleigh scattering spectral width. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention.

[0015] Figure 1 , the Add-Drop filter structure diagram of the present invention Figure 2 , the Add-Drop filter spectrum characteristic diagram of the present invention Figure 3 , the structure diagram of the atmospheric laser radar based on Add-Drop filter of the present invention Figure 4 , the cascaded Add-Drop filter spectrum, atmospheric Mie scattering and Rayleigh scattering spectrum of the present invention Figure 5The atmospheric Mie scattering and Rayleigh scattering signals filtered out by the cascade Add-Drop filter of the present invention are In the figure: 1. Bus waveguide of Add-Drop filter, 2. Dropping waveguide of Add-Drop filter, 3. Coupling unit of Add-Drop filter, 4. 1. Bus waveguide input port of Add-Drop filter, 2. Bus waveguide output port of Add-Drop filter, 3. Dropping waveguide backward output port of Add-Drop filter, 4. Dropping waveguide forward output port of Add-Drop filter, 5. Bandpass spectrum output from Dropping waveguide backward or forward output port of Add-Drop filter, 6. Bandpass spectrum output from Bus waveguide output port of Add-Drop filter, 7. Bandstop spectrum output from Bus waveguide output port of Add-Drop filter, 8. Spectral width (full width at half maximum) of Add-Drop filter, 9. Free spectral range of Add-Drop filter, 10. Narrow linewidth laser, 11. Laser frequency stabilization system, 12. Optical transmitting system, 13. Optical receiving system, 14. Cascaded Add-Drop filter, 15. Optical receiving system, 16. Cascaded Add-Drop filter, 17. Multi-channel photoelectric detection system, 18. Data acquisition and processing system, 19. Bandpass spectrum of cascaded Add-Drop filter, 20. Spectral spacing of adjacent Add-Drop filters, 21. Laser wavelength locking point, 22. Atmospheric Mie scattering without Doppler shift, 23. Atmospheric Rayleigh scattering without Doppler shift, 24. Spectral width of atmospheric Mie scattering (full width at half maximum), 25. Spectral width of atmospheric Rayleigh scattering (full width at half maximum), 26. Atmospheric Mie scattering with wind speed Doppler shift, 27. Atmospheric Rayleigh scattering with wind speed Doppler shift, 28. Atmospheric Mie scattering and Rayleigh scattering signals without Doppler shift filtered out by the Add-Drop filter corresponding to laser frequency stabilization, 29. Atmospheric Rayleigh scattering signals without Doppler shift filtered out by the Add-Drop filter on both sides of the laser wavelength, 30. Atmospheric Mie scattering and Rayleigh scattering signals with Doppler shift filtered out by the Add-Drop filter corresponding to laser frequency stabilization, 31. Atmospheric Rayleigh scattering signals with Doppler shift filtered out by the Add-Drop filter on both sides of the laser wavelength. DETAILED DESCRIPTION

[0016] The purpose of the present invention is to provide an atmospheric laser radar with an Add-Drop filter to solve the technical problems in the related field. In order to make the technical problems and technical solutions to be solved by the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] The Add-Drop filter structure of the present invention is shown in FIG. Figure 1 As shown, the Add-Drop filter spectral characteristics are as follows Figure 2 shown.

[0018] The Add-Drop filter consists of three parts: a bus waveguide (1), a dropping waveguide (2), and a coupling unit (3) between the bus waveguide and the dropping waveguide. Light is input from the input port (4) of the bus waveguide, and most of the light is output from the output port (5) of the bus waveguide with almost no attenuation. When the wavelength of light meets the resonance wavelength of the coupling unit (3), the light of this wavelength is coupled from the bus waveguide (1) to the dropping waveguide (2) and output from the backward output port (5) or the forward output port (6) of the dropping waveguide. Therefore, the backward output port (5) or the forward output port (6) of the dropping waveguide is equivalent to an optical bandpass filter, and the corresponding spectral characteristic is (8); the output port (4) of the bus waveguide is equivalent to an optical bandstop filter, and the corresponding spectral characteristic is (9). The spectral width of the Add-Drop filter corresponding to (8) and (9) is (10), and the free spectral range of the corresponding Add-Drop filter is (11).

[0019] The structure diagram of the atmospheric laser radar based on the Add-Drop filter of the present invention is as follows: Figure 3 shown.

[0020] A narrow linewidth laser (12) is used as a light source, and a laser frequency stabilization (13) system is used to lock the laser wavelength. The frequency-locked laser enters the atmosphere through an optical emission system (14). The laser echo in the atmosphere is received by an optical receiving system (15) and introduced into a cascaded Add-Drop filter optical discriminator (16). The output of the cascaded Add-Drop filter (16) is detected by a multi-channel photoelectric detection system (17) and introduced into a data acquisition and processing system (18).

[0021] The cascaded Add-Drop filter spectrum, atmospheric Mie scattering and Rayleigh scattering spectrum of the present invention are as follows: Figure 4 shown.

[0022] The cascaded Add-Drop filter connects the Bus waveguide output port (5) of the previous Add-Drop filter to the Bus waveguide input port (4) of the next Add-Drop filter, and the backward port (5) or forward port (6) of the Dropping waveguide is used as the output of this stage. Figure 4(19) is the bandpass spectrum characteristic of the cascaded Add-Drop type filter (16), and the spectrum interval between adjacent Add-Drop type filters is (20).

[0023] If the laser wavelength is locked to Figure 4 (21) in the figure corresponds to the wavelength λ L Add-Drop filter. The central wavelengths of atmospheric Mie scattering (22) without Doppler shift and atmospheric Rayleigh scattering (23) without Doppler shift are also at (21). The present invention requires that the line width of the narrow line width laser (12) is smaller than the spectral width (10) based on the Add-Drop filter, the free spectral range (11) of the Add-Drop filter is larger than the atmospheric Rayleigh scattering spectral width (25), and at the same time, twice the spectral interval (20) of adjacent Add-Drop filters is smaller than the atmospheric Rayleigh scattering spectral width (25).

[0024] Figure 4 The central wavelengths of atmospheric Mie scattering (26) with Doppler shift and atmospheric Mi Rayleigh scattering (27) with Doppler shift will deviate from (21).

[0025] When there is no Doppler shift, Figure 4 Medium wavelength λ L The corresponding Add-Drop filter can filter out part of the atmospheric Mie scattering and atmospheric Rayleigh scattering (28); wavelength λ L-2 , L-1 , L+1 , L+2 The corresponding Add-Drop filter can filter out part of the atmospheric Rayleigh scattering (29).

[0026] Because the bandpass spectrum characteristics (8) of the Add-Drop filter are accurately known, and the theoretical models of laser atmospheric Mie scattering and Rayleigh scattering are also accurately known, Figure 5 Medium wavelength λ L The corresponding signal strength (28), and wavelength λ L-2 , L-1 , L+1 , L+2 The corresponding signal intensity of atmospheric Rayleigh scattering (29) can be used to calculate the atmospheric Mie scattering and atmospheric Rayleigh scattering intensities.

[0027] In conclusion, Figure 3 The atmospheric lidar based on Add-Drop filter can directly measure the intensity of atmospheric aerosol scattering and atmospheric molecular scattering, and obtain high-precision optical parameters of atmospheric aerosols and molecules.

[0028] When there is a Doppler shift, Figure 4 Medium wavelength λ LThe signal filtered out by the Add-Drop filter corresponds to Figure 5 (30) in. Because the spectral width (23) of atmospheric Rayleigh scattering is larger than the spectral width (10) of the Add-Drop filter, the atmospheric Rayleigh scattering in (28) and (30) is equivalent. Therefore, the difference in intensity between (28) and (30) is mainly caused by the Doppler shift of atmospheric Mie scattering. Using the wavelength λ L The corresponding Add-Drop filter filters out the difference in atmospheric Mie scattering in the signal and can invert the atmospheric wind speed.

[0029] When there is a Doppler shift, the wavelength λ L-2 , L-1 , L+1 , L+2 The Add-Drop filter filters out part of the atmospheric Rayleigh scattering, corresponding to Figure 5 Calculate the wavelength λ in (29) and (31) L+1 , L+2 Signal and λ L-2 , L-1 The difference of the signal at different locations is different when the Doppler frequency shift is different. L-2 , L-1 , L+1 , L+2 The difference in the output atmospheric Rayleigh scattering signal can be used to invert the atmospheric wind speed.

[0030] In conclusion, Figure 3 The atmospheric lidar based on Add-Drop filter can detect the atmospheric wind speed by using the Mie scattering and Rayleigh scattering signals of the atmosphere.

[0031] It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Those skilled in the art should take the specification as a whole, and the technical solutions in the various embodiments can also be appropriately combined to form other implementations that can be understood by those skilled in the art.

Claims

1. An atmospheric laser radar based on an Add-Drop filter, characterized in that: It consists of narrow linewidth laser, laser frequency stabilization system, optical transmitting system, optical receiving system, cascaded Add-Drop filter, multi-channel photoelectric detection system, data acquisition and processing system; The output wavelength of the narrow linewidth laser is locked to the spectrum of the selected Add-Drop filter by using a laser frequency stabilization system; the frequency-stabilized laser is emitted into the atmosphere by using an optical transmitting system, and then the atmospheric echo is received by an optical receiving system and coupled into the cascaded Add-Drop filter; The Add-Drop filter that locks the laser wavelength can filter out part of the Mie scattering and Rayleigh scattering in the atmospheric echo; the Add-Drop filters on both sides of the laser wavelength can filter out part of the Rayleigh scattering in the atmospheric echo respectively; the filtered Mie scattering signal and Rayleigh scattering signal are converted into electrical signals using a multi-channel photoelectric detection system and imported into the data acquisition and processing system; When the atmospheric wind field can be ignored, because the atmospheric Mie scattering and Rayleigh scattering models of lasers are accurately known, the Mie scattering signal and multi-path Rayleigh scattering signal filtered out by the cascaded Add-Drop filter can be used to invert the atmospheric Mie scattering and Rayleigh scattering intensities, and then derive the corresponding atmospheric aerosol and molecular optical parameters; When the atmospheric wind field cannot be ignored, different atmospheric wind fields will produce different laser Doppler frequency shifts, thereby causing changes in the intensity of the filtered Mie scattering signal and the multi-path Rayleigh scattering signal; based on the above intensity changes, the atmospheric wind field can be inverted.

2. The atmospheric laser radar based on Add-Drop filter according to claim 1, characterized in that: The linewidth of a narrow-linewidth laser is smaller than the spectral width of an Add-Drop filter.

3. The atmospheric laser radar with an Add-Drop filter according to claim 1, characterized in that: The free spectral range of the Add-Drop filter is larger than the atmospheric Rayleigh scattering spectrum width.

4. The atmospheric laser radar with an Add-Drop filter according to claim 1, characterized in that: The twice of the spectral interval between two adjacent Add-Drop filters in the cascaded Add-Drop filters is less than the spectral width of the atmospheric Rayleigh scattering.

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