CN118112535A - Water vapor detection and light splitting system and method based on sampling fiber Bragg grating - Google Patents
Water vapor detection and light splitting system and method based on sampling fiber Bragg grating Download PDFInfo
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- 238000005070 sampling Methods 0.000 title claims abstract description 161
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 82
- 239000000835 fiber Substances 0.000 title claims abstract description 48
- 238000001514 detection method Methods 0.000 title claims abstract description 38
- 238000000034 method Methods 0.000 title claims description 18
- IJGRMHOSHXDMSA-UHFFFAOYSA-N nitrogen Substances N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 72
- 238000012545 processing Methods 0.000 claims abstract description 57
- 238000001069 Raman spectroscopy Methods 0.000 claims abstract description 56
- 230000005540 biological transmission Effects 0.000 claims abstract description 49
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 46
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims abstract description 20
- 238000002310 reflectometry Methods 0.000 claims description 34
- 239000013307 optical fiber Substances 0.000 claims description 9
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4818—Constructional features, e.g. arrangements of optical elements using optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
- G01D5/35309—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer
- G01D5/35316—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer using a Bragg gratings
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- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/88—Lidar systems specially adapted for specific applications
- G01S17/95—Lidar systems specially adapted for specific applications for meteorological use
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- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4816—Constructional features, e.g. arrangements of optical elements of receivers alone
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
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Abstract
The invention discloses a water vapor detection and light splitting system based on a sampling fiber Bragg grating, which comprises the following components: the device comprises a water vapor signal acquisition module, a nitrogen signal acquisition module, a first signal acquisition module and a second signal acquisition module; the water vapor signal acquisition module and the nitrogen signal acquisition module are respectively connected with the first signal acquisition module and the second signal acquisition module; the water vapor signal acquisition module is used for receiving and processing the echo signals to obtain water vapor Raman scattering signals and generating a first transmission signal and a second transmission signal; the first signal acquisition module is used for receiving and processing the first transmission signal to obtain a first Mi-Rayleigh signal and generating a first reflection echo signal; the second signal acquisition module is used for receiving and processing the second transmission signal to obtain a second Mi-Rayleigh signal and generating a second reflection echo signal; the nitrogen signal acquisition module is used for receiving the first reflected echo signal and the second reflected echo signal and processing the first reflected echo signal and the second reflected echo signal to obtain a nitrogen Raman scattering signal. The system has compact structure, good stability and strong light splitting performance.
Description
Technical Field
The invention relates to the technical field of laser radar remote sensing detection, in particular to a water vapor detection and light splitting system and method based on a sampling fiber Bragg grating.
Background
At present, continuous observation of water vapor can provide judgment basis for numerical weather forecast and can also be used for judging climate change trend. The strong solar background light noise limits the detection capability of the water vapor Raman laser radar in the daytime, and Mie-Rayleigh scattering signals cause serious interference on the fine extraction of the water vapor and nitrogen Raman signals. In order to improve the capacity of a light-splitting system for suppressing Mie-Rayleigh scattering in the detection process, the water vapor detection of the Raman laser radar system in the whole day is realized.
However, the internal structures of the light splitting system commonly used at present are as follows: the problems of large volume or difficult system adjustment exist in the spectroscopic devices such as interference filters, double grating monochromators, prism systems, fabry-Perot interferometers (FPI) and atomic filtration steam meters, and the spectroscopic devices are not suitable for detection application of roadbed-space-based Raman laser radars.
Therefore, how to provide a water vapor detection and light splitting system with compact structure, good stability and strong light splitting performance is a problem to be solved by those skilled in the art.
Disclosure of Invention
In view of the above, the invention provides a vapor detection and light splitting system and a method based on a sampling fiber Bragg grating, which are constructed by multistage cascading of the sampling fiber Bragg grating SFBG and the fiber Bragg grating FBG, can inhibit more than 7 Mi-Rayleigh signals and have the advantages of compact structure, good stability and strong light splitting performance.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a water vapor detection spectroscopic system based on a sampled fiber bragg grating, comprising: the device comprises a water vapor signal acquisition module, a nitrogen signal acquisition module, a first signal acquisition module and a second signal acquisition module;
the water vapor signal acquisition module and the nitrogen signal acquisition module are respectively connected with the first signal acquisition module and the second signal acquisition module;
The water vapor signal acquisition module is used for: receiving and processing the echo signals to obtain water vapor Raman scattering signals, and generating a first transmission signal and a second transmission signal;
the first signal acquisition module is used for: receiving and processing the first transmission signal to obtain a first Mi-Rayleigh signal and generating a first reflection echo signal;
The second signal acquisition module is used for: receiving and processing the second transmission signal to obtain a second m-rayleigh signal and generating a second reflected echo signal;
The nitrogen signal acquisition module is used for: and receiving the first reflected echo signal and the second reflected echo signal and processing the first reflected echo signal and the second reflected echo signal to obtain a nitrogen Raman scattering signal.
Preferably, the water vapor signal acquisition module specifically includes: the first grating, the second grating, the first coupler, the first sampling grating and the second sampling grating;
One end of the first grating is connected with the signal input port, and one end of the second grating is used as a first output port;
the other end of the first grating and the other end of the second grating are respectively connected with one end of the first coupler;
the other end of the first coupler is connected with one end of the first sampling grating and one end of the second sampling grating respectively;
The signal input port inputs echo signals, and a first processing signal is obtained after the echo signals sequentially pass through the first grating and the first coupler;
the first processing signal is reflected by the first sampling grating and the second sampling grating respectively, and then is processed by the second grating to obtain a water vapor Raman scattering signal at the first port;
And after the first processing signal passes through the first sampling grating and the second sampling grating respectively, a first transmission echo signal and a second transmission echo signal are correspondingly generated.
Preferably, the first signal acquisition module specifically includes: the second coupler, the third sampling grating, the fourth sampling grating and the fifth coupler;
one end of the second coupler is connected with the other end of the first sampling grating, and the other end of the second coupler is respectively connected with one end of the third sampling grating and one end of the fourth sampling grating;
the other end of the third sampling grating and the other end of the fourth sampling grating are respectively connected with one end of a fifth coupler, and the other end of the fifth coupler is used as a third output port;
the first transmission echo signal respectively enters the third sampling grating and the fourth sampling grating through the second coupler;
Respectively reflecting through the third sampling grating and the fourth sampling grating, and then combining to generate a first reflected echo signal;
and the first Mi-Rayleigh signal is generated at the third output port through the fifth coupler after being transmitted by the third sampling grating and the fourth sampling grating respectively.
Preferably, the second signal acquisition module specifically includes: the third coupler, the fifth sampling grating, the sixth sampling grating and the sixth coupler;
One end of the third coupler is connected with the other end of the second sampling grating, and the other end of the third coupler is respectively connected with one end of the fifth sampling grating and one end of the sixth sampling grating;
The other end of the fifth sampling grating and the other end of the sixth sampling grating are respectively connected with one end of a sixth coupler, and the other end of the sixth coupler is used as a fourth output port;
the second transmission echo signal respectively enters the fifth sampling grating and the sixth sampling grating through the third coupler;
Respectively reflecting through the fifth sampling grating and the sixth sampling grating, and then combining to generate a second reflected echo signal;
and the second Mi-Rayleigh signal is generated at the fourth output port through the sixth coupler after being transmitted through the fifth sampling grating and the sixth sampling grating respectively.
Preferably, the nitrogen signal acquisition module specifically includes: a third grating, a fourth grating, and a fourth coupler;
One end of the fourth coupler is used as a second output port, and the other end of the fourth coupler is connected with one end of the third grating and one end of the fourth grating respectively;
The other end of the third grating is connected with one end of the second coupler, and the other end of the fourth grating is connected with one end of the third coupler;
the first reflected echo signal passes through the third grating to generate a second processing signal;
the second reflected echo signal passes through the fourth grating to generate a third processing signal;
The second processing signal and the third processing signal are processed by the fourth coupler to output a nitrogen Raman scattering signal at the second output port.
Preferably, the first grating, the second grating, the third grating and the fourth grating have the same structure, all adopt fiber Bragg gratings, the center wavelength is 355nm, the half width height is 0.2nm, the maximum reflectivity is greater than 99%, and the out-of-band rejection rate is greater than 20dB.
Preferably, the first sampling grating and the second sampling grating have the same structure, all adopt sampling fiber Bragg gratings, the center wavelength is 386.17nm, 386.59nm and 387.01nm, the half width height is 0.03nm, the maximum reflectivity is greater than 90%, and the out-of-band rejection rate is greater than 30dB.
Preferably, the third sampling grating, the fourth sampling grating, the fifth sampling grating and the sixth sampling grating have the same structure, all adopt sampling fiber Bragg gratings, the center wavelengths are 407.80nm, 407.89nm and 407.98nm, the half width heights are 0.03nm, the maximum reflectivity is greater than 90%, and the out-of-band rejection rate is greater than 30dB.
Preferably, the first coupler, the second coupler and the third coupler have the same structure, and all adopt 2×2 optical fiber couplers;
the fourth coupler, the fifth coupler and the sixth coupler have the same structure, and all adopt 2 multiplied by 1 optical fiber couplers.
A water vapor detection and light splitting method based on a sampling fiber Bragg grating comprises the following steps:
the method comprises the steps that a water vapor Raman scattering signal is obtained based on receiving and processing echo signals by a water vapor signal obtaining module, and a first transmission signal and a second transmission signal are generated;
Receiving and processing the first transmission signal based on a first signal acquisition module to obtain a first Mi-Rayleigh signal and generating a first reflection echo signal;
receiving and processing the second transmission signal based on a second signal acquisition module to obtain a second m-rayleigh signal and generating a second reflected echo signal;
and receiving the first reflected echo signal and the second reflected echo signal based on the nitrogen signal acquisition module, and processing the first reflected echo signal and the second reflected echo signal to obtain a nitrogen Raman scattering signal.
Compared with the prior art, the invention discloses a water vapor detection and light splitting system and method based on a sampling fiber Bragg grating, which has the following beneficial effects:
1. The full width at half maximum of the sampling fiber Bragg grating SFBG adopted by the invention is less than 0.03nm, so that solar background light can be effectively restrained.
2. The invention adopts a light-splitting system in which the sampling fiber Bragg grating SFBG and the fiber Bragg grating FBG are cascaded, and can inhibit the Mie-Rayleigh signal (Mie-Rayleigh) by more than 7 numbers.
3. The water vapor beam splitting system has the advantages of miniaturization and light weight, the optical fiber has the advantages of high stability and small volume, and a new scheme is provided for detecting the atmosphere by the vehicle-mounted or airborne Raman laser radar in future development.
4. Compared with the traditional light splitting system or device, the light splitting system has better light splitting performance, the half-width is narrower than that of the traditional device, and the peak value of the highest reflectivity is more than 90%.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a water vapor detection spectroscopic system based on a sampling fiber bragg grating according to the present invention.
Fig. 2 is a schematic structural diagram of a preferred water vapor detection spectroscopic system based on a sampling fiber bragg grating according to the present invention.
Fig. 3 is a schematic diagram of the overall system structure of the water vapor detection raman lidar provided by the invention.
Fig. 4 is a schematic diagram of the spectral distribution of the echo signal when the excitation wavelength of the laser provided by the invention is 355 nm.
Fig. 5 is a schematic diagram of simulation results of the intensity and the height of each channel and the optical noise signal provided by the present invention.
Fig. 6 is a schematic diagram of signal-to-noise ratio of the daytime and nighttime system provided by the present invention.
Fig. 7 is a schematic diagram of the reflectivity and bandwidth of the first sampled grating SFBG 1 and the second sampled grating SFBG 2 at 386.16nm, 386.58nm, and 387.01 nm.
Fig. 8 is a schematic diagram of the reflectivity of the first sampled grating SFBG 1 and the second sampled grating SFBG 2 at 355 nm.
Fig. 9 is a schematic diagram of reflectivity and bandwidth of a third sampling grating SFBG 3, a fourth sampling grating SFBG 4, a fifth sampling grating SFBG 5, and a sixth sampling grating SFBG 6 at 407.81, 407.90, and 407.99nm according to the present invention.
Fig. 10 is a schematic diagram of reflectivity of a third sampling grating SFBG 3, a fourth sampling grating SFBG 4, a fifth sampling grating SFBG 5, and a sixth sampling grating SFBG 6 at 355nm according to the present invention.
Fig. 11 is a flowchart of a water vapor detection spectroscopic method based on a sampling fiber bragg grating according to the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
As shown in fig. 1, an embodiment of the present invention discloses a water vapor detection spectroscopic system based on a sampling fiber bragg grating, including: the device comprises a water vapor signal acquisition module, a nitrogen signal acquisition module, a first signal acquisition module and a second signal acquisition module;
The water vapor signal acquisition module and the nitrogen signal acquisition module are respectively connected with the first signal acquisition module and the second signal acquisition module;
The water vapor signal acquisition module is used for: receiving and processing the echo signals to obtain water vapor Raman scattering signals, and generating a first transmission signal and a second transmission signal;
The first signal acquisition module is used for: receiving and processing the first transmission signal to obtain a first Mi-Rayleigh signal and generating a first reflection echo signal;
the second signal acquisition module is used for: receiving and processing the second transmission signal to obtain a second m-rayleigh signal and generating a second reflected echo signal;
the nitrogen signal acquisition module is used for: and receiving the first reflected echo signal and the second reflected echo signal and processing the first reflected echo signal and the second reflected echo signal to obtain a nitrogen Raman scattering signal.
Example 2
As shown in fig. 2, an embodiment of the present invention discloses a water vapor detection spectroscopic system based on a sampling fiber bragg grating, including: the device comprises a water vapor signal acquisition module, a nitrogen signal acquisition module, a first signal acquisition module and a second signal acquisition module;
The water vapor signal acquisition module and the nitrogen signal acquisition module are respectively connected with the first signal acquisition module and the second signal acquisition module;
The water vapor signal acquisition module is used for: receiving and processing the echo signals to obtain water vapor Raman scattering signals, and generating a first transmission signal and a second transmission signal;
The first signal acquisition module is used for: receiving and processing the first transmission signal to obtain a first Mi-Rayleigh signal and generating a first reflection echo signal;
the second signal acquisition module is used for: receiving and processing the second transmission signal to obtain a second m-rayleigh signal and generating a second reflected echo signal;
the nitrogen signal acquisition module is used for: and receiving the first reflected echo signal and the second reflected echo signal and processing the first reflected echo signal and the second reflected echo signal to obtain a nitrogen Raman scattering signal.
Preferably, the water vapor raman scattering signal comprises a water vapor vibratory raman signal and a water vapor rotational raman signal; the nitrogen raman scattering signal includes a nitrogen vibration raman signal and a nitrogen rotation raman signal.
Preferably, the water vapor signal acquisition module specifically includes: the first grating FBG 1, the second grating FBG 2, the first coupler C 1, the first sampling grating SFBG 1 and the second sampling grating SFBG 2;
One end of the first grating FBG 1 is connected with the signal input port, and one end of the second grating FBG 2 is used as a first output port;
The other end of the first grating FBG 1 and one end of the second grating other FBG 2 are respectively connected with one end of a first coupler C 1;
The other end of the first coupler C 1 is connected with one end of the first sampling grating SFBG 1 and one end of the second sampling grating SFBG 2 respectively;
the signal input port inputs echo signals, and after the echo signals sequentially pass through the first grating FBG 1 and the first coupler C 1, first processing signals are obtained;
The first processing signal is respectively reflected by a first sampling grating SFBG 1 and a second sampling grating SFBG 2, and then is processed by a second grating FBG 2 to obtain a water vapor Raman scattering signal at a first port;
After the first processing signal passes through the first sampling grating SFBG 1 and the second sampling grating SFBG 2, a first transmission echo signal and a second transmission echo signal are correspondingly generated.
Preferably, the first signal acquisition module specifically includes: a second coupler C 2, a third sampling grating SFBG 3, a fourth sampling grating SFBG 4, and a fifth coupler C 5;
One end of the second coupler C 2 is connected with the other end of the first sampling grating SFBG 1, and the other end of the second coupler C 2 is connected with one end of the third sampling grating SFBG 3 and one end of the fourth sampling grating SFBG 4 respectively;
The other end of the third sampling grating SFBG 3 and the other end of the fourth sampling grating SFBG 4 are respectively connected with one end of a fifth coupler C 5, and the other end of the fifth coupler C 5 is used as a third output port;
The first transmission echo signal enters a third sampling grating SFBG 3 and a fourth sampling grating SFBG 4 through a second coupler C 2 respectively;
The first reflected echo signals are generated after being reflected by the third sampling grating SFBG 3 and the fourth sampling grating SFBG 4 respectively;
the first meter-rayleigh signal is generated at the third output port through the fifth coupler C 5 after being transmitted through the third sampled grating SFBG 3 and the fourth sampled grating SFBG 4, respectively.
Preferably, the second signal acquisition module specifically includes: third coupler C 3, fifth sampling grating SFBG 5, sixth sampling grating SFBG 6, and sixth coupler C 6;
One end of a third coupler C 3 is connected with the other end of the second sampling grating SFBG 2, and the other end of the third coupler C 3 is respectively connected with one end of a fifth sampling grating SFBG 5 and one end of a sixth sampling grating SFBG 6;
The other end of the fifth sampling grating SFBG 5 and the other end of the sixth sampling grating SFBG 6 are respectively connected with one end of a sixth coupler C 6, and the other end of the sixth coupler C 6 is used as a fourth output port;
The second transmission echo signal respectively enters a fifth sampling grating SFBG 5 and a sixth sampling grating SFBG 6 through a third coupler C 3;
the second reflected echo signals are generated after being reflected by the fifth sampling grating SFBG 5 and the sixth sampling grating SFBG 6 respectively;
The second meter-rayleigh signal is generated at the fourth output port through the transmission of the fifth sampled grating SFBG 5 and the sixth sampled grating SFBG 6, respectively, and then through the processing of the sixth coupler C 6.
Preferably, the nitrogen signal acquisition module specifically includes: a third grating FBG 3, a fourth grating FBG 4 and a fourth coupler C 4;
One end of a fourth coupler C 4 is used as a second output port, and the other end of the fourth coupler C 4 is respectively connected with one end of a third grating FBG 3 and one end of a fourth grating FBG 4;
The other end of the third grating FBG 3 is connected with one end of the second coupler C 2, and the other end of the fourth grating FBG 4 is connected with one end of the third coupler C 3;
the first reflected echo signal passes through the third grating FBG 3 to generate a second processing signal;
The second reflected echo signal passes through the fourth grating FBG 4 to generate a third processed signal;
the second processing signal and the third processing signal are processed by a fourth coupler C 4 to output a nitrogen raman scattering signal at the second output port.
Preferably, the first grating FBG 1, the second grating FBG 2, the third grating FBG 3 and the fourth grating FBG 4 have the same structure, all adopt fiber Bragg gratings, have center wavelengths of 355nm, have half-width heights of 0.2nm, have maximum reflectivity of more than 99%, and have out-of-band rejection of more than 20dB.
Preferably, the first sampling grating SFBG 1 and the second sampling grating SFBG 2 have the same structure, all adopt sampling fiber Bragg gratings, have the central wavelengths of 386.17nm, 386.59nm and 387.01nm, have the half-width heights of 0.03nm, have the maximum reflectivity of more than 90%, and have the out-of-band rejection rate of more than 30dB.
Preferably, the third sampling grating SFBG 3, the fourth sampling grating SFBG 4, the fifth sampling grating SFBG 5 and the sixth sampling grating SFBG 6 have the same structure, all adopt sampling fiber Bragg gratings, the center wavelengths are 407.80nm, 407.89nm and 407.98nm, the half-width heights are 0.03nm, the maximum reflectivity is greater than 90%, and the out-of-band rejection rate is greater than 30dB.
Preferably, the first coupler C 1, the second coupler C 2 and the third coupler C 3 have the same structure, and all use 2×2 fiber optic couplers;
The fourth coupler C 4, the fifth coupler C 5 and the sixth coupler C 6 have the same structure, and all use 2×1 fiber couplers.
Preferably, the nitrogen vibration Raman frequency shifts are 2330.41cm -1、2301.81cm-1 and 2273.14cm -1; the main peak frequency shift of the water vapor vibration Raman is 3653cm -1, and the left peak and the right peak are 3648cm -1 and 3658cm -1.
Preferably, the coupling mode theory is a main theoretical method for analyzing the characteristics of the fiber bragg grating, and a transmission matrix method can be obtained by simplifying the coupling mode theory. The transmission matrix method is mainly used for analyzing the non-uniform fiber gratings, namely the non-uniform FBG is divided into M uniform small sections, the transmission characteristic of each section of grating can be expressed by a 2X 2 matrix, and the transmission characteristic of the non-uniform FBG can be regarded as multiplication of the M uniform sections.
Example 3
The application of the light splitting system in the total system of the water vapor detection Raman laser radar is as follows:
As shown in fig. 3, the water vapor detection raman lidar total system includes: YAG laser, beam expander, telescope, focusing lens, optical fiber, beam splitting system, multiple photomultiplier PMTs and data processing terminal;
The working principle is as follows: YAG laser emits laser, after generating second harmonic through SHG (double frequency) and third harmonic through THG (triple frequency) in turn, laser with 355nm output wavelength is used as a light source, the laser is collimated and expanded by a beam expander and then emitted into the atmosphere, the laser beam interacts with particles and molecules in the atmosphere, a backward scattering echo signal is received by a telescope, the backward scattering echo signal is coupled by a focusing lens and enters a beam splitting system through an optical fiber, the backward scattering signal is filtered through an optical path cascaded by the FBG and the SFBG of the beam splitting system, the three channels respectively obtain a water vapor Raman scattering signal, a nitrogen Raman scattering signal and a meter-Rayleigh scattering signal, the meter-Rayleigh scattering signals finally obtained by the channels are obtained by combining a first meter-Rayleigh signal and a second meter-Rayleigh signal, the incident photons are converted into photoelectrons through the photoelectric effect of a photomultiplier, the photoelectron quantity is increased step by step through the effect of a series of dynodes, and finally the photomultiplier outputs an observable current pulse, and the current pulse is input into a data processing terminal, and the data processing terminal is processed and inverted by the data processing terminal to obtain a spectrum distribution of 355nm echo signal with 355nm when the laser has a wavelength of 355 nm; the data processing terminal can obtain the high-altitude water vapor content based on the obtained water vapor Raman scattering signal intensity and the nitrogen Raman scattering signal intensity through a water vapor mixing ratio formula.
The formula of the raman water vapor mixing ratio changing with the height is as follows:
Wherein C H represents a calibration constant of the system, P H (x) represents a water vapor Raman scattering signal intensity, P N (x) represents a nitrogen Raman scattering signal intensity, alpha λH (x ') and alpha λN (x') respectively represent extinction coefficients at water vapor and nitrogen Raman scattering wavelengths, and an index expression exp { … } represents an atmospheric transmittance correction function, which is related to the extinction coefficients.
According to the designed water vapor detection Raman laser radar system formed by the SFBG light splitting structure, the intensity of echo signals of each channel can be obtained according to the principle of measuring water vapor by the Raman laser radar, as shown in FIG. 5, the channel 1 is the water vapor Raman scattering signal intensity, and the water vapor Raman scattering signal intensity is respectively stronger than Mie-Rayleigh scattering signals and solar background light noise signals below 3 km. The channel 2 is the intensity of the Raman scattering signal of the nitrogen, and the nitrogen content accounts for 78% of the atmosphere, so that the Raman signal of the nitrogen is strongest. Channels 3 and 4 are the Mie-Rayleigh scattering signals after being suppressed.
As shown in FIG. 6, when the signal-to-noise ratio reaches 100, the detection height in the dark reaches 2.5km, and the detection height in the daytime reaches 1.5km, and when the signal-to-noise ratio is 10, the detection of water vapor in the atmosphere can reach 6km.
Example 4
SFBG reflectivity simulation experiment designed by the invention:
Major parameters of the SFBG signature spectrum include: the refractive index modulation depth delta neff, the total length L of the grating, the sampling period T and the duty cycle r, and the resolution of the SFBG can be influenced by changing parameters.
As shown in fig. 7, there is shown the reflectance spectrum of the first sampled grating SFBG 1 and the second sampled grating SFBG 2 around 386.6nm, where R represents the reflectance and C represents the center wavelength, where: the first reflection peak has a center wavelength of 386.16nm, a reflectivity of 78.3% and a FWHM of 0.006nm; the second reflection peak has a center wavelength of 386.59nm, a reflectivity of 97.5% and a FWHM of 0.01nm; the center wavelength of the third reflection peak is 387.00nm, the reflectivity is 98.9%, and the FWHM is 0.003nm; both reflectivity and FWHM are superior to the design parameters.
As shown in fig. 8, the reflectivities of the first sampled grating SFBG 1 and the second sampled grating SFBG 2 at 355nm are shown, and the reflectivities of the SFBG 1 and the SFBG 2 at 355nm are less than 1×10 -7, which indicates that the SFBG 1 and the SFBG 2 hardly reflect light with 355nm wavelength, and the reflectivities represent the rejection rate of the SFBG to the m-rayleigh signal, i.e., the rejection rate can provide 70dB for the m-rayleigh signal in the spectroscopic system.
By combining the structure of the spectroscopic system, the reflectivity of the FBG to 355nm is 99%, the reflectivity of the FBG to 355nm is 10 -4 through 2 FBGs, the reflectivity of the SFBG is 10 -7, and the reflectivity is 10 -11 under the condition of ignoring all errors, namely the spectroscopic system theoretically inhibits 110dB of the Mi-Rayleigh signal when obtaining the nitrogen Raman scattering signal.
The reflectivity of each of the third sampling grating SFBG 3, the fourth sampling grating SFBG 4, the fifth sampling grating SFBG 5 and the sixth sampling grating SFBG 6 in the range with the far offset center is smaller than 10 -4, and the design improves the signal-to-noise ratio and simultaneously suppresses the interference of sunlight. The optimized parameters of the third sampling grating SFBG 3, the fourth sampling grating SFBG 4, the fifth sampling grating SFBG 5 and the sixth sampling grating SFBG 6 are that the central wavelength lambda B = 407.81nm, the optical fiber refractive index n eff =1.465, the refractive index modulation depth delta neff =0.00005, the total length L of the gratings=13.3 mm, the sampling period T=0.835 mm and the duty ratio r=0.5.
Preferably, the center wavelength refers to the wavelength corresponding to the dominant peak or trough in the spectrum, typically used to characterize light or fluctuations; in physics and optics, the center wavelength is generally represented by λ (lambda), which is the wavelength value corresponding to the peak top position of the spectral distribution curve; the refractive index of an optical fiber refers to the ratio of the propagation velocity of light in the fiber relative to vacuum or air.
As shown in fig. 9, there are shown reflection spectra of the third sampling grating SFBG 3, the fourth sampling grating SFBG 4, the fifth sampling grating SFBG 5, and the sixth sampling grating SFBG 6 in the vicinity of 407.8nm, where R represents the reflectance and C represents the center wavelength, and wherein: the first reflection peak has a center wavelength of 407.81nm, a reflectivity of 89% and a FWHM of 0.01nm; the second reflection peak has a center wavelength of 407.90nm, a reflectivity of 97.6% and a FWHM of 0.011nm; the center wavelength of the third reflection peak is 407.99nm, the reflectivity is 98.9%, and the FWHM is 0.011nm; the reflectivity and FWHM are superior to the parameters of the design.
As shown in fig. 10, the reflectivity of the third, fourth, fifth and sixth sampled gratings SFBG 3, SFBG 4, SFBG 5, SFBG 6 at 355nm are all less than 1 x 10 -7, indicating that a single third, fourth, fifth and sixth sampled grating SFBG3, SFBG4, SFBG5, SFBG6 provides 70dB suppression for the m-rayleigh signal. In combination with the structure of the spectroscopic system, the spectroscopic system theoretically suppresses the Rayleigh scattering signal by 110dB when obtaining the nitrogen raman scattering signal. The third sampling grating SFBG 3, the fourth sampling grating SFBG 4, the fifth sampling grating SFBG 5 and the sixth sampling grating SFBG 6 have reflectivity less than 10 -4 in the range far from the offset center, which indicates that light of other wavelengths than the Raman signal is transmitted, and the design improves the signal-to-noise ratio and simultaneously suppresses the interference of sunlight.
Example 5
As shown in fig. 11, a water vapor detection and spectroscopy method based on a sampling fiber bragg grating includes:
the method comprises the steps that a water vapor Raman scattering signal is obtained based on receiving and processing echo signals by a water vapor signal obtaining module, and a first transmission signal and a second transmission signal are generated;
receiving and processing the first transmission signal based on the first signal acquisition module to obtain a first Mi-Rayleigh signal and generating a first reflection echo signal;
receiving and processing the second transmission signal based on the second signal acquisition module to obtain a second m-rayleigh signal and generating a second reflected echo signal;
And the nitrogen-based signal acquisition module receives the first reflected echo signal and the second reflected echo signal and processes the first reflected echo signal and the second reflected echo signal to obtain a nitrogen Raman scattering signal.
Compared with the prior art, the invention discloses a water vapor detection and light splitting system and method based on a sampling fiber Bragg grating, which has the following beneficial effects:
1. The full width at half maximum of the sampling fiber Bragg grating SFBG adopted by the invention is less than 0.03, and can effectively inhibit solar background light.
2. The invention adopts a light-splitting system in which the sampling fiber Bragg grating SFBG and the fiber Bragg grating FBG are cascaded, and can inhibit the Mie-Rayleigh signal (Mie-Rayleigh) by more than 7 numbers.
3. The water vapor beam splitting system has the advantages of miniaturization and light weight, the optical fiber has the advantages of high stability and small volume, and a new scheme is provided for detecting the atmosphere by the vehicle-mounted or airborne Raman laser radar in future development.
4. Compared with the traditional light splitting system or device, the light splitting system has better light splitting performance, the half-width is narrower than that of the traditional device, and the peak value of the highest reflectivity is more than 90%.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A water vapor detection spectroscopic system based on a sampled fiber bragg grating, comprising: the device comprises a water vapor signal acquisition module, a nitrogen signal acquisition module, a first signal acquisition module and a second signal acquisition module;
the water vapor signal acquisition module and the nitrogen signal acquisition module are respectively connected with the first signal acquisition module and the second signal acquisition module;
The water vapor signal acquisition module is used for: receiving and processing the echo signals to obtain water vapor Raman scattering signals, and generating a first transmission signal and a second transmission signal;
the first signal acquisition module is used for: receiving and processing the first transmission signal to obtain a first Mi-Rayleigh signal and generating a first reflection echo signal;
The second signal acquisition module is used for: receiving and processing the second transmission signal to obtain a second m-rayleigh signal and generating a second reflected echo signal;
The nitrogen signal acquisition module is used for: and receiving the first reflected echo signal and the second reflected echo signal and processing the first reflected echo signal and the second reflected echo signal to obtain a nitrogen Raman scattering signal.
2. The water vapor detection spectroscopic system based on a sampled fiber bragg grating of claim 1, wherein the water vapor signal acquisition module specifically comprises: the first grating, the second grating, the first coupler, the first sampling grating and the second sampling grating;
One end of the first grating is connected with the signal input port, and one end of the second grating is used as a first output port;
the other end of the first grating and the other end of the second grating are respectively connected with one end of the first coupler;
the other end of the first coupler is connected with one end of the first sampling grating and one end of the second sampling grating respectively;
The signal input port inputs echo signals, and a first processing signal is obtained after the echo signals sequentially pass through the first grating and the first coupler;
the first processing signal is reflected by the first sampling grating and the second sampling grating respectively, and then is processed by the second grating to obtain a water vapor Raman scattering signal at the first port;
And after the first processing signal passes through the first sampling grating and the second sampling grating respectively, a first transmission echo signal and a second transmission echo signal are correspondingly generated.
3. The water vapor detection spectroscopic system based on a sampled fiber bragg grating of claim 2, wherein the first signal acquisition module specifically comprises: the second coupler, the third sampling grating, the fourth sampling grating and the fifth coupler;
one end of the second coupler is connected with the other end of the first sampling grating, and the other end of the second coupler is respectively connected with one end of the third sampling grating and one end of the fourth sampling grating;
the other end of the third sampling grating and the other end of the fourth sampling grating are respectively connected with one end of a fifth coupler, and the other end of the fifth coupler is used as a third output port;
the first transmission echo signal respectively enters the third sampling grating and the fourth sampling grating through the second coupler;
Respectively reflecting through the third sampling grating and the fourth sampling grating, and then combining to generate a first reflected echo signal;
and the first Mi-Rayleigh signal is generated at the third output port through the fifth coupler after being transmitted by the third sampling grating and the fourth sampling grating respectively.
4. A water vapor detection spectroscopic system based on a sampled fiber bragg grating as defined in claim 3, wherein said second signal acquisition module comprises: the third coupler, the fifth sampling grating, the sixth sampling grating and the sixth coupler;
One end of the third coupler is connected with the other end of the second sampling grating, and the other end of the third coupler is respectively connected with one end of the fifth sampling grating and one end of the sixth sampling grating;
The other end of the fifth sampling grating and the other end of the sixth sampling grating are respectively connected with one end of a sixth coupler, and the other end of the sixth coupler is used as a fourth output port;
the second transmission echo signal respectively enters the fifth sampling grating and the sixth sampling grating through the third coupler;
Respectively reflecting through the fifth sampling grating and the sixth sampling grating, and then combining to generate a second reflected echo signal;
and the second Mi-Rayleigh signal is generated at the fourth output port through the sixth coupler after being transmitted through the fifth sampling grating and the sixth sampling grating respectively.
5. The water vapor detection spectroscopic system based on a sampled fiber bragg grating of claim 4, wherein the nitrogen signal acquisition module specifically comprises: a third grating, a fourth grating, and a fourth coupler;
One end of the fourth coupler is used as a second output port, and the other end of the fourth coupler is connected with one end of the third grating and one end of the fourth grating respectively;
The other end of the third grating is connected with one end of the second coupler, and the other end of the fourth grating is connected with one end of the third coupler;
the first reflected echo signal passes through the third grating to generate a second processing signal;
the second reflected echo signal passes through the fourth grating to generate a third processing signal;
The second processing signal and the third processing signal are processed by the fourth coupler to output a nitrogen Raman scattering signal at the second output port.
6. The water vapor detection and light splitting system based on sampling fiber Bragg gratings according to claim 5, wherein the first grating, the second grating, the third grating and the fourth grating have the same structure, all adopt fiber Bragg gratings, have center wavelengths of 355nm, half-width heights of 0.2nm, maximum reflectivity of more than 99%, and out-of-band rejection of more than 20dB.
7. The water vapor detection and light splitting system based on the sampled fiber bragg gratings as claimed in claim 2, wherein the first sampled grating and the second sampled grating have the same structure, the sampled fiber bragg gratings are adopted, the center wavelengths are 386.17nm, 386.59nm and 387.01nm, the half-width heights are 0.03nm, the maximum reflectivity is greater than 90%, and the out-of-band rejection rate is greater than 30dB.
8. The water vapor detection spectroscopic system based on sampled fiber bragg gratings as recited in claim 4, wherein said third sampled grating, said fourth sampled grating, said fifth sampled grating and said sixth sampled grating are identical in structure, and all employ sampled fiber bragg gratings with center wavelengths of 407.80nm, 407.89nm and 407.98nm, half-width heights of 0.03nm, maximum reflectivities of greater than 90%, and out-of-band rejection of greater than 30dB.
9. The water vapor detection spectroscopic system based on a sampled fiber bragg grating of claim 5, wherein said first coupler, said second coupler and said third coupler are identical in structure and each employ a 2 x 2 fiber coupler;
the fourth coupler, the fifth coupler and the sixth coupler have the same structure, and all adopt 2 multiplied by 1 optical fiber couplers.
10. The water vapor detection and light splitting method based on the sampling fiber Bragg grating is characterized by comprising the following steps of:
the method comprises the steps that a water vapor Raman scattering signal is obtained based on receiving and processing echo signals by a water vapor signal obtaining module, and a first transmission signal and a second transmission signal are generated;
Receiving and processing the first transmission signal based on a first signal acquisition module to obtain a first Mi-Rayleigh signal and generating a first reflection echo signal;
receiving and processing the second transmission signal based on a second signal acquisition module to obtain a second m-rayleigh signal and generating a second reflected echo signal;
and receiving the first reflected echo signal and the second reflected echo signal based on the nitrogen signal acquisition module, and processing the first reflected echo signal and the second reflected echo signal to obtain a nitrogen Raman scattering signal.
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