WO2020019153A1 - Radar laser femtoseconde et procédé de détection de composition de gaz - Google Patents

Radar laser femtoseconde et procédé de détection de composition de gaz Download PDF

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WO2020019153A1
WO2020019153A1 PCT/CN2018/096791 CN2018096791W WO2020019153A1 WO 2020019153 A1 WO2020019153 A1 WO 2020019153A1 CN 2018096791 W CN2018096791 W CN 2018096791W WO 2020019153 A1 WO2020019153 A1 WO 2020019153A1
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laser
fiber
detection
port
gas
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PCT/CN2018/096791
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English (en)
Chinese (zh)
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章振
夏海云
赵力杰
余赛芬
窦贤康
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中国科学技术大学
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Priority to PCT/CN2018/096791 priority Critical patent/WO2020019153A1/fr
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • 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
    • 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
    • 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
    • G01S7/491—Details of non-pulse systems
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Definitions

  • the present invention relates to the technical field of optical systems, and more particularly, to a femtosecond lidar and a gas component detection method.
  • the detection of atmospheric parameters with high precision and high spatiotemporal resolution has led to a deeper understanding of atmospheric characteristics. Due to the increasing frequency of accidents such as fires and explosions, real-time and high-precision gas detection at dangerous moments has gradually attracted attention.
  • the femtosecond laser has a high repetition frequency, ultra-short pulse width, wide spectrum, and high peak power, which makes it play an important role in the fields of ultra-fast spectroscopy technology, ultra-fast kinetic detection technology and optical frequency comb.
  • the detection field also has great development potential.
  • the femtosecond laser's real-time "time-frequency mapping” spectroscopy technology provides researchers with a powerful tool to overcome the rate limitations of traditional electronics.
  • the advantage of Raman amplification is that it can maintain a constant signal power level throughout the dispersion element. Based on this, they completed the real-time detection of single-point CO gas absorption characteristics, and the spectral accuracy reached 950MHz.
  • Xia Haiyun and others considered the non-linear time-frequency mapping brought by higher-order dispersion in real-time "time-frequency mapping” spectroscopy technology.
  • the stable repetition frequency of the femtosecond laser makes itself a very good optical frequency comb.
  • the femtosecond optical comb not only plays an important role in the field of high-precision atomic clocks, but also shows great advantages in the detection of gas components.
  • NRnewbury et al. Used dual-frequency comb interference spectroscopy technology to measure the radio spectrum interferogram one-to-one corresponding to the optical frequency comb spectrum.
  • gas detections including 700 absorption characteristics in the 1600-1670nm spectral range were completed, including CO 2 , CH 4 , H 2 O, HDO, and 13 CO 2, and the spectral resolution is less than 1KHz.
  • This optical frequency comb spectroscopy technology has a certain time resolution ability to monitor small changes in gas concentration, and the gas concentration resolution can reach 1 ppm (CO 2 ) and 3 ppb (CH 4 ) within 5 minutes. Due to the complexity of the optical frequency comb spectroscopy system, two optical frequency comb systems with a small difference in repetition frequency are usually required. The cost is high.
  • SMLink et al. Proposed a simplified dual-frequency comb interference system composed of a single semiconductor laser. The detection of water vapor absorption characteristics was performed. In this dual-frequency comb interference system, a birefringent crystal is placed in the laser cavity. The crystal decomposes the incident light into two beams with vertical polarization and different refractive indexes in the crystal. If an optical path difference is generated, two beams are emitted from the cavity. This method greatly simplifies the dual-frequency comb system.
  • the technical solution of the present invention provides a laser radar and a gas component detection method.
  • the system is simple and can realize real-time gas detection.
  • the present invention provides the following technical solutions:
  • a femtosecond lidar for detecting gas components includes:
  • the detection module includes an MZ interferometer; the MZ interferometer includes a beam splitter, a detection arm, a reference arm, and a beam combiner; the beam splitter is configured to divide the detection laser into a first part laser and a first A two-part laser; the MZ interferometer includes a detection arm and a reference arm; the detection arm is used to transmit the first part of the laser to the gas to be measured, and to obtain the reflection of the first part of the laser in the gas to be measured; Wave signal; the reference arm is used to delay process the second part of the laser to form a reference light, so that the reference light and the first part of the laser have a set delay time; the combiner is used to combine the The reference light and the reflected echo signal are coupled into a hybrid laser signal; the detection arm or the reference arm is connected to the combiner through an unbalanced dispersion fiber;
  • a light source receiving module configured to acquire the mixed laser signal and detect a gas component of the gas to be measured based on the mixed laser signal.
  • the light source module includes: a fiber femtosecond laser, a tunable filter, and a first fiber amplifier;
  • the fiber-optic femtosecond laser is used to emit a femtosecond laser pulse, and the femtosecond laser pulse passes through the tunable filter and the first fiber amplifier in order to form the detection laser pulse and enter the branch Beam device.
  • the detection arm includes: a fiber optic circulator, an optical transceiver system, and a folding mirror; the fiber optic circulator has a first port, a second port, and a third port, and light is incident on the Entering a first port, exiting from the second port, light entering the second port, and exiting from the third port;
  • the first part of the laser light is used to enter the first port, pass through the second port and the optical transceiver system in sequence, and then enter the gas to be measured, and after being reflected by the gas to be measured and the reflex mirror, Forming the reflected echo signal;
  • the reflected echo signal enters the second port through an optical transceiver system, exits through the third port, and enters an input port of the combiner through a first optical fiber;
  • the reference arm includes a delayer, and the second part of the laser is delayed by the delayer to form the reference light, and the reference light enters another input port of the combiner through a second optical fiber.
  • one of the first optical fiber and the second optical fiber is the unbalanced dispersion optical fiber.
  • the light source receiving module includes: a first dispersion fiber, a second fiber amplifier, a second dispersion fiber, a third fiber amplifier, a coupler, a photodetector, an oscilloscope, and a spectrometer;
  • the mixed laser signal passes through the first dispersion fiber, the second fiber amplifier, the second dispersion fiber, and the third fiber amplifier in sequence and enters an input port of the coupler;
  • the coupler has two output ports, which are respectively connected to the photodetector and the spectrometer;
  • the spectrometer is used to obtain the reflected echo signal and the reference light after time-domain widening and amplification of a part of the output of the corresponding output port of the coupler;
  • the photodetector is configured to obtain the reflected echo signal and the reference light after time-domain widening and amplification of another part output from the corresponding output port of the coupler, and to obtain the reflected echo signal and the reference Light is sent to the oscilloscope.
  • the dispersion coefficient of the unbalanced dispersion fiber is negative, and the detection arm is connected to the combiner through the unbalanced dispersion fiber;
  • the dispersion coefficient of the unbalanced dispersion fiber is a positive value
  • the reference arm is connected to the combiner through the unbalanced dispersion fiber.
  • the present invention also provides a method for detecting a gas component.
  • the detection method includes:
  • the detection laser is emitted through the light source module
  • the detection laser is divided into a first part laser and a second part laser by a detection module;
  • the detection module includes an M-Z interferometer;
  • the M-Z interferometer includes a beam splitter, a detection arm, a reference arm, and a beam combiner;
  • the detection arm or the reference arm is connected to the combiner through an unbalanced dispersion fiber;
  • the mixed laser signal is acquired through a light source receiving module, and a gas component of the gas to be measured is detected based on the mixed laser signal.
  • the light source module includes a fiber femtosecond laser, a tunable filter, and a first fiber amplifier;
  • the emitting the detection laser light through the light source module includes: emitting a femtosecond laser pulse through the fiber femtosecond laser, and selecting the spectral band through the tunable filter.
  • the adjustable filtering position includes at least one gas absorption. The position of the feature, after the laser pulse selected by the spectral band enters the first fiber amplifier for pulse amplification, the detection laser is formed and incident on the beam splitter.
  • the detection laser is divided into a first partial laser and a second partial laser by the beam splitter.
  • the detection arm includes: a fiber optic circulator, an optical transceiver system, and a fold-back mirror; the fiber optic circulator has a first port, a second port, and a third port, and light is incident on the incident first A port that exits from the second port, light that enters the second port, and exits from the third port; the reference arm includes a delayer;
  • Transmitting the first part of the laser to the gas to be measured by the detecting arm, obtaining a reflected echo signal of the first part of the laser in the gas to be measured, and transmitting the second part of the laser by the reference arm Delayed processing to form the reference light includes:
  • the first part of the laser light is used to enter the first port, pass through the second port and the optical transceiver system in sequence, and then enter the gas to be measured, and after being reflected by the gas to be measured and the reflection mirror
  • To form the reflected echo signal obtain the reflected echo signal through the optical transceiver system, send the reflected echo signal to the second port, exit through the third port, and pass through the first optical fiber
  • the time delay processing is performed on the second part of the laser light to form the reference light, and the reference light enters another input port of the combiner through a second optical fiber.
  • the light source receiving module includes: a first dispersion fiber, a second fiber amplifier, a second dispersion fiber, a third fiber amplifier, a coupler, a photodetector, an oscilloscope, and a spectrometer;
  • the acquiring the mixed laser signal through a light source receiving module, and detecting a gas component of the gas to be measured based on the mixed laser signal includes:
  • the real-time Fourier transform is performed on the mixed laser signal through the first dispersion fiber, the second fiber amplifier, the second dispersion fiber, and the third fiber amplifier in order, and the reference light and the Reflected echo signals are broadened and amplified in the time domain;
  • the reflected echo signal and the reference light after the time domain broadening and amplification enter the photodetector and the spectrometer through the coupler, and receive a part of the reflected echo signal through the photodetector and A part of the time domain interference signal of the reference pulse signal, the time domain interference signal is displayed by the oscilloscope, and a frequency domain interference diagram of another part of the reflected echo signal and another part of the reference pulse signal is received by the spectrometer.
  • the time-domain interference signal displayed by the oscilloscope is used to invert a gas component.
  • an unbalanced dispersion is achieved through the unbalanced dispersion fiber to offset the influence of the third-order dispersion on the interference fringe frequency chirp, and the frequency chirp caused by the unbalanced dispersion is used to absorb gas characteristics. Reflected in microwave frequency, complete the down conversion of optical frequency information to microwave frequency;
  • the detection method further includes: an initial optical frequency and a stop optical frequency corresponding to the interference fringes of the calibration frequency ⁇ .
  • the laser radar and the gas component detection method provided by the technical solution of the present invention introduce an unbalanced dispersion method, and the detection arm of the MZ (Mach-Zehnder) interferometer in the detection module or a reference
  • the introduction of a section of unbalanced dispersion fiber in the arm enables the MZ interferometer to generate interference fringes of frequency chirp.
  • the absorption characteristics of the detection laser after passing through the gas to be measured can be reflected in the microwave frequency spectrum of the interference fringes, and the gas absorption characteristics of the optical frequency are completed. Downconversion to microwave frequencies.
  • Coherent technology using a single frequency comb the system is simple and can be detected in real time.
  • FIG. 1 is a schematic structural diagram of a femtosecond lidar provided by an embodiment of the present invention
  • FIG. 2 is a schematic diagram illustrating the principle of real-time detection of multiple gases based on unbalanced dispersion according to an embodiment of the present invention.
  • the existing gas detection technology has large defects in real-time detection and multiple gas detections.
  • the femtosecond pulse has a high repetition frequency, the time delay required for the interference of two femtosecond pulses It must be very small, about a few hundred femtoseconds, which limits the dynamic range of measurement for femtosecond pulses.
  • dual-frequency comb interference can accurately measure the absorption characteristics of a gas in the spectral range, there are generally problems that the system is complex and cannot be detected in real time, which makes it difficult to be practically applied.
  • an unbalanced dispersion method is introduced.
  • the detection arm or reference arm of the MZ interferometer in the detection module introduces a section of unbalanced dispersion fiber, so that the MZ interferometer generates interference fringes with frequency chirp.
  • the detection laser passes the gas to be measured
  • the generated absorption characteristics can be reflected in the microwave frequency spectrum of the interference fringes, and the down-conversion of the gas absorption characteristics of the optical frequency to the microwave frequency is completed.
  • the coherent technology using a single frequency comb is simple and can be detected in real time.
  • an adjustable filter is added to the light source module, and the filtering position is set to an arbitrary detection gas absorption band, which can complete the remote sensing of any gas component in the laser spectral range, and realize a programmable real-time detection of multiple gases.
  • FIG. 1 is a schematic structural diagram of a femtosecond lidar provided by an embodiment of the present invention.
  • the lidar shown includes a light source module 100, a detection module 200, and a light source receiving module 300.
  • the light source module 100 is configured to emit a detection laser.
  • the detection module 200 includes: an M-Z interferometer 200.
  • the M-Z interferometer 200 includes a beam splitter 4, a reference arm, a detection arm, and a beam combiner 11.
  • the beam splitter 4 is configured to divide the detection laser light into a first partial laser light and a second partial laser light.
  • the beam splitter 4 has two output ends, which are respectively connected to the detection arm and the reference arm of the M-Z interferometer 200, and the two output ends of the beam splitter 4 are used to respectively emit the first part of the laser light and the second part of the laser light.
  • the detection arm and the reference arm of the M-Z interferometer 200 are respectively connected to two input ends of the combiner 11.
  • the detection arm is configured to transmit the first part of the laser to the gas to be measured, and obtain a reflection echo signal of the first part of the laser in the gas to be measured.
  • the reference arm is used to delay process the second part of the laser to form a reference light, so that the reference light and the first part of the laser have a set delay time.
  • the combiner 11 is configured to couple the reference light and the reflected echo signal into a hybrid laser signal.
  • the detection arm or the reference arm is connected to the combiner 11 through an unbalanced dispersive fiber.
  • the light source receiving module 300 is configured to acquire the mixed laser signal, and detect a gas component of the gas to be measured based on the mixed laser signal.
  • the femtosecond lidar shown in FIG. 1 introduces a section of unbalanced dispersion fiber in the detection arm or reference arm of the MZ interferometer 5 in the detection module.
  • the MZ interferometer 5 can generate frequency chirp through the method of unbalanced dispersion. Interference fringes.
  • the absorption characteristics of the detection laser after passing through the gas to be measured can be reflected in the microwave frequency spectrum of the interference fringes.
  • the gas absorption characteristics of the microwave frequencies are down-converted to the optical frequency.
  • the coherent technology using a single frequency comb is simple. , Real-time detection.
  • the light source module 100 includes a fiber femtosecond laser 1, a tunable filter 2, and a first fiber amplifier 3.
  • the output end of the fiber-optic femtosecond laser 1 is connected to the input end of the tunable filter 2.
  • the output end of the tunable filter 2 is connected to the input end of the first fiber amplifier 3.
  • An output end of the first fiber amplifier 3 is connected to an input end of the beam splitter 4.
  • the fiber-optic femtosecond laser 1 is used to emit a femtosecond laser pulse, and the femtosecond laser pulse passes through the tunable filter 2 and the first fiber amplifier 3 in sequence to form the detection laser pulse, which is incident.
  • the tunable filter 2 is added to the light source module 100, and the filtering position is set to an arbitrary detection gas absorption band, which can complete remote sensing of any gas component in the laser spectrum range, and realize a programmable real-time detection of multiple gases.
  • the detection arm includes: a fiber optic circulator 7, an optical transceiver system 8, and a fold-back mirror 9.
  • the fiber optic circulator 7 has a first port a, a second port b, and a third port c.
  • the incident first port a exits from the second port b, and the light enters the second port b and exits from the third port c.
  • the first port a of the optical fiber circulator 7 is connected to the output end of the beam splitter 4 for emitting the first part of the laser light.
  • the second port b of the optical fiber circulator 7 is connected to the input end of the optical transceiver system 8.
  • the third port c of the optical fiber circulator 7 is connected to one input end of the combiner 11 through the first optical fiber 10.
  • the first part of the laser light is used as the detection light, and is incident on the optical transceiver system 8 through the second port b. After the detection light is emitted through the optical transceiver system 8, it is incident on the gas to be measured
  • the first part of the laser light is used to enter the first port a, pass through the second port b and the optical transceiver system 8 in sequence, and then enter the gas to be measured, pass through the gas to be measured and the folding mirror. 9 After reflection, the reflected echo signal is formed.
  • the reflected echo signal enters the second port b through the optical transceiver system 8, exits through the third port c, and enters an input port of the combiner 11 through the first optical fiber 10.
  • the reference arm includes a delayer 5. An input end of the delayer 5 is connected to an output end of the beam splitter 4 for emitting a second part of laser light. The output end of the delayer 5 is connected to the other input end of the combiner 11 through the second optical fiber 6. The second part of the laser light is processed by the delayer 5 to form a delay time to form the reference light, and the reference light enters another input port of the combiner 11 through the second optical fiber 6.
  • One of the first optical fiber 10 and the second optical fiber 6 is the unbalanced dispersion optical fiber.
  • the detection arm is connected to the combiner 11 through the unbalanced dispersion fiber; when the dispersion coefficient of the unbalanced dispersion fiber is positive
  • the reference arm is connected to the combiner 11 through an unbalanced dispersion fiber.
  • the dispersion coefficient of the unbalanced dispersion fiber is negative, and the detection arm is connected to the combiner 11 through the unbalanced dispersion fiber, that is, the first fiber 10 is the unbalanced dispersion optical fiber.
  • the effect of third-order dispersion can be offset by the unbalanced dispersion fiber.
  • the light source receiving module includes: a first dispersion fiber 12, a second fiber amplifier 13, a second dispersion fiber 14, a third fiber amplifier 15, a coupler 16, a photodetector 17, an oscilloscope 18, and a spectrometer. 19.
  • the trigger signal of the fiber-optic femtosecond laser 1 is connected to an oscilloscope 18.
  • the first dispersion fiber 12, the second fiber amplifier 13, the second dispersion fiber 14, and the third fiber amplifier 15 constitute a real-time dispersion Fourier transform (time domain stretching) device.
  • An output end of the beam splitter 4 is connected to an input end of the first dispersive fiber 12.
  • An output end of the second dispersion fiber 12 is connected to an input end of the second fiber amplifier 13.
  • An output end of the second fiber amplifier 13 is connected to an input end of the second dispersion fiber 14.
  • An output end of the second dispersion fiber is connected to an input end of the third fiber amplifier 15.
  • An output end of the third fiber amplifier 15 is connected to an input port d of the coupler 16.
  • the mixed laser signal passes through the first dispersion fiber 12, the second fiber amplifier 13, the second dispersion fiber 14, and the third fiber amplifier 15 in sequence, and enters the input port d of the coupler 16.
  • the coupler 16 has two output ports e and f.
  • the output port e of the coupler 16 is connected to the photodetector 17, and the output port f of the coupler 16 is connected to the input of the spectrometer 19.
  • the spectrometer 19 is configured to obtain the reflected echo signal and the reference light after a part of the output of the coupler 16 corresponding to the output port e is time-domain widened.
  • the photodetector 17 obtains the reflected echo signal and the reference light after time-domain widening and amplification of another part of the output of the corresponding output port f of the coupler 16, and acquires the reflected echo signal and The reference light is sent to the oscilloscope 18.
  • the femtosecond lidar adopts real-time dispersion Fourier transform and design of introducing unbalanced dispersion in the MZ interferometer 5 as a detection characteristic of gas absorption.
  • the key lies in the reflected echo signal and reference optical beat frequency after unbalanced dispersion.
  • the signal is a microwave interference fringe with frequency chirp, and the gas absorption characteristics can be reflected in the interference fringe.
  • a microwave frequency comb containing the gas absorption characteristics can be obtained, and the microwave with the absorption characteristics of the optical frequency is completed. Frequency down conversion.
  • Coherent technology using a single femtosecond laser the system is simple and can be detected in real time.
  • the repetition frequency of the femtosecond pulse is 100 MHz, and a time-domain interference pattern can be detected every 10 ns, thereby realizing high-speed detection of gas components.
  • the dual-frequency comb interference although the gas absorption characteristics in the microwave frequency correspond to the optical frequency information after the interference, the dual-frequency comb interference system is complex and cannot be detected in real time.
  • the tunable filter 2 is added to the light source module 100, and the absorption band of the gas to be measured can be selected for filtering, and the real-time detection of each gas can be completed by adjusting the filtering position for multiple gases.
  • the laser radar described in the embodiment of the present invention is a femtosecond laser radar based on unbalanced dispersion, and can perform detection of various gases.
  • the laser radar according to the embodiment of the present invention introduces an unbalanced dispersion method based on the femtosecond laser ultra-fast ranging work, so that the interference fringes of the MZ interferometer 5 generate chirped microwaves. Frequency, the absorption characteristics of the detection gas will be reflected in the microwave frequency of the interference signal.
  • Real-time detection of gas components can be achieved by Fourier transform after receiving the time-domain interference signal.
  • an adjustable filter is added to select the absorption band of any gas to be measured for filtering, which can complete the real-time detection of multiple gases in the laser spectral range.
  • FIG. 2 is a schematic diagram of the principle of real-time detection of multiple gases based on unbalanced dispersion according to an embodiment of the present invention.
  • Light signal patterns at B, C, and D positions are a schematic diagram of the principle of real-time detection of multiple gases based on unbalanced dispersion according to an embodiment of the present invention.
  • FIG. 2A is a schematic diagram of a femtosecond laser spectrum and pulse of a light source module.
  • the vertical axis is amplitude
  • the horizontal axis on the left is frequency
  • the horizontal axis on the right is time t.
  • the laser emitted by the fiber-optic femtosecond laser enters the detection arm and reference arm of the MZ interferometer after filtering and pulse amplification.
  • the filtered and amplified spectrum is represented as F FBG (f).
  • the signal light is collimated into the air and reflected in the light.
  • the spectrum of the reflected signal light is the convolution of the filtered and amplified spectrum and the gas absorption spectrum:
  • FIG. 2B A schematic diagram of the spectrum of the reflected signal light and the reference light is shown in FIG. 2B.
  • the vertical axis is the amplitude and the horizontal axis is the frequency.
  • the reflected light is mixed with the delayed reference light after passing through the unbalanced dispersive fiber, and the mixed light enters the real-time dispersion Fourier transform device to complete the "time-frequency mapping".
  • the correspondence between the time-domain pulse and the frequency-domain signal is shown in Figure 2C.
  • the vertical axis is frequency and the horizontal axis is time. Due to the effect of non-equilibrium dispersion, the broadening of the reflected light pulse in the time domain is slightly wider, and the time-frequency relationship between the reflected light and the reference light is expressed as:
  • ⁇ 2 represents group velocity dispersion
  • ⁇ 3 represents third-order dispersion
  • L is a dispersion fiber length in a real-time dispersion Fourier transform device
  • ⁇ L is an unbalanced dispersion fiber length
  • ⁇ t is an MZ interferometer reference arm delay.
  • the non-equilibrium dispersion causes the reflected signal light to broaden slightly in the time domain
  • the third-order dispersion makes the time-frequency mapping relationship between the reflected signal light and the reference light non-linear, but This third-order dispersion-induced non-linearity can be offset by non-equilibrium dispersion.
  • the signal light and the reference light interfere with each other on the photodetector after the real-time dispersion Fourier transform device.
  • the interference fringe is a microwave frequency signal, and its frequency spectrum is expressed as Schematic diagrams of interference fringes in the time and frequency domains are shown in Figure 2D.
  • the time-frequency relationship between the two can be derived from f s and f r .
  • the vertical axis is frequency and the horizontal axis is time.
  • the interference fringes contain microwave frequency information of chirp.
  • the time-domain interference fringes are obtained by Fourier transform in the microwave frequency domain. Frequency comb, the absorption characteristics of the gas to be measured can be reflected in the microwave frequency comb, and the gas absorption characteristics of the optical frequency comb are converted to the microwave frequency comb.
  • the time-domain interferogram shown in FIG. 2D is subjected to a fast Fourier transform to obtain a microwave frequency comb.
  • the deconvolution algorithm can be used to obtain the performance of gas absorption characteristics at the microwave frequency F gas (rf).
  • the corresponding relationship between the fringe microwave frequency and the optical frequency yields the gas absorption spectrum F gas (f).
  • the gas absorption spectrum is compared with the gas absorption characteristics in the HITRAN database to accurately obtain the gas component to be measured.
  • the present invention collects time-domain interference fringes after real-time dispersion Fourier transform and inverts gas components. This detection method is real-time.
  • a tunable filter is added to the light source module. By selecting the filtering position, the absorption characteristics of multiple gases can be selectively detected, and a programmable real-time detection of multiple gas components is realized.
  • This solution uses real-time dispersion Fourier transform (time domain stretching) and MZ interferometer to introduce non-equilibrium dispersion as a method for detecting gas absorption characteristics.
  • the key point is the detection of gas absorption characteristics after non-equilibrium dispersion.
  • the light and reference light beat frequency signals are microwave interference fringes of frequency chirp, and the gas absorption characteristics can be reflected in the interference fringes.
  • a microwave frequency comb containing gas absorption characteristics can be obtained, and the optical frequency is completed. The down-conversion of the absorption characteristics to microwave frequencies.
  • the femtosecond laser has a high repetition frequency of 100 MHz, a time-domain interference pattern can be obtained every 10 ns, and real-time gas component detection can be achieved.
  • a tunable filter is added to the light source module, and the absorption band of the gas to be measured can be selected for filtering, which can complete real-time remote sensing of any gas component in the laser spectrum range.
  • another embodiment of the present invention further provides a gas component detection method.
  • the detection method is used in a laser radar as shown in FIG. 1.
  • the detection method includes:
  • Step S11 the detection laser is emitted through the light source module 100.
  • the light source module 100 includes a fiber femtosecond laser 1, a tunable filter 2, and a first fiber amplifier 3.
  • the detecting laser light emitted through the light source module 100 includes: emitting a femtosecond laser pulse through the fiber femtosecond laser 1 and performing spectral band selection through the tunable filter 2.
  • spectral band selection tunable filtering
  • the location includes at least one location of a gas absorption feature. When there are locations with multiple gas absorption characteristics, multiple gas component detection can be achieved.
  • the technical solution described in the embodiments of the present invention can be used for the detection of gas isotopes.
  • the laser pulse selected in the spectral band enters the first fiber amplifier 3 for pulse amplification to form the detection laser, and the detection laser emitted by the first fiber amplifier 3 enters the beam splitter 4.
  • Step S12 The detection laser is divided into a first part laser and a second part laser by the detection module 200.
  • the detection module 200 includes an M-Z interferometer 200; the M-Z interferometer 200 includes a beam splitter 4, a detection arm, a reference arm, and a beam combiner 11. In this step, the detection laser is divided into a first partial laser and a second partial laser by the beam splitter 4.
  • Step S13 transmitting the first part of the laser to the gas to be measured through the detecting arm, obtaining a reflected echo signal of the first part of the laser in the gas to be measured, and passing the second part through the reference arm
  • the laser performs delay processing to form reference light, so that the reference light and the first part of the laser have a set delay time.
  • the detection arm or the reference arm is connected to the combiner through an unbalanced dispersion fiber.
  • the detection arm includes: a fiber optic circulator 7, an optical transceiver system 8, and a fold-back mirror 9.
  • the fiber optic circulator 7 has a first port a, a second port b, and a third port c, and light enters the incident first port. a, exiting from the second port b, light entering the second port b, and exiting c from the third port; the reference arm includes a delayer 6.
  • the first part of the laser is transmitted to the gas to be measured by the detecting arm, and the reflected echo signal of the first part of the laser in the gas to be measured is obtained, and the The second part of the laser delay processing to form the reference light includes:
  • the first part of the laser light is used to enter the first port a, pass through the second port b and the optical transceiver system 8 in sequence, and then enter the gas to be measured, pass through the gas to be measured and the reentry After the reflection from the mirror 9, the reflected echo signal is formed.
  • the reflected echo signal is obtained through the optical transceiver system 8, and the reflected echo signal is sent to the second port b and passes through the third port.
  • c is emitted and enters an input port of the combiner 11 through the first optical fiber 10; the reflected echo signal includes an absorption characteristic of the gas to be measured;
  • the delay time is applied to the second part of the laser light through the delayer 5 to form the reference light, and the reference light enters another input port of the combiner 11 through the second optical fiber 6.
  • One of the first optical fiber 10 and the second optical fiber 6 is set as an unbalanced dispersion fiber according to the dispersion coefficient of the unbalanced dispersion fiber.
  • the unbalanced dispersion fiber has an unbalanced dispersion effect, and the influence of the third-order dispersion on the interference fringes frequency chirp can be offset by the unbalanced dispersion, and the frequency chirp caused by the unbalanced dispersion is used to reflect the gas absorption characteristics in the microwave frequency.
  • Step S14 coupling the reference light and the reflected echo signal into a hybrid laser signal through the combiner 11.
  • one of the first optical fiber 10 and the second optical fiber 6 is set as an unbalanced dispersion optical fiber.
  • Step S15 Obtain the mixed laser signal through the light source receiving module 300, and detect a gas component of the gas to be measured based on the mixed laser signal.
  • the light source receiving module 300 includes: a first dispersion fiber 12, a second fiber amplifier 13, a second dispersion fiber 14, a third fiber amplifier 15, a coupler 16, a photodetector 17, an oscilloscope 18, and a spectrometer 19.
  • the combiner 11 emits the mixed laser signal and enters the first dispersive optical fiber 12.
  • the first dispersion fiber 12, the second fiber amplifier 13, the second dispersion fiber 14, and the third fiber amplifier 15 constitute a real-time Fourier transform device.
  • the acquiring the mixed laser signal through the light source receiving module 300, and detecting a gas component of the gas to be measured based on the mixed laser signal includes:
  • the mixed laser signal is sequentially passed through the first dispersion fiber 12, the second fiber amplifier 13, the second dispersion fiber 14, and the third fiber amplifier 15 in real-time Fourier transform to convert the
  • the reference light and the reflected echo signal are broadened and amplified in the time domain;
  • the hybrid laser signal passes through a real-time Fourier transform device, and the reflected echo signal and the reference light are broadened and amplified in the time domain.
  • the reflected echo signal is due to Affected by unbalanced dispersion, it is used for slightly wider time-domain expansion, and the real-time "time-frequency mapping" is performed on the time-domain signal and frequency-domain signal after real-time Fourier transform.
  • the reflected echo signal and the reference light after the time domain broadening and amplification are caused to enter the photodetector 17 and the spectrometer 19 through the coupler 16 and receive a part of the photodetector 17 through the photodetector 17.
  • the time-domain interference signal of the reflected echo signal and a part of the reference pulse signal is displayed by the oscilloscope 18, and the other part of the reflected echo signal and the other part are received by the spectrometer 19
  • the frequency domain interferogram of the reference pulse signal is used to calibrate the time-frequency conversion equation.
  • the time-domain interference signal shown in 18 is used to invert a gas component.
  • the time domain interference signal displayed by the oscilloscope 18 is used for the inversion of gas composition information.
  • the frequency spectrum of the signal is at the microwave frequency. After the Fourier transform, the microwave frequency information is obtained. After the microwave frequency information corresponds to the optical frequency information, the gas characteristics can be inverted.
  • the optical frequency information containing the gas absorption characteristic is a convolution of the signal filtered by the filter 2 and the gas absorption characteristic signal, and the gas absorption characteristic signal is obtained by deconvolution.
  • the unbalanced dispersion fiber is used to achieve unbalanced dispersion to offset the influence of the third-order dispersion on the interference fringe frequency chirp, and the frequency chirp caused by the unbalanced dispersion is used to absorb the gas.
  • the characteristics are reflected in the microwave frequency.
  • the microwave frequency comb information is obtained, and the down-conversion of the optical frequency information to the microwave frequency information is completed.
  • the detection method further includes: an initial optical frequency and an ending optical frequency corresponding to the interference fringes of the calibration frequency ⁇ .
  • the time delay is adjusted, and the start frequency and end frequency of the optical signal corresponding to the start frequency and stop frequency of the interferogram are calibrated according to the delay time and the time-frequency conversion equation; finally, the gas in the microwave frequency comb is absorbed according to the calibration relationship.
  • the characteristics are converted into the optical frequency, and the obtained gas absorption characteristics are compared with the HITRAN database to complete the detection of gas components.
  • the gas detection method can be realized by the above-mentioned laser radar.
  • the gas detection method introduces an unbalanced dispersion method based on the ultra-fast distance measurement of femtosecond lasers, so that the interference fringes of the MZ interferometer 200 generate a chirped microwave frequency.
  • the absorption characteristics of the detection gas will be reflected in the microwave frequency of the interference signal, and the real-time detection of the gas component can be completed by receiving the time-domain interference signal.
  • an adjustable filter is added to select the absorption band of any gas to be measured for filtering, which can complete the real-time detection of multiple gases in the laser spectral range.

Abstract

L'invention concerne un radar laser femtoseconde et un procédé de détection de composition de gaz. Selon le procédé, un procédé de dispersion hors équilibre est introduit. Une fibre de dispersion hors équilibre est introduite dans un bras de détection ou un bras de référence d'un interféromètre M-Z dans un module de détection (200), de telle sorte que l'interféromètre M-Z génère des franges d'interférence à compression de fréquence. La détection de caractéristiques d'absorption générées par le laser après avoir traversé le gaz à détecter peut être mise en œuvre dans un spectre de fréquences micro-ondes des franges d'interférence, afin de réaliser la conversion descendante de caractéristiques d'absorption de gaz dans une fréquence optique vers une fréquence micro-ondes. L'état antérieur associé d'un peigne à fréquence unique est adopté, le système est simple, et la détection en temps réel peut être effectuée.
PCT/CN2018/096791 2018-07-24 2018-07-24 Radar laser femtoseconde et procédé de détection de composition de gaz WO2020019153A1 (fr)

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