A dual-modulation absorption spectroscopy gas detection system and method based on optical frequency comb

Abstract

The application discloses a kind of based on optical frequency comb two-stage modulation absorption spectrum gas detection system and method, facing multi-component gas sensing needs, with optical frequency comb ultrafast pulse as switch modulation, with ultra-narrow linewidth phase shift grating by PZT micro-displacement device selectively implement target waveband narrowband wavelength tuning for specific probe gas, realize the high sensitivity detection of gas concentration, with the characteristics of strong detection specificity, wide broadband spectrum gas coverage, overcome the limitation of traditional TDLAS technology multi-component gas sensing technology, solve the existing optical frequency comb broadband spectrum detection existing system optical path structure complex, long time continuous detection stability requirement is extremely high, broadband spectrum scanning efficiency is low and noisy, easily interfered by low frequency etc., realize high sensitivity, multi-component gas laser spectrum detection.

Description

Technical Field

[0001] This invention belongs to the field of laser spectroscopy gas sensing technology, and particularly relates to a dual-level modulation absorption spectroscopy gas detection system and method based on optical frequency comb. Background Technology

[0002] Tunable diode laser absorption spectroscopy (TDLAS) gas sensing technology primarily uses a tunable semiconductor laser as the light source. By applying a periodically scanning drive signal to adjust the operating temperature and drive current, the output wavelength is tuned, enabling complete measurement of the target gas absorption spectrum. To further improve the concentration detection sensitivity of TDLAS, wavelength modulation spectroscopy (WMS) superimposes high-frequency modulation on a low-frequency wavelength scanning signal to achieve ultra-trace gas sensing, and has been widely used in atmospheric monitoring, combustion diagnostics, industrial safety assurance, and chemical analysis. However, due to the limitation of the narrow linewidth laser's wavelength tuning range, TDLAS typically only supports wavelength scanning covering one or two molecular spectral lines, and cannot complete the detection of multi-component gases, becoming a significant bottleneck restricting its application.

[0003] Optical frequency combs, as a novel broadband laser source, possess highly coherent broadband laser characteristics, providing strong support for multi-component detection. Currently, broadband gas absorption spectroscopy techniques based on optical frequency combs include three categories: spatial dispersive spectroscopy, Michelson interferometric Fourier transform spectroscopy, and dual-comb spectroscopy. Although numerous reports have continuously demonstrated the high-precision and rapid gas spectral measurement capabilities of these three techniques, achieving stable and rapid broadband detection requires sophisticated optical instruments and highly complex optical path structures, placing extremely high demands on system stability. Therefore, related research often remains at the verification acquisition stage of broadband spectra, and long-term, stable, and continuous online gas concentration measurement is still not achievable. Furthermore, gas detection methods based on direct acquisition of broadband absorption spectra also require the simultaneous acquisition of unabsorbed spectral signals as background spectra to complete gas concentration calculations, increasing system complexity. Sensitivity is also difficult to further improve due to noise and frequency drift. Summary of the Invention

[0004] The purpose of this invention is to provide a dual-level modulation absorption spectroscopy gas detection system and method based on optical frequency combs. It addresses the needs of multi-component gas sensing, overcomes the limitations of traditional TDLAS technology for multi-component gas sensing, and solves the problems of complex optical path structure, extremely high stability requirements for long-term continuous detection, low broadband spectral scanning efficiency and high noise, and susceptibility to low-frequency interference in existing optical frequency comb broadband spectral detection. It achieves highly sensitive laser spectral detection of multi-component gases.

[0005] According to a first aspect of the embodiments of this application, a dual-level modulation absorption spectroscopy gas detection system based on an optical frequency comb is provided, comprising:

[0006] An optical frequency comb light source is used to generate pulsed lasers with a broadband spectrum as the first-stage high-frequency switching modulation.

[0007] The ultra-narrowband wavelength tuning module includes a pre-tunable filter, a phase-shifting fiber grating, and a PZT micro-displacer. The combination of the pre-tunable filter and the phase-shifting fiber grating is used to select an ultra-narrow linewidth mode of a specific wavelength in the spectrum of the optical frequency comb source. The PZT micro-displacer provides the phase-shifting fiber grating with a corresponding wavelength scanning frequency and wavelength modulation frequency, thereby forming a second-stage intermediate frequency wavelength modulation and outputting an ultra-narrow linewidth probe laser.

[0008] The gas detection optical path is used to realize the interaction between the ultra-narrow linewidth detection laser and the gas to be measured, thereby generating a transmitted pulsed laser.

[0009] A photodetector is used to receive the transmitted pulsed laser and convert it into an electrical pulse signal;

[0010] The first-stage signal demodulation module is used to demodulate the electrical pulse signal by the first-stage high-frequency switching modulation and output an electrical pulse intensity characterization signal.

[0011] The second-stage signal demodulation module is used to demodulate the electrical pulse intensity characterization signal by the second-stage intermediate frequency wavelength modulation, and output a second harmonic spectrum signal characterizing the gas concentration; and

[0012] The calculation module is used to calculate the concentration of the gas to be measured based on the second harmonic spectrum signal.

[0013] Furthermore, for time-division multiplexing detection of multi-component gases, the ultra-narrowband wavelength tuning module includes a pre-tunable filter, several phase-shifting fiber gratings, and a PZT micro-displacer. The wavelength of each phase-shifting fiber grating corresponds to the center wavelength of the absorption spectrum of a gas. The combination of the pre-tunable filter and the phase-shifting fiber grating is used to select an ultra-narrow linewidth mode of a specific wavelength in the spectrum of the optical frequency comb source. Each phase-shifting fiber grating is attached to the side surface of the PZT micro-displacer. The PZT micro-displacer provides the corresponding wavelength scanning frequency and wavelength modulation frequency, thereby applying intermediate frequency wavelength modulation to form a second-stage intermediate frequency wavelength modulation.

[0014] Furthermore, for frequency division multiplexing detection of multi-component gases, the ultra-narrowband wavelength tuning module includes an optical fiber beam splitter, an optical fiber coupler, and a combination of several pre-tunable filters, phase-shifting fiber gratings, and PZT micro-displacers. The optical fiber beam splitter divides the pulsed laser into several beams. In each combination, the wavelength of the phase-shifting fiber grating corresponds to the center wavelength of the absorption spectrum of a gas. The combination of the pre-tunable filter and the phase-shifting fiber grating is used to select an ultra-narrow linewidth mode of a specific wavelength in the spectrum of the optical frequency comb source. The phase-shifting fiber grating is attached to the side surface of the corresponding PZT micro-displacer, which provides the corresponding wavelength scanning frequency and wavelength modulation frequency to apply intermediate frequency wavelength modulation, forming a second-stage intermediate frequency wavelength modulation. The optical fiber coupler is used to couple the optical signals output by each phase-shifting fiber grating to the gas detection optical path.

[0015] Furthermore, the first-stage signal demodulation module includes a mixer, a radio frequency signal generator, and a first lock-in amplifier. The radio frequency signal generator provides a standard frequency signal, the mixer beats the electrical pulse signal to generate a difference frequency signal, and the first lock-in amplifier extracts the first harmonic amplitude of the difference frequency signal, thereby obtaining the corresponding electrical pulse intensity characterization signal.

[0016] Furthermore, the second-stage signal demodulation module is a second lock-in amplifier, used to extract the second harmonic amplitude corresponding to the second-stage intermediate frequency wavelength modulation frequency.

[0017] Furthermore, it also includes a data acquisition card, which is used to acquire the second harmonic spectrum signal output by the second-stage signal demodulation module, convert it into a digital signal, and output it to the calculation module.

[0018] Furthermore, it also includes a PZT controller, which is used to drive the PZT micro-displacement device to generate micro-displacement according to the drive signal provided by the data acquisition card, wherein the drive signal is a superposition signal of scanning sawtooth wave and modulated sine wave.

[0019] According to a second aspect of the embodiments of this application, a two-level modulation absorption spectroscopy gas detection method based on an optical frequency comb is provided, applied to the system described in the first aspect, the method comprising:

[0020] (1) Corresponding to a specific gas molecule spectral line, the ultra-narrow band wavelength tuning module selects an ultra-narrow linewidth mode from the optical frequency comb light source; the phase-shifted fiber grating is provided with a corresponding wavelength scanning frequency and wavelength modulation frequency through the PZT micro-displacer to form a second-level intermediate frequency wavelength modulation, and the phase-shifted fiber grating outputs an ultra-narrow linewidth probe laser.

[0021] (2) The photodetector converts the transmitted pulse laser generated by the interaction between the ultra-narrow linewidth detection laser and the gas to be measured in the gas detection optical path into an electrical pulse signal;

[0022] (3) The first-stage signal demodulation module demodulates the electrical pulse signal by performing the first-stage high-frequency switching modulation and outputs an electrical pulse intensity characterization signal, wherein the pulsed laser output by the optical frequency comb light source is used as the first-stage high-frequency switching modulation.

[0023] (4) The second-stage signal demodulation module demodulates the second-stage intermediate frequency wavelength modulation of the electrical pulse intensity characterization signal and outputs the second harmonic spectrum signal characterizing the gas concentration.

[0024] (5) The calculation module calculates the target gas concentration based on the collected second harmonic signal.

[0025] Furthermore, in the time-division multiplexing detection mode, the ultra-narrowband wavelength tuning module includes a pre-tunable filter and n phase-shift fiber Bragg gratings. G 1. G 2、…、 G n A PZT micro-displacer, the phase-shifted fiber grating G 1. G 2、…、 G n Series and parallel attachments are placed on the side of the PZT micro-displacement device, respectively at wavelengths l 1. l 2、…、 l n At the same time, there is an ultra-narrow transmission window, corresponding to the gas. g 1. g 2、…、 g n The position of the absorption spectral line;

[0026] Based on step (1), the working wavelength of the pre-tunable filter is automatically adjusted at time intervals to align with the corresponding absorption spectral line position of the gas to be measured in a time-division multiplexing manner, and scanned and modulated using a PZT micro-displacement device. Steps (2)-(5) are executed for each gas in a time-division manner to achieve quasi-synchronous measurement of multi-component gases.

[0027] Furthermore, in the frequency division multiplexing detection mode, the ultra-narrowband wavelength tuning module includes a tunable filter. F 1. F 2、…、 F n Phase-shifted fiber gratings G 1. G 2、…、 G nand PZT micro-displacement device T 1. T 2、…、 T n Each tunable filter, phase-shifted fiber grating, and PZT micro-displacer is combined to form an ultra-narrow linewidth modulation signal channel. The output optical signal of the optical frequency comb source is evenly split into n parts and guided through optical fibers into the n channels of the ultra-narrowband wavelength tuning module. Each channel is tuned at a specific wavelength. l 1. l 2、…、 l n The output narrow linewidth modulated probe light is coupled into the gas detection optical path for gas detection; steps (2)-(5) are executed simultaneously in n ultra-narrow linewidth modulated signal channels to synchronously acquire the concentrations of multiple gases.

[0028] The technical solutions provided by the embodiments of this application may include the following beneficial effects:

[0029] 1) Based on the optical frequency comb light source, using ultra-narrow linewidth phase-shifted fiber optic gratings, narrowband wavelength tuning of the target band is selectively implemented for specific probe gases to achieve high-sensitivity detection of gas concentration. It has the characteristics of strong detection specificity and wide coverage of broadband spectral gas range. It can achieve rapid synchronous measurement of multi-component gases through time-division / frequency-division multiplexing.

[0030] 2) The system uses ultrafast pulses from an optical frequency comb as switching modulation and uses an ultranarrow linewidth phase-shifting grating with the help of a PZT micro-displacer to achieve narrow linewidth laser wavelength modulation. It features high spectral scanning efficiency, fast response speed, high sensitivity, and high signal-to-noise ratio.

[0031] 3) The system proposed in this invention uses only optical fibers and electrical signal lines to connect the modules. The system has a simple optical path structure and features strong anti-interference ability and good stability.

[0032] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0033] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0034] Figure 1 This is a block diagram of a dual-level modulation absorption spectroscopy gas detection system based on an optical frequency comb, as shown in Example 1.

[0035] Figure 2 This is a schematic flowchart of the multi-component gas time-division multiplexing detection method in Example 1;

[0036] Figure 3 This is a block diagram of a dual-level modulation absorption spectroscopy gas detection system based on an optical frequency comb, as shown in Example 2.

[0037] Figure 4 This is a schematic flowchart of the multi-component gas frequency division multiplexing detection method in Example 2.

[0038] The attached diagram is labeled as follows: 1. Optical frequency comb light source; 2. Ultra-narrowband wavelength tuning module; 201. Fiber optic beam splitter; 202. Fiber optic coupler; 21. First pre-tunable filter; 211. Second pre-tunable filter; 212. Third pre-tunable filter; 22. First phase-shift fiber optic grating; 23. Second phase-shift fiber optic grating; 24. Third phase-shift fiber optic grating; 25. First PZT micro-displacement device; 251. Second PZT micro-displacement device; 252. Third PZT micro-displacement device; 3. Gas detection optical path; 4. Photodetector; 5. First-stage signal demodulation module; 51. Mixer; 52. RF signal generator; 53. First lock-in amplifier; 6. Second-stage signal demodulation module; 61. Second lock-in amplifier; 7. Data acquisition card; 8. Calculation module; 9. PZT controller. Detailed Implementation

[0039] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0040] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0041] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0042] This application provides a two-stage modulation absorption spectroscopy gas detection system based on an optical frequency comb, comprising: an optical frequency comb light source 1 for generating pulsed laser with a broadband spectrum as the first-stage high-frequency switching modulation; and an ultra-narrowband wavelength tuning module 2, including a pre-tunable filter, a phase-shifting fiber grating, and a PZT micro-displacement device. The combination of the pre-tunable filter and the phase-shifting fiber grating is used to select an ultra-narrow linewidth mode of a specific wavelength in the spectrum of the optical frequency comb light source 1. The PZT micro-displacement device provides the phase-shifting fiber grating with a corresponding wavelength scanning frequency and wavelength modulation frequency, thereby forming a second-stage intermediate-frequency wavelength modulation and outputting an ultra-narrow linewidth detection laser. The system comprises: a volume detection optical path 3, used to realize the interaction between the ultra-narrow linewidth detection laser and the gas to be measured, generating a transmitted pulse laser; a photodetector 4, used to receive the transmitted pulse laser and convert it into an electrical pulse signal; a first-stage signal demodulation module 5, used to demodulate the electrical pulse signal by performing the first-stage high-frequency switching modulation, and outputting an electrical pulse intensity characterization signal; a second-stage signal demodulation module 6, used to demodulate the electrical pulse intensity characterization signal by performing the second-stage intermediate-frequency wavelength modulation, and outputting a second harmonic spectrum signal characterizing the gas concentration; and a calculation module 8, used to calculate the concentration of the gas to be measured based on the second harmonic spectrum signal.

[0043] Specifically, the optical frequency comb light source 1 is a broadband laser light source with a repetition frequency of f r Output femtosecond-level ultrashort laser pulses, f r Typically ranging from tens to hundreds of megahertz; in the frequency domain, this is represented by equal frequency intervals. f r Several narrow linewidth laser patterns are arranged.

[0044] Specifically, the ultra-narrowband wavelength tuning module 2 can be configured as a set of pre-tunable filters, phase-shift fiber gratings, and PZT micro-displacers to perform single-component gas detection; the ultra-narrowband wavelength tuning module 2 can also be configured as a combination of several pre-tunable filters, several phase-shift fiber gratings, and several PZT micro-displacers to perform multi-component gas detection.

[0045] In one embodiment, for time-division multiplexing detection of multi-component gases, the ultra-narrowband wavelength tuning module 2 includes a pre-tunable filter, several phase-shift fiber gratings, and a PZT micro-displacer. The wavelength of each phase-shift fiber grating corresponds to the center wavelength of the absorption spectrum of a gas. The combination of the pre-tunable filter and the phase-shift fiber gratings is used to select an ultra-narrow linewidth mode of a specific wavelength in the spectrum of the optical frequency comb light source 1. Each phase-shift fiber grating is attached to the side surface of the PZT micro-displacer. The PZT micro-displacer provides the corresponding wavelength scanning frequency and wavelength modulation frequency, thereby applying intermediate frequency wavelength modulation to form a second-stage intermediate frequency wavelength modulation.

[0046] In another embodiment, for frequency division multiplexing detection of multi-component gases, the ultra-narrowband wavelength tuning module 2 includes an optical fiber beam splitter 201, an optical fiber coupler 202, and a combination of several pre-tunable filters, phase-shifting fiber gratings, and PZT micro-displacers. The optical fiber beam splitter 201 divides the pulsed laser into several beams. In each combination, the wavelength of the phase-shifting fiber grating corresponds to the center wavelength of the absorption spectrum of a gas. The combination of the pre-tunable filter and the phase-shifting fiber grating is used to select an ultra-narrow linewidth mode of a specific wavelength in the spectrum of the optical frequency comb light source 1. The phase-shifting fiber grating is attached to the side surface of the corresponding PZT micro-displacer, which provides the corresponding wavelength scanning frequency and wavelength modulation frequency to apply intermediate frequency wavelength modulation, forming a second-stage intermediate frequency wavelength modulation. The optical fiber coupler 202 is used to couple the optical signals output by each phase-shifting fiber grating to the gas detection optical path 3.

[0047] Specifically, the gas detection optical path 3 can be a long-path gas absorption cell or a hollow-core photonic crystal fiber, etc., to achieve full interaction between the gas to be measured and the ultra-narrow linewidth detection laser.

[0048] In specific implementations, the photodetector 4 is selected based on different absorption spectra and modulation bandwidths.

[0049] Specifically, the first-stage signal demodulation module 5 includes a mixer 51, an RF signal generator 52, and a first lock-in amplifier 53, used for demodulating the first-stage high-frequency switching modulation of the system, that is, extracting the pulse amplitude of the electrical pulse signal to obtain a pulse intensity characterization signal. The RF signal generator 52 provides a standard frequency signal, the mixer 51 beats the electrical pulse signal to generate a difference frequency signal, and the first lock-in amplifier 53 extracts the first harmonic amplitude of the difference frequency signal, thereby obtaining the corresponding electrical pulse intensity characterization signal.

[0050] The pulse intensity characterization signal is obtained as follows: the radio frequency signal generator 52 outputs a radio frequency sine wave signal with a frequency of... f r + δf r That is, the pulse repetition frequency differs from that of the optical frequency comb light source 1. δf r This is called the local oscillator signal; the local oscillator signal is mixed with the electrical pulse signal output by the photodetector 4 through the mixer 51 to generate a beat frequency, and the resulting frequency is the difference frequency. d f r The electrical pulse down-frequency signal; the first lock-in amplifier 53 extracts the frequency corresponding to the difference frequency from the electrical pulse down-frequency signal. δfr The first harmonic signal is used as the pulse intensity characterization signal.

[0051] Specifically, the second-stage signal demodulation module 6 is a second lock-in amplifier 61, used to extract the second harmonic amplitude corresponding to the second-stage intermediate frequency wavelength modulation frequency.

[0052] Specifically, the system may also include a data acquisition card 7, which is used to acquire the second harmonic spectrum signal output by the second-stage signal demodulation module 6, convert it into a digital signal and output it to the calculation module 8.

[0053] Specifically, the system may also include a PZT controller 9, which is used to drive the PZT micro-displacement device to generate micro-displacement according to the drive signal provided by the data acquisition card 7. The drive signal is a superposition signal of a scanning sawtooth wave and a modulated sine wave. The data acquisition card 7 may also be used to provide the second harmonic signal of the modulated sine wave to the second-stage signal demodulation module 6 as a demodulation reference.

[0054] This application also provides a two-stage modulation absorption spectroscopy gas detection method based on an optical frequency comb, applied to the above-mentioned system, which may include:

[0055] (1) Corresponding to a specific gas molecule spectral line, the ultra-narrow band wavelength tuning module 2 selects an ultra-narrow linewidth mode from the optical frequency comb light source 1; the phase-shifted fiber grating is provided with a corresponding wavelength scanning frequency and wavelength modulation frequency through the PZT micro-displacer to form a second-level intermediate frequency wavelength modulation, and the phase-shifted fiber grating outputs an ultra-narrow linewidth probe laser.

[0056] (2) The photodetector 4 converts the transmitted pulse laser generated by the interaction between the ultra-narrow linewidth detection laser and the gas to be tested in the gas detection optical path 3 into an electrical pulse signal;

[0057] (3) The first-stage signal demodulation module 5 demodulates the electrical pulse signal by performing the first-stage high-frequency switching modulation and outputs an electrical pulse intensity characterization signal, wherein the pulsed laser output by the optical frequency comb light source 1 serves as the first-stage high-frequency switching modulation.

[0058] (4) The second-stage signal demodulation module 6 demodulates the second-stage intermediate frequency wavelength modulation of the electrical pulse intensity characterization signal and outputs the second harmonic spectrum signal characterizing the gas concentration.

[0059] (5) The calculation module 8 calculates the target gas concentration based on the collected second harmonic signal.

[0060] Specifically, in time-division multiplexing detection mode, the ultra-narrowband wavelength tuning module 2 includes a pre-tunable filter and n phase-shift fiber Bragg gratings.G 1. G 2、…、 G n A PZT micro-displacer. The phase-shifting fiber grating. G 1. G 2、…、 G n Series and parallel attachments are placed on the side of the PZT micro-displacement device, respectively at wavelengths l 1. l 2、…、 l n At the same time, there is an ultra-narrow transmission window, corresponding to the gas. g 1. g 2、…、 g n The position of the absorption spectral line;

[0061] Based on step (1), the working wavelength of the pre-tunable filter is automatically adjusted at time intervals to align with the corresponding absorption spectral line position of the gas to be measured in a time-division multiplexing manner, and scanned and modulated using a PZT micro-displacement device. Steps (2)-(5) are executed for each gas in a time-division manner to achieve quasi-synchronous measurement of multi-component gases.

[0062] Specifically, in the frequency division multiplexing detection mode, the ultra-narrowband wavelength tuning module 2 includes a tunable filter. F 1. F 2、…、 F n Phase-shifted fiber gratings G 1. G 2、…、 G n and PZT micro-displacement device T 1. T 2、…、 T n Each tunable filter, phase-shifted fiber grating, and PZT micro-displacer is combined to form an ultra-narrow linewidth modulation signal channel. The output optical signal of the optical frequency comb source 1 is evenly split into n parts and guided through optical fibers to the n channels of the ultra-narrowband wavelength tuning module 2. Each channel is tuned to a specific wavelength. l 1. l 2、…、 l n The output narrow linewidth modulated probe light is coupled into the gas detection optical path 3 for gas detection.

[0063] Steps (2)-(5) are executed simultaneously in n ultra-narrow linewidth modulation signal channels to synchronously acquire the concentrations of multiple gases.

[0064] The time-division multiplexing detection and frequency-division multiplexing detection of multi-component gases are described below with reference to specific examples.

[0065] Example 1

[0066] Embodiment 1 of this application illustrates a dual-level modulation absorption spectroscopy gas detection system based on an optical frequency comb, which possesses time-division multiplexing multi-component detection capability. (Reference) Figure 1 As shown, the system includes: an optical frequency comb light source 1, an ultra-narrowband wavelength tuning module 2, a gas detection optical path 3, a photodetector 4, a first-stage signal demodulation module 5, a second-stage signal demodulation module 6, a data acquisition card 7, a computing module 8, and a PZT controller 9.

[0067] In this embodiment, the optical frequency comb light source 1 is based on the principle of a mode-locked femtosecond fiber laser, with a pulse repetition frequency of approximately 41.7 MHz and an output spectrum covering 1520 ~ 1600 nanometers, including near-infrared overtone absorption of various gas molecules such as ammonia, carbon dioxide, carbon monoxide, and nitrous oxide. The optical pulses repetitively output at a frequency of 41.7 MHz serve as the first-stage high-frequency switching modulation of the system.

[0068] The ultra-narrow wavelength tuning module 2 includes a first pre-tunable filter 21, a first phase-shift fiber grating 22, a second phase-shift fiber grating 23, a third phase-shift fiber grating 24, and a first PZT micro-displacer 25, which are used to realize wavelength scanning and modulation of ultra-narrow linewidth detection laser according to the target gas molecules, as the second-stage intermediate frequency wavelength modulation of the system.

[0069] The first pre-tunable filter 21 operates at a wavelength of 1495 ~ 1605 nm, and the filter center wavelength is tunable, wherein the 3dB bandwidth is 0.3 nm, and is used to select a specific wavelength laser mode in the output spectrum of the optical frequency comb light source 1.

[0070] The first phase-shifting fiber grating 22, the second phase-shifting fiber grating 23, and the third phase-shifting fiber grating 24 have operating center wavelengths of 1548.85 nm, 1567.97 nm, and 1572.27 nm, respectively, in their free state, and a 3dB bandwidth of 0.03 nm for each. These three operating wavelengths are customized based on the absorption wavelengths of ammonia, carbon monoxide, and carbon dioxide. The center wavelengths of these three molecular absorption lines are approximately 1549.20 nm, 1568.03 nm, and 1572.33 nm, respectively. The wavelengths of the three phase-shifting gratings in their free state are slightly smaller than the center wavelengths of these three gas absorption lines to ensure coverage of the absorption lines through subsequent scanning and modulation. The 3dB bandwidth of the transmission window is comparable to the linewidth of semiconductor light sources commonly used in WMS technology and is much smaller than the corresponding gas spectral linewidths, providing a high signal-to-noise ratio in wavelength-modulated absorption spectroscopy measurements.

[0071] The first PZT micro-displacement device 25 is a cuboid stacked piezoelectric ceramic assembly with an overall size of 7×7×20 cubic millimeters. The driving voltage is 0~150 volts, corresponding to a displacement of 0~30 micrometers. The grating is fixed by lateral axial bonding. By generating micro-displacement, the grating is stretched, and the transmission wavelength is changed to achieve wavelength tuning.

[0072] In this embodiment, the first pre-tunable filter 21, the first phase-shift fiber grating 22, the second phase-shift fiber grating 23, and the third phase-shift fiber grating 24 are connected in series via optical fibers. The tunable filter 21 selects the transmission window of different phase-shift fiber gratings by setting the filtering center wavelength. The first phase-shift fiber grating 22, the second phase-shift fiber grating 23, and the third phase-shift fiber grating 24 are all attached to the side surface of the first PZT micro-displacement device 25. The first PZT micro-displacement device 25 provides a wavelength scanning frequency of 10 Hz and a wavelength modulation frequency of 1.5 kHz, wherein the scanning and modulation amplitudes can be set according to different target gas spectral parameters.

[0073] The gas detection optical path 3 is configured as a long optical path multiple reflection gas absorption cell to realize the interaction between the gas sample to be tested and the detection laser, with an effective absorption optical path of 41 meters.

[0074] In this embodiment, the photodetector 4 is a near-infrared high-bandwidth avalanche photodetector, used to receive weak light pulse signals propagated through the gas detection optical path 3 and convert them into electrical pulse signals with a bandwidth of 200 MHz.

[0075] In this embodiment, the local oscillator signal frequency output by the radio frequency signal generator 52 is 41.75 MHz, then the difference frequency... δf r The frequency is 50 kHz, and the low-pass filter cutoff frequency of the first lock-in amplifier 53 is set to 10 kHz. Therefore, the obtained pulse intensity characterization signal still retains the second-stage intermediate frequency wavelength modulation frequency and wavelength scanning frequency of the system.

[0076] The second-stage signal demodulation module 6 is a second lock-in amplifier 61, used for demodulating the second-stage intermediate frequency wavelength modulation of the system. It extracts the second harmonic component corresponding to the 1.5 kHz wavelength modulation frequency from the pulse intensity characterization signal. The amplitude of the second harmonic is proportional to the concentration of the gas being measured, and therefore can characterize the gas concentration. The second harmonic reference signal used in this demodulation process comes from the data acquisition card 7.

[0077] The data acquisition card 7 is used, on the one hand, to acquire the second harmonic gas concentration characterization signal output by the second-stage signal demodulation module 6 and convert it into a digital quantity for output to the calculation module; on the other hand, it provides the driving signal of the first PZT micro-displacement device 25, namely the superposition signal of a 10 Hz scanning sawtooth wave and a 1.5 kHz modulated sine wave, to the PZT controller 9; at the same time, it provides the second harmonic signal of the modulated sine wave to the second lock-in amplifier 61 as a demodulation reference.

[0078] The calculation module 8, on the one hand, controls the filtering center wavelength of the first pre-tunable filter 21 through software programs and data communication to select different phase-shifted fiber optic grating transmission wavelengths for different target gas detection; on the other hand, the calculation module 8 receives the second harmonic signal digital quantity from the data acquisition card 7 and calculates the gas concentration value according to the calibration formula.

[0079] The PZT controller 9 drives the PZT micro-displacer 25 to generate micro-displacement according to the drive signal provided by the data acquisition card, thereby realizing the transmission wavelength scanning and modulation of the first phase-shifting fiber grating 22, the second phase-shifting fiber grating 23, and the third phase-shifting fiber grating 24.

[0080] The calibration formula is obtained as follows: for gases g i Using specific phase-shift fiber gratings G i Select wavelength l i The output is selected by a tunable filter from the phase-shifted fiber grating. G i The transmission window is then used to generate a wavelength of l i Ultra-narrow linewidth detection laser; utilizing a voltage value of V imin ~ V imax The sawtooth wave scanning signal drives the PZT micro-displacement device, causing the wavelength of the narrow-linewidth probe laser to be within... l imin ~ l imax Periodic scanning within the range to cover the gas g i The complete absorption spectrum; superimposed on the sawtooth wave scanning signal with an amplitude of V imod The intermediate frequency sinusoidal modulated signal, V imod The modulation depth is optimized to obtain the best second harmonic spectral signal-to-noise ratio; the second harmonic amplitude V is set. i2f With gas concentration C proportional relationship C = a i Vi2f + b i As a calibration formula, it is obtained by measuring multiple gas samples with different concentrations. g i Get V i2f and C The unknown quantity is determined by the fitting relationship. a i , b i To obtain the calibration formula.

[0081] The PZT controller 9 is used to amplify the PZT micro-displacement drive signal provided by the data acquisition card 7 to generate sufficient voltage to drive the first PZT micro-displacement 25 to produce a quantitative displacement.

[0082] Embodiment 1 of this application also provides a method for gas detection based on a two-level modulation absorption spectroscopy using an optical frequency comb, comprising:

[0083] Step 1) The ultra-narrow band wavelength tuning module 2 selects an ultra-narrow linewidth probe laser with wavelength tuning from the optical frequency comb light source 1 according to the specific spectral line of the gas to be measured. The first PZT micro-displacement device 25 is driven by the superposition signal of low frequency sawtooth wave and mid frequency sine wave to scan and modulate the wavelength of the narrow linewidth probe laser and output probe light pulse.

[0084] Step 2) The photodetector 4 receives the transmitted signal light passing through the gas detection optical path 3 and converts it into an electrical pulse signal;

[0085] Step 3) The first-level signal demodulation module 5 extracts the first harmonic amplitude corresponding to the pulse repetition frequency of the optical frequency comb light source from the electrical pulse signal to obtain an absorption signal containing the mid-frequency sine wave modulation and the low-frequency sawtooth wave scanning frequency components.

[0086] Step 4) Extract the second harmonic spectrum signal characterizing the gas concentration from the absorption signal using the second-stage signal demodulation module 6;

[0087] Step 5) The calculation module 8 calculates the target gas concentration based on the second harmonic spectrum signal acquired by the data acquisition card 7.

[0088] Furthermore, a time-division multiplexing multi-component gas detection method based on this detection method is illustrated in this embodiment, as follows:

[0089] The first phase-shifting fiber grating 22, the second phase-shifting fiber grating 23, and the third phase-shifting fiber grating 24, connected in series, select narrow-linewidth laser modes at wavelengths of 1548.85 nm, 1567.97 nm, and 1572.27 nm from the spectrum of the optical frequency comb light source 1, corresponding to the absorption spectra of ammonia, carbon monoxide, and carbon dioxide, respectively. Steps 1) to 5) are executed to automatically adjust the operating wavelength of the first pre-tunable filter 21 at timed intervals, selecting the three operating wavelengths in a time-division multiplexing manner to achieve quasi-synchronous measurement of the three gases.

[0090] refer to Figure 2 The specific testing process is as follows:

[0091] Step S01: The calculation module 8 controls the data acquisition card 7 to generate a sawtooth wave scanning signal superimposed with a 1.5 kHz sine wave modulation signal, with a scanning frequency of 10 Hz, which is used to drive the first PZT micro-displacement device 25.

[0092] Step S02: The calculation module 8 controls the first pre-tunable filter 21, sets the filter center wavelength to 1549.20 nm, controls the data acquisition card 7 to adjust the amplitude of the sawtooth wave scanning signal, and makes the ultra-narrowband wavelength tuning module 2 output a wavelength modulation probe light signal scanning between 1549.10 and 1549.30 nm, and sets the target component to ammonia.

[0093] Step S03: The photodetector 4 completes the conversion of the electrical pulse signal;

[0094] Step S04: The first-stage signal demodulation module 5 extracts the amplitude of the electrical pulse signal and completes the demodulation of the first-stage high-frequency switching modulation;

[0095] Step S05: The second-stage signal demodulation module 6 extracts the second harmonic spectrum signal and completes the demodulation of the second-stage intermediate frequency wavelength modulation;

[0096] Step S06: The calculation module 8 receives the second harmonic spectrum signal data transmitted by the data acquisition card 7 at a sampling rate of 1 MSa / s, calculates the ammonia concentration based on the amplitude of the second harmonic spectrum signal according to the calibration formula, and refreshes the obtained concentration at a frequency of 10 Hz.

[0097] Step S07: Similar to steps S02 to S06, set the target component as carbon monoxide and detect the carbon monoxide concentration;

[0098] Step S08: Similar to steps S02 to S06, set the target component as carbon dioxide and detect the carbon dioxide concentration;

[0099] Step S09: Return to step S02 and execute the loop.

[0100] According to the above process, the system's low-frequency wavelength scanning frequency is 10 Hz, which means that a concentration detection is completed every 0.1 seconds and a gas component switching is performed every 1 second. Therefore, the concentration detection values ​​of all component gases are output every 3 seconds.

[0101] The time-division multiplexing multi-component gas detection method is designed for application scenarios that require flexible selection and switching of target gases and do not have high requirements for effectiveness. It features a simple system structure, low cost, and flexible scalability.

[0102] Example 2

[0103] Embodiment 2 of this application illustrates another dual-level modulation absorption spectroscopy gas detection system based on an optical frequency comb, referencing... Figure 3 As shown, compared to Embodiment 1, the ultra-narrowband wavelength tuning module 2 of this system has a different design and implementation. It adds a second pre-tunable filter 211, a third pre-tunable filter 212, a second PZT micro-displacement device 251, and a third PZT micro-displacement device 252, and correspondingly adds an optical fiber beam splitter 201 and an optical fiber coupler 202. The optical frequency comb light source 1, gas detection optical path 3, photodetector 4, first-stage signal demodulation module 5, second-stage signal demodulation module 6, data acquisition card 7, calculation module 8, and PZT controller 9 are the same as in Embodiment 1, as detailed below:

[0104] The ultra-narrowband wavelength tuning module 2 includes an optical fiber beam splitter 201, an optical fiber coupler 202, a first pre-tunable filter 21, a second pre-tunable filter 211, a third pre-tunable filter 212, a first phase-shifting fiber grating 22, a second phase-shifting fiber grating 23, a third phase-shifting fiber grating 24, a first PZT micro-displacer 25, a second PZT micro-displacer 251, and a third PZT micro-displacer 252, forming a combination of three tunable filters, phase-shifting fiber gratings, and PZT micro-displacers, which are connected in parallel through the optical fiber beam splitter 201 and the optical fiber coupler 202.

[0105] Furthermore, the three branches of the ultra-narrowband wavelength tuning module 2 output narrow-linewidth probe lasers of 1548.85 nm, 1567.97 nm, and 1572.27 nm respectively for ammonia, carbon monoxide, and carbon dioxide; the first PZT micro-displacement device 25, the second PZT micro-displacement device 251, and the third PZT micro-displacement device 252 provide phase-synchronized, same-frequency, but different-amplitude wavelength scans according to the spectral parameters of the three gases, and apply intermediate-frequency wavelength modulation of different frequencies.

[0106] In this embodiment, the wavelength scanning frequency of the first PZT micro-displacement device 25, the second PZT micro-displacement device 251, and the third PZT micro-displacement device 252 is 10 Hz, and the wavelength modulation frequencies are 1.1 kHz, 1.3 kHz, and 1.5 kHz, respectively.

[0107] The first-stage signal demodulation module 5 is configured the same as in Example 1, and the obtained pulse intensity characterization signal still retains the three sets of second-stage intermediate frequency wavelength modulation frequencies and low-frequency wavelength scanning frequencies of the system.

[0108] The second lock-in amplifier 61 in the second-stage signal demodulation module 6 adopts a three-channel synchronous working mode to extract the second harmonic amplitude values ​​corresponding to three frequencies of 1.1 kHz, 1.3 kHz, and 1.5 kHz from the pulse intensity characterization signal. The three double-frequency reference signals used in this demodulation process come from the data acquisition card 7.

[0109] The data acquisition card 7 acquires the three second harmonic gas concentration characterization signals output by the second-stage signal demodulation module 6, converts them into digital signals, and outputs them to the calculation module 8. On the other hand, the data acquisition card 7 provides three driving signals for the first PZT micro-displacement device 25, the second PZT micro-displacement device 251, and the third PZT micro-displacement device 252, and simultaneously outputs three frequency-doubled signals of modulated sine waves to the second lock-in amplifier 61 as demodulation references.

[0110] The PZT controller 9 receives three drive signals, amplifies them synchronously, and drives the first PZT micro-displacement unit 25, the second PZT micro-displacement unit 251, and the third PZT micro-displacement unit 252 synchronously.

[0111] This embodiment, based on the gas detection method provided in Embodiment 1, illustrates another frequency division multiplexing multi-component gas detection method, as follows:

[0112] The ultra-narrowband wavelength tuning module 2 utilizes three parallel channels to simultaneously output ultra-narrow linewidth detection lasers with wavelengths of 1548.85 nm, 1567.97 nm, and 1572.27 nm, which are then combined and input into the gas detection optical path 3. Steps 1) through 5) are executed simultaneously on the three parallel channels to synchronously acquire the concentrations of ammonia, carbon monoxide, and carbon dioxide. Specifically, in step 1), the wavelength modulation frequencies of the first PZT micro-displacement device 25, the second PZT micro-displacement device 251, and the third PZT micro-displacement device 252 are different, corresponding to different second harmonic demodulation frequencies used in step 4). This enables simultaneous measurement of the three components of the gas based on multiple intermediate frequency modulation frequencies.

[0113] In the frequency division multiplexing detection example of ammonia, carbon monoxide, and carbon dioxide shown in this embodiment, the bandwidths of the first pre-tunable filter 21, the second pre-tunable filter 211, and the third pre-tunable filter 212 are all 0.3 nanometers. (Reference) Figure 4 The simultaneous detection process for the three gases is as follows:

[0114] Step S11: The calculation module 8 controls the data acquisition card 7 to generate three sawtooth wave scanning signals, all with a scanning frequency of 10 Hz, to drive the first PZT micro-displacement device 25, the second PZT micro-displacement device 251, and the third PZT micro-displacement device 252.

[0115] Step S12: The calculation module 8 controls the first pre-tunable filter 21 to set the filter center wavelength to 1549.20 nm, controls the second pre-tunable filter 211 to set the filter center wavelength to 1568.03 nm, and controls the third pre-tunable filter 212 to set the filter center wavelength to 1572.33 nm.

[0116] Step S13: The calculation module 8 controls the data acquisition card 7 to adjust the amplitude of the three sawtooth wave scanning signals, so that the output wavelength scanning ranges of the first phase-shifting fiber grating 22, the second phase-shifting fiber grating 23, and the third phase-shifting fiber grating 24 are 1549.10 ~ 1549.30 nm, 1567.93 ~ 1568.13 nm, and 1572.23 ~ 1572.43 nm, respectively.

[0117] Step S14: The calculation module 8 controls the data acquisition card 7 to superimpose sinusoidal modulation signals with frequencies of 1.1 kHz, 1.3 kHz, and 1.5 kHz onto the three sawtooth wave scanning signals respectively, and the modulation amplitude is set according to the pre-optimized modulation depth results;

[0118] Step S15: Photodetector 4 completes the conversion of electrical pulse signals;

[0119] Step S16: The first-stage signal demodulation module 5 extracts the amplitude of the electrical pulse signal and completes the demodulation of the first-stage high-frequency switching modulation;

[0120] Step S17: The second-stage signal demodulation module 6 uses 2.2 kHz, 2.6 kHz, and 3 kHz sine waves as reference signals to complete the demodulation of the second-stage intermediate frequency wavelength modulation based on the three frequencies.

[0121] Step S18: The calculation module 8 receives the three-channel second harmonic spectrum signal acquisition data transmitted by the data acquisition card 7 at a sampling rate of 1 MSa / s, and calculates the concentrations of ammonia, carbon monoxide and carbon dioxide based on the amplitude of the second harmonic spectrum signal according to their respective calibration formulas.

[0122] The above process continues to run, and based on a wavelength scanning rate of 10 Hz, the system completes a synchronous refresh of the concentration measurements of the three gases every 0.1 seconds.

[0123] The frequency division multiplexing multi-component gas detection method is designed for application scenarios with high timeliness requirements for simultaneous measurement of multiple gases, and can simultaneously acquire the concentration of multiple gas components within each wavelength scanning cycle.

[0124] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0125] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A dual-level modulation absorption spectroscopy gas detection system based on an optical frequency comb, characterized in that, include: An optical frequency comb light source is used to generate pulsed lasers with a broadband spectrum as the first-stage high-frequency switching modulation. The ultra-narrowband wavelength tuning module includes a pre-tunable filter, a phase-shifting fiber grating, and a PZT micro-displacer. The combination of the pre-tunable filter and the phase-shifting fiber grating is used to select an ultra-narrow linewidth mode of a specific wavelength in the spectrum of the optical frequency comb source. The PZT micro-displacer provides the phase-shifting fiber grating with a corresponding wavelength scanning frequency and wavelength modulation frequency, thereby forming a second-stage intermediate frequency wavelength modulation and outputting an ultra-narrow linewidth probe laser. The gas detection optical path is used to realize the interaction between the ultra-narrow linewidth detection laser and the gas to be measured, thereby generating a transmitted pulsed laser. A photodetector is used to receive the transmitted pulsed laser and convert it into an electrical pulse signal; The first-stage signal demodulation module is used to demodulate the electrical pulse signal by the first-stage high-frequency switching modulation and output an electrical pulse intensity characterization signal. The second-stage signal demodulation module is used to demodulate the second-stage intermediate frequency wavelength modulation of the electrical pulse intensity characterization signal and output a second harmonic spectrum signal characterizing the gas concentration. and The calculation module is used to calculate the concentration of the gas to be measured based on the second harmonic spectrum signal; For time-division multiplexing detection of multi-component gases, the ultra-narrowband wavelength tuning module includes a pre-tunable filter, several phase-shift fiber gratings, and a PZT micro-displacer. The wavelength of each phase-shift fiber grating corresponds to the center wavelength of the absorption spectrum of a gas. The combination of the pre-tunable filter and the phase-shift fiber gratings is used to select the ultra-narrow linewidth mode of a specific wavelength in the spectrum of the optical frequency comb source. Each phase-shift fiber grating is attached to the side surface of the PZT micro-displacer. The PZT micro-displacer provides the corresponding wavelength scanning frequency and wavelength modulation frequency, thereby applying intermediate frequency wavelength modulation to form a second-stage intermediate frequency wavelength modulation. For frequency division multiplexing detection of multi-component gases, the ultra-narrowband wavelength tuning module includes an optical fiber beam splitter, an optical fiber coupler, and a combination of several pre-tunable filters, phase-shifting fiber gratings, and PZT micro-displacers. The optical fiber beam splitter divides the pulsed laser into several beams. In each combination, the wavelength of the phase-shifting fiber grating corresponds to the center wavelength of the absorption spectrum of a gas. The combination of the pre-tunable filter and the phase-shifting fiber grating is used to select an ultra-narrow linewidth mode of a specific wavelength in the spectrum of the optical frequency comb source. The phase-shifting fiber grating is attached to the side surface of the corresponding PZT micro-displacer, which provides the corresponding wavelength scanning frequency and wavelength modulation frequency to apply intermediate frequency wavelength modulation, forming a second-stage intermediate frequency wavelength modulation. The optical fiber coupler is used to couple the optical signals output by each phase-shifting fiber grating to the gas detection optical path.

2. The dual-level modulation absorption spectroscopy gas detection system based on optical frequency comb according to claim 1, characterized in that, The first-stage signal demodulation module includes a mixer, an RF signal generator, and a first lock-in amplifier. The RF signal generator provides a standard frequency signal. The mixer beats the electrical pulse signal to generate a difference frequency signal. The first lock-in amplifier extracts the first harmonic amplitude of the difference frequency signal, thereby obtaining the corresponding electrical pulse intensity characterization signal.

3. The dual-level modulation absorption spectroscopy gas detection system based on optical frequency comb according to claim 1, characterized in that, The second-stage signal demodulation module is a second lock-in amplifier, used to extract the second harmonic amplitude corresponding to the second-stage intermediate frequency wavelength modulation frequency.

4. The dual-level modulation absorption spectroscopy gas detection system based on optical frequency comb according to claim 1, characterized in that, It also includes a data acquisition card, which is used to acquire the second harmonic spectrum signal output by the second-stage signal demodulation module, convert it into a digital signal and output it to the calculation module.

5. The dual-level modulation absorption spectroscopy gas detection system based on optical frequency comb according to claim 4, characterized in that, It also includes a PZT controller, which is used to drive the PZT micro-displacement device to generate micro-displacement according to the drive signal provided by the data acquisition card, wherein the drive signal is a superposition signal of scanning sawtooth wave and modulated sine wave.

6. A two-stage modulation absorption spectroscopy gas detection method based on an optical frequency comb, applied to the system described in any one of claims 1-5, characterized in that, The method includes: (1) Corresponding to a specific gas molecule spectral line, the ultra-narrow band wavelength tuning module selects an ultra-narrow linewidth mode from the optical frequency comb light source; the phase-shifted fiber grating is provided with a corresponding wavelength scanning frequency and wavelength modulation frequency through the PZT micro-displacer to form a second-level intermediate frequency wavelength modulation, and the phase-shifted fiber grating outputs an ultra-narrow linewidth probe laser. (2) The photodetector converts the transmitted pulse laser generated by the interaction between the ultra-narrow linewidth detection laser and the gas to be measured in the gas detection optical path into an electrical pulse signal; (3) The first-stage signal demodulation module demodulates the electrical pulse signal by performing the first-stage high-frequency switching modulation and outputs an electrical pulse intensity characterization signal, wherein the pulsed laser output by the optical frequency comb light source is used as the first-stage high-frequency switching modulation. (4) The second-stage signal demodulation module demodulates the second-stage intermediate frequency wavelength modulation of the electrical pulse intensity characterization signal and outputs the second harmonic spectrum signal characterizing the gas concentration. (5) The calculation module calculates the target gas concentration based on the collected second harmonic spectrum signal.

7. The detection method according to claim 6, characterized in that, In time-division multiplexing detection mode, the ultra-narrowband wavelength tuning module includes a pre-tunable filter and n phase-shift fiber Bragg gratings. G 1. G 2、…、 G n A PZT micro-displacer, the phase-shifted fiber grating G 1. G 2、…、 G n Series and parallel attachments are placed on the side of the PZT micro-displacement device, respectively at wavelengths λ 1. λ 2、…、 λ n At the same time, there is an ultra-narrow transmission window, corresponding to the gas. g 1. g 2、…、 g n The position of the absorption spectral line; Based on step (1), the working wavelength of the pre-tunable filter is automatically adjusted at time intervals to align with the corresponding absorption spectral line position of the gas to be measured in a time-division multiplexing manner, and scanned and modulated using a PZT micro-displacement device. Steps (2)-(5) are executed for each gas in a time-division manner to achieve quasi-synchronous measurement of multi-component gases.

8. The detection method according to claim 6, characterized in that, In frequency division multiplexing detection mode, the ultra-narrowband wavelength tuning module includes a tunable filter. F 1. F 2、…、 F n Phase-shifted fiber gratings G 1. G 2、…、 G n and PZT micro-displacement device T 1. T 2、…、 T n Each tunable filter, phase-shifted fiber grating, and PZT micro-displacer is combined to form an ultra-narrow linewidth modulation signal channel. The output optical signal of the optical frequency comb source is evenly split into n parts and guided through optical fibers into the n channels of the ultra-narrowband wavelength tuning module. Each channel is tuned at a specific wavelength. λ 1. λ 2、…、 λ n The output narrow linewidth modulated probe light is coupled into the gas detection optical path for gas detection; steps (2)-(5) are executed simultaneously in n ultra-narrow linewidth modulated signal channels to synchronously acquire the concentrations of multiple gases.

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