Real-time calibration high-precision optical fiber photoacoustic gas sensing system and method

Abstract

The invention belongs to the technical field of photoacoustic spectrum gas sensing, and discloses a real-time calibration high-precision optical fiber photoacoustic gas sensing system and a real-time calibration high-precision optical fiber photoacoustic gas sensing method. In the system, two diffusion gas chambers with the same structure are arranged in parallel, a sound wave sensitive diaphragm with certain flexibility is adopted to isolate gas, an elastic film is adopted to seal a reference cell to ensure that the temperature and the pressure intensity of gas in the reference cell are consistent with those in a detection cell, and a photoacoustic signal excited by standard gas in the reference cell is detected; and calibrating the sensitivity of the system. The structure is simple, the influence of environment temperature and pressure intensity change and light source power attenuation on detection can be resisted, the problem of precision deterioration of a traditional optical fiber photoacoustic sensor in a high and low temperature or non-normal pressure environment can be effectively solved, and the application range of an optical fiber photoacoustic sensing technology in environment application is expanded. The problem that a traditional optical fiber photoacoustic detection device is easily influenced by temperature and pressure intensity is solved, a temperature control device and a pressure stabilizing system do not need to be additionally arranged, and the optical fiber photoacoustic detection device has the advantages of being simple in structure, high in reliability and capable of achieving self-calibration.

Description

Technical Field

[0001] The invention belongs to the technical field of photoacoustic spectroscopy gas sensing, and relates to a high-precision optical fiber photoacoustic gas sensing system and method for real-time calibration. Background Art

[0002] Fiber optic photoacoustic gas sensing technology has many advantages such as intrinsic safety, anti-electromagnetic interference, high sensitivity, and remote measurement. It can be used in industrial gas detection, national defense border inspection, and environmental pollutant monitoring. However, due to the principle of photoacoustic spectroscopy itself, this scheme will be interfered by factors such as changes in ambient temperature and pressure and light source power attenuation, causing the system's detection sensitivity to the gas to be measured to change, thereby affecting the reliability of the system. The literature Research on temperature and pressure interference in photoacoustic spectroscopy gas detection. Microwave and Optical Technology Letters, 66.1 (2024): e33971 studied the effects of temperature and pressure on the photoacoustic gas monitoring device and proposed a temperature compensation method, but did not propose a correction method for the effect of air pressure on the photoacoustic gas detection system. Literature Pressure-Compensated Fiber-Optic Photoacoustic Sensors for TraceSO2 Analysis in Gas Insulation Equipment.Analytical Chemistry.2024,96.27(2024):10995–11001 A SO2 gas fiber photoacoustic sensor with pressure compensation is proposed for the high-pressure environment in SF6 electrical equipment. Although the sensor breaks the limitation of the system performance caused by the reduced sensitivity of the microphone under high-pressure environment and realizes the simultaneous sensing of air pressure and gas concentration by the fiber photoacoustic sensor, the system can only work under a specific pressure and cannot be automatically calibrated according to the change of ambient air pressure. Usually, the fiber photoacoustic gas sensing system adopts an external temperature control device and a voltage stabilizing system to make the system work in a constant temperature and pressure environment. However, this increases the maintenance cost of the system to a certain extent and limits the application scenarios of the system. Therefore, it is of great application significance to design a high-precision fiber photoacoustic gas sensing system and method with real-time calibration. Summary of the invention

[0003] The purpose of the present invention is to propose a high-precision fiber-optic photoacoustic gas sensing system and method for real-time calibration. Two diffusion gas chambers with the same structure are placed side by side and use a sound wave sensitive diaphragm with a certain flexibility to isolate the gas. An elastic film is used to seal the reference pool to ensure that the gas temperature and pressure in the reference pool are consistent with those in the detection pool. The system sensitivity is calibrated by detecting the photoacoustic signal excited by the built-in standard gas in the reference pool. The scheme has a simple structure and can resist the influence of ambient temperature and pressure changes and light source power attenuation on detection. It can effectively solve the problem of accuracy degradation of traditional fiber-optic photoacoustic sensors in high and low temperature or abnormal pressure environments, and further expand the scope of application of fiber-optic photoacoustic sensing technology in environmental applications.

[0004] The principle of the present invention is as follows: the photoacoustic pressure wave P excited in the non-sealed non-resonant photoacoustic tube pa The change with frequency f can be expressed as:

[0005]

[0006] Where P0, L and V represent the laser power, the length and volume of the photoacoustic tube, respectively. γ(p,T) is the heat capacity ratio of the background gas (usually air), which is a function of the air pressure p and the temperature T. β1(p,T) and β2(p,T) describe the thermal and acoustic damping in the process of generating the photoacoustic signal. α(p,T) is the absorption coefficient of the gas to be measured. When the volume is fixed, changes in temperature and air pressure will affect the physical properties of the gas and the laser absorption coefficient, resulting in drastic changes in the detection sensitivity of the system and reducing the detection reliability of the system. In addition, the power of the light source will decay as the system runs longer. Therefore, a reference cell with the same structure as the detection cell is installed in the system, and a standard gas is built in. Both the reference cell and the detection cell are diffuse photoacoustic cells, and a breathable membrane is attached to the outside of the diffusion hole to avoid changes in the sound field in the photoacoustic cell. The outside of the diffusion hole of the reference cell is sealed with an elastic rubber film. When the temperature or air pressure changes, the gas in the reference cell expands and contracts or the atmospheric pressure squeezes the elastic rubber film to bulge or dent, which ensures that the gas temperature and pressure in the reference cell are consistent with those in the detection cell, and thus the gas detection sensitivity is consistent. When the light source power decays, the light power entering the reference cell and the detection cell through the optical switch is consistent, thereby avoiding the influence of the light source power change on the detection accuracy. Before detecting the gas to be tested, the system sensitivity can be pre-calibrated by detecting the photoacoustic signal excited by the standard gas in the reference cell, thereby correcting the concentration of the gas to be tested detected in the detection cell and improving the measurement accuracy and reliability of the system.

[0007] The technical solution of the present invention:

[0008] A high-precision fiber optic photoacoustic gas sensing system with real-time calibration, comprising a DFB laser 1, an optical switch 2, a single-mode optical fiber 3, a dual-core optical fiber 4, a reference cell 5A, a detection cell 5B, a detection optical fiber ceramic pin 6A, a comparison ceramic pin 6B, a reference cell diffusion hole 7A, a detection cell diffusion hole 7B, a reference cell gas permeable membrane 8A, a detection cell gas permeable membrane 8B, a flexible acoustic wave sensitive diaphragm 9, an elastic rubber film 10, a broadband light source 11, an optical circulator 12, a spectrometer 13 and a control circuit 14;

[0009] The control circuit 14 is connected to the spectrometer 13 and the DFB laser 1 respectively, the DFB laser 1 is further connected to the optical switch 2, the optical switch 2 is respectively connected to the single-mode optical fiber 3 and the dual-core optical fiber 4; the spectrometer 13 is further connected to the optical circulator 12, the optical circulator 12 is respectively connected to the wide-spectrum light source 11 and the dual-core optical fiber 4; the single-mode optical fiber 3 extends into the detection pool 5B, one of the dual-core optical fibers 4 extends into the reference pool 5A, a flexible acoustic wave sensitive diaphragm 9 is arranged between the detection pool 5B and the reference pool 5A, and the dual-core optical fiber 4 Another optical fiber is connected to the detection optical fiber ceramic pin 6A; the comparison ceramic pin 6B and the detection optical fiber ceramic pin 6A are correspondingly inserted into the detection pool 5B and the reference pool 5A, and the two are correspondingly located on both sides of the flexible sound wave sensitive diaphragm 9; the reference pool 5A and the detection pool 5B are correspondingly provided with a reference pool diffusion hole 7A and a detection pool diffusion hole 7B, and the reference pool diffusion hole 7A and the detection pool diffusion hole 7B are correspondingly covered with a reference pool breathable membrane 8A and a detection pool breathable membrane 8B, and the reference pool breathable membrane 8A is covered with an elastic rubber film 10 on the outside;

[0010] The control circuit 14 drives the DFB laser 1 to output laser light, and the laser light is controlled by the optical switch 2 to be incident on the dual-core optical fiber 4 and the single-mode optical fiber 3 in a time-sharing manner; the laser light incident on one optical fiber of the dual-core optical fiber 4 enters the reference pool 5A, and the laser light incident on the single-mode optical fiber 3 enters the detection pool 5B, and the flexible acoustic wave sensitive diaphragm 9 detects the photoacoustic signal at the same time; the wide-spectrum light source 11 emits detection light, which is incident on the other optical fiber of the dual-core optical fiber 4 through the optical circulator 12, and is transmitted to the detection optical fiber ceramic pin 6 and the flexible acoustic wave sensitive diaphragm 9 to interfere, and the returned interference signal is transmitted to the spectrometer 13 through the optical circulator 12, and the control circuit 14 collects the interference spectrum for demodulation.

[0011] The reference cell 5A and the detection cell 5B have completely identical internal dimensions and structural parameters. The reference cell 5A is filled with a standard gas to be tested of known concentration. The concentration of the standard gas to be tested should be such that a stable photoacoustic signal that can be clearly detected can be excited by the incident laser. The reference cell 5A and the detection cell 5B use the plane where the flexible acoustic wave sensitive diaphragm 9 is located as a symmetry plane and separate the two air cavities. The detection optical fiber ceramic pin 6A and the comparison ceramic pin 6B, the reference cell diffusion hole 7A and the detection cell diffusion hole 7B are all symmetrically installed.

[0012] The flexible sound wave sensitive diaphragm 9 is circular, is tightly fixed around, has a flat surface without wrinkles or gaps, and has good surface tension and acoustic sensitivity.

[0013] The detection optical fiber ceramic pin 6A and the comparison ceramic pin 6B are the same type of optical fiber ceramic pins, with their centers facing the center of the flexible acoustic wave sensitive diaphragm 9 and the same distance from the flexible acoustic wave sensitive diaphragm 9, with the distance range being 0.15mm-1mm.

[0014] The control circuit 14 includes the functions of spectrum acquisition, signal demodulation phase locking and DFB laser driving, and a spectrum phase demodulation algorithm based on white light interference is programmed inside.

[0015] The broadband light source 11 is a near-infrared broadband light source with a central wavelength of 1550 nm and a spectrum width of not less than 40 nm.

[0016] The wavelength range of the spectrometer 13 is 1525-1570 nm, and the frame rate is higher than 15 kHz.

[0017] A high-precision optical fiber photoacoustic gas sensing method with real-time calibration, wherein the laser is incident on two reference cells 5A and detection cells 5B with the same structure through an optical switch 2 in time division, one of the reference cells 5A and detection cells 5B is fed with standard gas, and the other is used to sense the concentration of the gas to be measured, and is separated by a flexible acoustic wave sensitive membrane 9; the reference cell diffusion holes 7A on the reference cell 5A and detection cell 5B, and the detection cell diffusion holes 7B correspond to the reference cell gas permeable membrane 8A and the detection cell gas permeable membrane 8B, and the upper part of the reference cell gas permeable membrane 5A is sealed by an elastic rubber film 10, when the ambient temperature or pressure changes , the elastic rubber film 10 is raised or sunken to ensure that the internal temperature and air pressure of the reference pool 5A and the detection pool 5B are consistent, so that the gas detection sensitivity is the same; the detected photoacoustic signal causes the flexible acoustic wave sensitive diaphragm 9 to vibrate, and the intensity of the excited photoacoustic signal is measured according to the change in the length of the Fabry-Perot (FP) cavity formed by the flexible acoustic wave sensitive diaphragm 9 and the detection optical fiber ceramic pin 6A; when the laser is incident on the reference pool 5A, the standard gas photoacoustic signal is detected to pre-calibrate the system sensitivity, and when the laser is incident on the detection pool 5B, the photoacoustic signal excited by the gas to be tested is detected and the gas concentration is inverted. The specific steps are as follows:

[0018] First, a certain concentration of standard gas passes through the reference cell breathable membrane 8A from the reference cell diffusion hole 7A to fill the reference cell 5A, and the reference cell breathable membrane 8A is covered with an elastic rubber membrane 10 to ensure that the reference cell 5A is sealed; the gas to be measured passes through the detection cell breathable membrane 8B from the detection cell diffusion hole 7B to fill the detection cell 5B; the control circuit 14 drives the DFB laser 1, and the laser emitted by the DFB laser 1 is coupled into one optical fiber in the dual-core optical fiber 4 and the single-mode optical fiber 3 through the optical switch 2 in a time-sharing manner. The laser is incident on the reference cell 5A through the dual-core optical fiber 4 to excite a photoacoustic signal, and the photoacoustic signal causes the soft wave between the reference cell 5A and the detection cell 5B. The acoustic wave sensitive diaphragm 9 vibrates; the detection optical fiber ceramic pin 6A and the flexible acoustic wave sensitive diaphragm 9 form an FP interference cavity, the wide-spectrum light source 11 emits a wide-spectrum detection light, enters another optical fiber in the dual-core optical fiber 4 through the optical circulator 12, and is output from the detection optical fiber ceramic pin 6A. The wide-spectrum light source 11 is reflected on the end face of the detection optical fiber ceramic pin 6A and the surface of the flexible acoustic wave sensitive diaphragm 9, and then interferes and couples again into another optical fiber in the dual-core optical fiber 4, and is incident on the spectrometer 13 through the optical circulator 12. The control circuit 14 collects the interference spectrum information and demodulates the FP cavity length, and calculates the system sensitivity in combination with the standard gas concentration;

[0019] Then, the optical switch 2 is switched to allow the laser to be incident on the detection pool 5B through the single-mode optical fiber 3 to stimulate the photoacoustic signal. The photoacoustic signal causes the flexible acoustic wave sensitive diaphragm 9 to vibrate, causing the FP cavity length between the flexible acoustic wave sensitive diaphragm 9 and the detection optical fiber ceramic pin 6A to change; the broadband light source 11 emits broadband light through the optical circulator 12 and the dual-core optical fiber 4 to enter the detection optical fiber ceramic pin 6A and the flexible acoustic wave sensitive diaphragm 9 to interfere, and the interference light containing the concentration information of the gas to be measured is transmitted through the dual-core optical fiber 4 and the optical circulator 12 to enter the spectrometer 13, and the control circuit reads the interference spectrum of the spectrometer 13 to obtain the amplitude of the photoacoustic signal of the gas to be measured; finally, the concentration of the gas to be measured is obtained by the ratio of the amplitude of the photoacoustic signal of the gas to be measured to the system sensitivity.

[0020] The beneficial effects of the present invention are as follows: by filling a reference gas chamber with the same structure as the photoacoustic detection cell with standard gas to pre-calibrate the system sensitivity, the detection accuracy of the system can be improved. Two identical gas chambers are separated by a flexible diaphragm, and the diaphragm is used for photoacoustic pressure wave sensing. The outside of the reference gas chamber is sealed with an elastic rubber film to balance the pressure in the cavity so that the pressure and temperature inside the reference cell and the detection cell are the same. The present invention solves the problem that traditional fiber optic photoacoustic detection devices are easily affected by temperature and pressure. It does not require additional temperature control devices and voltage stabilization systems. It has the advantages of simple structure, high reliability and self-calibration, and provides a highly competitive technical solution for high-precision trace gas detection in complex environments using fiber optic photoacoustic gas sensing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the system structure of the present invention.

[0022] In the figure: 1DFB laser; 2 optical switch; 3 single-mode optical fiber; 4 dual-core optical fiber; 5A reference cell; 5B detection cell; 6A detection optical fiber ceramic pin; 6B comparison ceramic pin; 7A reference cell diffusion hole; 7B detection cell diffusion hole; 8A reference cell breathable membrane; 8B detection cell breathable membrane; 9 flexible sound wave sensitive diaphragm; 10 elastic rubber film; 11 wide-spectrum light source; 12 optical circulator; 13 spectrometer; 14 control circuit. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is described in detail below in conjunction with the technical scheme and the accompanying drawings.

[0024] A high-precision fiber optic photoacoustic gas sensing system for real-time calibration mainly comprises a DFB laser 1, an optical switch 2, a single-mode optical fiber 3, a dual-core optical fiber 4, a reference cell 5A, a detection cell 5B, a detection optical fiber ceramic pin 6A, a comparison ceramic pin 6B, a reference cell diffusion hole 7A, a detection cell diffusion hole 7B, a reference cell gas permeable membrane 8A, a detection cell gas permeable membrane 8B, a flexible acoustic wave sensitive diaphragm 9, an elastic rubber film 10, a broadband light source 11, an optical circulator 12, a spectrometer 13, and a control circuit 14. The reference pool 5A and the detection pool 5B contain standard gas of specific concentration and gas to be tested of unknown concentration respectively, and reference pool diffusion holes 7A and detection pool diffusion holes 7B are opened at symmetrical positions, which are respectively covered with reference pool breathable membrane 8A and detection pool breathable membrane 8B, and the reference pool breathable membrane 8A is sealed by elastic rubber film 10; control circuit 14 drives DFB laser 1 to output laser, and the laser is controlled by optical switch 2 to be incident on dual-core optical fiber 4 and single-mode optical fiber 3 in time-sharing; the laser incident on one optical fiber in dual-core optical fiber 4 enters reference pool 5A, and the laser incident on single-mode optical fiber 3 enters detection pool 5B; the excited photoacoustic signal causes the intermediate flexible acoustic wave sensitive diaphragm 9 to vibrate; the flexible acoustic wave sensitive A detection optical fiber ceramic pin 6A and a comparison ceramic pin 6B are inserted on both sides of the sensitive diaphragm 9, and an FP cavity is formed between the flexible acoustic wave sensitive diaphragm 9 and the detection optical fiber ceramic pin 6A; the detection light emitted by the wide-spectrum light source 11 is incident on the other optical fiber of the dual-core optical fiber 4 through the optical circulator 12, and is transmitted to the detection optical fiber ceramic pin 6 and the flexible acoustic wave sensitive diaphragm 9 to interfere, and the interference signal is transmitted to the spectrometer 13 through the optical circulator 12, and the control circuit 14 collects the interference spectrum for demodulation; the standard gas photoacoustic signal amplitude and the photoacoustic signal amplitude of the gas to be measured are respectively obtained according to the channel opened by the optical switch 2, and the concentration of the gas to be measured can be obtained by calculating the ratio of the photoacoustic signal amplitude of the gas to be measured to the sensitivity.

[0025] The DFB laser 1 has a central wavelength of 1532.83 nm and a power of 20 mW. The standard gas filled is C2H2 gas with a concentration of 100 ppm. The wide-spectrum detection light source 11 is an SLD light source with a central wavelength of 1550 nm and a bandwidth of 50 nm. The spectrometer 13 is a high-speed micro-spectrometer with a spectrum acquisition rate of 15 kHz. The flexible acoustic wave sensitive diaphragm 9 is a circular polyphenylene sulfide film with a diameter of 9 mm and a thickness of 10 μm. The reference cell 5A and the detection cell 5B have a diameter of 4 mm and a length of 25 mm.

[0026] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-precision fiber optic photoacoustic gas sensing system with real-time calibration, characterized in that: The high-precision optical fiber photoacoustic gas sensing system comprises a DFB laser (1), an optical switch (2), a single-mode optical fiber (3), a dual-core optical fiber (4), a reference cell (5A), a detection cell (5B), a detection optical fiber ceramic pin (6A), a comparison ceramic pin (6B), a reference cell diffusion hole (7A), a detection cell diffusion hole (7B), a reference cell gas permeable membrane (8A), a detection cell gas permeable membrane (8B), a flexible acoustic wave sensitive diaphragm (9), an elastic rubber film (10), a wide-spectrum light source (11), an optical circulator (12), a spectrometer (13) and a control circuit (14); The control circuit (14) is connected to the spectrometer (13) and the DFB laser (1) respectively; the DFB laser (1) is further connected to the optical switch (2); the optical switch (2) is respectively connected to the single-mode optical fiber (3) and the dual-core optical fiber (4); the spectrometer (13) is further connected to the optical circulator (12); the optical circulator (12) is respectively connected to the wide-spectrum light source (11) and the dual-core optical fiber (4); the single-mode optical fiber (3) extends into the detection pool (5B); one optical fiber in the dual-core optical fiber (4) extends into the reference pool (5A); a flexible acoustic wave sensitive diaphragm (9) is provided between the detection pool (5B) and the reference pool (5A); Another optical fiber in the optical fiber (4) is connected to the detection optical fiber ceramic pin (6A); the comparison ceramic pin (6B) and the detection optical fiber ceramic pin (6A) are correspondingly inserted into the detection pool (5B) and the reference pool (5A), and the two are correspondingly located on both sides of the flexible sound wave sensitive membrane (9); the reference pool (5A) and the detection pool (5B) are correspondingly provided with a reference pool diffusion hole (7A) and a detection pool diffusion hole (7B), and the reference pool diffusion hole (7A) and the detection pool diffusion hole (7B) are correspondingly covered with a reference pool gas permeable membrane (8A) and a detection pool gas permeable membrane (8B), and the reference pool gas permeable membrane (8A) is covered with an elastic rubber film (10) on the outside; The control circuit (14) drives the DFB laser (1) to output laser light, and the laser light is controlled by the optical switch (2) to be incident on the dual-core optical fiber (4) and the single-mode optical fiber (3) in a time-sharing manner; the laser light incident on one optical fiber of the dual-core optical fiber (4) enters the reference pool (5A), and the laser light incident on the single-mode optical fiber (3) enters the detection pool (5B), and the flexible acoustic wave sensitive membrane (9) detects the photoacoustic signal at the same time; the detection light emitted by the wide-spectrum light source (11) is incident on the other optical fiber of the dual-core optical fiber (4) through the optical circulator (12), and is transmitted to the detection optical fiber ceramic pin 6 and the flexible acoustic wave sensitive membrane (9) to interfere, and the returned interference signal is transmitted to the spectrometer (13) through the optical circulator (12), and the control circuit (14) collects the interference spectrum for demodulation.

2. The high-precision fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The reference cell (5A) and the detection cell (5B) have completely identical internal dimensions and structural parameters. The reference cell (5A) is filled with a standard gas to be tested of known concentration. The reference cell (5A) and the detection cell (5B) use the plane where the flexible acoustic wave sensitive diaphragm (9) is located as a symmetric plane and separate the two air cavities. The detection optical fiber ceramic pin (6A) and the comparison ceramic pin (6B), the reference cell diffusion hole (7A) and the detection cell diffusion hole (7B) are all symmetrically installed.

3. The high-precision fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The flexible sound wave sensitive diaphragm (9) is circular, is tightly fixed around, and has a smooth surface without wrinkles or gaps.

4. The high-precision fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The detection optical fiber ceramic pin (6A) and the comparison ceramic pin (6B) are optical fiber ceramic pins of the same type, with their centers facing the center of the flexible sound wave sensitive diaphragm (9) and the same distance from the flexible sound wave sensitive diaphragm (9), with the distance range being 0.15 mm-1 mm.

5. The high-precision fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The control circuit (14) includes the functions of spectrum acquisition, signal demodulation phase locking and DFB laser driving, and a spectrum phase demodulation algorithm based on white light interference is programmed inside.

6. The high-precision fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The wide-spectrum light source (11) is a near-infrared broadband light source with a central wavelength of 1550 nm and a spectrum width of not less than 40 nm.

7. The high-precision fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The wavelength range of the spectrometer (13) is 1525-1570 nm, and the frame rate is higher than 15 kHz.

8. A high-precision fiber optic photoacoustic gas sensing method with real-time calibration, characterized in that: Laser light is incident on two reference cells (5A) and detection cells (5B) of the same structure in time division through an optical switch (2); a standard gas is introduced into one of the reference cells (5A) and detection cells (5B); the other is used to sense the concentration of the gas to be measured and is separated by a flexible sound wave sensitive membrane (9); the reference cell diffusion holes (7A) on the reference cell (5A) and detection cell (5B) and the detection cell diffusion holes (7B) correspond to the reference cell gas permeable membrane (8A) and detection cell gas permeable membrane (8B); and the upper part of the reference cell gas permeable membrane 5A is sealed by an elastic rubber film (10); when the ambient temperature or pressure changes, the elastic rubber film (10) 0) is convex or concave to ensure that the internal temperature and air pressure of the reference pool (5A) and the detection pool (5B) are consistent, so that the gas detection sensitivity is the same; the detected photoacoustic signal causes the flexible acoustic wave sensitive diaphragm (9) to vibrate, and the intensity of the excited photoacoustic signal is measured according to the change in the length of the Fabry-Perot (FP) cavity formed by the flexible acoustic wave sensitive diaphragm (9) and the detection optical fiber ceramic pin (6A); when the laser is incident on the reference pool (5A), the standard gas photoacoustic signal is detected to pre-calibrate the system sensitivity; when the laser is incident on the detection pool (5B), the photoacoustic signal excited by the gas to be measured is detected and the gas concentration is inverted; the specific steps are as follows: First, a standard gas of a certain concentration is filled into a reference cell (5A) through a reference cell air permeable membrane (8A) from a reference cell diffusion hole (7A), and the reference cell air permeable membrane (8A) is covered with an elastic rubber membrane 10 to ensure that the reference cell (5A) is sealed; the gas to be measured is filled into a detection cell (5B) through a detection cell air permeable membrane (8B) from a detection cell diffusion hole (7B); a control circuit (14) drives a DFB laser (1), and laser light emitted by the DFB laser (1) is coupled into one optical fiber in a dual-core optical fiber (4) and a single-mode optical fiber (3) through an optical switch (2) in a time-sharing manner, and the laser light is incident into the reference cell (5A) through the dual-core optical fiber (4) to excite a photoacoustic signal, and the photoacoustic signal causes the reference cell (5A) and the detection cell (5B) to be connected. The flexible acoustic wave sensitive diaphragm (9) in the middle vibrates; the detection optical fiber ceramic plug (6A) and the flexible acoustic wave sensitive diaphragm (9) form an FP interference cavity; the wide-spectrum light source (11) emits a wide-spectrum detection light which enters another optical fiber in the dual-core optical fiber (4) through an optical circulator (12) and is output from the detection optical fiber ceramic plug (6A); the wide-spectrum light source (11) is reflected at the end face of the detection optical fiber ceramic plug (6A) and the surface of the flexible acoustic wave sensitive diaphragm (9) and then interferes and couples again into another optical fiber in the dual-core optical fiber (4) and is incident on the spectrometer (13) through the optical circulator (12); the control circuit (14) collects interference spectrum information and demodulates the FP cavity length, and calculates the system sensitivity in combination with the standard gas concentration; Then, the optical switch (2) is switched to allow the laser to enter the detection pool (5B) through the single-mode optical fiber (3) to excite the photoacoustic signal. The photoacoustic signal causes the flexible acoustic wave sensitive diaphragm (9) to vibrate, causing the FP cavity length between the flexible acoustic wave sensitive diaphragm (9) and the detection optical fiber ceramic plug (6A) to change. The wide-spectrum light source (11) emits wide-spectrum light through the optical circulator (12) and the dual-core optical fiber (4) to enter the detection optical fiber ceramic plug (6A) and the flexible acoustic wave sensitive diaphragm (9) to interfere with each other. The interference light containing the concentration information of the gas to be measured is transmitted through the dual-core optical fiber (4) and the optical circulator (12) to enter the spectrometer (13). The control circuit reads the interference spectrum of the spectrometer (13) to obtain the amplitude of the photoacoustic signal of the gas to be measured. Finally, the concentration of the gas to be measured is obtained by the ratio of the amplitude of the photoacoustic signal of the gas to be measured to the system sensitivity.

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