A high-precision fiber optic photoacoustic gas sensing system and method for real-time calibration

Abstract

This invention belongs to the field of photoacoustic spectroscopy gas sensing technology, and discloses a high-precision fiber optic photoacoustic gas sensing system and method with real-time calibration. Two identical diffusion chambers are placed side-by-side in the system, and the gas is isolated by a flexible acoustic wave-sensitive diaphragm. An elastic thin film seals the reference cell to ensure that the gas temperature and pressure inside the reference cell are consistent with those in the detection cell. The system sensitivity is calibrated by detecting the photoacoustic signal excited by the built-in standard gas in the reference cell. This structure is simple and can resist the influence of changes in ambient temperature and pressure and the attenuation of light source power on detection. It effectively solves the problem of accuracy degradation of traditional fiber optic photoacoustic sensors under high and low temperature or non-pressure environments, expanding the adaptability of fiber optic photoacoustic sensing technology in environmental applications. This invention solves the problem of traditional fiber optic photoacoustic detection devices being easily affected by temperature and pressure, eliminating the need for additional temperature control devices and voltage stabilization systems. It has the advantages of simple structure, high reliability, and self-calibration capability.

Description

Technical Field

[0001] This invention belongs to the field of photoacoustic spectroscopy gas sensing technology, and relates to a high-precision fiber optic photoacoustic gas sensing system and method with real-time calibration. Background Technology

[0002] Fiber optic photoacoustic gas sensing technology boasts numerous advantages, including intrinsic safety, resistance to electromagnetic interference, high sensitivity, and remote sensing capabilities, making it applicable in fields such as industrial gas detection, national defense border inspection, and environmental pollutant monitoring. However, due to the inherent principles of photoacoustic spectroscopy, this approach is susceptible to interference from factors such as changes in ambient temperature and pressure, and attenuation of light source power. This can cause variations in the system's detection sensitivity to the target gas, thereby affecting the system's reliability. 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 photoacoustic gas monitoring devices and proposed a temperature compensation method. However, it did not propose a method to correct the influence of gas pressure on the photoacoustic gas detection system. The paper "Pressure-Compensated Fiber-Optic Photoacoustic Sensors for Trace SO2 Analysis in Gas Insulation Equipment" (Analytical Chemistry, 2024, 96.27(2024):10995–11001) proposes a pressure-compensated fiber-optic photoacoustic sensor for SO2 gas in the high-voltage environment of SF6 electrical equipment. While this sensor overcomes the limitation of microphone sensitivity reduction under high-pressure conditions and achieves simultaneous sensing of gas pressure and concentration, the system can only operate at a specific pressure and cannot automatically calibrate according to changes in ambient gas pressure. Typically, fiber-optic photoacoustic gas sensing systems employ external temperature control devices and voltage stabilization systems to operate in a constant temperature and pressure environment. However, this increases maintenance costs and limits application scenarios. Therefore, designing a high-precision fiber-optic photoacoustic gas sensing system and method with real-time calibration is of significant practical importance. Summary of the Invention

[0003] The purpose of this invention is to propose a high-precision fiber optic photoacoustic gas sensing system and method with real-time calibration. Two identical diffusion chambers are placed side-by-side, with a flexible acoustic wave-sensitive diaphragm isolating the gas. An elastic thin film seals the reference cell to ensure that the gas temperature and pressure inside the reference cell are consistent with those in the detection cell. The system sensitivity is calibrated by detecting the photoacoustic signal excited by the standard gas inside the reference cell. This scheme has a simple structure and can resist the effects of changes in ambient temperature and pressure and attenuation of light source power on detection. It effectively solves the problem of accuracy degradation of traditional fiber optic photoacoustic sensors under high and low temperature or non-high pressure environments, further expanding the adaptability of fiber optic photoacoustic sensing technology in environmental applications.

[0004] The principle of this invention is as follows: A photoacoustic pressure wave P is excited in a non-sealed, non-resonant photoacoustic tube. pa The variation with frequency f can be expressed as:

[0005]

[0006] Where P0, L, and V represent the laser power, the length of the photoacoustic tube, and its volume, respectively. γ(p,T) is the heat capacity ratio of the background gas (usually air), a function of pressure p and temperature T. β1(p,T) and β2(p,T) describe the thermal and acoustic damping during photoacoustic signal generation. α(p,T) is the absorption coefficient of the gas to be measured. With a fixed volume, changes in temperature and pressure affect the gas's physical properties and the laser absorption coefficient, leading to drastic changes in the system's detection sensitivity and reducing its reliability. Furthermore, the light source power attenuates over time. Therefore, a reference cell with a structure identical to the detector cell is installed in the system, containing a standard gas. Both the reference and detector cells are diffusion-type photoacoustic cells, with a breathable membrane attached to the outside of the diffusion aperture to prevent changes in the sound field within the photoacoustic cell. The diffusion aperture of the reference cell is sealed with an elastic rubber film. When temperature or air pressure changes, the gas in the reference cell expands and contracts, or atmospheric pressure compresses it, causing the elastic rubber diaphragm to bulge or dent. This ensures that the gas temperature and pressure in the reference cell are consistent with those in the detection cell, thus ensuring consistent gas detection sensitivity. When the light source power decreases, the light power entering the reference cell and detection cell via the optical switch remains consistent, thereby avoiding the impact of light source power changes on detection accuracy. Before detecting the gas to be measured, 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 measured detected in the detection cell and improving the system's measurement accuracy and reliability.

[0007] The technical solution of this invention:

[0008] A real-time calibrated high-precision fiber optic photoacoustic gas sensing system includes a DFB laser 1, an optical switch 2, a single-mode fiber 3, a dual-core fiber 4, a reference cell 5A, a detector cell 5B, a detector fiber ceramic ferrule 6A, a contrast ceramic ferrule 6B, a reference cell diffuser 7A, a detector cell diffuser 7B, a reference cell gas-permeable membrane 8A, a detector 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] Control circuit 14 is connected to spectrometer 13 and DFB laser 1 respectively. DFB laser 1 is further connected to optical switch 2. Optical switch 2 is connected to single-mode fiber 3 and dual-core fiber 4 respectively. Spectrometer 13 is further connected to optical circulator 12. Optical circulator 12 is connected to broadband light source 11 and dual-core fiber 4 respectively. Single-mode fiber 3 extends into detector cell 5B. One fiber of dual-core fiber 4 extends into reference cell 5A. A flexible acoustic wave sensitive diaphragm 9 is provided between detector cell 5B and reference cell 5A. Another optical fiber is connected to the detection fiber ceramic ferrule 6A; the comparison ceramic ferrule 6B and the detection fiber ceramic ferrule 6A are inserted into the detection cell 5B and the reference cell 5A respectively, and the two are located on both sides of the flexible acoustic wave sensitive diaphragm 9; the reference cell 5A and the detection cell 5B are respectively opened with reference cell diffusion holes 7A and detection cell diffusion holes 7B, and reference cell breathable membranes 8A and 8B are respectively covered on the reference cell diffusion holes 7A and 7B, and the reference cell breathable membrane 8A is covered with an elastic rubber film 10.

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

[0011] The reference cell 5A and the detector cell 5B have completely identical internal dimensions and structural parameters. The reference cell 5A is filled with a standard gas of known concentration. The concentration of the standard gas is such that the incident laser can excite a stable photoacoustic signal that can be clearly detected. The reference cell 5A and the detector cell 5B are separated into two gas cavities with the plane of the flexible acoustic wave sensitive diaphragm 9 as the plane of symmetry. The detection fiber ceramic ferrule 6A and the comparison ceramic ferrule 6B, the reference cell diffuser hole 7A and the detector cell diffuser hole 7B are all symmetrically installed.

[0012] The flexible acoustic wave sensitive diaphragm 9 is circular, tightly fixed around its perimeter, and has a smooth, wrinkle-free, and seamless surface, exhibiting good surface tension and acoustic sensitivity.

[0013] The detection fiber ceramic ferrule 6A and the comparison ceramic ferrule 6B are the same type of fiber ceramic ferrule, with their centers directly facing the center of the flexible acoustic wave sensitive diaphragm 9, and the distances from the flexible acoustic wave sensitive diaphragm 9 are the same, ranging from 0.15mm to 1mm.

[0014] The control circuit 14 includes functions for spectral acquisition, signal demodulation and phase-locked loop, and DFB laser driving, and internally implements a spectral phase demodulation algorithm based on white light interference.

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

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

[0017] A high-precision fiber optic photoacoustic gas sensing method with real-time calibration is disclosed. A laser beam is incident on two identical reference cells 5A and 5B via an optical switch in a two-times interval. A standard gas is introduced into one of the reference cells 5A and 5B, while the other is used to sense the concentration of the gas to be measured, and they are separated by a flexible acoustic wave-sensitive diaphragm 9. Reference cell diffuser holes 7A and 7B on the reference cells 5A and 5B respectively correspond to reference cell permeable membranes 8A and 8B. The permeable membrane 5A of the reference cell is sealed above an elastic rubber film 10. When the ambient temperature or pressure changes... The elastic rubber film 10 has protrusions or depressions to ensure that the internal temperature and gas pressure of the reference cell 5A and the detector cell 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. 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 ceramic ferrule of the detection fiber optic cable 6A. When the laser is incident on the reference cell 5A, the photoacoustic signal of the standard gas is detected to pre-calibrate the system sensitivity. When the laser is incident on the detector cell 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 standard gas of a certain concentration fills the reference cell 5A through the reference cell diffuser 7A via the reference cell permeable membrane 8A. An elastic rubber film 10 covers the reference cell permeable membrane 8A to ensure the reference cell 5A is sealed. The gas to be tested fills the detector cell 5B through the detector cell permeable membrane 8B via the detector cell diffuser 7B. The control circuit 14 drives the DFB laser 1. The laser emitted by the DFB laser 1 is time-divided and coupled into one fiber of the dual-core fiber 4 and the single-mode fiber 3 via the optical switch 2. The laser is incident on the reference cell 5A through the dual-core fiber 4, exciting a photoacoustic signal. This photoacoustic signal causes a reaction between the reference cell 5A and the detector cell 5B. The flexible acoustic wave sensitive diaphragm 9 vibrates; the probe fiber ceramic ferrule 6A and the flexible acoustic wave sensitive diaphragm 9 form an FP interference cavity. The broadband light source 11 emits broadband probe light, which enters the other fiber in the dual-core fiber 4 through the optical circulator 12 and is output from the probe fiber ceramic ferrule 6A. After reflection from the end face of the probe fiber ceramic ferrule 6A and the surface of the flexible acoustic wave sensitive diaphragm 9, the broadband light source 11 interferes and recouples into the other fiber in the dual-core 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 by combining it with the standard gas concentration.

[0019] Then, switching optical switch 2 causes the laser to be incident on the detector cell 5B through single-mode fiber 3, exciting a photoacoustic signal. The photoacoustic signal causes the flexible acoustic wave sensitive diaphragm 9 to vibrate, causing a change in the FP cavity length between the flexible acoustic wave sensitive diaphragm 9 and the ceramic ferrule 6A of the detector fiber. The broadband light source 11 emits broadband light, which enters the detector fiber ceramic ferrule 6A and the flexible acoustic wave sensitive diaphragm 9 through optical circulator 12 and dual-core fiber 4, causing interference. The interference light containing the concentration information of the gas to be measured is transmitted through dual-core fiber 4 and optical circulator 12 into 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.

[0020] The beneficial effects of this invention are as follows: The system's detection accuracy is improved by pre-calibrating the system sensitivity by filling a reference gas chamber with a structure identical to the photoacoustic detection cell. Two identical gas chambers are separated by a flexible diaphragm, which is also used for photoacoustic pressure wave sensing. The reference gas chamber is sealed externally with an elastic rubber membrane to balance the internal pressure, ensuring that the gas pressure and temperature inside the reference and detection cells are the same. This invention solves the problem of traditional fiber optic photoacoustic detection devices being susceptible to temperature and pressure variations. It eliminates the need for additional temperature control devices and voltage stabilization systems, offering advantages such as simple structure, high reliability, and self-calibration capabilities. It provides a highly competitive technical solution for high-precision trace gas detection in complex environments using fiber optic photoacoustic gas sensing technology. Attached Figure Description

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

[0022] In the diagram: 1. DFB laser; 2. Optical switch; 3. Single-mode fiber; 4. Dual-core fiber; 5. A. Reference cell; 5. B. Probe cell; 6. A. Ceramic ferrule for probe fiber; 6. B. Ceramic ferrule for contrast; 7. A. Diffuser aperture for reference cell; 7. B. Diffuser aperture for probe cell; 8. A. Gas-permeable membrane for reference cell; 8. A. Gas-permeable membrane for probe cell; 9. Flexible acoustic wave sensitive diaphragm; 10. Elastic rubber film; 11. Broadband light source; 12. Optical circulator; 13. Spectrometer; 14. Control circuit. Detailed Implementation

[0023] The specific embodiments of the present invention are described in detail below with reference to the technical solutions and accompanying drawings.

[0024] A real-time calibrated high-precision fiber optic photoacoustic gas sensing system mainly includes a DFB laser 1, an optical switch 2, a single-mode fiber 3, a dual-core fiber 4, a reference cell 5A, a detector cell 5B, a detector fiber ceramic ferrule 6A, a contrast ceramic ferrule 6B, a reference cell diffuser 7A, a detector cell diffuser 7B, a reference cell gas-permeable membrane 8A, a detector 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. Reference cell 5A and detector cell 5B contain a standard gas of a specific concentration and a gas to be tested of an unknown concentration, respectively. A diffuser hole 7A for the reference cell and a diffuser hole 7B for the detector cell are symmetrically positioned, and are respectively covered by a breathable membrane 8A for the reference cell and a breathable membrane 8B for the detector cell. The breathable membrane 8A for the reference cell is sealed by an elastic rubber film 10. Control circuit 14 drives DFB laser 1 to output laser light. The laser light is time-divisionally incident into a dual-core fiber 4 and a single-mode fiber 3, controlled by optical switch 2. The laser light incident into one fiber of the dual-core fiber 4 enters reference cell 5A, and the laser light incident into the single-mode fiber 3 enters detector cell 5B. The excited photoacoustic signal causes the intermediate flexible acoustic wave sensitive diaphragm 9 to vibrate. A detection fiber ceramic ferrule 6A and a contrast ceramic ferrule 6B are inserted on both sides of the sensing diaphragm 9, forming an FP cavity between the flexible acoustic wave sensitive diaphragm 9 and the detection fiber ceramic ferrule 6A. The broadband light source 11 emits detection light, which is incident on the other fiber of the dual-core fiber 4 through the optical circulator 12 and transmitted to the detection fiber ceramic ferrule 6 and the flexible acoustic wave sensitive diaphragm 9, where they interfere. 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 amplitude of the standard gas photoacoustic signal and the amplitude of the gas to be tested are obtained according to the channel opened by the optical switch 2. The concentration of the gas to be tested can be obtained by calculating the ratio of the amplitude of the gas to be tested to the sensitivity.

[0025] The DFB laser 1 has a center wavelength of 1532.83 nm and a power of 20 mW. The standard gas used is C2H2 gas with a concentration of 100 ppm. The broadband light source 11 is an SLD light source with a center wavelength of 1550 nm and a bandwidth of 50 nm. The spectrometer 13 is a high-speed miniature spectrometer with a spectral 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 detector cell 5B have a diameter of 4 mm and a length of 25 mm.

[0026] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection 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 fiber optic photoacoustic gas sensing system includes a DFB laser (1), an optical switch (2), a single-mode fiber (3), a dual-core fiber (4), a reference cell (5A), a detector cell (5B), a detector fiber ceramic ferrule (6A), a contrast ceramic ferrule (6B), a reference cell diffuser (7A), a detector cell diffuser (7B), a reference cell permeable membrane (8A), a detector cell 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 control circuit (14) is connected to the spectrometer (13) and the DFB laser (1) respectively. The DFB laser (1) is connected to the optical switch (2). The optical switch (2) is connected to the single-mode fiber (3) and the dual-core fiber (4) respectively. The spectrometer (13) is connected to the optical circulator (12). The optical circulator (12) is connected to the broadband light source (11) and the dual-core fiber (4) respectively. The single-mode fiber (3) extends into the detector cell (5B). One fiber of the dual-core fiber (4) extends into the reference cell (5A). A flexible acoustic wave sensitive diaphragm (9) is provided between the detector cell (5B) and the reference cell (5A). The other fiber of the dual-core fiber (4) is connected to the detector fiber ceramic ferrule (6A). The contrast ceramic ferrule (6B) and the probe fiber ceramic ferrule (6A) are respectively inserted into the probe cell (5B) and the reference cell (5A), which are located on both sides of the flexible acoustic wave sensitive diaphragm (9); the reference cell (5A) and the probe cell (5B) are respectively opened with reference cell diffusion holes (7A) and probe cell diffusion holes (7B), and reference cell breathable membranes (8A) and probe cell breathable membranes (8B) are respectively covered on the reference cell diffusion holes (7A) and probe cell diffusion holes (7B); the reference cell breathable membrane (8A) is covered with an elastic rubber film (10); when the ambient temperature or pressure changes, the elastic rubber film (10) bulges or dents to ensure that the internal temperature and air pressure of the reference cell (5A) and the probe cell (5B) are consistent; The control circuit (14) drives the DFB laser (1) to output laser light. The laser light is controlled by the optical switch (2) to be incident into the dual-core fiber (4) and the single-mode fiber (3) in a time-division manner. The laser light incident into one fiber of the dual-core fiber (4) enters the reference cell (5A), and the laser light incident into the single-mode fiber (3) enters the detector cell (5B). The flexible acoustic wave sensitive diaphragm (9) detects the photoacoustic signal at the same time. The broadband light source (11) emits detection light, which is incident into the other fiber of the dual-core fiber (4) through the optical circulator (12) and transmitted to the ceramic ferrule (6A) of the detection fiber and the flexible acoustic wave sensitive diaphragm (9) to generate light. Interference occurs, and the returned interference signal is transmitted to the spectrometer (13) via the optical circulator (12). The control circuit (14) collects the interference spectrum for demodulation. The internal dimensions and structural parameters of the reference cell (5A) and the detector cell (5B) are completely identical. The reference cell (5A) is filled with a standard gas of known concentration. The reference cell (5A) and the detector cell (5B) are symmetrical about the plane of the flexible acoustic wave sensitive diaphragm (9) and are separated into two gas cavities. The detector fiber ceramic ferrule (6A) and the contrast ceramic ferrule (6B), the reference cell diffuser hole (7A) and the detector cell diffuser hole (7B) are all symmetrically installed. The flexible acoustic wave sensitive diaphragm (9) is circular, tightly fixed around its perimeter, and has a smooth, wrinkle-free, and seamless surface. The detection fiber ceramic ferrule (6A) and the comparison ceramic ferrule (6B) are the same type of fiber ceramic ferrule, 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), ranging from 0.15 mm to 1 mm.

2. The high-precision fiber optic photoacoustic gas sensing system according to claim 1, characterized in that, The control circuit (14) includes functions of spectrum acquisition, signal demodulation and phase-locked loop, and DFB laser driving. It internally implements a spectral phase demodulation algorithm based on white light interference.

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

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

5. A detection method based on the high-precision fiber optic photoacoustic gas sensing system according to any one of claims 1-4, characterized in that, The specific steps are as follows: First, a standard gas of a certain concentration fills the reference cell (5A) through the reference cell diffuser (7A) via the reference cell permeable membrane (8A). An elastic rubber film (10) covers the reference cell permeable membrane (8A) to ensure the reference cell (5A) is sealed. The gas to be tested fills the detector cell (5B) through the detector cell diffuser (7B) via the detector cell permeable membrane (8B). The control circuit (14) drives the DFB laser (1). The laser emitted by the DFB laser (1) is time-divided and coupled into one fiber and one-mode fiber (3) of the dual-core fiber (4) via the optical switch (2). The laser is incident on the reference cell (5A) via the dual-core fiber (4) to excite a photoacoustic signal. The photoacoustic signal causes the reference cell (5A) and the detector cell (7A) to react. 5B) The flexible acoustic wave sensitive diaphragm (9) in the middle vibrates; the probe fiber ceramic ferrule (6A) and the flexible acoustic wave sensitive diaphragm (9) form an FP cavity. The broadband light source (11) emits broadband probe light, which enters the other fiber in the dual-core fiber (4) through the optical circulator (12) and is output from the probe fiber ceramic ferrule (6A). The broadband light source (11) is reflected by the end face of the probe fiber ceramic ferrule (6A) and the surface of the flexible acoustic wave sensitive diaphragm (9) and then interferes and recouples into the other fiber in the dual-core fiber (4). It 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. The system sensitivity is calculated by combining the standard gas concentration. Then, the optical switch (2) is switched so that the laser is incident on the detector cell (5B) through the single-mode 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 ceramic ferrule of the detector fiber (6A) to change. The broadband light source (11) emits broadband light through the optical circulator (12) and the dual-core fiber (4) into the ceramic ferrule of the detector fiber (6A) and the flexible acoustic wave sensitive diaphragm (9) to interfere. The interference light containing the concentration information of the gas to be measured is transmitted through the dual-core fiber (4) and the optical circulator (12) into 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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