Trace gas detection system based on anti-resonance hollow-core optical fiber mode interferometer

Abstract

The invention provides a trace gas detection system based on an anti-resonance hollow-core optical fiber mode interferometer, and relates to the technical field of optical sensing, and the trace gas detection system comprises a transmission module which comprises a gas sensor and is used for transmitting pump light and detection light, the refractive index change caused by the photothermal effect is reflected to the phase change of the probe light through the photothermal interference type (PTI) sensing technology; the gas chamber module is used for taking an anti-resonance hollow-core optical fiber as a place where light and gas interact and taking a fiber core as a gas chamber; and the signal detection module comprises a photoelectric detector and is used for converting the detection light into an electric signal. An air chamber is formed in an air fiber core of the AR-HCF, a mode interference type sensor is constructed based on an AR-HCF micro-unit, the air chamber is constructed by the air fiber core of the AR-HCF, a hole is formed in the upper side face of the AR-HCF by femtosecond laser, the speed of air entering the fiber core is increased, phase change generated during gas spectrum absorption is demodulated through a phase-sensitive optical fiber interferometer, and the gas spectrum absorption rate is increased. And obtaining gas composition and concentration information.

Description

Technical Field

[0001] The invention relates to the technical field of optical sensing, in particular to a trace gas detection system based on an anti-resonance hollow-core optical fiber mode interferometer. Background Art

[0002] In recent years, with the rapid development of science and technology and economy, people's living standards have been significantly improved, but with it comes an accelerated rate of resource consumption and increasingly severe environmental pollution problems. The toxic and harmful gases produced in the industrial production process have increased sharply, which not only leads to frequent gas poisoning accidents, but also seriously pollutes the atmospheric environment. In particular, waste gases such as sulfur dioxide and carbon monoxide emitted by thermal power plants, steel mills, and fertilizer plants are the main causes of air pollution and acid rain, which damage the ecological balance, lead to land acidification and loss of nutrients, and seriously damage forests. At the same time, the flammable and explosive gases generated by internal faults of transformers in the power system also threaten the performance and life of the equipment. Therefore, the development of a real-time harmful gas monitoring system, the development of a new gas sensor, and the timely detection of the content of harmful gases in the ambient air are of great significance for protecting national property, reducing casualties in mines, optimizing industrial system design, and atmospheric environmental monitoring.

[0003] As a device that collects gas information and converts it into easily identifiable signals, gas sensors play a key role in environmental monitoring and industrial safety. However, traditional gas sensors have problems such as poor anti-interference ability, low sensitivity and insufficient precision. Fiber optic gas sensors have unique advantages in inferring the type and concentration of gas by measuring the optical properties related to the measured gas. Among them, gas sensors based on spectral absorption hollow photonic crystal fiber (HC-PBF) have attracted much attention due to their high sensitivity. However, HC-PBF also has some defects in application, such as large fusion loss with single-mode optical fiber, high cost and non-compact structure due to long gas chamber length, transmission loss and physical damage caused by side openings, etc. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a trace gas detection system and method based on antiresonant hollow core fiber mode interferometer, construct a gas chamber on the ARHCF, and demodulate the phase change generated during gas spectral absorption through a phase-sensitive fiber interferometer to obtain composition and concentration information.

[0005] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0006] A trace gas detection system based on an antiresonant hollow core fiber mode interferometer, comprising:

[0007] The light source module includes a pump light source and a detection light source. The pump light source is used to stimulate the photothermal effect of the gas being measured, and the detection light source is used to generate a single-wavelength laser far away from the gas absorption peak.

[0008] A transmission module, including a gas sensor, is used to transmit pump light and detection light, and to reflect the refractive index change caused by the photothermal effect to the phase change of the detection light through a photothermal interferometry (PTI) sensing technology;

[0009] A gas chamber module is used to use an antiresonant hollow core fiber as a place for light and gas to interact, with the fiber core acting as a gas chamber;

[0010] A signal detection module, including a photodetector, for converting detection light into an electrical signal;

[0011] The demodulation module, including a lock-in amplifier, is used to amplify and detect the electrical signal carrying the gas concentration information.

[0012] Furthermore, the pump light source is used to stimulate the photothermal effect of the gas being measured, and the detection light source is used to generate a single-wavelength laser far away from the gas absorption peak, including:

[0013] The pump light source is a DFB laser modulated by a sawtooth signal and a sine signal generated by a waveform generator, and the distributed feedback DFB laser is externally triggered to tune and output a pump light of a specific wavelength to stimulate the photothermal effect of the gas being measured;

[0014] The detection light source is a single-wavelength detection light output to generate a single-wavelength laser far away from the gas absorption peak.

[0015] Furthermore, the core device of the gas sensor is a mode interferometer based on ARHCF, and the mode interferometer includes a single-mode fiber SMF, a gradient-index multimode fiber GIF and an anti-resonant hollow-core fiber ARHCF.

[0016] Further, the gas sensor, for transmitting the pump light and the detection light, comprises:

[0017] The pump light and probe light output by the light source pass through the SMF and GIF and enter the ARHCF to excite high-order modes;

[0018] According to the higher-order modes and the fundamental mode, the mode interferometer is The interference between the fundamental mode and the higher-order mode is used to obtain the phase change relationship between the refractive index and , where n FM and n HM are the effective refractive indices of the fundamental mode and the higher-order mode, n extis the refractive index of the medium in the ARHC-PBF core, λ is the wavelength of the light wave, L is the length of the ARHCF, (2k+1)π represents the term of the phase difference, and k is an integer.

[0019] Furthermore, the preparation process of the mode interferometer is:

[0020] Weld SMF and GIF;

[0021] The GIF was cut at 245 m from the fusion point using a precision cutting system, and two SMF-GIF samples were prepared;

[0022] The cut samples were welded with ARHCF;

[0023] The ARHCF was cut off at 4.3 cm from the fusion point using a precision cutting system;

[0024] The cut sample is welded with the SMF-GIF sample prepared in the second step;

[0025] A hole is opened on the side of the ARHCF optical fiber, specifically including: connecting the spectrometer and the light source at both ends of the interferometer; placing the ARHCF optical fiber under a 20x objective lens, adjusting the focusing position, and the focusing position is located between the two holes in the ARHCF optical fiber core; setting the femtosecond laser energy and the laser irradiation time; observing the spectrum during the irradiation process, if the loss increases, it proves that the position of the hole damages the air hole in the fiber core, and the sample preparation fails.

[0026] Furthermore, the refractive index change caused by the photothermal effect is reflected on the phase change of the detection light through the photothermal interference (PTI) sensing technology, including:

[0027] Make sure the optical paths of the probe light and the pump light are coaxial and collinear;

[0028] Modulating the wavelength of the pump light to stimulate the photothermal effect of the pump light;

[0029] According to the photothermal effect, it is converted into the change of gas refractive index through interferometer;

[0030] According to the optical paths of the probe light and the pump light, the change in refractive index is converted into a change in the phase of the probe light through photothermal interferometry (PTI) sensing technology.

[0031] Further, the photothermal interferometry (PTI) sensing technology includes:

[0032] Performing wavelength modulation processing on the pump light to obtain wavelength-modulated pump light;

[0033] The measured gas is excited by the wavelength-modulated pump light to produce a photothermal effect;

[0034] The photothermal effect is used to load the photothermal information into the detection laser through an interferometer to obtain the phase change of the detection light;

[0035] The detection laser is harmonically demodulated to convert phase changes into intensity changes.

[0036] Furthermore, the antiresonant hollow core optical fiber is used as a place for light and gas to interact, and the core is used as a gas chamber, including:

[0037] The air chamber is constructed with the air core of ARHCF and holes are made on its sides;

[0038] The modulated pump beam is incident on a gas chamber filled with target gas molecules;

[0039] The target gas molecules produce characteristic absorption of the pump light to obtain changes in various physical quantities of the gas molecules;

[0040] According to the analysis of the change of physical quantity, the change of gas refractive index can be obtained;

[0041] According to the change of the refractive index, the change of the optical path of the detection light when it passes through the gas chamber is obtained;

[0042] According to the change of optical path, the phase change result of the detection light is obtained through an optical interferometer;

[0043] By inverting the phase change results of the detection light, the sample concentration and temperature information can be obtained.

[0044] Further, the detection light is converted into an electrical signal, including:

[0045] The pump light and the detection light are passed through a filter together to obtain the detection light, and the detection light is input into a photodetector to be converted into an electrical signal.

[0046] Further, the electrical signal carrying the gas concentration information is amplified and detected, including:

[0047] The electrical signal carrying gas information is input into the lock-in amplifier for amplification and detection to obtain the concentration information of the measured gas.

[0048] The above solution of the present invention includes at least the following beneficial effects:

[0049] The photothermal interference (PTI) sensing technology can indirectly detect the trace presence of gas, achieve high-sensitivity trace gas detection, and achieve a detection capability of several ppm level; the length of the gas chamber is significantly shortened to tens of centimeters, making the entire sensor structure more compact, and the AR-HCF has a larger core diameter, which improves the interaction efficiency between the gas and the light field, so that the system can more quickly reflect the changes in gas concentration, and has a strong detection capability for flammable and explosive gases such as methane and acetylene; the gas sensing unit adopts an all-fiber structure, which has the advantages of small size, anti-electromagnetic interference, and low cost; precise opening between two adjacent cladding holes on the AR-HCF optical fiber ensures the smooth entry of gas and avoids destroying the periodic structure of the optical fiber, reducing transmission loss, increasing the rate of gas entering the gas chamber, and greatly shortening the interaction time between light and gas; through the optical fiber fusion splicing process and parameter setting, low-loss and high-strength fusion of single-mode optical fiber and AR-HCF is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a flow chart of a trace gas detection system based on an antiresonant hollow core fiber mode interferometer provided by an embodiment of the present invention.

[0051] Figure 2 It is a schematic diagram of a gas detection system based on an antiresonant hollow-core fiber mode interferometer provided by an embodiment of the present invention.

[0052] Figure 3 It is a schematic diagram of the principle of a photothermal interference (PTI) sensing technology provided by an embodiment of the present invention.

[0053] Figure 4 It is a schematic diagram of a mode interferometer based on ARHCF and a schematic diagram of an ARHCF end face provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in a form and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0055] like Figure 1 As shown, an embodiment of the present invention provides a trace gas detection system based on an antiresonant hollow core fiber mode interferometer, comprising the following steps:

[0056] The light source module 11 includes a pump light source and a detection light source, wherein the pump light source is used to excite the photothermal effect of the gas being measured, and the detection light source is used to generate a single-wavelength laser far away from the gas absorption peak;

[0057] The transmission module 12 includes a gas sensor for transmitting pump light and detection light, and reflects the refractive index change caused by the photothermal effect to the phase change of the detection light through the photothermal interference (PTI) sensing technology;

[0058] The gas chamber module 13 is used to use the anti-resonant hollow core optical fiber as a place for light and gas to interact, and the fiber core as a gas chamber;

[0059] The signal detection module 14 includes a photodetector for converting the detection light into an electrical signal;

[0060] The demodulation module 15 includes a phase-locked amplifier, which is used to amplify and detect the electrical signal carrying the gas concentration information.

[0061] In the embodiment of the present invention, a DFB laser is used as a pump light source, which can provide a stable, single-frequency laser output and effectively stimulate the photothermal effect of the measured gas; the detection light source generates a single-wavelength laser far away from the gas absorption peak, avoiding direct attenuation of the detection light by gas absorption, ensuring stable transmission of the detection light and accurate measurement of phase changes; through photothermal interference sensing technology, the refractive index change caused by the gas photothermal effect is converted into a phase change of the detection light, thereby realizing non-contact, high-sensitivity gas concentration measurement; an anti-resonant hollow-core optical fiber is used as an air chamber, and the core is a cavity structure that can accommodate the measured gas. At the same time, the transmission characteristics of the optical fiber enable the light and gas to fully interact with each other, thereby enhancing the detection effect; the photodetector efficiently converts the detection light into an electrical signal, thereby improving the response speed and detection accuracy of the system, and the phase-locked amplifier is specifically used to amplify and detect weak electrical signals carrying gas concentration information, effectively filtering out noise, improving the signal-to-noise ratio, and ensuring accurate measurement of gas concentration.

[0062] In a specific embodiment of the present invention, a Figure 2The gas detection system shown in the figure consists of a light source part, a transmission part, a gas chamber part, a signal detection part, and a demodulation part. The waveform generator outputs a sawtooth signal and a sine signal. The added signal of the two is input to the DFB laser as a pump light source, and the external trigger tuned DFB laser outputs a laser of a specific wavelength. The absorption wavelength of the detected gas determines the wavelength output by the DFB. The laser of a specific wavelength is input to the EDFA through the isolator for amplification, and the filter 1 filters out the background noise of the EDFA and is input to the interferometer sensor unit through the coupler. When the gas chamber is filled with the detection gas, the pump light interacts with the detected gas in the interferometer sensor unit. The detection light source outputs a single-wavelength laser, which is the same as the gas absorption wavelength, and is input to the interferometer sensor unit through the isolator and coupler. The interaction between the pump laser and the gas causes changes in the environment inside the interferometer, and this change information is loaded into the detection light by the sensor unit. The pump light and the detection light pass through filter 2 together, the pump light is filtered, the detection light is input into the photodetector and converted into an electrical signal, and finally the signal carrying the gas concentration information is input into the phase-locked amplifier for amplification and detection, and finally the concentration information of the measured gas is displayed in a specific program in the computer.

[0063] In a preferred embodiment of the present invention, the pump light source is used to excite the photothermal effect of the gas to be measured, and the detection light source is used to generate a single-wavelength laser far away from the gas absorption peak, including:

[0064] The pump light source is a DFB laser modulated by a sawtooth signal and a sine signal generated by a waveform generator, and the distributed feedback DFB laser is externally triggered to tune and output a pump light of a specific wavelength to stimulate the photothermal effect of the gas being measured;

[0065] The detection light source is a single-wavelength detection light output to generate a single-wavelength laser far away from the gas absorption peak.

[0066] In the embodiment of the present invention, by externally triggering and tuning the DFB laser, a pump light of a specific wavelength can be accurately output. The DFB laser has a built-in grating structure, which can achieve smooth and tunable control of the wavelength, and accurately control the wavelength of the pump light, which can ensure that the photothermal effect occurs effectively on the target gas; the detection light source is a single-wavelength detection light output away from the gas absorption peak, which helps to reduce background noise and interference and improve the signal-to-noise ratio of the detection signal. The single-wavelength detection light helps to improve the dynamic range of the system, so that the system can simultaneously detect high-concentration and low-concentration gases.

[0067] In a preferred embodiment of the present invention, the core device of the gas sensor is a mode interferometer based on ARHCF, and the mode interferometer includes a single-mode fiber SMF, a gradient-index multimode fiber GIF and an anti-resonant hollow-core fiber ARHCF.

[0068] In the embodiment of the present invention, AR-HCF has extremely low dispersion, optical nonlinearity and extremely high laser damage threshold. Through the combination of SMF, GIF and AR-HCF, the mode interferometer can use the mode transmission characteristics in different optical fibers to produce interference effects. GIF can accept more light, and its refractive index gradually changes along the axial direction of the optical fiber, which helps to reduce the propagation loss of light inside the optical fiber and improve the transmission efficiency and capacity. The mode coupling between GIF, SMF and AR-HCF will produce complex interference patterns. The hollow core structure of AR-HCF minimizes the interaction between light and optical fiber materials during transmission. By using the characteristics of the hollow core of ARHCF, the measured gas can be 100% overlapped with the transmission light field, reducing the light transmission loss and improving the efficiency of photothermal pumping.

[0069] In a specific embodiment of the present invention, the optical fibers used include SMF, wherein the core and cladding diameters are 9 m and 125 m, respectively, GIF, wherein the core and cladding diameters are 62.5 m and 125 m, respectively, and ARHCF, wherein the core and cladding diameters are 45 m and 245 m, respectively; when connecting, such as Figure 4 As shown in FIG. 1 , the structure of the mode interferometer consists of a section of ARHCF with a length of L, both ends of which are fused with a graded-index multimode optical fiber with a length of 245 m. Finally, both ends of the GIF are fused with a single-mode optical fiber, and a microchannel connects the optical fiber surface and the air core of the ARHCF.

[0070] In a preferred embodiment of the present invention, a gas sensor for transmitting pump light and detection light comprises:

[0071] The pump light and probe light output by the light source pass through the SMF and GIF and enter the ARHCF to excite high-order modes;

[0072] According to the higher-order modes and the fundamental mode, the mode interferometer is The interference between the fundamental mode and the higher-order mode is used to obtain the phase change relationship between the refractive index and , where n FM and n HM are the effective refractive indices of the fundamental mode and the higher-order mode, n ext is the refractive index of the medium in the ARHC-PBF core, λ is the wavelength of the light wave, L is the length of the ARHCF, (2k+1)π represents the term of phase difference, and k is an integer.

[0073] In the embodiment of the present invention, the gas sensing unit is an all-fiber structure, which has the advantages of small size, resistance to electromagnetic interference, low cost and easy integration. The excitation of high-order modes increases the mode diversity in the interferometer, enhances the interference effect, and makes the measurement of phase changes more sensitive and accurate. By utilizing the interference between the fundamental mode and the high-order mode, the mode interferometer can cover a wider range of refractive index changes; the relationship between the refractive index and the phase change provides a method for directly measuring the refractive index change of the medium, thereby achieving high-precision measurement; by adjusting the length of the ARHCF, the refractive index of the core medium, and the wavelengths of the pump light and the probe light, the phase change is highly sensitive to the refractive index, has the potential to achieve high-resolution measurement, and can accurately monitor small changes.

[0074] In a specific embodiment of the present invention, the ARHCF-based mode interferometer is the core device of the gas sensor. The light output by the light source is input into the GIF through the single-mode optical fiber. After the light passes through the GIF, the mode field is amplified, and then enters the ARHCF to excite the high-order mode. Finally, the output light converges into the output SMF through the GIF. Since the core diameters of the single-mode optical fiber and the ARHCF do not match, the mode field difference is large, and the role of the GIF is to match the mode sizes of the two. When the mode meets the phase matching condition, the mode interferometer occurs interference between the fundamental mode and the high-order mode.

[0075] In a preferred embodiment of the present invention, the preparation process of the mode interferometer is:

[0076] Step 1: Weld SMF and GIF;

[0077] Step 2: Use a precision cutting system to cut the GIF at 245m from the welding point and prepare two SMF-GIF samples;

[0078] Step 3: The cut sample is welded with the ARHCF. To avoid the collapse of the ARHCF air holes, the welding process needs to be in manual mode. The welding machine parameters are set as follows: discharge time xx milliseconds, discharge current xx mA, and the discharge position is x microns away from the end face of the single-mode fiber.

[0079] Step 4: Use the precision cutting system to cut off the ARHCF at 4.3 cm from the welding point;

[0080] Step 5: Weld the cut sample with the SMF-GIF sample prepared in the second step;

[0081] Step 6: Drilling a hole on the side of the ARHCF optical fiber; the steps include:

[0082] The two ends of the interferometer are connected to a spectrometer and a light source;

[0083] Place the ARHCF fiber under a 20x objective lens and adjust the focus position (located between the two holes in the ARHCF fiber core); set the femtosecond laser energy to XXmW and the laser irradiation time to xx seconds; observe the spectrum during irradiation. If the loss increases, it proves that the opening position damages the air hole in the fiber core, and the sample preparation fails.

[0084] In the embodiment of the present invention, the structure has ultra-high sensitivity, ultra-short gas chamber, and has strong detection capability for inflammable and explosive gases such as methane and acetylene. The unique ARHCF optical fiber side opening scheme improves the efficiency of gas entering the optical fiber and reduces the gas response time;

[0085] In a specific embodiment of the present invention, SMF is fused with GIF, and the fusion program is set to a common multimode fusion program. The GIF is cut off at 245m from the fusion point using a precision cutting system; these two steps are repeated to prepare two SMF-GIF samples. The cut sample is fused with the ARHCF; since the optical fiber is large in size and the core is an air core, the general fusion program cannot automatically identify the ARHCF, so manual fusion is required. The fusion parameters are adjusted to avoid large fusion losses caused by the collapse of the air hole at the fusion point. The ARHCF is cut off at 4.3cm from the fusion point using a precision cutting system. The cut sample is fused with the SMF-GIF sample prepared in the second step, and the fusion steps are the same as the third step. A hole is opened on the side of the ARHCF optical fiber; the two ends of the prepared sample are connected to a light source and a spectrometer to detect whether the periodic structure of the ARHCF optical fiber will be destroyed during the punching process; the ARHCF optical fiber is placed under a 20x objective lens, and the focus position is adjusted so that the focus position is located between the two holes in the ARHCF optical fiber core. The femtosecond laser energy is set to XXmW, and the laser irradiation time is xx seconds. During the irradiation process, observe the spectrum. If the loss increases, it means that the position of the opening damages the air hole in the fiber core, and the sample preparation fails. The number of side openings on the 4.3 cm ARHCF fiber is kept at about 5.

[0086] In a preferred embodiment of the present invention, the refractive index change caused by the photothermal effect is reflected on the phase change of the detection light by using the photothermal interference (PTI) sensing technology, including:

[0087] Make sure the optical paths of the probe light and the pump light are coaxial and collinear;

[0088] Modulating the wavelength of the pump light to stimulate the photothermal effect of the pump light;

[0089] According to the photothermal effect, it is converted into the change of gas refractive index through interferometer;

[0090] According to the optical paths of the probe light and the pump light, the change in refractive index is converted into a change in the phase of the probe light through photothermal interferometry (PTI) sensing technology.

[0091] In the embodiment of the present invention, the coaxial and collinear optical path design ensures that the pump light and the detection light propagate on the same path, reducing the error caused by the optical path offset; by modulating the wavelength of the pump light, the precise wavelength modulation can more effectively stimulate the photothermal effect of the pump light and improve the sensitivity of the change of the physical parameters of the gas; the photothermal effect allows measurement without direct contact with the gas sample, reducing interference and pollution during the measurement process. The photothermal effect is not limited to temperature changes, but can also be extended to the detection of various physical parameters such as pressure and concentration, broadening the application scope of the sensing technology; the mode interferometer can accurately capture the interference phenomenon between the fundamental mode and the higher-order mode, and convert the tiny refractive index change into a measurable phase change. The PTI technology uses the pump-detection principle to monitor the change process of the physical parameters of the gas over time in real time. Combined with the optical fiber transmission technology, the PTI technology has the potential for high-precision sensing over a long distance, and is suitable for remote monitoring and distributed sensing systems.

[0092] In a specific embodiment of the present invention, the detection light, pump light, and gas sample are coaxial and collinear. By changing the wavelength of the pump light source, the wavelength of the pump light is modulated. Since the detection laser is far away from the gas absorption peak, it will not cause gas absorption. While the pump light is at the gas absorption peak, the target gas molecules can produce characteristic absorption of the pump light, thereby causing the energy of the gas molecules to increase and the thermal motion to intensify, which in turn leads to changes in the temperature, pressure, density and other physical quantities in the gas chamber. The changes in the temperature, pressure and density in the gas chamber are optically manifested as changes in the gas refractive index. Since the detection light and the pump light are coaxial, the change in the refractive index will cause the optical path of the detection light to change in the gas chamber when it passes through the optical interferometer. The optical interferometer has extremely high sensitivity to the optical path difference, and a small change in the optical path will cause the optical interferometer interference light intensity to jitter; and according to the optical path of the detection light and the pump light, when the detection light passes through the same optical path in the gas chamber, its cumulative phase is also modulated. The phase change of the detection light can be accurately detected by sensitive interferometer interferometry.

[0093] In a preferred embodiment of the present invention, the photothermal interferometry (PTI) sensing technology includes:

[0094] Performing wavelength modulation processing on the pump light to obtain wavelength-modulated pump light;

[0095] The measured gas is excited by the wavelength-modulated pump light to produce a photothermal effect;

[0096] The photothermal effect is used to load the photothermal information into the detection laser through an interferometer to obtain the phase change of the detection light;

[0097] The detection laser is harmonically demodulated to convert phase changes into intensity changes.

[0098] In an embodiment of the present invention, the wavelength of the pump light is modulated to shift the frequency of the photothermal signal to a high frequency, thereby avoiding excessive noise at a low frequency; harmonic demodulation is performed through a phase-locked amplifier, and a narrowband low-pass filter is used to filter out broadband noise, thereby obtaining a higher signal-to-noise ratio; the changes in the interference results of the detection light are used to invert the sample concentration and temperature information, and the characteristics of the two technologies of photothermal spectroscopy and wavelength modulation are combined to accurately control the wavelength of the pump light and selectively match it with the specific absorption peak of the target gas, thereby significantly enhancing the photothermal effect and improving the sensitivity of detection. The photothermal effect is converted into a phase change of the detection light through an interferometer. The phase information is more accurate and stable than the intensity information, which helps to improve the accuracy of the measurement. The harmonic demodulation process converts the phase change into an intensity change, and the dynamic changes of the gas parameters are monitored according to the phase.

[0099] In a specific embodiment of the present invention, Figure 3 As shown in the figure, the schematic diagram of the photothermal interferometry (PTI) sensing technology system consists of detection light, pump light, photodetector, laser driver, phase-locked amplifier, and signal processing module. The gas to be measured is excited by the pump light to produce photothermal effect, and the photothermal information is loaded onto the detection laser through the interferometer. Only when the detection laser reaches the photodetector is it converted into an electrical signal, and finally the phase change is converted into intensity change by harmonic demodulation through the phase-locked amplifier.

[0100] In a preferred embodiment of the present invention, an antiresonant hollow core optical fiber is used as a place for light and gas to interact, and the fiber core is used as a gas chamber, including:

[0101] Open a hole on the side of the ARHCF optical fiber;

[0102] The modulated pump beam is incident on a gas chamber filled with target gas molecules;

[0103] The target gas molecules produce characteristic absorption of the pump light to obtain changes in various physical quantities of the gas molecules;

[0104] According to the analysis of the change of physical quantity, the change of gas refractive index can be obtained;

[0105] According to the change of the refractive index, the change of the optical path of the detection light when it passes through the gas chamber is obtained;

[0106] According to the change of optical path, the phase change result of the detection light is obtained through an optical interferometer;

[0107] By inverting the phase change results of the detection light, the sample concentration and temperature information can be obtained.

[0108] In the embodiment of the present invention, the core of the ARHCF is used as a gas chamber. Compared with the traditional HC-PBF, it has a larger core, a faster gas exchange rate, and a more complete interaction between light and gas. The phase change generated when the gas spectrum is absorbed is demodulated by a phase-sensitive fiber interferometer to obtain the composition and concentration information;

[0109] In a specific embodiment of the present invention, a wavelength-modulated pump beam is incident on a cell filled with gas, exciting the gas molecules to a higher energy state before returning to the initial state through molecular collisions. This process will cause local heating of the gas, thereby slightly changing the temperature, pressure and density of the target gas, and ultimately adjusting the refractive index of the gas. When the probe light passes through the same optical path in the gas chamber, its accumulated phase is also modulated. The phase change of the probe light can be accurately detected by a sensitive interferometer. Finally, the phase change is converted into an intensity change by harmonic demodulation, and the phase change generated when the gas spectrum is absorbed is demodulated by a phase-sensitive mode interferometer, and the composition and concentration information is inverted.

[0110] In a preferred embodiment of the present invention, converting the detection light into an electrical signal comprises:

[0111] The pump light and the detection light are passed through a filter together to obtain the detection light, and the detection light is input into a photodetector to be converted into an electrical signal.

[0112] In the embodiment of the present invention, the filter can effectively filter out the pump light and its harmonic stray light to ensure the purity of the detection light signal; the pump light usually has a high power density and will directly or indirectly interfere with the detection light signal. By separating the pump light from the detection light through the filter, such interference can be avoided to ensure the authenticity of the detection light signal; although the intensity of the detection light is usually much lower than the pump light, after filtering, the detection light signal is enhanced, so that the photoelectric detector can capture the signal more easily, thereby improving the detection sensitivity of the signal. By filtering out unnecessary stray light, the filter helps to balance the ratio of signal to noise, making the signal easier to identify and extract.

[0113] In a preferred embodiment of the present invention, amplifying and detecting the electrical signal carrying gas concentration information includes:

[0114] The electrical signal carrying gas information is input into the lock-in amplifier for amplification and detection to obtain the concentration information of the measured gas.

[0115] In an embodiment of the present invention, the phase-locked amplifier can amplify signals of a specific frequency, effectively suppress noise and interference, stably amplify weak electrical signals, reduce errors caused by signal fluctuations, and make the measurement results more stable and reliable; the phase-locked amplifier can process low-concentration gas signals, quickly amplify and detect gas signals, and thus quickly provide measurement results of gas concentration.

[0116] It should be noted that the system is a system corresponding to the above method, and all implementation methods in the above method embodiment are applicable to this embodiment and can achieve the same technical effect.

[0117] The embodiment of the present invention further provides a computing device, comprising: a processor, a memory storing a computer program, wherein when the computer program is executed by the processor, the method described above is executed. All implementations in the above method embodiment are applicable to this embodiment and can achieve the same technical effect.

[0118] The embodiment of the present invention also provides a computer-readable storage medium storing instructions, which, when executed on a computer, enable the computer to execute the method described above. All implementations in the above method embodiment are applicable to this embodiment and can achieve the same technical effect.

[0119] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A trace gas detection system based on antiresonant hollow core fiber mode interferometer, characterized in that: include: A light source module, including a pump light source and a detection light source, wherein the pump light source is used to excite the photothermal effect of the gas being measured, and the detection light source is used to generate a single-wavelength laser far away from the gas absorption peak; A transmission module, including a gas sensor for transmitting pump light and detection light and reflecting the refractive index change caused by the photothermal effect on the phase change of the detection light; A gas chamber module is used to use an antiresonant hollow core fiber as a place for light and gas to interact, with the fiber core acting as a gas chamber; A signal detection module, comprising a photodetector for converting detection light into an electrical signal; The demodulation module includes a phase-locked amplifier for processing the electrical signal to obtain gas information.

2. The trace gas detection system based on antiresonant hollow core fiber mode interferometer according to claim 1 is characterized in that: The pump light source is a DFB laser modulated by a sawtooth signal and a sinusoidal signal generated by a waveform generator, and the distributed feedback DFB laser is externally triggered to tune the output of pump light of a specific wavelength to stimulate the photothermal effect of the measured gas; the detection light source is a single-wavelength detection light output to generate a single-wavelength laser far away from the gas absorption peak.

3. The trace gas detection system based on antiresonant hollow core fiber mode interferometer according to claim 2 is characterized in that: The gas sensor comprises an ARHCF-based mode interferometer, which comprises a single-mode fiber SMF, a graded-index multimode fiber GIF and an anti-resonant hollow-core fiber ARHCF.

4. The trace gas detection system based on antiresonant hollow core fiber mode interferometer according to claim 3 is characterized in that: Gas sensors are used to transmit pump light and detection light, including: The pump light and probe light output by the light source pass through the single-mode fiber SMF and the graded-index multimode fiber GIF and enter the antiresonant hollow-core fiber ARHCF to excite high-order modes. According to the higher-order modes and the fundamental mode, the mode interferometer is The interference between the fundamental mode and the higher-order mode is used to obtain the phase change relationship between the refractive index and , where n FM and n HM are the effective refractive indices of the fundamental mode and the higher-order mode, n ext is the refractive index of the medium in the ARHC-PBF core, λ is the wavelength of the light wave, L is the length of the ARHCF, (2k+1)π represents the term of phase difference, and k is an integer.

5. The trace gas detection system based on antiresonant hollow core fiber mode interferometer according to claim 4 is characterized in that: The preparation process of the mode interferometer is: Weld SMF and GIF; The GIF was cut at 245 m from the fusion point using a precision cutting system, and two SMF-GIF samples were prepared; The cut samples were welded with ARHCF; The ARHCF was cut off at 4.3 cm from the fusion point using a precision cutting system; The cut samples were welded to the SMF-GIF samples; Opening holes on the side of the ARHCF optical fiber specifically includes: connecting the spectrometer and the light source at both ends of the interferometer; Place the ARHCF optical fiber under a 20x objective lens and adjust the focus position so that the focus position is between the two holes in the ARHCF optical fiber core; set the femtosecond laser energy and laser irradiation time; observe the spectrum during irradiation. If the loss increases, it proves that the opening position damages the air hole in the fiber core, and the sample preparation fails.

6. The trace gas detection system based on antiresonant hollow core fiber mode interferometer according to claim 5 is characterized in that: The refractive index change caused by the photothermal effect is reflected in the phase change of the detection light, including: Make sure the optical paths of the probe light and the pump light are coaxial and collinear; Modulating the wavelength of the pump light to stimulate the photothermal effect of the pump light; According to the photothermal effect, it is converted into the change of gas refractive index through interferometer; According to the optical paths of the probe light and the pump light, the change of the refractive index is converted into the change of the phase of the probe light.

7. The trace gas detection system based on antiresonant hollow core fiber mode interferometer according to claim 6, characterized in that: Convert the change of refractive index into the change of the phase of the detection light, including: Performing wavelength modulation processing on the pump light to obtain wavelength-modulated pump light; The measured gas is excited by the wavelength-modulated pump light to produce a photothermal effect; The photothermal effect is used to load the photothermal information into the detection laser through an interferometer to obtain the phase change of the detection light; The detection laser is harmonically demodulated to convert phase changes into intensity changes.

8. The trace gas detection system based on antiresonant hollow core fiber mode interferometer according to claim 7, characterized in that: The antiresonant hollow core fiber is used as the place where light and gas interact, and the core is used as the gas chamber, including: The air chamber is constructed with the air core of ARHCF and holes are made on its sides; The modulated pump beam is incident on a gas chamber filled with target gas molecules; The target gas molecules produce characteristic absorption of the pump light to obtain changes in various physical quantities of the gas molecules; According to the analysis of the change of physical quantity, the change of gas refractive index can be obtained; According to the change of the refractive index, the change of the optical path of the detection light when it passes through the gas chamber is obtained; According to the change of optical path, the phase change result of the detection light is obtained through an optical interferometer; By inverting the phase change results of the detection light, the sample concentration and temperature information can be obtained.

9. The trace gas detection system based on antiresonant hollow core fiber mode interferometer according to claim 8, characterized in that: Convert the detection light into electrical signals, including: The pump light and the detection light are passed through a filter together to obtain the detection light, and the detection light is input into a photodetector to be converted into an electrical signal.

10. The trace gas detection system based on antiresonant hollow core fiber mode interferometer according to claim 9, characterized in that: A lock-in amplifier processes the electrical signal to obtain gas information, including: The electrical signal carrying gas information is input into the lock-in amplifier for amplification and detection to obtain the concentration information of the measured gas.

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