A single-wavelength infrared fiber optic gas sensor

Abstract

The present invention discloses a single-wavelength infrared fiber optic gas sensor, comprising a light source unit, a sensing detection unit, and a detection and acquisition unit. The light source unit comprises a single-wavelength narrowband light source and a light source controller. The sensing detection unit comprises a sensing gas chamber, a gas sensing path, and a fiber optic sensing element. The input end of the fiber optic sensing element is connected to the single-wavelength narrowband light source. The fiber optic sensing element is a chalcogenide glass fiber. A sensing region is provided in the middle of the chalcogenide glass fiber. The sensing region is a flat fiber structure, and the surface of the sensing region is coated with a graphene oxide coating. The sensing region is located within the sensing gas chamber. The detection and acquisition unit comprises a light intensity detector and a data acquisition and analysis device. The input end of the light intensity detector is connected to the output end of the fiber optic sensing element, and the output end of the light intensity detector is connected to the data acquisition and analysis device. The sensor of the present invention has the advantages of high measurement accuracy, good stability, high sensitivity, long-distance operation, good cost-effectiveness, and small size.

Description

Technical Field

[0001] The invention relates to an optical fiber sensor, in particular to a single-wavelength infrared optical fiber gas sensor. Background Art

[0002] With the development of industrial production and the advancement of social sciences, people are paying more and more attention to the safety and environmental issues caused by various gaseous pollutants, such as volatile organic compounds (VOCs), greenhouse gases, and toxic and hazardous gases (NH3, NO2, NO, formaldehyde, SO2, etc.). Therefore, gas sensors, as devices that can respond to specific gases and output signals, have a wide range of applications in various fields related to national livelihoods.

[0003] Mid-infrared (MIR) is defined as the spectral range between 3μm and 20μm, covering the fundamental vibrational region of chemicals. Each vibrational mode is unique to each molecule, hence the name "fingerprint region." Accurate gas sensing has important applications in today's environmental and healthcare sectors. Mid-infrared fiber optic sensors can detect toxic and hazardous gases in the workplace and living environment in real time. Mid-infrared fiber optic sensors offer advantages such as ease of operation, high sensitivity, and flexible application scenarios. They have a wide detection range, high measurement accuracy, and can be used for on-site monitoring. Furthermore, compared to electrochemical sensors, they are less susceptible to secondary metal contamination, offer long-term performance, and are stable. Traditional MIR fiber optic sensors rely on portable broadband MIR light as their primary measurement light source. Mid-infrared spectroscopy is used for judgment and provides signals that can be used as alerts. However, using broadband MIR light as a light source requires a spectrometer to collect the signal, which means that traditional broadband MIR fiber optic sensors require a large, complex, and costly setup. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a single-wavelength infrared fiber optic gas sensor to address the shortcomings of the existing technology. The device uses a single-wavelength narrow-band light source to excite the infrared characteristic absorption wavelength of the gas and uses a light intensity detector to collect the output signal. It can detect the gas to be tested more accurately, avoid interference from other gas molecules, and achieve high-precision measurement of specific gases.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: a single-wavelength infrared fiber optic gas sensor, including a light source unit, a sensing detection unit and a detection acquisition unit, the light source unit is composed of a single-wavelength narrowband light source and a light source controller, the single-wavelength narrowband light source is connected to the light source controller, the sensing detection unit is composed of a sensing air chamber, a gas sensing path and an optical fiber sensing element, the sensing air chamber is communicated with the gas sensing path, the input end of the optical fiber sensing element is connected to the single-wavelength narrowband light source, the optical fiber sensing element is a chalcogenide glass optical fiber, the structure of the chalcogenide glass optical fiber includes a core and a coating layer arranged on the outside of the core, a sensing area is provided in the middle of the chalcogenide glass optical fiber, the coating layer of the sensing area is removed, the sensing area is a flat optical fiber structure, and a plurality of first layers are evenly spaced on the upper surface of the flat optical fiber structure. A groove, a plurality of second grooves are arranged at equal intervals on the lower surface of the flat optical fiber structure, the plurality of first grooves correspond one to the plurality of second grooves in an upper and lower direction, the surface of the sensing area is coated with a graphene oxide coating, the sensing area is placed in the sensing air chamber, the detection and acquisition unit is composed of a light intensity detector and a data acquisition and analysis device, the input end of the light intensity detector is connected to the output end of the optical fiber sensing element, the output end of the light intensity detector is connected to the data acquisition and analysis device, the data acquisition and analysis device is used to analyze the sensor signal transmitted by the light intensity detector, and respectively obtain a blank spectrum S1 measured under an air background and a sensor spectrum S2 collected under different gas concentrations, and obtain a specific infrared absorption spectrum relationship diagram of the gas to be measured under different concentrations by dividing the blank spectrum S1 by the sensor spectrum S2 and taking a logarithmic function of the output value.

[0006] The single-wavelength infrared fiber gas sensor of the present invention is a gas sensor based on chalcogenide glass fiber, which uses chalcogenide glass fiber for mid-infrared band sensing. Chalcogenide glass fiber has good transmittance characteristics in the mid-infrared band and has corrosion resistance and anti-crystallization characteristics. It also has the advantages of being insensitive to microwaves and having adjustable components. The present invention removes the coating layer of the chalcogenide glass fiber sensing area and prepares it into a flat fiber structure. The first groove and the second groove on the upper and lower surfaces of the flat fiber structure form a periodic microstructure. The waveguide geometry of the flat fiber structure significantly affects the number of internal reflections, thereby increasing the transmission depth of the evanescent wave, and can achieve more internal reflections of infrared light and more effective light coupling in the waveguide, thereby greatly enhancing the analysis signal and the achievable signal-to-noise ratio. The evanescent wave can sense changes in external environmental parameters. When the gas molecules to be measured come into contact with the molecules in the functional layer, they will be adsorbed on the surface of the functional layer. The present invention obtains information about the gas molecules to be measured by detecting changes in absorption intensity at specific wavelength positions caused by changes in the concentration of the gas to be measured.

[0007] The single-wavelength infrared fiber optic gas sensor proposed by the present invention utilizes the interaction between the evanescent wave leaked during transmission of chalcogenide glass optical fiber and gas molecules, ultimately causing a change in output intensity at the output end of the optical fiber, thereby establishing a relationship between light intensity and gas concentration. The theoretical basis for using infrared evanescent wave spectral absorption detection is that the energy of the energy level transitions occurring in different gas molecules corresponds to the evanescent wave leaked during optical fiber transmission of light and the energy of light of a specific wavelength, which is reflected in the specific absorption of the evanescent wave energy by different gases. Therefore, to use infrared optical fiber for qualitative and quantitative analysis of gases, it is first necessary to target the infrared characteristic absorption wavelength of the gas molecules to provide a basis for the selection of a single-wavelength narrowband light source and gas analysis. Since different gas molecules have different absorption wavelengths, infrared single-wavelength fiber optic gas sensors are only used to sense gases with specific infrared absorption wavelengths. Fiber changes can be detected at the infrared absorption wavelength of the gas to be measured. Other fault gases do not have infrared absorption peaks at this wavelength and therefore cannot be detected, eliminating interference from other gases.

[0008] When the single-wavelength infrared fiber optic gas sensor of the present invention is in use, light of a specific wavelength emitted by a single-wavelength narrowband light source couples to the input end of the fiber optic sensor element and enters the sensor element. A light intensity detector collects the signal from the output end of the fiber optic sensor element and transmits the sensor signal to a data acquisition and analysis device. The present invention only requires a light intensity detector at the output end of the fiber optic sensor element to detect intensity changes in the output signal, eliminating the need for a spectrometer to analyze the signal. By comparison, the single-wavelength infrared fiber optic gas sensor of the present invention significantly reduces cost, is easy to operate, and can be integrated. It also offers higher measurement accuracy for specific gases, avoids cross-interference from other gas molecules, and offers improved stability, thus better meeting the specific requirements of environmental gas detection.

[0009] Preferably, the flat optical fiber structure is prepared by hot pressing. By hot pressing the chalcogenide glass optical fiber to prepare the flat optical fiber structure, the penetration depth of the evanescent wave is increased while ensuring the mechanical strength of the optical fiber and reducing the loss.

[0010] Furthermore, the hot pressing device used to prepare the flat optical fiber structure includes a hot pressing mold, a heating device, an elastic clamp, an optical fiber clamp and a microscope, the hot pressing mold includes an upper mold and a lower mold, the bottom of the upper mold is provided with a first protrusion protruding downward, the top of the lower mold is provided with a second protrusion protruding upward, the lower surface of the first protrusion is provided with a plurality of third grooves at equal intervals, the upper surface of the second protrusion is provided with a plurality of fourth grooves at equal intervals, the plurality of third grooves correspond to the plurality of fourth grooves one by one above and below, the ends of the first protrusion and the second protrusion are respectively provided with transition areas, the first protrusion and the second protrusion are provided with transition areas, The rising portion is used to press the chalcogenide glass optical fiber to be hot-pressed up and down to obtain a flat optical fiber structure. The upper mold and the lower mold are respectively connected to the heating device, and the heating device is used to heat the upper mold and the lower mold. The elastic clamp is provided at both ends of the upper mold and the lower mold, and the elastic clamp is used to clamp the upper mold and the lower mold up and down and apply pressure. The optical fiber clamp is provided on both sides of the upper mold and the lower mold, and the optical fiber clamp is used to clamp the two ends of the chalcogenide glass optical fiber to be hot-pressed. The microscope is provided on one side of the upper mold and the lower mold, and the microscope is used to observe the thickness of the flat optical fiber structure during the hot pressing process.

[0011] Preferably, the number of the planar optical fiber structures is one or more, and the plurality of planar optical fiber structures are arranged at intervals along the length direction of the chalcogenide glass optical fiber.

[0012] Furthermore, the thickness of a single planar fiber structure is 100-110 μm and its length is 3-4 cm. The spacing between adjacent planar fiber structures in a plurality of planar fiber structures is 3-4 cm, and the length of the sensing area containing multiple planar fiber structures is 15-20 cm. The length of the transition region is 1-1.5 cm, and the distance between adjacent first grooves on each planar fiber structure is 3-8 μm. The distance between adjacent first grooves on each planar fiber structure is 3-8 μm, meaning that microstructures with a period of 3-8 μm are formed on the upper and lower surfaces of the planar fiber structure, increasing the penetration strength of the evanescent wave and thereby improving sensor sensitivity. The design of the transition region, which is 1-1.5 cm in length, reduces energy loss during light transmission from the traditional cylindrical structure to the planar fiber structure, thereby improving sensor sensitivity.

[0013] Preferably, the graphene oxide coating is pressed onto the surface of the planar optical fiber structure by hot pressing, and is closely fitted with the multiple first grooves and the multiple second grooves.

[0014] Preferably, the thickness of the graphene oxide coating is 300 to 800 nm.

[0015] Preferably, the output wavelength of the single-wavelength narrow-band light source is 4.23 μm, 4.60 μm, 5.20 μm or 6.14 μm, the bandwidth is 160 to 200 nm, and the total output power is not less than 100 mW.

[0016] Preferably, the chalcogenide glass optical fiber is As2S3, As2Se3, Ge-As-Se or Ge-As-S chalcogenide glass bare core optical fiber, and the core diameter of the chalcogenide glass optical fiber is 300-500 μm.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) High measurement accuracy. The present invention targets the infrared characteristic absorption wavelength of the gas, uses a single-wavelength narrow-band light source for excitation, and utilizes a light intensity detector to collect the output signal. This can more accurately detect the gas to be measured, avoid interference from other gas molecules, and achieve high-precision measurement of specific gases.

[0019] (2) Good stability. The present invention uses chalcogenide glass optical fiber as the optical fiber sensing element, which has stable performance, can be used for a long time, is corrosion-resistant, has strong anti-electromagnetic interference ability, and can work normally in complex environments;

[0020] (3) High sensitivity. The present invention uses a flat optical fiber structure as the sensing area, which can increase the penetration depth of the evanescent wave, facilitate interaction with gas molecules, and significantly improve the sensitivity of the sensor;

[0021] (4) Long-distance operation. The present invention uses chalcogenide glass optical fiber as the optical fiber sensing element. The required sensing chamber is small in size, which enables remote detection and long-distance real-time monitoring, and is flexible in use scenarios.

[0022] (5) Good economic efficiency. The present invention uses a single-wavelength narrowband light source and a light intensity detector for measurement, without the need for an infrared broadband light source and a spectrometer. The equipment cost is low, which can greatly improve economic efficiency.

[0023] (6) Small size. The present invention uses a single-wavelength narrowband light source and a light intensity detector for measurement, eliminating the need for an infrared broadband light source and spectrometer. This effectively reduces the size of the sensor. Furthermore, the diameter of the chalcogenide glass optical fiber used as the optical fiber sensing element is less than 1 mm, making it compact and very convenient to install. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of a single-wavelength infrared fiber gas sensor in an embodiment;

[0025] Figure 2 FIG2 is a diagram showing a state in which the chalcogenide glass optical fiber is placed flat on the second protrusion of the lower mold;

[0026] Figure 3 This is a diagram of the state when the upper die and lower die are clamped up and down by the elastic clamp;

[0027] Figure 4 A top view of a single flat optical fiber structure in an embodiment;

[0028] Figure 5 is a front view of a single flat optical fiber structure in an embodiment;

[0029] Figure 6 A top view of a chalcogenide glass optical fiber with three flat optical fiber structures in the sensing area;

[0030] Figure 7 FIG. 4 is an absorption spectrum of nitric oxide by the single-wavelength infrared optical fiber gas sensor in the embodiment. DETAILED DESCRIPTION

[0031] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0032] The single wavelength infrared fiber optic gas sensor of the embodiment, such as Figure 1 As shown, it includes a light source unit, a sensing detection unit and a detection acquisition unit. The light source unit consists of a single-wavelength narrowband light source 1 and a light source controller 2. The single-wavelength narrowband light source 1 is connected to the light source controller 2. The sensing detection unit consists of a sensing air chamber 3, a gas sensing path 4 and an optical fiber sensing element 5. The sensing air chamber 3 is communicated with the gas sensing path 4. The input end of the optical fiber sensing element 5 is connected to the single-wavelength narrowband light source 1. The optical fiber sensing element 5 is a chalcogenide glass optical fiber. The structure of the chalcogenide glass optical fiber includes a core and a coating layer arranged on the outside of the core. A sensing area is provided in the middle of the chalcogenide glass optical fiber. The coating layer of the sensing area is removed. The sensing area is a flat optical fiber structure 6. A plurality of first grooves 61 are evenly spaced on the upper surface of the flat optical fiber structure 6, and a plurality of first grooves 61 are evenly spaced on the lower surface of the flat optical fiber structure 6. A plurality of second grooves 62 are provided, and the plurality of first grooves 61 correspond one to another in the upper and lower parts of the plurality of second grooves 62. The surface of the sensing area is coated with a graphene oxide coating. The sensing area is placed in the sensing air chamber 3. The detection and acquisition unit is composed of a light intensity detector 7 and a data acquisition and analysis device 8. The input end of the light intensity detector 7 is connected to the output end of the optical fiber sensing element 5, and the output end of the light intensity detector 7 is connected to the data acquisition and analysis device 8. The data acquisition and analysis device 8 is used to analyze the sensing signal transmitted by the light intensity detector 7, and obtain the blank spectrum S1 measured under the air background and the sensing spectrum S2 collected under different gas concentrations respectively. The blank spectrum S1 is divided by the sensing spectrum S2 and the output value is logarithmically functioned to obtain a specific infrared absorption spectrum relationship diagram of the gas to be measured under different concentrations.

[0033] In this embodiment, the number of the flat optical fiber structure 6 is one, the thickness is 100-110 μm, the length is 3-4 cm, and the top view thereof is shown in FIG. Figure 4 , front view Figure 5 The number of the flat fiber structures 6 can also be multiple, and the multiple flat fiber structures 6 are spaced apart along the length direction of the chalcogenide glass fiber. The spacing between two adjacent flat fiber structures in the multiple flat fiber structures is 3 to 4 cm, and the length of the sensing area with multiple flat fiber structures is 15 to 20 cm. The distance between two adjacent first grooves on each flat fiber structure is 3 to 8 μm. See the top view of the chalcogenide glass fiber with three flat fiber structures in the sensing area. Figure 6 .

[0034] In this embodiment, the graphene oxide coating is pressed onto the surface of the planar optical fiber structure 6 by hot pressing, and is closely attached to the plurality of first grooves 61 and the plurality of second grooves 62. The thickness of the graphene oxide coating is 300-800 nm.

[0035] In this embodiment, the output wavelength of the single-wavelength narrowband light source 1 is 5.20 μm, the bandwidth is 160-200 nm, and the total output power is not less than 100 mW.

[0036] In this embodiment, the chalcogenide glass optical fiber adopts As2S3 chalcogenide glass bare core optical fiber, and the diameter of the core of the chalcogenide glass optical fiber is 400 μm.

[0037] In this embodiment, the flat optical fiber structure 6 is prepared by hot pressing. Figure 2 and Figure 3As shown, the hot pressing device used to prepare the flat optical fiber structure 6 includes a hot pressing mold, a heating device 95, an elastic clamp 96, an optical fiber clamp 97 and a microscope 98. The hot pressing mold includes an upper mold 91 and a lower mold 92. The bottom of the upper mold 91 is provided with a first protrusion 93 that protrudes downward, and the top of the lower mold 92 is provided with a second protrusion 94 that protrudes upward. The lower surface of the first protrusion 93 is provided with a plurality of third grooves (not shown in the figure) at equal intervals, and the upper surface of the second protrusion 94 is provided with a plurality of fourth grooves 99 at equal intervals. The plurality of third grooves correspond to the plurality of fourth grooves 99 one by one. The first protrusion 93 and the second protrusion 94 are respectively provided with a length of 1 to 1.5 cm at both ends. The first protrusion 93 and the second protrusion 94 are used to press the chalcogenide glass optical fiber to be hot-pressed up and down to obtain the flat optical fiber structure 6. The upper mold 91 and the lower mold 92 are respectively connected to the heating device 95, and the heating device 95 is used to heat the upper mold 91 and the lower mold 92. The elastic clamp 96 is provided at both ends of the upper mold 91 and the lower mold 92. The elastic clamp 96 is used to clamp the upper mold 91 and the lower mold 92 up and down and pressurize them. The optical fiber clamp 97 is provided on both sides of the upper mold 91 and the lower mold 92. The optical fiber clamp 97 is used to clamp the two ends of the chalcogenide glass optical fiber to be hot-pressed. The microscope 98 is provided on one side of the upper mold 91 and the lower mold 92. The microscope 98 is used to observe the thickness of the flat optical fiber structure 6 during the hot pressing process.

[0038] The preparation method of the above-mentioned single-wavelength infrared optical fiber gas sensor comprises the following steps:

[0039] 1. Preparation of optical fiber sensing elements

[0040] 1-1. Removal of coating layer in the sensing area of ​​chalcogenide glass optical fiber

[0041] A 40-50 cm long, 400 μm diameter chalcogenide glass optical fiber was cut, and a certain length of the central region was selected as the sensing region. The sensing region was immersed in a dichloromethane solution with a mass concentration of greater than 97% for 2-5 minutes to remove the coating layer on the surface of the sensing region. After removal, the surface of the sensing region was cleaned with alcohol with a mass concentration of greater than 99.7% and deionized water.

[0042] 1-2. Modification of the surface functional layer of the sensing area

[0043] 50-100 μL of a graphene oxide dispersion with a mass volume concentration of 2 mg / mL was dropped onto the surface of the chalcogenide glass optical fiber from which the coating layer had been removed using an ultra-precision pipette;

[0044] 1-3. Preparation of flat optical fiber structure by hot pressing

[0045] Fix the two ends of the chalcogenide glass optical fiber obtained in step 1-1 with a fiber holder, and straighten the optical fiber so that it is flat on the second raised portion of the lower mold. Figure 2As shown; Place the upper die on the lower die and clamp the upper die and lower die up and down by the elastic clamp, as shown Figure 3 As shown; the temperature of the upper mold and the lower mold is heated to 180-230°C by a heating device, and pressure is applied by an elastic clamp. After the graphene oxide on the surface of the chalcogenide glass fiber is heated to a high temperature, it is tightly adhered to the periodic microstructure on the surface of the flat fiber structure; during the pressurization process, the thickness of the flat fiber structure is observed through a microscope. When the thickness of the flat fiber structure reaches 100-110 μm, the pressurization is stopped, and after cooling, the chalcogenide glass fiber is removed;

[0046] 2. Construction of single-wavelength infrared fiber optic gas sensor

[0047] Build Figure 1 The single-wavelength infrared fiber optic gas sensor shown.

[0048] When the above-mentioned single-wavelength infrared fiber optic gas sensor is in use, light of a specific wavelength emitted by a single-wavelength narrow-band light source is coupled to the input end of the fiber optic sensing element and enters the fiber optic sensing element. The light intensity detector detects and collects the light intensity output by the fiber optic sensing element and transmits the sensing signal to the data acquisition and analysis device. The data acquisition and analysis device analyzes the sensing signal to obtain a blank spectrum S1 measured under an air background and a sensing spectrum S2 collected under different gas concentrations. By dividing the blank spectrum S1 by the sensing spectrum S2 and taking a logarithmic function of the output value, a specific infrared absorption spectrum relationship diagram of the gas to be measured at different concentrations is obtained.

[0049] The strongest characteristic absorption wavelengths of some gases are shown in Table 1. By selecting a single wavelength light source output based on the strongest characteristic absorption wavelength of a gas, a specific gas can be detected to avoid cross-influence and improve detection results.

[0050] Table 1

[0051] Gas chemical formula Strongest characteristic absorption wavelength NO 5.20μm <![CDATA[CO2]]> 4.23μm CO 4.60μm <![CDATA[CH4]]> 3.31μm <![CDATA[H2O]]> 5.94μm <![CDATA[NH3]]> 10.30μm <![CDATA[SO2]]> 7.28μm <![CDATA[O3]]> 9.50μm <![CDATA[NO2]]> 6.14μm

[0052] When the above single wavelength infrared fiber optic gas sensor is used for nitric oxide gas detection, the obtained nitric oxide gas absorption spectrum is shown in Figure 7 The five volume concentrations of nitric oxide gas (5%, 10%, 15%, 20%, 25%) were respectively exposed to the detection area of ​​the flat optical fiber structure, and the relationship between the absorption intensity of nitric oxide at 5.20μm and the volume concentration of nitric oxide was measured to establish the relationship between the absorption intensity of nitric oxide at 5.20μm and the volume concentration of nitric oxide. Figure 7 The slope of the concentration-absorption intensity graph shown is the sensitivity of the single-wavelength optical fiber sensor based on As2S3 chalcogenide glass fiber.

Claims

1. A single-wavelength infrared fiber optic gas sensor, comprising a light source unit, a sensing unit, and a detection and collection unit, characterized in that: The light source unit is composed of a single-wavelength narrowband light source and a light source controller, and the single-wavelength narrowband light source is connected to the light source controller. The sensing detection unit is composed of a sensing air chamber, a gas sensing path and an optical fiber sensing element. The sensing air chamber is connected to the gas sensing path, and the input end of the optical fiber sensing element is connected to the single-wavelength narrowband light source. The optical fiber sensing element is a chalcogenide glass optical fiber. The structure of the chalcogenide glass optical fiber includes a core and a coating layer arranged on the outside of the core. A sensing area is provided in the middle of the chalcogenide glass optical fiber, and the coating layer of the sensing area is removed. The sensing area is a flat optical fiber structure. A plurality of first grooves are evenly spaced on the upper surface of the flat optical fiber structure, and the distance between two adjacent first grooves on each flat optical fiber structure is 3 to 8 μm, a plurality of second grooves are arranged at equal intervals on the lower surface of the flat optical fiber structure, the plurality of first grooves correspond one to another in the upper and lower directions, the surface of the sensing area is coated with a graphene oxide coating, the sensing area is placed in the sensing air chamber, the detection and acquisition unit is composed of a light intensity detector and a data acquisition and analysis device, the input end of the light intensity detector is connected to the output end of the optical fiber sensing element, the output end of the light intensity detector is connected to the data acquisition and analysis device, the data acquisition and analysis device is used to analyze the sensor signal transmitted by the light intensity detector, and respectively obtain a blank spectrum S1 measured under an air background and a sensor spectrum S2 collected under different gas concentrations, and the blank spectrum S1 is divided by the sensor spectrum S2 and a logarithmic function is taken on the output value to obtain a specific infrared absorption spectrum relationship diagram of the gas to be measured under different concentrations.

2. A single-wavelength infrared fiber optic gas sensor according to claim 1, characterized in that: The flat optical fiber structure is prepared by hot pressing.

3. A single-wavelength infrared fiber optic gas sensor according to claim 2, characterized in that: The hot pressing device used to prepare the flat optical fiber structure includes a hot pressing mold, a heating device, an elastic clamp, an optical fiber clamp and a microscope. The hot pressing mold includes an upper mold and a lower mold. The bottom of the upper mold is provided with a first protrusion protruding downward, and the top of the lower mold is provided with a second protrusion protruding upward. The lower surface of the first protrusion is provided with a plurality of third grooves at equal intervals, and the upper surface of the second protrusion is provided with a plurality of fourth grooves at equal intervals. The plurality of third grooves correspond to the plurality of fourth grooves one by one above and below. The ends of the first protrusion and the second protrusion are respectively provided with transition areas. The first protrusion and the second protrusion are provided with transition areas. The upper mold and the lower mold are respectively connected to the heating device, and the heating device is used to heat the upper mold and the lower mold. The elastic clamp is provided at both ends of the upper mold and the lower mold, and the elastic clamp is used to clamp the upper mold and the lower mold up and down and apply pressure. The optical fiber clamp is provided on both sides of the upper mold and the lower mold, and the optical fiber clamp is used to clamp both ends of the chalcogenide glass optical fiber to be hot pressed. The microscope is provided on one side of the upper mold and the lower mold, and the microscope is used to observe the thickness of the flat optical fiber structure during the hot pressing process.

4. The single-wavelength infrared fiber optic gas sensor according to claim 1, characterized in that: The number of the planar optical fiber structures is one or more, and the plurality of planar optical fiber structures are arranged at intervals along the length direction of the chalcogenide glass optical fiber.

5. The single-wavelength infrared fiber optic gas sensor according to claim 4, characterized in that: The thickness of a single flat optical fiber structure is 100-110 μm and the length is 3-4 cm; the spacing between two adjacent flat optical fiber structures among the multiple flat optical fiber structures is 3-4 cm; the length of the sensing area with the multiple flat optical fiber structures is 15-20 cm; and the length of the transition area is 1-1.5 cm.

6. The single-wavelength infrared fiber optic gas sensor according to claim 1, characterized in that: The graphene oxide coating is pressed onto the surface of the planar optical fiber structure by hot pressing, and is closely fitted with the multiple first grooves and the multiple second grooves.

7. The single-wavelength infrared fiber optic gas sensor according to claim 1, characterized in that: The thickness of the graphene oxide coating is 300-800 nm.

8. The single-wavelength infrared fiber optic gas sensor according to claim 1, characterized in that: The output wavelength of the single-wavelength narrow-band light source is 4.23 μm, 4.60 μm, 5.20 μm or 6.14 μm, the bandwidth is 160-200 nm, and the total output power is not less than 100 mW.

9. The single-wavelength infrared fiber optic gas sensor according to claim 1, characterized in that: The chalcogenide glass optical fiber is As2S3, As2Se3, Ge-As-Se or Ge-As-S chalcogenide glass bare core optical fiber, and the core diameter of the chalcogenide glass optical fiber is 300-500 μm.

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