A distributed fiber optic temperature sensing system based on laser absorption spectroscopy

Abstract

The application provides a distributed optical fiber temperature sensing system based on laser absorption spectrum, and belongs to the field of optical fiber sensors, and comprises a coupler for receiving laser, a distributed optical fiber temperature sensor, a plurality of selective lenses, a mirror and a spectrum analysis module; the input end of the hollow optical fiber is connected with the first output end of the coupler; the selective lenses are equidistantly arranged in the hollow optical fiber, the surface of the selective lenses is provided with a dielectric film, and the side, away from the coupler, of the dielectric film is coated with an anti-reflection film with a thickness of 1 / 4 lambda, wherein lambda is the wavelength of the laser; the mirror is arranged at the end of the hollow optical fiber, away from the coupler; the input end of the spectrum analysis module is connected with the second output end of the coupler; the spectrum analysis module obtains the temperature value through the one-to-one correspondence relationship between the ratio of the spectral absorption integral values of two different absorption spectrum lines and the temperature when the temperature changes, so that the measurement of the temperature is realized. The system can realize high-sensitivity, high-resolution and high-precision distributed temperature measurement.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical fiber sensors, and particularly relates to a distributed optical fiber temperature sensing system based on laser absorption spectrum. BACKGROUND

[0002] Temperature is one of the basic physical quantities given by the International System of Units, and temperature distribution measurement is often required in industrial production and scientific experiments, such as temperature distribution along long-distance oil pipelines and communication cable pipelines, temperature field inside large power transformers, temperature field distribution of boilers, ships, large buildings, warehouses, high-pressure containers, tunnels, and even aircraft and spacecraft fuselages, etc. In the production processes of many industries such as chemical industry, electronics, metallurgy, and pharmaceutical industry, multiple-point temperature needs to be monitored simultaneously.

[0003] The commonly used temperature sensors at present are thermocouples and thermistor temperature sensors, which have the advantages of heat resistance and stability, but are easily affected by external electromagnetic fields and are also affected by the arrangement method, and are point temperature measurement. In the past twenty years, optical fiber temperature sensors have been gradually applied in industrial production and life, and compared with traditional temperature sensors, they have many advantages such as small size, light weight, anti-electromagnetic interference, small transmission loss, easy to multiplex into a network, and buryability, and are widely used in temperature monitoring in the fields of energy exploration, aerospace, civil engineering, etc.

[0004] The distributed optical fiber sensor based on OFDR and the optical fiber grating sensor are the mainstream distributed optical temperature sensors, and their principle is to detect the corresponding physical quantities by using the sensitive characteristics of the reflected wavelength to temperature, strain and pressure, etc. However, the disadvantage is that in the case of a single sensor, strain and temperature cannot be decoupled, and if accurate measurement is to be achieved, multiple optical fiber temperature sensors with different materials need to be arranged, which is difficult to arrange on site and has high cost. And the temperature measurement range is generally -40℃ to 120℃, the temperature measurement accuracy is high under normal temperature conditions, but the measurement accuracy is reduced in high temperature and low temperature zones.

[0005] Tunable diode laser absorption spectroscopy (TDLAS) is a technique based on molecular absorption spectroscopy to realize temperature and gas component analysis. Laser energy is absorbed by the gas to be measured in the linear path of measurement, and the corresponding absorption spectrum is obtained. The absorption spectrum contains the information of gas concentration, temperature and pressure in the measurement path. Due to its high sensitivity, strong environmental adaptability and fast response, it has been successfully applied to industrial analysis, environmental monitoring and other fields. Tunable diode laser absorption spectroscopy includes direct absorption method and wavelength modulation method. Among them, the absorption method is more intuitive, the spectral absorption rate signal obtained by measurement shows the strength of the gas absorption to the laser intensity, and the interference between the spectral lines, various noises and other information can be easily analyzed and judged from the obtained signal. The measurement result is directly calculated, and does not need to be calibrated by standard gas. The experimental system is also simpler.

[0006] The solid glass fiber in the optical fiber cannot carry high power, while the hollow optical fiber does not have this problem, is damage-resistant, has faster transmission speed, and can avoid signal distortion caused by nonlinear effects, ensuring the quality of the transmitted laser beam, so it has more advantages than traditional optical fibers in high-precision sensors, laser beam transmission and time-frequency measurement. In addition, the hollow optical fiber has low light transmission loss in the mid-infrared waveband, small volume, easy bending and other characteristics, and does not affect the transmission of laser signals within the normal bending range. Therefore, the hollow optical fiber is an ideal gas cell in the absorption spectrum measurement system, and is convenient for miniaturization of devices, and is suitable for on-site measurement, so real-time measurement of the site using the hollow optical fiber has wide application prospects. SUMMARY

[0007] In order to overcome the shortcomings of the prior art, the present application provides a distributed optical fiber temperature sensing system based on laser absorption spectroscopy.

[0008] In order to achieve the above purpose, the present application provides the following technical scheme:

[0009] A distributed optical fiber temperature sensing system based on laser absorption spectroscopy, comprising:

[0010] A coupler for receiving laser;

[0011] A distributed optical fiber temperature sensor, comprising:

[0012] A hollow optical fiber, the input end of which is connected to the first output end of the coupler;

[0013] A plurality of selective lenses are equidistantly arranged in the hollow optical fiber, and the surface of the selective lens is provided with a dielectric film, and the side away from the coupler is coated with a 1 / 4 lambda thick anti-reflection film; wherein lambda is the wavelength of the laser;

[0014] a mirror disposed in the hollow optical fiber away from the one end of the coupler;

[0015] a spectrum analysis module having an input end connected to the second output end of the coupler;

[0016] wherein the laser beams of different wave bands are output into the coupler, enter the hollow optical fiber through the coupler, are transmitted and reflected by the multiple equidistantly distributed selective lenses in the hollow optical fiber, and are reflected back into the coupler as temperature measurement signals, the temperature measurement signals are guided into the spectrum analysis module by the coupler, the spectrum analysis module obtains the temperature value through the one-to-one correspondence between the ratio of the spectral absorption integral values of two different absorption spectral lines and the temperature when the temperature changes, and realizes the measurement of the temperature.

[0017] Further, the application further comprises a laser emission module having an output end connected to the input end of the coupler, and the laser emission module comprises:

[0018] a signal generation circuit;

[0019] a semiconductor laser temperature current control module having an input end connected to the output end of the signal generation circuit;

[0020] a near-infrared DFB semiconductor laser having an input end connected to the output end of the semiconductor laser temperature current control module;

[0021] a laser output interface having an input end connected to the output end of the near-infrared DFB semiconductor laser and an output end connected to the input end of the coupler.

[0022] Further, the trigger signal emitted by the signal generation circuit is a square wave, and the period thereof is (n+1)T0; wherein T0=2L0 / c, c is the speed of light, and L0 is the interval distance of the selective lenses.

[0023] Further, the spectrum analysis module comprises:

[0024] an amplifier having an input end connected to the second output end of the coupler;

[0025] an oscilloscope having an input end connected to the output end of the amplifier;

[0026] a computer having an input end connected to the output end of the oscilloscope.

[0027] Further, the ratio of the spectral absorption integral values of the two different absorption spectral lines is:

[0028]

[0029] wherein A1 and A2 are the spectral absorption integral values, I0 is the laser intensity without gas absorption, I tLet P be the laser intensity after absorption by the gas medium, X be the gas volume concentration, S be the line intensity of the gas characteristic spectral line, L be the distance the laser travels in the gas, T be the temperature of the gas medium, and R be the ratio of the line intensities of the gas characteristic spectral lines.

[0030] Furthermore, the intensity of the spectral line is:

[0031]

[0032] Where T0 is the reference temperature, Q is the total molecular intramolecular segmentation function, and E″ is the molecular intramolecular segmentation function. i For the energy of the low transition state, v 0,i denoted as the molecular transition frequency, h as Planck's constant, k as Boltzmann's constant, and c as the speed of light. When the temperature is below 2500K and the wavelength is less than 2.5μm, the last term is denoted as 1.

[0033] Furthermore, the distributed fiber optic temperature sensor is embedded in the object being measured, and its temperature response time is:

[0034]

[0035] Where, τ m To determine the temperature response time of the distributed fiber optic temperature sensor embedded in the object being measured, let Q' be the heat required for the distributed fiber optic temperature sensor and the object to reach thermal equilibrium, Q be the thermal conductivity between the distributed fiber optic temperature sensor and the object, ρ be the density of the gas medium inside the distributed fiber optic temperature sensor, c be the specific heat capacity of the gas medium inside the distributed fiber optic temperature sensor, V be the gas volume inside the distributed fiber optic temperature sensor, T2 be the temperature of the object being measured, T1 be the temperature of the gas medium inside the distributed fiber optic temperature sensor, r2 be the outer diameter of the hollow fiber optic cable, r1 be the inner diameter of the hollow fiber optic cable, λ be the thermal conductivity of the hollow fiber optic material, and A be the thermal conductivity of the material. m This represents the thermal conductivity area of ​​a distributed fiber optic temperature sensor.

[0036] Furthermore, when the distributed fiber optic temperature sensor is placed on the surface of the object being measured, its temperature response time is:

[0037]

[0038] Where, τ d The temperature response time is measured by placing the distributed fiber optic temperature sensor on the surface of the object being measured. ρ is the density of the gas medium inside the distributed fiber optic temperature sensor, c is the specific heat capacity of the gas medium inside the distributed fiber optic temperature sensor, V is the gas volume inside the distributed fiber optic temperature sensor, h is the convective heat transfer coefficient of the distributed fiber optic temperature sensor, and A is the convective heat transfer area of ​​the distributed fiber optic temperature sensor.

[0039] Further, the inner diameter of the hollow optical fiber is 1mm, and the volume is 0.78cm 3 .

[0040] The application provides a distributed optical fiber temperature sensing system based on laser absorption spectrum.

[0041] The application provides a distributed optical fiber temperature sensor based on laser absorption spectrum, which uses a hollow optical fiber as a gas chamber, and a plurality of selective lenses are arranged in the hollow optical fiber periodically; laser absorption spectrum signals of different measurement regions in a time domain are obtained by laser passing through the distributed optical fiber temperature sensor; a spectral absorption rate integral value corresponding to an absorption spectrum line is obtained by a spectral analysis module; a temperature value is obtained by a one-to-one corresponding relationship between a ratio of the spectral absorption rate integral values corresponding to different absorption spectrum lines and the temperature; and thus, distributed measurement of the temperature is realized. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the application and the design scheme thereof, the drawings required by the embodiments will be briefly introduced as follows. The drawings in the following description are only partial embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0043] Figure 1 FIG. 1 is a schematic diagram of a distributed optical fiber temperature sensing system based on laser absorption spectrum.

[0044] Figure 2 FIG. 3 is a structure diagram of a selective lens.

[0045] Figure 3 FIG. 4 is a temperature measurement principle diagram of a distributed optical fiber temperature sensor based on laser absorption spectrum, (a) is a buried temperature measurement, and (b) is a convection type temperature measurement.

[0046] Figure 4 FIG. 5 is a temperature measurement process of a distributed optical fiber temperature sensor based on laser absorption spectrum.

[0047] Figure 5 FIG. 6 is a trend of water vapor spectrum line intensity and its ratio with temperature change. DETAILED DESCRIPTION

[0048] In order to make those skilled in the art better understand the technical scheme of the application and can implement it, the application will be described in detail below in combination with the drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical scheme of the application, and cannot be used to limit the protection scope of the application.

[0049] In addition, the terms "first", "second" and the like are used only for descriptive purposes and do not imply or imply relative importance. In the description of the present application, it should be noted that unless otherwise specified or limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected, it can be mechanically connected, or it can be electrically connected, it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more, which will not be described here.

[0050] Embodiments:

[0051] The present application provides a kind of distributed fiber temperature sensing system based on laser absorption spectrum, specifically as shown in Figure 1 It includes: laser emitting module, for output laser;Coupler 10, its input end is connected with the output end of laser emitting module;Distributed fiber temperature sensor 12, its input end is connected with the first output end of coupler 10, for output temperature measurement signal;It includes: hollow optical fiber, its input end is connected with the first output end of coupler 10;A plurality of selective lenses, equidistantly arranged in hollow optical fiber, selective lens surface is provided with dielectric film, and the side away from coupler 10 is coated with 1 / 4 λ thickness antireflection film;Wherein λ is laser wavelength;Mirror, is arranged in the end of hollow optical fiber away from coupler 10;Spectrum analysis module, its input end is connected with the second output end of coupler 10, for analyzing temperature measurement signal reflected from distributed fiber temperature sensor 12;

[0052] Different waveband laser is input from laser emitting module into coupler 10, enters into hollow optical fiber through coupler 10, and a plurality of equidistantly distributed selective lenses in hollow optical fiber project and reflect laser, and temperature measurement signal is reflected from the first output end of coupler 10 back into coupler 10, and temperature measurement signal is guided into spectrum analysis module by coupler 10, and the spectrum analysis module obtains temperature value by the one-to-one correspondence relationship between the ratio of the integral value of spectral absorptivity of two different absorption spectral lines and temperature when temperature changes, to realize the measurement of temperature.

[0053] The following are specific implementation details and principles of the present application:

[0054] The laser controller in the present application is a double-channel DFB laser controller, model WL-100-D-B-DFB-A, current modulation range 0mA-300mA, temperature modulation range 0.0℃-65.0℃, modulation accuracy ±0.1℃;Power supply AC 100-240V±10%, 50 / 60Hz, power 40W.

[0055] The DFB semiconductor laser in the application is a near-infrared molecular absorption DFB laser, has 14 pins, and the output power is 250 mW.

[0056] The amplifier in the application is a 16-channel amplifier, the frequency is 10 Hz-150 MHz, the amplification multiple is 10 times, the working temperature is 10 DEG C-40 DEG C, and the working power supply is DC+12V.

[0057] The oscilloscope in the application is PicoScope5442B, the channel number is 4, the bandwidth is 60 MHz, the minimum vertical sensitivity is 2 mV / div, the maximum vertical sensitivity is 4 V / div, the sampling rate is random 1 Gsps, and the vertical resolution is 16 bit.

[0058] The selective lens in the application adopts medium film light splitting, one side laser incidence occurs transmission and reflection, and the other side is coated with 1 / 4 lambda thickness antireflection film to make the laser completely transmit.

[0059] The n lenses in the sensor are periodically arranged, the interval is L0, T0 is set as 2L0 / c, the fiber end is a mirror, and c is the speed of light.

[0060] The trigger signal in the application is a square wave, and the period is (n+1)T0.

[0061] The modulation signal in the application can be a triangular wave, a square wave and the like.

[0062] The temperature distribution type sensor measurement principle in the application is as follows:

[0063] When a monochromatic laser passes through a gas medium, the intensity change satisfies Beer-Lambert law:

[0064]

[0065] Taking the logarithm of the above formula and integrating in the frequency domain:

[0066]

[0067] For the first two lenses in the sensor:

[0068]

[0069]

[0070] Subtracting the two formulas, the characteristic spectral line intensity between any two lenses can be derived:

[0071]

[0072] In the present application, hollow optical fiber is used as the absorption cell, and direct absorption method is used for temperature measurement, and the principle is as follows:

[0073] The line intensity of the spectral line represents the strength of the spectral line for light intensity absorption, which is the comprehensive effect of absorption and radiation when the energy level of the molecule jumps. For a specific molecular absorption spectral line, the spectral line intensity is only related to the temperature, and in actual application, it can be calculated by the following formula:

[0074]

[0075] Wherein, T0 is the reference temperature, Q is the total molecular internal partition function, E i " is the energy of the low transition state, v 0,i is the molecular transition frequency, h is the Planck constant, k is the Boltzmann constant, c is the speed of light, and the last term is 1 under the condition that the temperature is lower than 2500K and the wavelength is less than 2.5μm.

[0076] The change of the gas absorption spectral line intensity with temperature depends on the low transition state energy of the molecule. For different positions of the absorption spectral line, due to the difference of the low transition state energy E i " , the spectral line intensity change curve is also different when the temperature changes. The principle of TDLAS technology for measuring gas temperature is that according to the different spectral line intensity change amplitudes of two spectral lines in different temperature ranges, the relative change of the spectral line intensity is used to measure the temperature. The intensity ratio of the two absorption spectral lines can be expressed as:

[0077]

[0078] After selecting the spectral line, there is a corresponding relationship between the spectral line intensity ratio and the gas temperature. Therefore, the gas temperature can be obtained by measuring the spectral line intensity ratio. For the measurement using direct absorption method, the measured spectral absorption integral value ratio is the same as the spectral line intensity ratio, as shown in the following formula:

[0079]

[0080] Wherein, A1, A2 are the spectral absorption integral values, I0 is the laser intensity without gas absorption, I t is the laser intensity after absorption by the gas medium, P is the pressure of the gas medium, X is the volume concentration of the gas, S is the line intensity of the gas characteristic spectral line, L is the distance of the laser propagating in the gas, T is the temperature of the gas medium, and R is the line intensity ratio of the gas characteristic spectral line.

[0081] Therefore, when the direct absorption method is used for temperature measurement, the integral value ratio of spectral absorption is equal to the spectral intensity ratio, and is a single value function of temperature, and is irrelevant to gas concentration, pressure and other factors.

[0082] The application provides a distributed optical fiber temperature sensor based on laser absorption spectrum.

[0083] The buried use mode of the application pre-buries the sensor in a measurement object, such as a long-distance oil pipeline, a communication cable pipeline or a large building, and the sensor directly exchanges heat with the measurement object.

[0084]

[0085] For the gas in the hollow optical fiber, the temperature response time is:

[0086]

[0087] Wherein, τ m is the temperature response time of the distributed optical fiber temperature sensor buried in the measurement object, Q' is the heat required for the distributed optical fiber temperature sensor and the measurement object to reach thermal equilibrium, Q is the heat conduction heat of the distributed optical fiber temperature sensor and the measurement object, rho is the gas medium density in the distributed optical fiber temperature sensor, c is the specific heat capacity of the gas medium in the distributed optical fiber temperature sensor, V is the gas volume in the distributed optical fiber temperature sensor, T2 is the temperature of the measurement object, T1 is the gas medium temperature in the distributed optical fiber temperature sensor, r2 is the outer diameter of the hollow optical fiber, r1 is the inner diameter of the hollow optical fiber, lambda is the thermal conductivity coefficient of the material of the hollow optical fiber, A m is the heat conduction area of the distributed optical fiber temperature sensor.

[0088] The convection use mode of the application places the sensor on the surface of the measurement object or in the space to be measured according to requirements, and the Nusselt number is:

[0089]

[0090] The lumped parameter method can be used for analysis, and the temperature response time is:

[0091]

[0092] Wherein, tau d is the temperature response time of the distributed optical fiber temperature sensor placed on the surface of the measurement object, rho is the gas medium density in the distributed optical fiber temperature sensor, c is the specific heat capacity of the gas medium in the distributed optical fiber temperature sensor, V is the gas volume in the distributed optical fiber temperature sensor, h is the convective heat transfer coefficient of the distributed optical fiber temperature sensor, and A is the convective heat transfer area of the distributed optical fiber temperature sensor.

[0093] The hollow optical fiber used in the present application is produced by the U.S. Polymicro Technologies Company, model HWEA10001600, inner diameter 1 mm, volume 0.78 cm3.

[0094] The following is an embodiment of the present application:

[0095] This embodiment fills H2O in the distributed optical fiber temperature sensor, and realizes distributed temperature measurement of high-temperature chemical production processes (minimum temperature higher than 100℃), with the specific implementation steps as follows:

[0096] Step one, periodically arrange n selective semi-transparent lenses in the distributed optical fiber temperature sensor, with the end being a mirror, and the period being L0.

[0097] Step two, fill H2O in the distributed optical fiber temperature sensor, and place the temperature sensor in the high-temperature chemical production process. According to the need of temperature measurement environment, a certain bending arrangement can be made, such as shown in the measurement site, and it will not affect the measurement signal. Figure 1 Step three, the conventional arrangement mode of the sensor can be divided into two categories, such as shown in

[0098] Step three, the conventional arrangement mode of the sensor can be divided into two categories, such as shown in Figure 3 (a) buried arrangement and (b) convection arrangement. The sensor can be buried in advance in the temperature measurement area, or directly placed in the temperature measurement space, and the response time of the temperature sensor in both ways is less than 1x10-4s.

[0099] Step four, the signal generation circuit 2 controls the 1387.70 nm semiconductor laser temperature current control module 3, controls the 1387.70 nm laser 4 to scan in a certain waveband range, and outputs through the laser output interface 6.

[0100] Step five, connect the output laser to the coupler 10, and access the distributed optical fiber temperature sensor. The laser transmits and reflects when passing through each selective lens, the reflected light is accessed to the amplifier 13 through the coupler 10, the signal is amplified and then input to the oscilloscope 15, the oscilloscope 15 is connected with the computer 16, and data acquisition and processing are performed.

[0101] Step six, the other side of the selective lens is coated with an anti-reflection film with a thickness of 1 / 4λ (λ = 1387.70 nm), and the laser reflected back through the next lens will be completely transmitted without reflection.

[0102] Step seven, the trigger signal is a square wave, the period is (n+1)T0, and in the 0-T0 moment, it is in the trigger state, and in the T0-(n+1)T0 moment, there is no signal output.

[0103] Step eight, the modulated signal is a triangle wave, the period is (n+1)TO, the triangle wave signal is outputted in 0-T0, and no signal is outputted in T0-(n+1)TO.

[0104] Step nine, the coupler 10 receives the signal with the period of TO from t=T0 to t=(n+1)TO, and inputs the signal to the amplifier 13 for signal amplification.

[0105] Step ten, the amplified signal can be displayed through the oscilloscope 15, and the computer can be connected to analyze the signal with the period of TO to obtain the absorption spectrum signal of each section.

[0106] Step eleven, the absorption spectrum signal measured by the distributed optical fiber temperature sensor is processed, and the ratio of the integral values of the spectral absorption rate (equal to the ratio of the spectral line intensity) can be obtained.

[0107] Step twelve, the #1 spectral line 1388.139nm, the #2 absorption spectral line 1388.329nm and the #3 absorption spectral line 1388.454nm are selected in the wave band near 1387.70nm, the change relationship of the line intensity with the temperature and the change relationship of the line intensity ratio with the temperature can be obtained. The ratios #1 / #2 and #2 / #3 have linear relationships with the temperature, and the ratio #1 / #2 is more sensitive to the temperature change in the temperature range of 300K-2000K, so the #1 spectral line 1388.139nm and the #2 absorption spectral line 1388.329nm can be selected to realize the distributed temperature measurement of the high-temperature chemical production process.

[0108] The above-described embodiments are only the preferred specific implementation of the present application, the protection scope of the present application is not limited to this, any skilled person in the art can obtain the simple change or equivalent replacement of the technical solution within the technical range disclosed by the present application, and all of the above belong to the protection scope of the present application.

Claims

1. A distributed optical fiber temperature sensing system based on laser absorption spectroscopy, characterized in that, include: Coupler (10), which is used to receive laser light; Distributed fiber optic temperature sensor (12), comprising: The hollow optical fiber has its input end connected to the first output end of the coupler (10); Multiple selective lenses are equidistantly arranged within the hollow optical fiber. Each selective lens has a dielectric film on its surface, and an anti-reflection film with a thickness of 1 / 4λ is deposited on the side away from the coupler (10); where λ is the laser wavelength. A reflector is disposed at one end of the hollow optical fiber away from the coupler (10); The input terminal of the spectral analysis module is connected to the second output terminal of the coupler (10); Lasers of different wavelengths are output to coupler (10) and enter hollow optical fiber through coupler (10). Multiple selective lenses distributed at equal intervals in hollow optical fiber transmit and reflect the laser and reflect the temperature measurement signal back to coupler (10). Coupler (10) then imports the temperature measurement signal into the spectral analysis module. The spectral analysis module obtains the temperature value by the one-to-one correspondence between the ratio of the integral values ​​of the spectral absorptivity of two different absorption lines corresponding to the temperature when the temperature changes, thus realizing the temperature measurement. It also includes: a laser emitting module, the output of which is connected to the input of the coupler (10), the laser emitting module comprising: Signal generation circuit (2); The input terminal of the semiconductor laser temperature and current control module (3) is connected to the output terminal of the signal generation circuit (2); The input terminal of the near-infrared DFB semiconductor laser (4) is connected to the output terminal of the semiconductor laser temperature and current control module (3); The laser output interface (6) has its input end connected to the output end of the near-infrared DFB semiconductor laser (4) and its output end connected to the input end of the coupler (10).

2. A distributed optical fiber temperature sensing system based on laser absorption spectroscopy according to claim 1, characterized in that, The trigger signal emitted by the signal generating circuit (2) is a square wave with a period of (n+1)T0; where T0=2L0 / c, c is the speed of light, and L0 is the spacing distance of the selective lens.

3. A distributed optical fiber temperature sensing system based on laser absorption spectroscopy according to claim 1, characterized in that, The spectral analysis module includes: The amplifier (13) has its input terminal connected to the second output terminal of the coupler (10); An oscilloscope (15) is connected to the output of the amplifier (13) at its input terminal; The computer (16) has its input terminal connected to the output terminal of the oscilloscope (15).

4. A distributed optical fiber temperature sensing system based on laser absorption spectroscopy according to claim 1, characterized in that, The ratio of the integral values ​​of the spectral absorbance corresponding to the different absorption lines is: wherein , is the spectral absorption integral value, is the laser intensity without gas absorption, is the laser intensity after absorption by the gas medium, is the pressure of the gas medium, is the volume concentration of the gas, is the line intensity of the gas characteristic spectral line, is the distance of laser propagation in the gas, is the temperature of the gas medium, is the line intensity ratio of the gas characteristic spectral line.

5. A distributed optical fiber temperature sensing system based on laser absorption spectroscopy according to claim 4, characterized in that, The line intensity of the gas characteristic spectral lines is: where S( T ) is the line intensity of the gas characteristic spectrum line, is the reference temperature, Q is the total intramolecular partition function, is the energy of the lower transition state, is the molecular transition frequency, h is the Planck constant, k is the Boltzmann constant, c is the speed of light, and the last term is 1 in the case where the temperature is lower than 2500 K and the wavelength is less than 2.5 μm, i represents the identification index of the lower transition state, and is used to distinguish different molecular lower transition energy levels.

6. A distributed optical fiber temperature sensing system based on laser absorption spectroscopy according to claim 1, characterized in that, The distributed optical fiber temperature sensor (12) is embedded in the object being measured, and its temperature response time is: wherein, is the temperature response time of the distributed fiber optic temperature sensor (12) to be buried in the measurement object, is the heat required for the distributed fiber optic temperature sensor (12) to reach thermal equilibrium with the measurement object, is the heat conduction of the distributed fiber optic temperature sensor (12) to the measurement object, is the density of the gaseous medium within the distributed fiber optic temperature sensor (12), is the specific heat capacity of the gaseous medium within the distributed fiber optic temperature sensor (12), is the volume of the gaseous medium within the distributed fiber optic temperature sensor (12), is the temperature of the measurement object, is the temperature of the gaseous medium within the distributed fiber optic temperature sensor (12), is the outer diameter of the hollow optical fiber, is the inner diameter of the hollow optical fiber, is the thermal conductivity of the material of the hollow optical fiber, is the heat conduction area of the distributed fiber optic temperature sensor (12).

7. A distributed optical fiber temperature sensing system based on laser absorption spectroscopy according to claim 1, characterized in that, When the distributed fiber optic temperature sensor (12) is placed on the surface of the object being measured, its temperature response time is: wherein, is the temperature response time of the distributed fiber optic temperature sensor (12) to be placed on the surface of the object to be measured, is the density of the gaseous medium within the distributed fiber optic temperature sensor (12), is the specific heat capacity of the gaseous medium within the distributed fiber optic temperature sensor (12), is the volume of the gaseous medium within the distributed fiber optic temperature sensor (12), is the convective heat transfer coefficient of the distributed fiber optic temperature sensor (12), is the convective heat transfer area of the distributed fiber optic temperature sensor (12).

8. A distributed optical fiber temperature sensing system based on laser absorption spectroscopy according to claim 1, characterized in that, The hollow optical fiber has an inner diameter of 1 mm and a volume of 0.78 cm 3 .

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