CN111337057B - Optical fiber interferometer temperature compensation device and method based on distributed temperature sensing - Google Patents
Optical fiber interferometer temperature compensation device and method based on distributed temperature sensing Download PDFInfo
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Abstract
The invention provides a temperature compensation device and method for an optical fiber interferometer based on distributed temperature sensing. The temperature compensation device comprises a signal light input module, an optical fiber interferometer, a DTS signal processing module and a signal light output module, and is characterized in that: through using wavelength division multiplexer, compound into a bundle of light with the probe light of distributed temperature sensing and transmit to utilize wavelength division multiplexer will follow interferometer interference arm and return backward raman scattered light and separate out, realize the distributed measurement to fiber optic interferometer interference arm temperature, combine the coefficient of thermal expansion of interference arm optic fibre according to this, calculate the influence of temperature to the change of optic fibre axial length, through getting rid of the influence that this part of change brought and then realize temperature compensation when handling output signal. Compared with the traditional interferometer temperature compensation structure, the device has the advantages of optimized system structure, reduced application cost, improved measurement efficiency, high measurement precision and the like, and can be widely applied to the temperature compensation of various optical fiber interferometers.
Description
Technical Field
The invention relates to a temperature compensation device, in particular to an optical fiber interferometer temperature compensation device based on distributed temperature sensing. The invention also relates to a temperature compensation method.
Background
The optical fiber interferometer is an important structure for realizing the interference of light by using an optical fiber, and is widely applied to the sensing field. Fiber optic interferometer sensing technology has made tremendous progress over the past decades since the seventies of the last century, with the development of optical communications and opto-electronic technologies. Optical fiber sensors have gained important applications in a wide variety of fields such as civil structure detection, power systems, chemical sensing, medicine, biology, petroleum and gas, and aerospace. Fiber optic interferometer sensing technology has many inherent advantages over conventional sensing technology, including being operable in extreme environments, light weight, small size, high sensitivity, multi-parametric, etc.
Like other interferometers, the fiber interferometer mainly includes two processes of splitting and combining beams. In the optical fiber, light can be separated at one position through flexible design, then propagates in the optical fiber in different modes, and finally is combined at another position, and the interference phenomenon occurs when the interference condition is met. They can be divided into four major categories, namely Mach-Zehnder (Mach-Zehnder) interferometers, Michelson (Michelson) interferometers, Fabry-perot (Fabry-perot) interferometers and Sagnac (Sagnac) interferometers. Fiber optic interferometers are typically affected by environmental factors when making physical measurements, "temperature" is one of the most common. The uneven temperature distribution on one interference arm of the optical fiber interferometer, the temperature difference between the interference arms, the instantaneous change of the ambient temperature and the like can cause great influence on the interference result, and how to eliminate the problem is an inevitable problem of applying the structure of the optical fiber interferometer.
In 2002, Francois Gonthier et al in the United states invented a passive thermal compensation method for full-fiber Mach-Zehnder interferometers (US10258913), the main content of which is to change the constituent components of interferometer fiber and dope GeO2、P2O5、B2O5And F and the like. In this way the required thermal dependence of the interferometer over a given temperature range can be obtained, with changes to the interferometer for temperature compensation. This method is accomplished without additional equipment, but is more complex to manufacture and over long distancesIt is inconvenient to leave the application and may fail to compensate for temperature fluctuations outside a given range.
In 2003, the inventor of Tianjin university invented a photoelectric integrated acceleration geophone (CN 03100433.4), in which a Mach-Zehnder waveguide interferometer is constructed to measure acceleration and detect seismic waves, and an electronic temperature compensation circuit is used for solving the temperature compensation problem of the interferometer in the design; in 2009, chen et al of shanner information technology (shenzhen) limited invented an interferometer and compensation method for ambient temperature compensation (CN 200910107132.3), in which a temperature compensator (mainly a heater) is added to the interferometer arms to compensate the drift generated by the ambient temperature, so as to make the operation of the interferometer more stable. The above-mentioned problem of temperature compensation is solved when dealing with the interferometer arms of the fiber optic interferometer, but all the problems are solved by using electronic circuits, which leads to a complicated system structure and increased costs, and also enables local compensation in a small range.
In 2018, Zhao Yong and Reming, et al, university in northeast invented a temperature and refractive index double-parameter sensing device (CN201810039338.6) based on an optical fiber dislocation structure and a Sagnac ring, and the invention reduced the influence of temperature on an interferometer by using a cascading Sagnac ring mode until reaching the design requirement to realize temperature compensation, but this mode would increase an additional optical fiber optical path, and at the same time, the device would not be suitable for large-scale and high-precision testing.
The temperature compensation of the traditional optical fiber interferometer usually adopts the schemes of an electronic circuit, a compact optical fiber interferometer structure, changing optical fiber materials and the like, and has the defects that the temperature compensation can only be applied to temperature measurement and compensation in a limited space range, and the temperature change and distribution of an optical path in a long-distance space cannot be monitored; however, if multi-point positioning detection is performed, the device structure becomes complicated, and the cost increases. The invention provides a scheme for temperature compensation by using a distributed temperature sensing technology for solving the problems, the scheme not only can realize temperature monitoring on each part along an optical fiber light path, but also can finish measurement by using only one optical fiber under the condition of not adding other instruments, thereby greatly simplifying the system structure, reducing the application cost, improving the measurement efficiency and ensuring the measurement precision.
Since the first distributed temperature sensing system based on rayleigh scattering light appeared in 1982, the distributed temperature sensing technology has been rapidly developed, and the principle is that the temperature-carrying signal is optically demodulated at one end of the optical fiber by utilizing the characteristic that certain specific light propagating in the optical fiber is subjected to temperature modulation, so as to realize the technology of distributed temperature measurement. In the solution for implementing the distributed optical fiber temperature sensing technology, the temperature-modulated signal can be divided into scattered light and transmitted light, and the former is most commonly used. The scattered light utilized by distributed temperature sensor technology is mainly classified into three categories: rayleigh scattered light, raman scattered light, and brillouin scattered light. The Raman scattered light has the characteristics of only temperature dependence and high sensitivity, and the temperature change and distribution information can be easily obtained from the Raman scattered light. According to investigation, the distributed temperature sensing technology still aims at directly measuring temperature information at present, and has not been indirectly applied to the temperature compensation aspect of the optical fiber interferometer.
Disclosure of Invention
The invention aims to provide a distributed temperature sensing-based optical fiber interferometer temperature compensation device which is low in cost and high in measurement efficiency and measurement accuracy. The invention also aims to provide a temperature compensation method using the optical fiber interferometer temperature compensation device based on distributed temperature sensing.
The temperature compensation device of the optical fiber interferometer based on distributed temperature sensing comprises a signal light input module 1, an interference upper light path 2, an interference lower light path 3, a DTS signal processing module 4 and a signal light output module 5; the method is characterized in that: the signal light input module 1 is respectively connected to an interference upper light path 2 and an interference lower light path 3 through connecting optical fibers; the interference upper optical path 2 is connected with a DTS signal processing module 4 through a connecting optical fiber; the interference lower optical path 3 is connected with the DTS signal processing module 4 through a connecting optical fiber; the interference upper optical path 2 and the interference lower optical path 3 are respectively connected to the signal light output module 5 through connecting optical fibers, and the full optical path adopts a polarization-maintaining optical fiber and a polarization-maintaining device.
The temperature compensation device of the optical fiber interferometer based on distributed temperature sensing can also comprise:
1. the interference upper optical path 2 is formed by sequentially connecting a first wavelength division multiplexer 21, an upper connecting optical fiber 22, a second wavelength division multiplexer 23, an upper interference optical fiber arm 24 and a third wavelength division multiplexer 25; the interference lower optical path 3 is formed by sequentially connecting a fourth wavelength division multiplexer 31, a lower connecting optical fiber 32, a fifth wavelength division multiplexer 33, a lower path interference optical fiber arm 34 and a sixth wavelength division multiplexer 35; the optical path structures of the interference upper optical path 2 and the interference lower optical path 3 are the same, and except the lengths of the interference optical fiber arms 24 and 34, the parameters of other components and devices thereof are the same.
2. The signal light input module 1 specifically includes: the laser light source 11 is connected to the isolator 13 through a connecting optical fiber a12, and then connected to the first 1 × 2 optical fiber coupler 15 through a connecting optical fiber, two output ends 15a, 15b of the first 1 × 2 optical fiber coupler 15 are respectively connected to the first input end 21a of the first wavelength division multiplexer 5 in the interference upper optical path 32 and the first input end 31a of the fourth wavelength division multiplexer 31 in the interference lower optical path 33 through connecting optical fibers.
3. The DTS signal processing module 4 specifically includes: the DTS demodulation system 43 receives the back raman scattered light separated from the upper path interference fiber arm 24 by the second wavelength division multiplexer 23 in the interference upper optical path 2 through the connection fiber; receiving back Raman scattered light separated from a drop interference fiber arm 34 by a fifth wavelength division multiplexer 33 in the interference lower optical path 3 through a connecting fiber; the DTS demodulation system 43 is connected with the pulse light source 41 through a line 42 and controls the output of the pulse light source 41; the pulse light source 41 is connected to the second input end 21b of the first wavelength division multiplexer 21 in the upper interference optical path 2 and the second input end 31b of the fourth wavelength division multiplexer 31 in the lower interference optical path 3 through connecting optical fibers.
4. The signal light output module 5 specifically includes: two input ends 51a, 51b of the second 2 × 2 optical fiber coupler 51 are respectively connected to the first output end 25a of the third wavelength division multiplexer in the interference upper optical path 2 and the first output end 35a of the sixth wavelength division multiplexer 35 in the interference lower optical path 3 through connecting optical fibers; two output ends 51c and 51d of the second 2 × 2 fiber coupler 51 are respectively connected to the first photodetector 53 and the second photodetector 54 through connecting fibers, and the parameters of the first photodetector 53 and the second photodetector 54 are the same.
The compensation method of the temperature compensation device of the optical fiber interferometer based on the distributed temperature sensing comprises the following steps:
(1) setting a calibration temperature T0；
(2) The laser light source 11 and the pulse light source 41 are turned on, the temperature distribution of the upper path interference optical fiber arm 24 and the lower path interference optical fiber arm 34 is obtained through the DTS demodulation system, and the corresponding temperature fluctuation delta t of each position is calculated1nAnd Δ t2m；
(3) Calculating temperature fluctuation distribution information delta l of the interference arm1nΔt1nAnd Δ l2mΔt2m；
(4) Comparing the interference arms at the calibrated temperature, and calculating the influence of temperature fluctuation on the interference arms according to the inherent parameters of the optical fibers of the interference arms;
(5) the effects are taken into account from the data and eliminated at the final calculation, as required, to achieve temperature compensation.
The compensation method of the present invention may further include:
1. the effect is a change in the axial length of the fiber.
2. The calculation method of the temperature compensation comprises the following steps:
ΔL1＝Δl11Δt11Δα11+Δl12Δt12Δα12+...+Δl1nΔt1nΔα1n
ΔL2＝Δl21Δt21Δα21+Δl22Δt22Δα22+...+Δl2mΔt2mΔα2m
in the formula,. DELTA.L1And Δ L2Respectively, the change of the upper path interference optical fiber arm and the lower path interference optical fiber arm caused by the influence of temperature, delta alpha1i(i ═ 1,2,3.. n) corresponds to Δ l1iCoefficient of thermal expansion of, Δ α2j(i ═ 1,2,3.. m) corresponds to Δ l2jThe coefficient of thermal expansion of (a).
The invention provides a temperature compensation scheme of an optical fiber interferometer interference arm based on distributed temperature sensing, which is designed according to the following idea: the signal light used by the optical fiber interferometer for measuring physical quantity is compounded with the probe light used by the distributed temperature sensing into a beam of light by using a wavelength division multiplexer for transmission, and the transmission can be completed by using only one optical fiber light path; the backward Rayleigh scattering light excited by the detection light in the light path of the interferometer arm can be separated by another wavelength division multiplexer and input into a demodulation system to obtain temperature distribution information on the interferometer arm, and then the temperature compensation can be carried out on the interferometer arm according to experimental requirements. The device is particularly suitable for remarkably eliminating the influence of temperature on the measurement result when the fiber interferometer carries out high-precision physical quantity change measurement, and particularly when the fiber interferometer carries out long-distance space measurement, the temperature compensation can cover each part of the interferometer arm. Compared with the traditional interferometer temperature compensation structure, the device has the advantages of simplified system structure, reduced application cost, high measurement efficiency, high measurement precision and the like, and can be widely applied to the temperature compensation of various optical fiber interferometers.
Compared with the prior art, the invention has the advantages that:
(1) as a device applied to temperature compensation of an interferometer, the distributed temperature sensing technology is applied to the structure of the optical fiber interferometer, so that the temperature of each position on an interference optical fiber arm can be measured more comprehensively and more specifically, the influence of temperature change on the interferometer is reduced to the minimum, and the measurement of physical quantities except the temperature by the interferometer is more accurate;
(2) the interferometer signal transmission light and the distributed temperature sensing detection light are combined into one light path by the wavelength division multiplexer for transmission, so that the complexity of the light path design structure is reduced, and the construction cost of the system is reduced;
(3) the Stokes light and the anti-Stokes light in the backward Raman scattering light in the optical fiber are separated by using a wavelength division multiplexer, so that the loss of light intensity is reduced, and meanwhile, the sensing light carrying temperature information is obtained;
(4) the full optical path design is adopted, and the device has the advantages of small volume, high measurement precision, good temperature stability, good vibration resistance stability and the like.
Drawings
FIG. 1 is a schematic temperature compensation flow diagram of a distributed temperature sensing based fiber optic interferometer temperature compensation scheme;
FIG. 2 is a schematic structural diagram of an apparatus for a distributed temperature sensing based fiber optic interferometer temperature compensation scheme;
fig. 3 is a schematic diagram of the expanded structure of the DTS demodulation system.
Detailed Description
The invention is described in more detail below by way of example with reference to the accompanying drawings.
The device for compensating the temperature of the interference arm of the optical fiber interferometer based on distributed temperature sensing comprises a signal light input module 1, an interference upper light path 2, an interference lower light path 3, a DTS signal processing module 4 and a signal light output module 5;
the whole light path adopts a polarization maintaining optical fiber; the signal light input module 1 is respectively connected to the interference upper optical path 2 and the interference lower optical path 3 through connecting optical fibers 16 and 18; the interference upper optical path 2 is connected with the DTS signal processing module 4 through connecting optical fibers 17, 27 and 28; the interference lower optical path 3 is connected with the DTS signal processing module 4 through connecting optical fibers 19, 37 and 38; the interference upper optical path 2 and the interference lower optical path 3 are connected to the signal light output module 5 via connection optical fibers 26, 36, respectively.
The interference upper light path 2 and the interference lower light path 3 specifically comprise:
1) the interference upper optical path 2 is respectively composed of a first wavelength division multiplexer 21, a second wavelength division multiplexer 23, an upper interference optical fiber arm 24, a third wavelength division multiplexer 25 and a connecting optical fiber 22;
2) the interference lower optical path 3 is composed of a fourth wavelength division multiplexer 31, a fifth wavelength division multiplexer 33, a lower path interference optical fiber arm 34, a sixth wavelength division multiplexer 35 and a connecting optical fiber 32 respectively;
3) the optical path structures of the interference upper optical path 2 and the interference lower optical path 3 are the same, and except the lengths of the interference optical fiber arms 24 and 34, the parameters of other components and devices thereof are the same.
The signal light input module 1 specifically includes:
the laser light source 11 is connected to the isolator 13 through the connecting fiber 12, and then connected to the first 1 × 2 fiber coupler 15 through the connecting fiber 14, two output ends 15a, 15b of the first 1 × 2 fiber coupler 15 are respectively connected to the first input end 21a of the first wavelength division multiplexer 5 in the interference upper optical path 32 and the first input end 31a of the fourth wavelength division multiplexer 31 in the interference lower optical path 33 through the connecting fibers 16, 18.
The DTS signal processing module 4 specifically includes:
1) the DTS demodulation system 43 receives the back raman scattered light separated from the upper interference fiber arm 24 by the second wavelength division multiplexer 23 in the interference upper optical path 2 through the connection fibers 27, 28; receiving back raman scattered light separated from the drop interference fiber arm 34 by the fifth wavelength division multiplexer 33 in the interference lower optical path 3 through the connection fibers 37, 38;
2) the DTS demodulation system 43 is connected with the pulse light source 41 through a line 42 and can control the output of the pulse light source; the pulsed light source 41 is connected to the second input end 21b of the first wavelength division multiplexer 21 in the upper interference optical path 2 and the second input end 31b of the fourth wavelength division multiplexer 31 in the lower interference optical path 3 through the connecting optical fibers 17 and 19, respectively.
The signal light output module 5 specifically includes:
the two input ends 51a, 51b of the second 2 × 2 fiber coupler 51 are connected to the first output end 25a of the third wavelength division multiplexer in the interference upper optical path 2 and the first output end 35a of the sixth wavelength division multiplexer 35 in the interference lower optical path 3 through the connection fibers 26, 36, respectively; two output ends 51c, 51d of the second 2 × 2 fiber coupler 51 are connected to a first photodetector 53 and a second photodetector 54 through connecting fibers 52, 54, respectively, and the parameters of the first photodetector 53 and the second photodetector 54 are the same.
A method for compensating temperature of an interference arm of an optical fiber interferometer by using distributed temperature sensing comprises the following specific processes:
1) set the calibration temperature T of the experiment0；
2) The laser light source 11 and the pulse light source 41 are turned on, and the upper trunk is obtained through the DTS demodulation systemThe temperature distribution of the interference fiber arm 24 and the drop interference fiber arm 34 is calculated, and the corresponding temperature fluctuation Deltat of each position is calculated1nAnd Δ t2m；
3) Calculating temperature fluctuation distribution information delta l of the interference arm1nΔt1nAnd Δ l2mΔt2m；
4) Comparing the interference arms at the calibrated temperature, and calculating the influence of temperature fluctuation on the interference arms according to the inherent parameters of the optical fibers of the interference arms, wherein the influence is mainly the change of the axial length of the optical fibers;
5) temperature compensation can be achieved by taking the above-mentioned effects into account and removing them from the data at the time of final calculation, as required.
The process of measuring the temperature distribution and performing temperature compensation by the distributed temperature sensing system can be expressed as follows:
as the laser pulses propagate in the fiber, and back to the beginning of the fiber, each laser pulse produces a flux of Stokes (Stokes) raman backscattered light of:
Φs＝KsSνs 4ΦeRs(T)exp[-(α0+αs)L] (1)
the luminous flux of Anti-Stokes raman backscattered light can be expressed as:
Φa＝KaSνa 4ΦeRa(T)exp[-(α0+αa)L] (2)
in the formula phieIs the luminous flux of incident light, S is the scattering cross section, KsAnd KaCoefficient relating to the Stokes scattering cross-section, Anti-Stokes scattering cross-section, v, respectively, of the fibresV and vaFrequencies, alpha, of Stokes scattered photons and Anti-Stokes scattered photons, respectively0，αs，αaThe average propagation losses of incident light, Stokes light and Anti-Stokes light in the fiber, L is the fiber length, Rs(T) and Ra(T) are coefficients related to population numbers at the low and high energy levels of the fiber molecules, respectively, Stokes Raman backscattered light and Anti-Stokes RamanTemperature modulation function of backscattered light:
Rs(T)＝{1-exp[-hΔν/(kT)]}-1 (3)
Ra(T)＝{exp[hΔν/(kT)]-1}-1 (4)
in the formula, h is a Planck constant, Deltav is the difference between the upper and lower Raman energy levels, namely the phonon frequency of the optical fiber molecule is 13.2THz, k is Boltzmann number, and T is the absolute temperature. The intensity ratio of Anti-Stokes Raman scattered light to Stokes Raman scattered light I (T) is:
and obtaining the temperature information of each section of the optical fiber according to the intensity ratio of the two.
After the standard temperature is set, two beams of light input by the second wavelength division multiplexer 23 or the fifth wavelength division multiplexer 33 are amplified by an avalanche diode (APD) and then input into the signal processor, and the distribution condition of the temperature along the upper path interference optical fiber arm 24 or the lower path interference optical fiber arm 34 can be obtained through inquiry and feedback between the signal processor and a computer, and meanwhile, the output of the pulse light source 41 can be further adjusted through adjusting the driver.
And obtaining the temperature fluctuation on the optical fiber by subtracting the measured temperature distribution information from the standard temperature value. The temperature fluctuation distribution of the upper interference fiber arm 24 can be expressed as Δ l11Δt11、Δl12Δt12、Δl13Δt13……Δl1nΔt1n(ii) a The temperature fluctuation distribution of the drop interference fiber arm 34 can be expressed as Δ l21Δt21、Δl22Δt22、Δl23Δt23……Δl2mΔt2m. Wherein Δ l1i(i-1, 2,3.. n) is a corresponding length of the upper interference fiber arm 24, which is not overlapped with each other, and satisfies l1＝Δl11+Δl12+...+Δl1nWherein l is1For the length of the on-path interference fiber arm 24, Δ t1iTo correspond to Δ l1iPartial temperature variations (difference from standard reference temperature); the physical quantities for which the drop interference fiber arm 34 is designed are similar in meaning to the corresponding physical quantities for the add interference fiber arm 24. In general, when l1＝l2When n is m.
The corresponding temperature compensation calculation method comprises the following steps:
ΔL1＝Δl11Δt11Δα11+Δl12Δt12Δα12+...+Δl1nΔt1nΔα1n (6)
ΔL2＝Δl21Δt21Δα21+Δl22Δt22Δα22+...+Δl2mΔt2mΔα2m (7)
in the formula,. DELTA.L1And Δ L2The changes of the upper path interference fiber arm 24 and the lower path interference fiber arm 34 respectively caused by the temperature influence, delta alpha1i(i ═ 1,2,3.. n) corresponds to Δ l1iCoefficient of thermal expansion of, Δ α2j(i ═ 1,2,3.. m) corresponds to Δ l2jThe coefficient of thermal expansion of (a). Typically, the coefficient of thermal expansion of an optical fiber is substantially the same throughout.
Through the thermal compensation calculation, the thermal compensation calculation result can be considered after the interferometer is used for carrying out experiments and obtaining data, the final result measured by the interferometer can be unrelated to the temperature through the process, and the interference of the temperature to the experiments is eliminated.
According to the method for temperature compensation of the interference arm of the optical fiber interferometer based on distributed temperature sensing, the wavelength division multiplexer is used for compounding the signal light and the detection light of the distributed temperature sensing into a beam of light for transmission, the requirement of an additional light path is reduced, and the wavelength division multiplexer is used for separating the backward Raman scattering light, so that the simplified design of a temperature compensation device is realized, the acquisition of temperature distribution information of the interference arm is realized, and the subsequent temperature compensation work is more accurate.
The selection and parameters of the device in fig. 2 are as follows:
(1) the central wavelength of the laser light source 11 is 1550 nm;
(2) the central wavelength of the pulse light source 41 is 1550 nm;
(3) the working wavelength of the optical fiber isolator 13 is 1550nm, the insertion loss is 0.8dB, and the isolation is more than 35 dB;
(4) the first 1X 2 optical fiber coupler 15 and the second 2X 2 optical fiber coupler 51 have working wavelength of 1550nm and splitting ratio of 50: 50;
(5) the first, the second, the fourth and the fifth wavelength division multiplexers 21, 23, 31 and 33 have working wavelength of 1550 +/-10 nm, insertion loss of 0.3dB and isolation of more than 40 dB;
(6) the third and the sixth wavelength division multiplexers 23 and 33 have the working wavelength of 1445/1550/1655 +/-10 nm, the insertion loss of 0.6dB and the isolation of more than 40 dB;
(7) the first and second photodetectors 53 and 55 have a light detection range of 1100-1700 nm and a responsivity greater than 0.85.
The specific working process of the temperature compensation device is as follows:
the tunable laser 11 is used for providing light source signal light for the system; the output light enters the first 1 × 2 optical fiber coupler 15 after passing through the isolator 13, the isolator 13 is used for preventing the backward transmission light from entering the tunable laser 11 to influence the output of the laser, and the first 1 × 2 optical fiber coupler 15 evenly distributes the input light energy to the two output ends to enter the interference upper optical path 2 and the interference lower optical path 3. The output detection light of the pulse light source 41 is also input into the interference upper optical path 2 and the interference lower optical path 3, respectively.
Taking the interference upper optical path 2 as an example, two input lights are combined into one light by the first wavelength division multiplexer 21, and then enter the upper interference optical fiber arm 24 by the second wavelength division multiplexer 23, wherein when backward raman scattering light caused by the probe light passes through the second wavelength division multiplexer 23, the stokes light and the anti-stokes light therein are separated and transmitted to the DTS demodulation system 43 along the connecting optical fibers 27 and 28, respectively; the forward transmission signal light and the probe light are demultiplexed after passing through the third wavelength division multiplexer 25, wherein the signal light will continue to be transmitted backward along the connection optical fiber 26, and the probe light output end is suspended.
The DTS demodulation system 43 receives the stokes light and the anti-stokes light in the upper interference fiber arm 24 transmitted from the connecting fibers 27 and 28, calculates the temperature distribution of the upper interference fiber arm 24, and the temperature distribution data can be used for temperature compensation of the interference arm; similarly, the scattered light carrying temperature information from the drop interference fiber arm 34 is processed to obtain the temperature distribution of the drop interference fiber arm 24. The DTS demodulation system 43 is also capable of controlling the output of the pulsed light source 41 according to the processed data structure.
The light output from the upper interference light path 2 and the lower interference light path 3 respectively enters the second 2 × 2 fiber coupler 51 through the connecting fibers 26 and 36, and is finally detected by the first and second photoelectric detectors 53 and 55, and then the change of the physical quantity monitored by the interferometer can be calculated through differential operation.
Claims (7)
1. An optical fiber interferometer temperature compensation device based on distributed temperature sensing comprises a signal light input module (1), an interference upper light path (2), an interference lower light path (3), a DTS signal processing module (4) and a signal light output module (5); the method is characterized in that: the signal light input module (1) is respectively connected to the interference upper light path (2) and the interference lower light path (3) through connecting optical fibers; the interference upper optical path (2) is connected with the DTS signal processing module (4) through a connecting optical fiber; the interference lower optical path (3) is connected with the DTS signal processing module (4) through a connecting optical fiber; the interference upper optical path (2) and the interference lower optical path (3) are respectively connected to the signal light output module (5) through connecting optical fibers, and the full optical path adopts a polarization-maintaining optical fiber and a polarization-maintaining device;
the interference upper optical path (2) is formed by sequentially connecting a first wavelength division multiplexer (21), an upper connecting optical fiber (22), a second wavelength division multiplexer (23), an upper interference optical fiber arm (24) and a third wavelength division multiplexer (25); the interference lower optical path (3) is formed by sequentially connecting a fourth wavelength division multiplexer (31), a lower connecting optical fiber (32), a fifth wavelength division multiplexer (33), a lower interference optical fiber arm (34) and a sixth wavelength division multiplexer (35); the optical path structures of the interference upper optical path (2) and the interference lower optical path (3) are the same, and except the lengths of the interference optical fiber arms (24 and 34), the parameters of other components and devices thereof are the same.
2. The distributed temperature sensing-based fiber optic interferometer temperature compensation device according to claim 1, wherein the signal light input module (1) specifically comprises: the laser light source (11) is connected with the isolator (13) through a connecting optical fiber a (12) and then connected with the first 1 x 2 optical fiber coupler (15) through the connecting optical fiber, and two output ends (15a, 15b) of the first 1 x 2 optical fiber coupler (15) are respectively connected with a first input end (21a) of a first wavelength division multiplexer (21) in the interference upper optical path (2) and a first input end (31a) of a fourth wavelength division multiplexer (31) in the interference lower optical path (3) through the connecting optical fiber.
3. The distributed temperature sensing-based optical fiber interferometer temperature compensation device according to claim 1, wherein the DTS signal processing module (4) specifically comprises: the DTS demodulation system (43) receives the back Raman scattering light separated from the upper path interference optical fiber arm (24) by a second wavelength division multiplexer (23) in the upper interference optical path (2) through a connecting optical fiber; receiving back Raman scattered light separated from a lower path interference optical fiber arm (34) by a fifth wavelength division multiplexer (33) in an interference lower optical path (3) through a connecting optical fiber; the DTS demodulation system (43) is connected with the pulse light source (41) through a line (42) and controls the output of the pulse light source (41); the pulse light source (41) is respectively connected with a second input end (21b) of a first wavelength division multiplexer (21) in the interference upper optical path (2) and a second input end (31b) of a fourth wavelength division multiplexer (31) in the interference lower optical path (3) through connecting optical fibers.
4. The distributed temperature sensing-based fiber optic interferometer temperature compensation device according to claim 1, wherein the signal light output module (5) specifically comprises: two input ends (51a, 51b) of the second 2 x 2 optical fiber coupler (51) are respectively connected with a first output end (25a) of a third wavelength division multiplexer in the interference upper optical path (2) and a first output end (35a) of a sixth wavelength division multiplexer (35) in the interference lower optical path (3) through connecting optical fibers; two output ends (51c, 51d) of the second 2 x 2 optical fiber coupler (51) are respectively connected with the first photoelectric detector (53) and the second photoelectric detector (54) through connecting optical fibers, and the parameters of the first photoelectric detector (53) and the second photoelectric detector (54) are the same.
5. A compensation method using the distributed temperature sensing-based optical fiber interferometer temperature compensation device of claim 1, characterized by comprising the following steps:
(1) setting a calibration temperature T0；
(2) The laser light source (11) and the pulse light source (41) are turned on, the temperature distribution of the upper path interference optical fiber arm (24) and the lower path interference optical fiber arm (34) is obtained through a DTS demodulation system, and the corresponding temperature fluctuation delta t of each position is calculated1nAnd Δ t2m；
(3) Calculating temperature fluctuation distribution information delta l of the interference arm1nΔt1nAnd Δ l2mΔt2m；
(4) Comparing the interference arms at the calibrated temperature, and calculating the influence of temperature fluctuation on the interference arms according to the inherent parameters of the optical fibers of the interference arms;
(5) the effects are taken into account from the data and eliminated at the final calculation, as required, to achieve temperature compensation.
6. The compensation method of claim 5, wherein: the effect is a change in the axial length of the fiber.
7. The compensation method of claim 5, wherein the temperature compensation is calculated by:
ΔL1＝Δl11Δt11Δα11+Δl12Δt12Δα12+...+Δl1nΔt1nΔα1n
ΔL2＝Δl21Δt21Δα21+Δl22Δt22Δα22+...+Δl2mΔt2mΔα2m
in the formula,. DELTA.L1And Δ L2Respectively, the change of the upper path interference optical fiber arm and the lower path interference optical fiber arm caused by the influence of temperature, delta alpha1iTo correspond to Δ l1iI 1,2,3.. n, Δ α2jTo correspond to Δ l2jJ-1, 2,3.
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