阅读说明：本技术 一种同时测量温度与应变的光频域反射系统 (Optical frequency domain reflection system capable of simultaneously measuring temperature and strain ) 是由 刘香莲 徐淑婉 白清 梁昌硕 方正 高妍 张红娟 王宇 刘昕 靳宝全 于 2021-07-30 设计创作，主要内容包括：本发明公开了一种同时测量温度与应变的光频域反射系统,具体属于分布式光纤传感技术领域。通过可调谐激光器发出扫频光进入环形器,探测光从环形器一端出口经波分复用器进入待测光纤,产生拉曼散射光和后向瑞利散射光,完成温度和应变的测量；经波分复用器分别解复用出瑞利散射信号,斯托克斯和反斯托克斯信号进行分别解调,采用相关算法对后向瑞利散射光谱偏移量进行计算来实现温度和应变检测,采用拉曼双路分析脉冲响应方法进行温度补偿,从而解决了温度与应变之间的交叉敏感问题,实现了温度与应变的同时测量。(The invention discloses an optical frequency domain reflection system for simultaneously measuring temperature and strain, and particularly belongs to the technical field of distributed optical fiber sensing. Emitting frequency sweeping light by a tunable laser to enter a circulator, and entering detection light into an optical fiber to be measured from an outlet at one end of the circulator through a wavelength division multiplexer to generate Raman scattering light and backward Rayleigh scattering light so as to finish measurement of temperature and strain; the Rayleigh scattering signals are respectively demultiplexed by the wavelength division multiplexer, the Stokes signals and the anti-Stokes signals are respectively demodulated, backward Rayleigh scattering spectrum offset is calculated by adopting a correlation algorithm to realize temperature and strain detection, and a Raman two-way analysis impulse response method is adopted to carry out temperature compensation, so that the problem of cross sensitivity between temperature and strain is solved, and the simultaneous measurement of the temperature and the strain is realized.)

1. A system for simultaneous temperature and strain measurement in the optical frequency domain, comprising:

the device comprises a tunable laser (1), a first optical fiber coupler (2), a second optical fiber coupler (3), a third optical fiber coupler (4), an optical fiber circulator (5), a wavelength division multiplexer (6), an optical fiber to be tested (7), a fourth optical fiber coupler (9), a polarization beam splitter (10), a balanced photoelectric detector (11), an avalanche diode (12), a delay optical fiber (13), a fifth optical fiber coupler (15), a photoelectric detector (16), a data acquisition module (17), a first signal processing device (18) and a second signal processing device (19);

the output end of the tunable laser (1) is connected with the input end A of the first optical fiber coupler (2), the output end B of the first optical fiber coupler (2) is connected with the input end of the second optical fiber coupler (3), and the output end F of the second optical fiber coupler (3) is connected with the first port G of the optical fiber circulator (5); a second port H of the optical fiber circulator (5) is connected with an input port I of the wavelength division multiplexer (6), an output port J of the wavelength division multiplexer (6) is connected with an optical fiber (7) to be tested, and a third port K of the optical fiber circulator (5) is connected with an input end W of a fourth optical fiber coupler (9); the output end of the fourth optical fiber coupler (9) is connected with the input end L of the polarization beam splitter (10); two output ends of the polarization beam splitter (10) are respectively connected with an input end M and an input end N of the balanced photoelectric detector (11), and an output end of the balanced photoelectric detector (11) is connected with an input end O of the data acquisition module (17); the output end S of the third optical fiber coupler (4) is connected with the input end T of the fifth optical fiber coupler (15) through a delay optical fiber (13), the output end U of the third optical fiber coupler (4) is connected with the input end V of the fifth optical fiber coupler (15), and the output end of the fifth optical fiber coupler (15) is connected with the input end X of the data acquisition module (17) through a photoelectric detector (16); two output ports P and Q of the wavelength division multiplexer (6) are correspondingly connected with two input ends of the avalanche diode (12), and the output end of the avalanche diode (12) is correspondingly connected with an input end R1 and an input end R2 of the data acquisition module (17); an output Y port of the data acquisition module (17) is connected with a first signal processing device (18), and an output Z port of the data acquisition module (17) is connected with a second signal processing device (19).

2. Optical frequency domain reflectometry system for simultaneous temperature and strain measurement as in claim 1, characterized by the fact that the first polarization controller (8) is arranged on the line connecting the output D of the second fiber coupler (3) with the input E of the fourth fiber coupler (9); and a second polarization controller (14) is arranged on a circuit connecting the output end U of the third optical fiber coupler (4) with the input end V of the fifth optical fiber coupler (15).

Technical Field

The invention relates to the technical field of distributed optical fiber sensing, in particular to an optical frequency domain reflection system for simultaneously measuring temperature and strain.

Background

In recent years, optical fiber sensors have attracted wide research interest worldwide, and optical fiber sensing technology is widely applied to safety monitoring of large structures such as pipelines and bridges in geological settlement disaster areas due to the advantages of long measuring distance, electromagnetic interference resistance, corrosion resistance and the like. Due to their distributed capabilities, exhibit advantages over conventional sensors. In terms of methods, Optical Time Domain Reflectometry (OTDR) and Optical Frequency Domain Reflectometry (OFDR) have found methods that meet various practical needs. The OFDR adopts continuous sweep frequency optical detection, has the characteristics of high spatial resolution and large dynamic range, and the sensitivity of a coherent detection scheme is high, so that the spatial resolution of millimeter wave bands can be obtained. The OFDR fills the blank of the OTDR in the measurement range, and has important application value in the actual temperature and strain monitoring applications of intelligent materials, structural health monitoring and the like.

However, the distributed optical fiber sensor is sensitive to both strain and temperature, so that temperature change and strain change cannot be distinguished, and errors can be introduced when strain or temperature is monitored. Therefore, in the process of researching an Optical Frequency Domain Reflectometer (OFDR), two parameters of temperature and strain need to be accurately measured, and the problem of cross sensitivity is solved, so that the simultaneous measurement of the temperature and the strain is realized.

Disclosure of Invention

The invention provides an optical frequency domain reflecting system for simultaneously measuring temperature and strain, which solves the problem of cross sensitivity by detecting Rayleigh scattering spectrum frequency shift (optical frequency domain reflecting system) and a Raman double-path analysis pulse response method (Raman optical frequency domain reflecting system). since the Raman optical frequency domain reflecting system is only sensitive to temperature, the Raman optical frequency domain reflecting system is adopted to carry out temperature compensation on the Raman optical frequency domain reflecting system, thereby simplifying the calculation of a double-parameter sensing matrix and effectively solving the problem of cross sensitivity; and the auxiliary interferometer is adopted to inhibit the nonlinearity of the sweep frequency light source, and the polarization diversity receiving system is adopted to eliminate the influence of polarization fading, so that the simultaneous measurement of temperature and strain under high spatial resolution is realized.

The technical scheme adopted by the invention for solving the technical problems is as follows: constructing a light frequency domain reflectometry system for simultaneous temperature and strain measurement, comprising:

the device comprises a tunable laser, a first optical fiber coupler, a second optical fiber coupler, a third optical fiber coupler, an optical fiber circulator, a wavelength division multiplexer, an optical fiber to be tested, a fourth optical fiber coupler, a polarization beam splitter, a balanced photoelectric detector, an avalanche diode, a delay optical fiber, a fifth optical fiber coupler, a photoelectric detector, a data acquisition module, a first signal processing device and a second signal processing device;

the output end of the tunable laser is connected with the input end A of the first optical fiber coupler, the output end B of the first optical fiber coupler is connected with the input end of the second optical fiber coupler, and the output end F of the second optical fiber coupler is connected with the first port G of the optical fiber circulator; a second port H of the optical fiber circulator is connected with an input port I of the wavelength division multiplexer, an output port J of the wavelength division multiplexer is connected with an optical fiber to be tested, and a third port K of the optical fiber circulator is connected with an input end W of a fourth optical fiber coupler; the output end of the fourth optical fiber coupler is connected with the input end L of the polarization beam splitter; the two output ends of the polarization beam splitter are respectively connected with the input end M and the input end N of the balance photoelectric detector, and the output end of the balance photoelectric detector is connected with the input end O of the data acquisition module; the output end S of the third optical fiber coupler is connected with the input end T of the fifth optical fiber coupler through a delay optical fiber, the output end U of the third optical fiber coupler is connected with the input end V of the fifth optical fiber coupler, and the output end of the fifth optical fiber coupler is connected with the input end X of the data acquisition module through a photoelectric detector; two output ports P and Q of the wavelength division multiplexer are correspondingly connected with two input ends of an avalanche diode, and two output ends of the avalanche diode are correspondingly connected with an input end R1 and an input end R2 of the data acquisition module; an output Y port of the data acquisition module is connected with the first signal processing device, and an output Z port of the data acquisition module is connected with the second signal processing device.

A first polarization controller is arranged on a circuit connecting the output end D of the second optical fiber coupler and the input end E of the fourth optical fiber coupler; and a second polarization controller is arranged on a circuit connecting the output end U of the third optical fiber coupler with the input end V of the fifth optical fiber coupler.

Compared with the prior art, the optical frequency domain reflection system for simultaneously measuring the temperature and the strain is combined with the optical frequency domain reflection system and the Raman optical frequency domain reflection system, the temperature and the strain are demodulated through Stokes and anti-Stokes two-way impulse response analysis and backward Rayleigh scattering spectrum frequency shift in the detection optical fiber, the problem of cross sensitivity of temperature and strain sensing is solved, and the phenomenon that the signal-to-noise ratio of the system is deteriorated and the sensing precision and the real-time performance are influenced due to phase noise caused by nonlinear frequency sweep light sources and polarization fading is avoided; the invention can compensate the phase noise, improve the signal to noise ratio, further improve the system measurement accuracy and realize high-precision sensing.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

fig. 1 is a schematic structural diagram of an optical frequency domain reflection system for simultaneously measuring temperature and strain according to the present invention.

In the figure, 1, a tunable laser; 2. a first fiber coupler; 3. a second fiber coupler; 4. a third fiber coupler; 5. a fiber optic circulator; 6. a wavelength division multiplexer; 7. an optical fiber to be tested; 8. a first polarization controller; 9. a fourth fiber coupler; 10. a polarizing beam splitter; 11. a balanced photodetector; 12. an avalanche diode; 13. a delay optical fiber; 14. a second polarization controller; 15. a fifth fiber coupler; 16. a photodetector; 17. a data acquisition module; 18. a first signal processing device; 19. and a second signal processing means.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described are only for illustrating the present invention and are not to be construed as limiting the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, the present invention provides a light frequency domain reflection system for simultaneously measuring temperature and strain, comprising:

the device comprises a tunable laser 1, a first optical fiber coupler 2, a second optical fiber coupler 3, a third optical fiber coupler 4, an optical fiber circulator 5, a wavelength division multiplexer 6, an optical fiber to be tested 7, a fourth optical fiber coupler 9, a polarization beam splitter 10, a balanced photoelectric detector 11, an avalanche diode 12, a delay optical fiber 13, a fifth optical fiber coupler 15, a photoelectric detector 16, a data acquisition module 17, a first signal processing device 18 and a second signal processing device 19;

the output end of the tunable laser 1 is connected with the input end A of the first optical fiber coupler 2, the output end B of the first optical fiber coupler 2 is connected with the input end of the second optical fiber coupler 3, and the output end F of the second optical fiber coupler 3 is connected with the first port G of the optical fiber circulator 5; a second port H of the optical fiber circulator 5 is connected with an input port I of the wavelength division multiplexer 6, an output port J of the wavelength division multiplexer 6 is connected with an optical fiber 7 to be tested, and a third port K of the optical fiber circulator 5 is connected with an input end W of a fourth optical fiber coupler 9; the output end of the fourth optical fiber coupler 9 is connected with the input end L of the polarization beam splitter 10; two output ends of the polarization beam splitter 10 are respectively connected with an input end M and an input end N of the balanced photoelectric detector 11, and an output end of the balanced photoelectric detector 11 is connected with an input end O of the data acquisition module 17; an output end S of the third optical fiber coupler 4 is connected with an input end T of a fifth optical fiber coupler 15 through a delay optical fiber 13, an output end U of the third optical fiber coupler 4 is connected with an input end V of the fifth optical fiber coupler 15, and an output end of the fifth optical fiber coupler 15 is connected with an input end X of a data acquisition module 17 through a photoelectric detector 16; two output ports P and Q of the wavelength division multiplexer 6 are correspondingly connected with two input ends of the avalanche diode 12, and two output ends of the avalanche diode 12 are correspondingly connected with an input end R1 and an input end R2 of the data acquisition module 17; an output Y port of the data acquisition module 17 is connected with a first signal processing device 18, and an output Z port of the data acquisition module 17 is connected with a second signal processing device 19.

A first polarization controller 8 is arranged on a circuit connecting the output end D of the second optical fiber coupler 3 and the input end E of the fourth optical fiber coupler 9; a second polarization controller 14 is arranged on a line connecting the output end U of the third optical fiber coupler 4 with the input end V of the fifth optical fiber coupler 15.

The working principle of the invention is as follows: the invention sends out laser signals with constant optical power, continuous phase and monotonous frequency change along with time through the tunable laser 1, and the laser signals enter the optical fiber 7 to be measured through the port H of the optical fiber circulator 5 and the wavelength division multiplexer 6 to generate backward Rayleigh scattered light and Raman scattered light so as to finish the measurement of temperature and strain; backward Rayleigh scattered light is input from the other port K of the optical fiber circulator 5 and is collected together with reference light after beat frequency; the Raman scattering light is output and collected from two ports of the wavelength division multiplexer 6; rayleigh scattering frequency shift demodulation and Stokes and anti-Stokes double-path impulse response analysis are completed, and the problem of cross sensitivity between temperature and strain is solved; moreover, the polarization diversity receiving processing is carried out on the system, so that the influence that the beat frequency signal possibly cannot be detected due to the random polarization state can be eliminated, and the signal-to-noise ratio of the system is improved; the nonlinearity of the system light source is added with auxiliary interferometer processing, so that the phase noise in the system can be eliminated, and the simultaneous measurement of temperature and strain is ensured under the condition of improving the precision.

The following describes an embodiment of the present invention with reference to fig. 1: as shown in fig. 1, a tunable laser 1 emits a laser signal (with a wavelength of 1550 nm) with a sinusoidal variation of optical power and an increasing frequency, and the optical signal enters a first optical fiber coupler 2 and is divided into 99% of main interference light and 1% of auxiliary interference light by the first optical fiber coupler 2.

The main interference light is output to the input end of the second optical fiber coupler 3 through a port B of the first optical fiber coupler 2, and is divided into 90% detection light and 10% reference light through the second optical fiber coupler 3, the detection light is input to a first port G of the optical fiber circulator 5, and is output to an input port I of the wavelength division multiplexer 6 from a second port H of the optical fiber circulator 5, and is output to the optical fiber 7 to be tested from an output port J of the wavelength division multiplexer 6, and the reference light is output to an input port E of the fourth optical fiber coupler 9 through the first polarization controller 8. The backward scattered light (1550 nm) generated by the optical fiber 7 to be measured returns to the second port H of the optical fiber circulator 5, and is output to the input port W of the fourth optical fiber coupler 9 through the third port K of the optical fiber circulator 5. The fourth fiber coupler 9 combines the backward scattered light of the fiber under test from the input port W and the reference light from the input port E into a main interference combined light in a ratio of 50:50, and outputs to the polarization beam splitter 10. The polarization beam splitter 10 divides the main interference combined light into two beams of light with mutually orthogonal polarization states, wherein a fast axis component of the main interference combined light is formed by combining a fast axis component of backward scattering light of the optical fiber to be detected and a fast axis component of reference light and is output to an input port M of the balanced photoelectric detector 11; the slow axis component of the main interference combined light is formed by combining the slow axis component of the backward scattering light of the optical fiber to be detected and the slow axis component of the reference light, and is output to the input port N of the balanced photoelectric detector 11. In the balanced photoelectric detector 11, coherent beat frequency is generated between the fast axis component of the backward scattering light of the optical fiber to be detected and the fast axis component of the reference light, and the fast axis component of the reference light is converted into an electric signal, so that a main interference fast axis beat frequency signal is obtained; and the slow axis component of the backward scattering light of the optical fiber to be detected and the slow axis component of the reference light generate coherent beat frequency and are converted into electric signals, so that main interference slow axis beat frequency signals are obtained. By adjusting the first polarization controller 8, after the power of the main interference fast axis beat signal and the power of the main interference slow axis beat signal are close to each other, the square of the main interference fast axis beat signal of the balanced photodetector 11 and the square of the main interference slow axis beat signal of the balanced photodetector 11 are summed and output to the input port O of the data acquisition module 17, so that polarization diversity reception of two orthogonal polarized lights is realized, the signal-to-noise ratio deterioration caused by polarization fading is reduced, and the signal-to-noise ratio of the system is improved. The data acquisition module 17 receives a signal from the main interference system from the input port O for demodulation and analysis, then outputs the signal through the Y port of the data acquisition device 17 to enter the first signal processing device 18, and calculates a change value of an offset by taking cross-correlation of the rayleigh scattering spectrum data of the local optical fiber relative to an invariant state to demodulate strain information distributed along the optical fiber, thereby realizing simultaneous measurement of temperature and strain.

In addition, the detection light is input to the first port G of the optical fiber circulator 5, and is output from the second port H of the optical fiber circulator 5 to the input port I of the wavelength division multiplexer 6, and is output from the output port J of the wavelength division multiplexer 6 to the optical fiber 7 to be tested, and the stokes light (1660 nm) and the anti-stokes light (1450 nm) generated by the optical fiber to be tested are demultiplexed by the wavelength division multiplexer 6 and are output from the output ports P and Q to the avalanche diode 12 to be converted into electrical signals, and are output to the input port R1 and the input port R2 of the data acquisition module 17. And then the temperature information is output through a Z port of the data acquisition device 17 and enters a second signal processing device 19, and unit impulse response analysis is carried out by using Stokes and anti-Stokes two-way signals to demodulate the temperature information distributed along the optical fiber.

The auxiliary interference light is output to the input port of the third optical fiber coupler 4 through the C port of the first optical fiber coupler 2, and is divided into standard light and delay light in a ratio of 50:50 through the third optical fiber coupler 4. Wherein, the standard light is output from the U port of the third fiber coupler 4 to the V port of the fifth fiber coupler 15 through the second polarization controller 14. The delayed light is output from the S port of the third fiber coupler 4 to the T port of the fifth fiber coupler 15 through the delay fiber 13, and the normal light and the delayed light are combined again at the fifth fiber coupler 15 in a ratio of 50:50 to be auxiliary interference combined light. The auxiliary interference combined light is output from the output port of the fifth optical fiber coupler 15 and is output to the input port X of the data acquisition module 17 through the photodetector 16. The data acquisition module 17 receives the signal from the auxiliary interference system from the input port X and analyzes the signal to obtain system phase noise information, so as to compensate the phase noise of the signal from the main interference system, thereby reducing the system phase noise.

The optical fiber to be measured is calibrated under different temperatures and strains respectively; because of the Raman optical frequency domain reflection systemIs only sensitive to temperature, so that the temperature sensing coefficients of two systems are obtained on calibration curves of different temperaturesAndobtaining strain sensing coefficient from calibration curve of different strainAnd 0; when the temperature and the strain change simultaneously in the actual measurement, the Rayleigh scattering spectrum frequency shift is demodulated by using the optical frequency domain reflection systemThe unit pulse response of the sensing optical fiber is demodulated by using a Raman optical frequency domain reflection systemThe corresponding temperature change is obtained by using the following relationshipChange in strain of：

While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.