CN-116067479-B - Dynamic and static combined measurement distributed optical fiber sensing system with separable temperature strain

CN116067479BCN 116067479 BCN116067479 BCN 116067479BCN-116067479-B

Abstract

A temperature strain separable dynamic and static combined measurement distributed optical fiber sensing system, comprising: the invention carries out temperature sensing on the back Raman scattered light of the pulse while receiving the Rayleigh scattered light of the detection pulse by sequentially arranging a laser, an optical modulator, a radio frequency signal generator, an optical filter, a DFB laser, a polarization controller, a first acousto-optic modulator, a scrambler, an erbium-doped fiber amplifier, two optical circulators, an optical wavelength division multiplexer, a receiving module and a signal acquisition and processing module, and the time intervals of adjacent pumping pulses and detection pulses are controlled to perform three-bit pulse encoding and decoding, so that respective back Raman scattering signals of the individual pulses in the pulse pair are separated in time, and the simultaneous measurement of dynamic variables (vibration) and static variables (temperature and static strain) is finally realized, and the spatial resolution of the measurement is ensured not to be lost.

Inventors

FAN XINYU
HE ZUYUAN
HUANG LINJING

Assignees

上海交通大学

Dates

Publication Date: 20260505
Application Date: 20230303

Claims (8)

1. The dynamic and static combined measurement distributed optical fiber sensing system is characterized by comprising a laser, an optical modulator, a radio frequency signal generator, an optical filter, a DFB laser, a polarization controller, a first acousto-optic modulator, a polarization scrambler, an erbium-doped optical fiber amplifier, two optical circulators, an optical wavelength division multiplexer, a receiving module and a signal acquisition and data processing module which are sequentially arranged, wherein the measuring optical fiber, the erbium-doped optical fiber amplifier and the optical wavelength division multiplexer are respectively arranged at three ports of a second optical circulator, a second optical modulator with a signal end connected with the optical modulator is further arranged between the laser and the erbium-doped optical fiber amplifier, the receiving module is connected with the laser to receive local light, the optical modulator, the optical filter, the DFB laser, the polarization controller, the first optical circulator, the first acousto-optic modulator and the polarization scrambler form a base Yu Buli optical time domain analysis branch, namely a BOTDA branch, the second optical modulator forms a detection pulse as a phase sensitive optical time domain reflection branch, namely a phi-OTDR, and the Brillouin scattering light output by the measuring optical fiber and a pumping pulse output by the BOTDA branch is stimulated in the stimulated light generating stimulated light; the back Rayleigh scattered light and the back Raman scattered light of the pulse pair enter the optical wavelength division multiplexer through the second optical circulator and enter the receiving module after being separated according to the wavelength, the back Rayleigh scattered light of the phi-OTDR detection pulse enters the receiving module and interferes with the local light to obtain a current signal, the back Raman scattered light of the pulse pair enters the receiving module and is converted into the current signal to realize Raman scattering-based Raman optical time domain reflection, and the signal generated by the receiving module is demodulated by the signal acquisition and data processing module and simultaneously obtains vibration measurement data, temperature and static strain information and temperature information for different locations.
2. The distributed optical fiber sensing system of claim 1, wherein in the BOTDA branch, the output of the optical modulator is controlled by a dc source and a voltage controlled oscillator, and the output of the voltage controlled oscillator is controlled by a first rf signal generator, so that the output rf signal is a sweep frequency signal within a fixed frequency range.
3. The distributed optical fiber sensing system for dynamic and static combined measurement according to claim 1, wherein the output of the first acousto-optic modulator in the BOTDA branch and the output of the second acousto-optic modulator in the phi-OTDR branch are controlled by a second radio frequency signal generator, wherein the first and second acoustic optical modulators respectively generate pumping pulses and detecting pulses, and the radio frequency signal generator controls the pulse width and the interval of the pumping pulses and the detecting pulses so as to realize three-bit pulse coding; The three-bit pulse coding is realized by pulse pairs consisting of pumping pulses and detection pulses which are generated periodically, wherein the pulse pairs comprise three different code patterns of '101', '110', '011', and '0', the first '1' from left to right of each code pattern represents the detection pulse, the second '1' represents the pumping pulse, and '0' represents the interval T p =τ p between the pumping pulse and the detection pulse, and the pulse width of the pumping pulse and the pulse width of the detection pulse, namely the code element length is tau p .
4. The distributed optical fiber sensing system for dynamic and static combined measurement according to claim 1, wherein the output end of the laser is provided with a first optical fiber coupler, the input end of the optical modulator is connected with the first optical fiber coupler, the second optical modulator and the receiving module are respectively connected with the first optical fiber coupler through a second optical fiber coupler, and the output ends of the optical modulator and the scrambler are respectively connected with the erbium-doped optical fiber amplifier through a third optical fiber coupler.
5. The distributed optical fiber sensing system for dynamic and static combined measurement according to claim 3, wherein the receiving module comprises a polarization diversity photodetector for receiving back-raman scattered light and two avalanche photodetectors for receiving back-raman scattered light, wherein the back-raman scattered light consists of two wavelengths of light, and the two wavelengths of back-raman scattered light are received by the two avalanche photodetectors respectively; for the backward Raman scattered light of two wavelengths of the pulse pair received by the two avalanche photodetectors, respectively carrying out the same data processing, namely, firstly, carrying out the de-encoding of the backward Raman scattered light, separating the superimposed backward Raman scattered light of the two pulses to obtain the intensity distribution of the backward Raman scattered light of the two pulses of each pulse along the optical fiber, so as to demodulate the temperature change on the optical fiber, and combining the temperature demodulation result of the backward Raman scattered light and the temperature and strain demodulation result based on the amplitude of the backward Raman scattered light because the backward Raman scattered light is insensitive to the strain.
6. A dynamic and static joint measurement distributed optical fiber sensing system according to claim 3, wherein the "011" code pattern is shifted forward by one symbol distance to ensure uniform time intervals of probe pulses in each adjacent code pattern; The code pattern is that periodically generates I.e. starting from the first line and ending with the third line, and then again starting in the same order, the adjacent pattern intervals are fixed to Wherein: To measure the speed of light in the fiber, L c is the length of the measuring fiber.
7. The dynamic-static combined measurement distributed optical fiber sensing system according to claim 1 or 5, wherein the demodulation includes simultaneous phi-OTDR demodulation, brillouin frequency shift demodulation, and raman scattering light intensity ratio demodulation, wherein: a) phi-OTDR demodulation, namely, carrying out narrow-band filtering on Rayleigh scattering signals corresponding to three code patterns, and then directly carrying out phi-OTDR demodulation to obtain vibration measurement data; b) The method comprises the steps of brillouin frequency shift demodulation, namely taking amplitude values of Rayleigh scattering signals corresponding to three code patterns after narrow-band filtering in the first step, normalizing the Rayleigh scattering signals at each position to obtain corresponding brillouin gain, moving the whole brillouin gain corresponding to the 1 st code pattern, namely '101', forward by a code element distance, namely a space resolution distance, obtaining a brillouin gain spectrum according to a brillouin sweep period, obtaining brillouin frequency shift through the brillouin gain spectrum, and further demodulating temperature and static strain information at different positions on a measuring optical fiber; c) And (3) carrying out pulse decoding on the Raman scattering signals corresponding to the 3 rd group code pattern, namely '011', by a distance of one code element, combining the Raman scattering signals corresponding to the 1 st group code pattern and the 2 nd group code pattern, namely '110', to obtain the Raman scattering signals of the two pulses, and calculating to obtain the ratio of the Raman scattering anti-Stokes light to the Stokes light intensity to obtain the temperature information of different positions on the measuring optical fiber.
8. A temperature strain separable dynamic and static combined measurement distributed optical fiber sensing method based on the system of any one of claims 1-7, comprising the steps of: step 1, clock synchronization; step 2, setting a brillouin pump light of the sweep frequency; Step 3, modulating the light pulse pair; Step 4, disturbing and amplifying the pulse light; Step 5, data acquisition; step 6, data demodulation; step 7, calculating temperature strain separation, namely Brillouin frequency shift And the amount of temperature change Amount of strain change The linear relation between is Wherein c 11 is Brillouin strain coefficient, c 12 is Brillouin temperature coefficient, raman scattering ratio R (T) and temperature variation The relation between is that Wherein c 22 is a Raman temperature coefficient, and temperature and static strain information of different positions L on the measuring optical fiber are demodulated by combining the measured Brillouin frequency shift and the Raman scattering intensity ratio.

Description

Dynamic and static combined measurement distributed optical fiber sensing system with separable temperature strain Technical Field The invention relates to a technology in the field of optical fiber sensing, in particular to a dynamic and static combined measurement distributed optical fiber sensing system with separable temperature strain. Background The distributed optical fiber sensing system is widely applied to various fields of building structure health monitoring, rail traffic monitoring, submarine security protection and the like, and can realize simultaneous measurement of long-distance and multiple points. The sensing optical fiber used for the distributed optical fiber sensing system has various options (common single mode optical fiber, polarization maintaining optical fiber, multimode optical fiber, few-mode optical fiber, multi-core optical fiber and the like), in order to utilize the existing laid optical fiber for sensing, the most economical scheme is to utilize the common single mode optical fiber for sensing, but the distributed optical fiber sensing system utilizing the single mode optical fiber as the sensing optical fiber generally only measures one physical quantity, or can simultaneously measure temperature and strain but has the problem of cross sensitivity. The existing distributed optical fiber sensing technology using two pulses can not overcome the temperature strain cross-sensitivity problem while simultaneously detecting temperature change and static strain change, namely, the temperature change and the change caused by the static strain can not be distinguished, so that errors occur in measurement or measurement scenes are limited. In addition, when two pulses are used for sensing, the back raman scattering light has high frequency band overlap ratio, and the back raman scattering of the two pulses cannot be distinguished in a frequency domain by using a conventional means, which can cause the degradation of the spatial resolution of temperature measurement and affect the measurement effect. Disclosure of Invention The invention provides a temperature strain separable dynamic and static state combined measurement distributed optical fiber sensing system, which aims at the temperature strain cross-sensitivity problem and the dynamic and static state strain simultaneous measurement problem in the existing distributed optical fiber sensing, and the temperature strain separable dynamic and static state combined measurement distributed optical fiber sensing system senses the temperature of the back Raman scattered light of a pulse while receiving the Rayleigh scattered light of a detection pulse, and controls the time interval of adjacent pumping pulses and detection pulses to perform three-bit pulse encoding and decoding, so that the respective back Raman scattered signals of the independent pulses in the pulse pair are separated in time, and the simultaneous measurement of dynamic variables (vibration) and static variables (temperature and static strain) is finally realized, and the spatial resolution of the measurement is ensured not to be lost. The invention is realized by the following technical scheme: The invention relates to a temperature strain separable dynamic and static combined measurement distributed optical fiber sensing system, which comprises a laser, an optical modulator, a radio frequency signal generator, an optical filter, a DFB laser, a polarization controller, a first acousto-optic modulator, a scrambler, an erbium-doped optical fiber amplifier, two optical circulators, an optical wavelength division multiplexer, a receiving module and a signal acquisition and processing module which are sequentially arranged, wherein the measuring optical fiber, the erbium-doped optical fiber amplifier and the optical wavelength division multiplexer are respectively arranged at three ports of a second optical circulator, a second optical modulator with a signal end connected with the optical modulator is further arranged between the laser and the erbium-doped optical fiber amplifier, the receiving module is connected with the laser to receive local light, the optical modulator, the optical filter, the DFB laser, the polarization controller, the first optical circulator, the first acousto-optic modulator and the scrambler form a base Yu Buli Brillouin Optical Time Domain Analysis (BOTDA) branch, and the second optical modulator forms detection pulses as phase sensitive optical time domain reflection The pulse pair of the back Rayleigh scattered light and the back Raman scattered light enter the optical wavelength division multiplexer through the optical circulator to be separated according to the wavelength and then enter the receiving module,The back Rayleigh scattered light of the detection pulse enters the receiving module and interferes with the local light to obtain a current signal, the back Rayleigh scattered light of the pulse pair enters the receiving module and is