Phase-sensitive optical time domain reflectometer type distributed optical fiber acoustic wave sensor based on improved PGC algorithm
阅读说明：本技术 基于改良pgc算法的相位敏感光时域反射计型分布式光纤声波传感器 (Phase-sensitive optical time domain reflectometer type distributed optical fiber acoustic wave sensor based on improved PGC algorithm ) 是由 张春熹 马皓钰 马福 王夏霄 刘海霞 于 2019-11-05 设计创作，主要内容包括：本发明公开了一种基于改良PGC算法的相位敏感光时域反射计型分布式光纤声波传感器,其特征在于它包括窄线宽激光器、声光调制器、第一隔离器、掺铒光纤放大器、环形器、传感光纤、第二隔离器、耦合器、第一反射镜、第二反射镜、压电陶瓷、信号发生器、光电探测器、数模转换器、DSP芯片。所述DSP芯片中PGC解调采用DCM与Arctan算法相结合的算法。本发明在运算过程中完全消除了贝塞尔函数的影响,将J<Sub>1</Sub>(C)与J<Sub>2</Sub>(C)通过两路信号的自身运算消除,从而消除了传统PGC-DCM或PGC-Arctan算法中载波调制深度C的影响,提升了解调结果的准确性,减少了误差因素的干扰。(The invention discloses a phase-sensitive optical time domain reflectometer type distributed optical fiber acoustic wave sensor based on an improved PGC algorithm, which is characterized by comprising a narrow-linewidth laser, an acoustic-optical modulator, a first isolator, an erbium-doped optical fiber amplifier, a circulator, a sensing optical fiber, a second isolator, a coupler, a first reflector, a second reflector, piezoelectric ceramics, a signal generator, a photoelectric detector, a digital-to-analog converter and a DSP chip. PGC demodulation in the DSP chip adopts an algorithm combining DCM and Arctan algorithm. The invention completely eliminates Bessel in the operation processInfluence of the Erer function, will J 1 (C) And J 2 (C) Through self-operation elimination of two paths of signals, the influence of the carrier modulation depth C in the traditional PGC-DCM or PGC-Arctan algorithm is eliminated, the accuracy of demodulation results is improved, and the interference of error factors is reduced.)
1. A phase-sensitive optical time domain reflectometer type distributed optical fiber acoustic wave sensor based on an improved PGC algorithm is characterized by comprising a narrow-linewidth laser (1), an acoustic-optical modulator (2), a first isolator (3), an erbium-doped optical fiber amplifier (4), a circulator (5), a sensing optical fiber (6), a second isolator (7), a coupler (8), a first reflector (9), a second reflector (10), piezoelectric ceramics (11), a signal generator (12), a photoelectric detector (13), a digital-to-analog converter (14) and a DSP chip (15),
the narrow-linewidth laser (1) is connected with the acousto-optic modulator (2) through a single-mode optical fiber, and the acousto-optic modulator (2) is connected to the input end of the first isolator (3) through the same single-mode optical fiber; the output end of the first isolator (3) is connected to the erbium-doped fiber amplifier (4) through a single-mode fiber; the erbium-doped fiber amplifier (4) is connected to the port 1 of the circulator (5) through a single-mode fiber; 2 ports of the circulator (5) are connected to the input end of the second isolator (7) through a single-mode sensing optical fiber; 3 ports of the circulator (5) are connected into 1 port of the coupler (8) through a single mode fiber; 2, 4 ports of the coupler (8) are respectively connected into the first reflector (9) and the piezoelectric ceramic (11) through single-mode optical fibers; the signal input end of the piezoelectric ceramic (11) is connected with a signal generator (12) through an electric wire, and the optical output end of the piezoelectric ceramic is connected with the second reflector (10) through a single-mode optical fiber; the 3 ports of the coupler (8) are connected with the optical input end of the photoelectric detector (13) through a single-mode optical fiber; the electrical output end of the photoelectric detector (13) is connected with a digital-to-analog converter (14) through an electric wire, and the digital-to-analog converter (14) is connected with a DSP chip (15) through an electric wire.
2. The phase-sensitive optical time domain reflectometry (OPTDR) type distributed optical fiber acoustic wave sensor based on the improved PGC algorithm as claimed in claim 1, wherein PGC demodulation in the DSP chip adopts an algorithm combining DCM and Arctan algorithm.
3. The phase-sensitive optical time domain reflectometry (OPTDR) type distributed optical fiber acoustic wave sensor based on the improved PGC algorithm as claimed in claim 2, wherein the interference signals I are respectively identical to the frequency-doubled carrier signal G cos ω0t and a double frequency carrier signal H cos2 omega0t are multiplied to obtain a1 and b1, the obtained results a1 and b1 are respectively subjected to low-pass filtering to obtain a2 and b2, the results a2 and b2 are respectively subjected to differentiation to obtain a3 and b3, the results a3 and b3 are respectively multiplied by b2 and a2, and the obtained two-path signal results a4 and b4 are subjected to division, absolute value taking, arithmetic square root and arc tangent operation in sequence to obtain a demodulation signal result.
4. The distributed optical fiber acoustic wave sensor based on phase sensitive optical time domain reflectometry of modified PGC algorithm as claimed in claim 3, wherein the output signal of the interferometer
the amplitude is G, H respectively, and the angular frequency is omega0And 2 omega0Is mixed with the output signal I of the interferometer, and the mixing results a1 and b1 are calculated by the following formula:
wherein A is the amplitude of the DC component in the interferometer output signal I, B is the amplitude of the AC component in the interferometer output signal I, C is the carrier modulation depth, t is the time,
after a1 and b1 are respectively subjected to low-pass filtering, the following results are obtained:
a2 and b2 adopt a differential cross multiplication method, and signals obtained by differentiation are as follows:
the two terms obtained after the cross multiplication of a3 and b3 are respectively:
in the formula, J1(C) As Bessel first order function, J2(C) Is a bessel second order function.
Technical Field
The invention belongs to the field of optical fiber distributed acoustic wave sensors, and particularly relates to a phase-sensitive optical time domain reflectometer type distributed optical fiber acoustic wave sensor based on an improved PGC algorithm.
Background
A distributed optical fiber acoustic wave sensing system based on a phase-sensitive optical time domain reflectometer (Φ -OTDR) realizes distributed measurement and reduction of acoustic wave signals by using phase change of backscattered light in optical fiber transmission. Besides the inherent advantages of distributed fiber vibration sensing (DVS), the system also has the capability of monitoring dynamic strain of vibration and sound waves in a long-distance real-time multipoint quantitative manner, and has a wider application prospect. Taylor et al, university of texas a & M, in 1993, first proposed an optical time domain reflectometer based on rayleigh backscattered light and employing an ultra narrow linewidth laser. In 2005, Taylor proposed the application of Φ -OTDR to intrusion detection and performed field experiments.
The phi-OTDR replaces a light source with a narrow linewidth laser on the basis of the traditional OTDR, and the interference intensity of the back scattering light is greatly enhanced. Continuous light emitted from a narrow-linewidth laser is modulated into pulsed light via a modulator. The pulsed light Modulator is typically an Electro-Optical Modulator (EOM), an Acousto-Optical Modulator (AOM), or a Semiconductor Optical Amplifier (SOA). Pulsed light enters the sensing Fiber through the circulator after passing through an Erbium-Doped Fiber Amplifier (EDFA), and generated backscattered light is transmitted to the photoelectric detector through the circulator to be converted into an electric signal, and the electric signal is subjected to information processing through the data processing module. When a vibration signal acts on the sensing optical fiber, the refractive index of the optical fiber changes due to the photoelastic effect of the optical fiber, so that the phase of the backward scattering light changes, and the interference result is influenced. And subtracting the collected disturbed and undisturbed back scattering light curves, and determining the position of a peak of the differential curve to monitor and position the external disturbance event.
The phase generation carrier modulation method is to apply a carrier modulation signal with a very high frequency to a sensing arm of an interferometer, make a vibration signal become a sideband of the carrier signal, remove interference of a noise signal through operations such as low-high pass filtering and mixing, and restore information such as intensity and phase of the vibration signal from the carrier signal. In terms of demodulation, carrier modulation has many options, and the most common are the Differential Cross Multiplication (DCM) algorithm and the Arctan (Arctan) algorithm.
The PGC-DCM algorithm shows that the demodulation result is related to factors such as the visibility v, the light intensity factor A, the carrier modulation depth C and the like. All other factors affecting the above factors, such as the output intensity of the laser, the light intensity attenuation of the light in the fiber sensor, the splitting ratio of the coupler, the polarization change of the transmitted light, etc., will affect the demodulation result.
Compared with the PGC-DCM demodulation algorithm, the PGC-Arctan demodulation algorithm has a simple algorithm structure so as to reduce the signal processing time, and the demodulation result does not contain factors such as light intensity, visibility and the like, so that the instability of the demodulation result caused by factors such as unstable light source can be avoided, but only when J is used1(C)/J2(C) When the carrier modulation depth is 1, the demodulation accuracy can be guaranteed, and therefore, distortion of the demodulation result caused by the deviation of the carrier modulation depth is a main problem of the PGC-Arctan algorithm.
Disclosure of Invention
The invention aims at the problems in the background technology and aims to solve the problem that the signal demodulation result in the PGC demodulation algorithm is influenced by the carrier modulation depth C, so that a more accurate demodulation signal is obtained.
The technical scheme is as follows:
the invention discloses a phase-sensitive optical time domain reflectometer type distributed optical fiber acoustic wave sensor based on an improved PGC algorithm, which comprises a narrow-linewidth laser, an acoustic-optical modulator, a first isolator, an erbium-doped optical fiber amplifier, a circulator, a sensing optical fiber, a second isolator, a coupler, a first reflector, a second reflector, piezoelectric ceramics, a signal generator, a photoelectric detector, a digital-to-analog converter and a DSP chip,
the narrow-linewidth laser is connected with the acousto-optic modulator through a single-mode optical fiber, and the acousto-optic modulator is connected to the input end of the first isolator through the same single-mode optical fiber; the output end of the first isolator is connected to the erbium-doped fiber amplifier through a single-mode fiber; the erbium-doped fiber amplifier is connected to the port 1 of the circulator through a single-mode fiber; 2 ports of the circulator are connected to the input end of the second isolator through a single-mode sensing optical fiber; the port 3 of the circulator is connected to the port 1 of the coupler through a single mode fiber; 2, 4 ports of the coupler are respectively connected into the first reflector and the piezoelectric ceramic through single-mode optical fibers; the signal input end of the piezoelectric ceramic is connected with a signal generator through an electric wire, and the optical output end of the piezoelectric ceramic is connected with the second reflector through a single-mode optical fiber; the 3 ports of the coupler are connected with the optical input end of the photoelectric detector through single-mode optical fibers; the electrical output end of the photoelectric detector is connected with a digital-to-analog converter through an electric wire, and the digital-to-analog converter is connected with the DSP chip through an electric wire.
Preferably, the PGC demodulation in the DSP chip adopts an algorithm combining DCM and Arctan algorithms.
Specifically, the interference signals I are respectively identical to the frequency multiplication carrier signal Gcos omega0t and a double frequency carrier signal H cos2 omega0t are multiplied to obtain a1 and b1, the obtained results a1 and b1 are respectively subjected to low-pass filtering to obtain a2 and b2, the results a2 and b2 are respectively subjected to differentiation to obtain a3 and b3, the results a3 and b3 are respectively multiplied by b2 and a2, and the obtained two-path signal results a4 and b4 are subjected to division, absolute value taking, arithmetic square root and arc tangent operation in sequence to obtain a demodulation signal result.
In particular, the output signal of the interferometer
the amplitude is G, H respectively, and the angular frequency is omega0And 2 omega0Is mixed with the output signal I of the interferometer, and the mixing results a1 and b1 are calculated by the following formula:
wherein A is the amplitude of the DC component in the interferometer output signal I, B is the amplitude of the AC component in the interferometer output signal I, C is the carrier modulation depth, t is the time,is a signal to be detected; j is a Bessel function; gcos omega0t represents an angular frequency of ω0Amplitude G signal, H cos2 omega0t represents an angular frequency of 2 ω0Signal of amplitude H; k is 0, 1, 2, 3 … …;
respectively low-pass filtering a1 and b1 to filter out one time of carrier wave and above high-frequency components, and obtaining:
a2 and b2 adopt a differential cross multiplication method, and signals obtained by differentiation are as follows:
the two terms obtained after the cross multiplication of a3 and b3 are respectively:
in the formula, J1(C) As Bessel first order function, J2(C) Is a bessel second order function.
The invention has the advantages of
Completely eliminating the influence of Bessel function in the operation process, and adding J1(C) And J2(C) Through self-operation elimination of two paths of signals, the influence of the carrier modulation depth C in the traditional PGC-DCM or PGC-Arctan algorithm is eliminated, the accuracy of demodulation results is improved, and the interference of error factors is reduced.
Drawings
FIG. 1 is a block diagram of the present invention
FIG. 2 is a block diagram of an improved PGC demodulation algorithm
Detailed Description
The invention is further illustrated by the following examples, without limiting the scope of the invention:
with reference to fig. 1, a phase-sensitive optical time domain reflectometer-based distributed optical fiber acoustic wave sensor based on an improved PGC algorithm includes a narrow-linewidth laser 1, an acoustic-optical modulator 2, a first isolator 3, an erbium-doped fiber amplifier 4, a circulator 5, a sensing fiber 6, a second isolator 7, a coupler 8, a first mirror 9, a second mirror 10, a piezoelectric ceramic 11, a signal generator 12, a photodetector 13, a digital-to-analog converter 14, a DSP chip 15,
the narrow-linewidth laser 1 is connected with the acousto-optic modulator 2 through a single-mode optical fiber, and the acousto-optic modulator 2 is connected to the input end of the first isolator 3 through the same single-mode optical fiber; the output end of the first isolator 3 is connected to an erbium-doped fiber amplifier 4 through a single-mode fiber; the erbium-doped fiber amplifier 4 is connected to port 1 of the circulator 5 through a single-mode fiber; a port 2 of the circulator 5 is connected to the input end of a second isolator 7 through a single-mode sensing optical fiber; the 3 ports of the circulator 5 are connected into the 1 port of the coupler 8 through a single mode fiber; ports 2 and 4 of the coupler 8 are respectively connected into a first reflector 9 and a piezoelectric ceramic 11 through single-mode optical fibers; the signal input end of the piezoelectric ceramic 11 is connected with a signal generator 12 through an electric wire, and the optical output end of the piezoelectric ceramic is connected with the second reflector 10 through a single-mode optical fiber; the 3 ports of the coupler 8 are connected with the optical input end of the photoelectric detector 13 through a single-mode optical fiber; the electrical output of the photodetector 13 is connected to a digital-to-analog converter 14 via an electrical wire, and the digital-to-analog converter 14 is connected to a DSP chip 15 via an electrical wire.
The sensing optical fiber is attached to a pipeline or a building to be measured, laser is emitted by the narrow-linewidth laser and is modulated into pulse light by the acousto-optic modulator. Pulsed light is amplified in optical power through the erbium-doped optical fiber amplifier, then enters the sensing optical fiber through the circulator, and is subjected to vibration or sound wave signals changed by the sensing structure, so that Rayleigh back scattering light is generated and returns to the circulator. The circulator receives the rayleigh backscattered light and transmits the rayleigh backscattered light to the 50:50 coupler, the coupler divides the rayleigh backscattered light (average optical power) containing information into two beams, one beam is reflected by the reflector 1, and the other beam is modulated by the piezoelectric ceramic output modulation signal (acting on the optical fiber) and then reflected by the reflector 2. The modulation signal is output and controlled by the signal generator (the frequency should be much larger than the signal to be measured). The two beams of return light interfere through the coupler, the interference light is transmitted to the photoelectric detector to be converted into an electric signal, the electric signal is converted into a digital electric signal through the digital-to-analog converter, and finally an original vibration or sound wave signal is demodulated and output through an improved PGC demodulation algorithm in the DSP. And setting a corresponding alarm threshold value, and performing difference on a curve without vibration or sound wave signals and a curve with vibration or sound wave signals, so that the positioning and alarm functions can be completed.
In the DSP chip 15, a modified version of PGC demodulation algorithm is used, combining the conventional DCM and Arctan algorithms.
Referring to fig. 2, the interference signal is multiplied by a frequency-doubled carrier signal and a frequency-doubled carrier signal, and the obtained results are low-pass filtered and differentiated respectively, and then multiplied by the signal before differentiation. And dividing the two obtained signal results, sequentially taking absolute values and arithmetic square roots, and finally performing arc tangent operation to obtain a demodulation signal result.
Output signal of interferometer
the amplitude is G, H respectively, and the angular frequency is omega0And 2 omega0Is mixed with the output signal I of the interferometer, and the mixing results a1 and b1 are calculated by the following formula:
wherein A is the amplitude of the DC component in the interferometer output signal I, B is the amplitude of the AC component in the interferometer output signal I, C is the carrier modulation depth, t is the time,is a signal to be detected; j is a Bessel function; g cos omega0t represents an angular frequency of ω0Amplitude G signal, H cos2 omega0t represents an angular frequency of 2 ω0Signal of amplitude H; k is 0, 1, 2, 3 … …;
respectively low-pass filtering a1 and b1 to filter out one time of carrier wave and above high-frequency components, and obtaining:
a2 and b2 adopt a differential cross multiplication method, and signals obtained by differentiation are as follows:
the two terms obtained after the cross multiplication of a3 and b3 are respectively:
in the formula, J1(C) As Bessel first order function, J2(C) Is a bessel second order function.
Completely eliminating the influence of Bessel function in the operation process, and adding J1(C) And J2(C) Through self-operation elimination of two paths of signals, the influence of the carrier modulation depth C in the traditional PGC-DCM or PGC-Arctan algorithm is eliminated, the accuracy of demodulation results is improved, and the interference of error factors is reduced.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
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