CN107167168A - Phase sensitive optical time domain reflection distributed optical fiber sensing system accurate positioning method - Google Patents

Abstract

The invention relates to a precise positioning method for a phase-sensitive optical time-domain reflection distributed optical fiber sensing system, comprising the following steps: constructing a Rayleigh scattered light digital signal matrix corresponding to a plurality of optical pulses, selecting the signal matrix to be measured, and determining the spatial resolution of the system Perform "phase comparison at both ends of the signal matrix to be tested - comparison between the length of the signal matrix to be tested and the spatial resolution of the system - midpoint segmentation of the signal matrix to be tested" until certain conditions are met and the method is exited. The present invention combines the advantages of phase positioning and the idea of "dichotomy", realizes the precise positioning of the disturbance source in the distributed optical fiber sensor through interval halving and iterative approximation, with very few calculations and judgments, and ensures the high resolution and stability of the system space At the same time, the system response speed is improved, and the method is suitable for various Ф-OTDR optical fiber sensing systems of coherent detection and demodulation.

Description

Precise Positioning Method for Phase Sensitive Optical Time Domain Reflectometry Distributed Optical Fiber Sensing System

technical field

The invention relates to a precise positioning method for a phase-sensitive optical time domain reflection distributed optical fiber sensing system, which belongs to the application field of optical fiber sensing technology.

Background technique

Phase-sensitive Optical Time Domain Reflectometry (Phase-sensitive Optical Time Domain Reflectometry, abbreviated as Ф-OTDR or Phase-sensitive OTDR) is a fully distributed optical fiber sensing system with anti-electromagnetic interference, anti-corrosion, small size and high safety It has the advantages of high reliability, high spatial resolution, simple equipment laying, no blind spots, and low maintenance costs. The introduction of optical coherent demodulation detection makes Ф-OTDR have higher sensitivity and phase demodulation ability. In recent years, coherent Ф-OTDR has attracted widespread attention and has been put into practical use. At present, Ф-OTDR has demonstrated its great value in many application fields. For example, in the field of security, Ф-OTDR can be used as a monitoring facility for large-scale important borders and facilities (such as national borders, oil wells, and oil and gas pipelines), realizing monitoring Real-time unmanned monitoring of various intrusion, destruction and theft events; in the transportation system, Ф-OTDR can be used to monitor the position and speed of trains, and to monitor the traffic flow at intersections, etc.; in the power system, Ф-OTDR can be used for cables and connections Partial discharge detection of the head and cable perimeter safety monitoring; in geological monitoring, Ф-OTDR can realize real-time monitoring and early warning of geological disasters such as landslides and earthquakes; in structural safety monitoring, Ф-OTDR can realize monitoring of bridges and other large Real-time distributed measurement of structural health of critical buildings.

As an active detection technology, Ф-OTDR uses the Rayleigh scattered light of the optical fiber for distributed sensing, and the external environment change information can be obtained and recovered by the amplitude and phase of the back Rayleigh scattered light. In the disturbance source location of the coherent Ф-OTDR system, the amplitude difference scheme is widely used at present (Tu G, Zhang X, Zhang Y, et al. The Development of an-OTDR System for Quantitative Vibration Measurement[J]. IEEEPhotonics Technology Letters , 2015, 27(12): 1349-1352.; Distributed optical fiber sensor and information demodulation method, Chinese invention patent, inventors: Liang Kezhen, Pan Zhengqing, Cai Haiwen, Ye Qing, Zhou Jun, authorized announcement number: CN10262869B), and In fact, phase positioning can be used to obtain a higher signal-to-noise ratio (Pang F, He M, LiuH, et al. A Fading-Discrimination Method for Distributed Vibration Sensor Using Coherent Detection of ϕ-OTDR[J]. IEEE Photonics Technology Letters , 2016, 28(23).). However, Ф-OTDR is a distributed sensor, and each point of its sensing fiber can be used as an independent sensor. The longer the sensing fiber, the more sensing data will be generated, which will increase the amount of calculation for demodulation and affect the system response. speed. Disturbances are generally sparsely scattered in the sensing range, and most sensors are actually in an idle working state. Therefore, the system does not need to perform the same demodulation on each sensor. Properly ignoring these idle sensors can greatly speed up the system positioning speed.

Contents of the invention

In order to solve the above problems, the present invention proposes a precise positioning method for a phase-sensitive optical time-domain reflection distributed optical fiber sensing system. Combining the positioning advantages brought by phase demodulation and the idea of "dichotomy", it can ensure system stability and space At the same time as the resolution, it reduces the amount of system calculation, improves the system response speed, and solves the problem of slow system response due to the large amount of sensing data in the Ф-OTDR system. OTDR system.

To achieve the above object, the present invention adopts the following technical solutions:

A precise positioning method for a phase-sensitive optical time-domain reflection distributed optical fiber sensing system, the applied phase-sensitive optical time-domain reflection distributed optical fiber sensing system includes a narrow linewidth laser, a 1×2 optical fiber coupler, and an acousto-optic modulator , erbium-doped fiber amplifier, fiber circulator, sensing fiber, arbitrary waveform generator, 2×2 fiber coupler, balanced light detector, data acquisition card, computer; the narrow linewidth laser is coupled through 1×2 fiber The optical signal of the sensor probe is divided into two channels, one is the optical signal of the sensing probe modulated into optical pulses by the acousto-optic modulator, and the optical power is amplified by the erbium-doped optical fiber amplifier, which is input to the first port of the optical fiber circulator and output to the transmission port by the second port. Sensing optical fiber, the generated Rayleigh backscattered light is input from No. 2 port and output from No. 3 port; the other output of the 1×2 fiber coupler is the sensing of the local reference optical signal and the output of No. 3 port of the optical fiber circulator The signal enters the 2×2 fiber coupler for multiplexing, and the two output ports of the 2×2 fiber coupler are connected to the balanced photodetector. The balanced photodetector performs photoelectric conversion, and the data acquisition card performs analog-to-digital conversion and transmits it to the computer for signal processing. deal with.

Subsequent signal processing consists of the following steps:

Step 1: Construct the data matrix of the signal: take the digital signal corresponding to a single light pulse as a row vector, and the digital signals corresponding to multiple continuous light pulses as the first row, the second row, ... , the Mth line, where M represents the number of light pulses, and constructs a digital signal matrix D = [D _{i, j} ] _M × _K , where D _{i, j} represents the i -th light pulse collected by the data acquisition card corresponding to The digital signal value of Rayleigh scattered light on the jth data point of the sensing fiber, K represents the total length of the digital signal corresponding to a single light pulse; the digital signal matrix D is divided into multiple k columns, where k ≤ K , and the length is l The signal matrix S = [S _{i, j} ] _M × _k is used as the data matrix to be tested.

Step 2: Determine the spatial resolution of the system: define the spatial resolution of the system with light pulses L = c×T/(2×n), where c represents the speed of light in vacuum, T represents the duration of the light pulse, and n represents the refractive index of the optical fiber .

Step 3: Use the phase demodulation algorithm to extract the column phases φ _Left and φ _Right at both ends of the data matrix S to be measured, and their positions are denoted by j _Left and j _Right respectively. If φ _Left and φ _Right are the same, it is determined that there is no disturbance in the interval ( j _Left , j _Right ), and other untested data matrices to be tested are searched, and step 3 is repeated until all the intervals to be tested are detected; if If φ _Left and φ _Right are different, it is determined that there is a disturbance in the interval ( j _Left , j _Right ), and proceed to step 4.

Step 4: Check whether the length l of the data matrix S to be tested is smaller than the system spatial resolution L , if so, use any position in S to indicate the location of the disturbance source, repeat step 3, otherwise go to step 5.

Step 5: Extract the phase φ _Middle of a certain column near the middle position of the data matrix S to be tested, and its position is represented by j _Middle , then divide the data matrix S to be tested into two intervals ( j _Left , j _Middle ) and ( j _Middle , j _Right ), take these two intervals as the new data matrix S to be tested, and repeat step 3.

Principle of the present invention is as follows:

When a certain point on the sensing fiber is disturbed, it can be seen from the elasto-optic effect of light that an additional phase shift ∆ ϕ will be introduced when the light pulse passes through the disturbed point, and the additional phase shift is modulated by the external disturbance. The optical pulse will continue to propagate in the fiber with this additional phase shift ∆ϕ , and the Rayleigh scattered light with the same phase as that of the optical pulse will be generated during the propagation process . , and the additional phase shift is only caused by the disturbance, and the signal fading noise and no disturbance will not introduce the additional phase shift. Based on this principle, it is only possible to determine whether a disturbance has occurred in the section according to the similarity of the phases of the two ends of a certain interval and the energy changes of the two phases, that is, if there is no disturbance in the interval, the phases of the two ends of the interval are the same, and the energy does not change; if there is a disturbance in the interval, the phases of the two ends of the interval are different, and the energy changes. Based on this characteristic, and because the disturbance exists sparsely in the sensing range of Ф-OTDR, the system searches for the position of the disturbance source in a certain interval, which can be compared to solving the root of the equation, and uses the idea of dichotomy to perform interval halving and iteration Accurate positioning of the disturbance source can be achieved by approximation. In the process of realizing dichotomous positioning, since a large number of idle sensing points on the sensing fiber are ignored, only a small number of sensing data of key positions are demodulated and judged, so the positioning speed of the system can be greatly accelerated.

Compared with prior art, the beneficial effect of the present invention is:

The present invention combines the advantages of phase positioning and the idea of iterative search by dichotomy, realizes the required spatial resolution of the Ф-OTDR optical fiber sensing system with very few calculations, and improves the system response speed. At the same time, the invention locates the disturbance source by analyzing the Rayleigh scattered light phase, thereby ensuring the stability of the system.

The present invention is based on a conventional coherent Ф-OTDR optical fiber sensing system, but this solution can be applied to various Ф-OTDR optical fiber sensing systems for coherent detection and demodulation, and has certain versatility and adaptability.

Description of drawings

Fig. 1 is a schematic structural diagram of a phase-sensitive optical time-domain reflection optical fiber sensing system in the present invention.

Figure 2 is a flow chart of the method of the present invention.

detailed description

In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will describe in detail with reference to the accompanying drawings and specific implementation examples. Since this solution can be expanded or deformed in many ways, and the devices involved can be replaced with devices of different models with similar functions, this should not limit the scope of protection of this patent.

Referring to Fig. 1, the phase-sensitive optical time-domain reflection distributed optical fiber sensing system applied by this method includes a narrow linewidth laser 1, a 1×2 fiber coupler 2, an acousto-optic modulator 3, an erbium-doped optical fiber amplifier 4, and an optical fiber ring Device 5, sensing fiber 6, arbitrary waveform generator 7, 2×2 fiber coupler 8, balanced light detector 9, data acquisition card 10, computer 11, piezoelectric ceramic tube 12.

The components of each part of the system are described as follows:

A narrow linewidth laser 1 is used to generate laser light with high coherence.

1×2 fiber optic coupler 2, used to split the laser into two paths, one path is used as the sensing probe light, and the other path is used as the local reference light, the instantaneous optical power of the sensing probe light is much greater than the local reference light, and the coupling splitting ratio can be selected is 90:10;

The acousto-optic modulator 3 is used to modulate the laser light into pulsed light, and at the same time, allow the laser pulse to obtain a frequency shift of a fixed frequency. In this example, the frequency shift of the light by using the acousto-optic modulator is 200MHz;

The erbium-doped fiber amplifier 4 is used to amplify the laser pulse power and increase the Rayleigh scattered light intensity excited in the sensing fiber 6 to increase the sensing range of the system. In this example, the maximum gain of the erbium-doped fiber amplifier used is 20dBm;

The optical fiber circulator 5 is a three-port optical fiber circulator, and its optical characteristic is that the light input from the No. 1 port can only be output from the No. 2 port, and the light input from the No. 2 port can only be output from the No. 3 port. In this scheme, the sensing probe light is input from the first port of the fiber optic circulator and output from the second port, and the Rayleigh backscattered light received from the second port is output from the third port.

The sensing fiber 6 is a single-mode fiber for standard communication.

The arbitrary waveform generator 7 generates a pulse sequence with adjustable frequency, and controls the acousto-optic modulator 3 to realize optical pulse output, and the pulse signal is also used as a collection trigger source of the data acquisition card 10 . In this example, the arbitrary waveform generator model outputs a pulse sequence with a repetition frequency of 2kHz and an optical pulse width, that is, the duration of the optical pulse is 50ns.

2×2 fiber coupler 8, used for multiplexing the backscattered light of the sensing fiber and the local reference light, and the coupling splitting ratio is 50:50.

The balanced photodetector 9 is used for photoelectric conversion to detect optical coherent signals, and its output is an electrical signal with a frequency shifted by the acousto-optic modulator 3 .

The data acquisition card 10 is used to realize signal analog-to-digital conversion, collect the electrical signal output by the balanced photodetector 9 and convert it into a digital signal and transmit it to the computer 11 .

The computer 11 is used for processing the digital signal collected by the data acquisition card 10 .

Piezoelectric ceramic tube 12 is used to introduce disturbance. In order to simulate external disturbance events, a piezoelectric ceramic tube 12 is set on the sensing fiber 6 as a disturbance source, and the optical fiber is wound on it, and a signal generator is used to apply a changing voltage on the piezoelectric ceramic tube 12, and the piezoelectric ceramic Tube expansion and contraction create disturbances that are transmitted directly to the sensing fiber 6 . In this example, the sensing fiber 6 has a total length of about 40 km, the piezoelectric ceramic tube 12 is about 20 km away from the optical fiber circulator 5, the vibration frequency of the piezoelectric ceramic is 100 Hz, and the fiber winding length is about 2 m. In the actual application of the system, the external vibration event simulated by the piezoelectric ceramic 12 can occur anywhere in the entire sensing fiber.

The narrow-linewidth laser 1 is divided into two paths through a 1×2 fiber coupler 2, and one path is the optical signal of the sensing probe modulated into an optical pulse by the acousto-optic modulator 3, and the optical power is amplified by the erbium-doped fiber amplifier 4, and input into the optical fiber The first port of the circulator 5 is output to the sensing fiber 6 through the second port, and the generated Rayleigh backscattered light is input through the second port and output through the third port; the other output of the 1×2 fiber coupler 2 The local reference optical signal and the sensor signal output from the third port of the optical fiber circulator 5 enter the 2×2 fiber coupler 8 for multiplexing, and the two output ports of the 2×2 fiber coupler 8 are connected to the balanced optical detector 9, The balanced light detector 9 performs photoelectric conversion, and the data acquisition card 10 performs analog-to-digital conversion and sends it to the computer 11 for signal processing.

Referring to Fig. 2, the precise positioning method of the phase-sensitive optical time-domain reflection distributed optical fiber sensing system according to the present invention, its subsequent signal processing includes the following steps:

Step 1: Take the digital signal corresponding to a single light pulse as a row vector, and the digital signals corresponding to multiple continuous light pulses are sequentially taken as the first row, the second row, ..., the Mth row according to the time sequence of the light pulse emission, where M is the number of light pulses, constructing a digital signal matrix D=[D _{i, j} ] _M × _K , wherein, D _{i, j} represents that the i -th light pulse collected by the data acquisition card 9 corresponds to the j -th sensor fiber The digital signal value of Rayleigh scattered light at each data point; in this example, Rayleigh scattered light signals corresponding to 50 continuous light pulses are collected, and the size of the digital signal matrix is 50×599432. The matrix is divided into 50 interval matrices to be measured whose length l is about 1km, taking the interval (20.0446km, 21.0479km) as an example, extracting the Rayleigh scattering digital signal of this interval from the digital signal matrix D, as the The data matrix S to be tested has a matrix size of 50×14650.

Step 2: Determine the spatial resolution of the system: the spatial resolution of the system defined by light pulses L = c×T/(2×n)≈5 m, where c = 3×10 ⁸ m/s, T = 50 ns, n = 1.47.

Step 3: Use the phase demodulation algorithm to extract the column phases φ _Left and φ _Right at both ends of the data matrix S to be measured, and their positions are j _Left and j _Right respectively. If φ _Left and φ _Right are the same, it is determined that there is no disturbance in the interval ( j _Left , j _Right ), and other untested data matrices to be tested are searched, and step 3 is repeated until all the intervals to be tested are detected; if If φ _Left and φ _Right are different, it is determined that there is a disturbance in the interval ( j _Left , j _Right ), and proceed to step 4.

Step 4: Check whether the length l of the data matrix S to be tested is smaller than the spatial resolution L of the system, if so, use any position j in S to indicate the location of the disturbance source, repeat step 3, otherwise go to step 5.

Step 5: Extract a certain column phase φ _Middle near the middle position of the data matrix S to be tested, and its position is j _Middle , then divide the data matrix S to be tested into two intervals ( j _Left , j _Middle ) and ( j _Middle , j _Right ), take these two intervals as the new data matrix S to be tested, and repeat step 3.

Through the iterative calculation of steps 3-5, the location of the disturbance source is obtained at the S coordinate location (7896, 7965), that is, the spatial location (20.5853km, 20.5901km), and the spatial resolution is about 5m. In this example, the midpoint of the interval is used as the location of the disturbance source, that is, the location of the disturbance source is 20.5877 km, and the error is about ±2.5m.

Claims (1)

1. a kind of phase sensitive optical time domain reflection distributed optical fiber sensing system accurate positioning method, its phase sensitive light applied Time Domain Reflectometry distributed optical fiber sensing system includes narrow linewidth laser（1）, 1 × 2 fiber coupler（2）, acousto-optic modulator （3）, erbium-doped fiber amplifier（4）, optical fiber circulator（5）, sensor fibre（6）, AWG（7）, 2 × 2 optical fiber couplings Clutch（8）, balance photo-detector（9）, data collecting card（10）, computer（11）；Described narrow linewidth laser（1）By 1 × 2 fiber couplers（2）It is divided into two-way, passes through acousto-optic modulator all the way for pickup probe optical signal（3）Light pulse is modulated to, and By erbium-doped fiber amplifier（4）Carry out luminous power amplification, input optical fibre circulator（5）A port and defeated by No. two ports Go out to sensor fibre（6）, the rayleigh backscattering light of generation inputs by No. two ports and exported by No. three ports；1 × 2 optical fiber coupling Clutch（2）Another road of output is local reference optical signal and optical fiber circulator（5）No. three ports output transducing signal enter Enter 2 × 2 fiber couplers（8）Middle multiplex, 2 × 2 fiber couplers（8）Two output ports and balance photo-detector（9）Connection, Balance photo-detector（9）Carry out opto-electronic conversion and by data collecting card（10）Carry out analog-to-digital conversion and be transferred to computer（11）Carry out Signal transacting；Characterized in that, follow-up signal processing comprises the following steps：

Step 1：Build the data matrix of signal：Using the corresponding data signal of single light pulse as row vector, multiple continuous light The corresponding data signal of pulse by the time sequencing of light pulse emission successively as the 1st row, the 2nd row ... ..., theMOK, whereinM Light pulse number is represented, data signal matrix D=[D is built _{I, j} ] _M × _K , wherein, D _{I, j} Represent the data collecting card（9）Collect iIndividual light pulse correspondence sensor fibre thejRayleigh scattering light digital signal value in individual data point,KRepresent single light pulse Corresponding data signal is always counted；Multistage will be divided into data signal matrix DkRow, whereink ≤ K, length islSignal square Battle array S=[S _{I, j} ] _M × _k It is used as testing data matrix；

Step 2：Determine System spatial resolution：System spatial resolution is defined with light pulseL=c × T/ (2 × n), wherein, c The light velocity in vacuum is represented,TLight pulses duration is represented, n represents optical fibre refractivity；

Step 3：Described testing data matrix S two ends row phase is extracted using phase demodulation algorithmφ _LeftWithφ _Right, its position Put and use respectivelyj _LeftWithj _RightRepresent；Ifφ _LeftWithφ _RightIt is identical, then interval where judging it (j _Left, j _Right) interior unperturbed It is dynamic, other testing data matrixes not after testing are found, repeat step 3, until all interval detections to be measured are completed；Ifφ _LeftWithφ _RightDifference, then interval where judging it (j _Left, j _Right) interior in the presence of disturbance, carry out step 4；

Step 4：Check described testing data matrix S lengthlWhether described System spatial resolution is less thanL, if so, then sharp Source position is disturbed with the positional representation of any one in S, otherwise repeat step 3 carries out step 5；

Step 5：Extract described testing data matrix S centre positions certain row phase nearbyφ _Middle, its position is usedj _MiddleTable Show, then by testing data matrix S be divided into two sections of intervals (j _Left, j _Middle) and (j _Middle, j _Right), respectively with the two areas Between be used as new testing data matrix S, repeat step 3.