CN109443590B - Phase-sensitive OTDR (optical time Domain reflectometer) measurement method based on frequency-space domain matching and injection locking technology - Google Patents
Phase-sensitive OTDR (optical time Domain reflectometer) measurement method based on frequency-space domain matching and injection locking technology Download PDFInfo
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Abstract
The invention provides a phase-sensitive OTDR and a measuring method based on frequency-space domain matching and injection locking technology. The phase-sensitive OTDR comprises a pulse light sequence generating device and an echo signal detecting device; the pulse light sequence generating device comprises a master laser, a slave laser, an electro-optic modulator, an acousto-optic modulator, an arbitrary waveform generator, an arbitrary function generator and a first circulator; the echo signal detection device comprises a first erbium-doped fiber amplifier, a second circulator, a second erbium-doped fiber amplifier and a photoelectric detector. The technology adopts an arbitrary wave modulation type injection locking technology to realize the rapid tuning of the laser frequency, fundamentally avoids the nonlinear problem in the frequency scanning process, and has high-precision sensing capability. The invention adopts frequency domain-space domain matching technology for data demodulation, and by matching the frequency domain information of multiple space domain points, the requirement of data demodulation on the number of frequency domain points is obviously reduced, the requirement on hardware bandwidth is greatly reduced, and the measurement range is expanded.
Description
Technical Field
The embodiment of the invention relates to the technical field of sensing, in particular to a phase-sensitive OTDR measuring method based on frequency-space domain matching and injection locking technology.
Background
Compared with other distributed sensing technologies, the phase-sensitive optical time domain reflectometer (phi-OTDR) technology based on the Rayleigh scattering effect has the advantages of simple structure and high sensitivity. According to the technology, laser pulses with narrow line widths are injected into an optical fiber, so that interference superposition signals of backward Rayleigh scattering light within a half pulse width are obtained, and the interference superposition signals are extremely sensitive to external temperature or strain changes. The intensity change of the echo signal shows that the response sensitivity of temperature or strain can reach the mK and n epsilon orders respectively.
A difficulty with the Φ -OTDR technique is the quantitative measurement of temperature or strain. Frequency domain correlation is one type of technique that can achieve quantitative measurements. The method correlates echo signals of multiple frequencies in the frequency domain to calculate temperature or strain changes. This method has no fading noise problem. The frequency domain correlation method at present needs a large number of sweep frequency points and has a large bandwidth demand, so that the measurement range is small, and the practical application value of the technology is obviously restricted from the aspects of economy and practicability. In addition, the existing frequency domain related scheme adopts a microwave tuning method or an internal modulation method, wherein the frequency sweeping speed of the microwave tuning method is low, the measurement speed is low, dynamic measurement cannot be carried out, and the frequency modulation linearity of the microwave tuning method is low and the measurement precision is low.
Disclosure of Invention
In this context, embodiments of the present invention are expected to provide a phase-sensitive OTDR and a measurement method based on frequency-space domain matching and injection locking technology, so as to solve the problems of a small measurement range and a large bandwidth requirement in the existing frequency domain correlation Φ -OTDR technique, thereby implementing dynamic measurement of temperature or strain with a large range and high sensitivity.
In a first aspect of the embodiments of the present invention, a phase-sensitive OTDR based on frequency-space domain matching and injection locking technology is provided, including a pulsed light sequence generating device and an echo signal detecting device; the pulse light sequence generating device comprises a master laser, a slave laser, an electro-optic modulator, an acousto-optic modulator, an arbitrary waveform generator, an arbitrary function generator and a first circulator; the echo signal detection device comprises a first erbium-doped fiber amplifier, a second circulator, a second erbium-doped fiber amplifier and a photoelectric detector; the output laser of the master laser is modulated by the electro-optical modulator, and the modulated laser is injected into the slave laser through the first circulator, wherein the frequency of a modulation signal of the electro-optical modulator is changed in a step mode, and the modulation signal is generated by the arbitrary waveform generator; the output light of the slave laser is output to the acousto-optic modulator through the first circulator, and the pulse light sequence modulated by the acousto-optic modulator is amplified by the first erbium-doped fiber amplifier and then injected into the optical fiber to be detected through the second circulator; the arbitrary function generator is used for generating a preset square wave signal and outputting the signal to the acousto-optic modulator; and backward Rayleigh scattering echo signals in the optical fiber to be detected are output to the second erbium-doped optical fiber amplifier through the second circulator, and are detected by the photoelectric detector after being amplified by the second erbium-doped optical fiber amplifier.
The filter is arranged between the second erbium-doped fiber amplifier and the photoelectric detector and used for filtering spontaneous radiation noise of the second erbium-doped fiber amplifier.
In a second aspect of the embodiments of the present invention, there is provided a method for measuring a phase-sensitive OTDR based on frequency-space domain matching and injection locking technology, the method being implemented based on the phase-sensitive OTDR based on frequency-space domain matching and injection locking technology as described above; the measuring method comprises the following steps: inputting a first pulsed light sequence generated by the pulsed light sequence generation device into the echo signal detection device at a first transmitting time, and receiving a first backward Rayleigh scattering echo signal corresponding to the first pulsed light sequence through the photoelectric detector at a first receiving time, wherein the first pulsed light sequence comprises n detection light pulses with preset frequencies; n is a positive integer; inputting a second pulsed light sequence generated by the pulsed light sequence generation device into the echo signal detection device at a second transmitting time, and receiving a second backward Rayleigh scattering echo signal corresponding to the second pulsed light sequence through the photoelectric detector at a second receiving time, wherein the second pulsed light sequence comprises the n detection light pulses with the predetermined frequency; wherein the second transmission time is subsequent to the first transmission time; the first backward rayleigh scattering echo signal comprises a backward rayleigh scattering echo signal of each probe light pulse in the first pulse light sequence at each position of the optical fiber to be measured, and the second backward rayleigh scattering echo signal comprises a backward rayleigh scattering echo signal of each probe light pulse in the second pulse light sequence at each position of the optical fiber to be measured; obtaining a first frequency domain-space domain characteristic diagram of the first backward Rayleigh scattering echo signal and a second frequency domain-space domain characteristic diagram of the second backward Rayleigh scattering echo signal; the first frequency domain-space domain characteristic diagram and the second frequency domain-space domain characteristic diagram take the position on the optical fiber to be detected as a first dimensional coordinate, the frequency of the detected light pulse as a second dimensional coordinate, and the signal intensity or the signal amplitude value received by the photoelectric detector as a third dimensional coordinate; selecting a reference data area with a preset size from the first frequency domain-space domain characteristic diagram, determining a matching data area corresponding to the reference data area from the second frequency domain-space domain characteristic diagram, and calculating the displacement of the reference data area and the matching data area on a second dimensional coordinate so as to determine the frequency delay between the first frequency domain-space domain characteristic diagram and the second frequency domain-space domain characteristic diagram according to the displacement; and calculating the temperature variation or the strain variation of the optical fiber to be detected according to the frequency delay.
Further, the reference data region comprises data points in a predetermined size neighborhood of a first position point preset in the first frequency domain-spatial domain feature map; the step of determining the matching data region corresponding to the reference data region in the second frequency domain-spatial domain feature map comprises the following steps: in the second frequency domain-spatial domain characteristic diagram, a data area formed by data points in a preset size neighborhood of a second position point which is the same as the first-dimension coordinate of the preset first position point is used as a data area to be matched; moving the data area to be matched along a second dimensional coordinate axis of the second frequency domain-spatial domain characteristic diagram, obtaining a difference matrix between the data area to be matched and the reference data area, which is obtained by moving each time in the moving process, and calculating the square sum of all elements of the difference matrix obtained each time; and determining a difference matrix corresponding to the minimum sum of squares of all elements of the difference matrix in the moving process, and taking a data area to be matched corresponding to the difference matrix as the matched data area.
Further, the step of calculating the temperature variation or the strain variation of the optical fiber to be measured includes: calculating the strain variation of the optical fiber to be measured according to the following formula:
where Δ v denotes the frequency delay, v denotes the fundamental frequency of the light wave, pεRepresenting the elasto-optic coefficient, Δ ε representing the amount of change in strain, KεRepresenting the strain coefficient.
Further, the temperature variation of the optical fiber to be measured is calculated according to the following formula:
where Δ v denotes a frequency delay, v denotes a fundamental frequency of light waves, ξ denotes a thermo-optic coefficient, α denotes a thermal expansion coefficient, Δ T denotes a temperature change amount, and KT denotes a temperature coefficient.
The phase-sensitive OTDR and the measurement method based on the frequency-space domain matching and injection locking technology have the following beneficial effects:
the invention adopts the arbitrary wave modulation type injection locking technology to realize the rapid tuning of the laser frequency. The technology fundamentally avoids the problem of nonlinearity in the frequency scanning process, and has high-precision sensing capability.
In addition, the technology utilizes an arbitrary wave modulation technology, so that the frequency tuning speed is greatly improved, and the technology has the capability of measuring a rapidly changing signal.
The invention adopts the frequency domain-space domain matching technology for the demodulation of the data, and changes the strategy that the prior art only carries out correlation on the frequency domain information of one point. By matching the frequency domain information of the multi-space domain points, the requirement of data demodulation on the number of the frequency domain points can be obviously reduced, the requirement on hardware bandwidth is greatly reduced (the bandwidth in the prior art is about 4GHz, and can be reduced to 500MHz and 1/8 of the original bandwidth by using the method and the device), and the measurement range of the system is expanded.
Drawings
The above and other objects, features and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which:
fig. 1 is a schematic diagram showing an optical path structure of a phase-sensitive OTDR based on frequency-space domain matching and injection locking technique according to an embodiment of the present invention;
FIG. 2 is a flow diagram illustrating an exemplary process of a phase sensitive OTDR measurement method based on frequency-space domain matching and injection locking techniques in accordance with an embodiment of the present invention;
FIG. 3 is a flowchart illustrating one possible process of step S250 in FIG. 2;
FIG. 4 is a diagram illustrating a frequency domain-spatial matching method;
FIG. 5A is a schematic diagram showing the variation of signal strength received at different locations of an optical fiber;
FIG. 5B is a graph showing the change in signal strength when the signal-to-noise ratio is low;
fig. 5C is a diagram showing comparison of demodulation results of the one-dimensional correlation operation method and the two-dimensional image matching method under different window lengths.
In the drawings, the same or corresponding reference numerals indicate the same or corresponding parts.
Detailed Description
The principles and spirit of the present invention will be described with reference to a number of exemplary embodiments. It is understood that these embodiments are given solely for the purpose of enabling those skilled in the art to better understand and to practice the invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
According to the embodiment of the invention, the invention provides a phase-sensitive OTDR and a measurement method based on frequency-space domain matching and injection locking technology.
In this document, it is to be understood that any number of elements in the figures are provided by way of illustration and not limitation, and any nomenclature is used for differentiation only and not in any limiting sense.
The principles and spirit of the present invention are explained in detail below with reference to several representative embodiments of the invention.
Exemplary devices
The embodiment of the invention provides a phase-sensitive (namely phase-sensitive) Optical Time Domain Reflectometer (OTDR) based on frequency-space Domain matching and injection locking technology, which comprises a pulse light sequence generating device and an echo signal detecting device; the pulse light sequence generating device comprises a master laser, a slave laser, an electro-optic modulator, an acousto-optic modulator, an arbitrary waveform generator, an arbitrary function generator and a first circulator; the echo signal detection device comprises a first erbium-doped fiber amplifier, a second circulator, a second erbium-doped fiber amplifier and a photoelectric detector; the output laser of the master laser is modulated by the electro-optical modulator, and the modulated laser is injected into the slave laser through the first circulator, wherein the frequency of a modulation signal of the electro-optical modulator is changed in a step mode, and the modulation signal is generated by the arbitrary waveform generator; the output light of the slave laser is output to the acousto-optic modulator through the first circulator, and the pulse light sequence modulated by the acousto-optic modulator is amplified by the first erbium-doped fiber amplifier and then injected into the optical fiber to be detected through the second circulator; the arbitrary function generator is used for generating a preset square wave signal and outputting the signal to the acousto-optic modulator; and backward Rayleigh scattering echo signals in the optical fiber to be detected are output to the second erbium-doped optical fiber amplifier through the second circulator, and are detected by the photoelectric detector after being amplified by the second erbium-doped optical fiber amplifier.
Fig. 1 shows a phase-sensitive OTDR based on frequency-space domain matching and injection locking technique of the present invention, which includes a pulse light sequence generating device and an echo signal detecting device.
As shown in fig. 1, the pulse light sequence generating apparatus includes a master LASER 1-1 (LASER 1 shown in fig. 1), a slave LASER 1-2 (LASER 2 shown in fig. 1), an electro-optical modulator (EOM)1-3, an acousto-optical modulator (AOM)1-4, an Arbitrary Waveform Generator (AWG)1-5, an Arbitrary Function Generator (AFG)1-6, and a first circulator (AOM) 1-7.
The echo signal detection device comprises a first erbium-doped fiber amplifier (EDFA 1 shown in figure 1)1-8, a second circulator 1-9, a second erbium-doped fiber amplifier (EDFA 2 shown in figure 1) 1-10 and a Photoelectric Detector (PD) 1-11.
The output laser light of the main laser 1-1 is modulated by an electro-optical modulator 1-3, and the modulated laser light is injected as injection light into the slave laser 1-2 via a first circulator 1-7, wherein the frequency of the modulation signal of the electro-optical modulator 1-3 is changed in steps (the step change represents the same interval of frequency change, such as v0, v0+5MHz, v0+10MHz, v0+15MHz, and the like), and the modulation signal is generated by an arbitrary waveform generator 1-5. The modulation signal of any waveform generator 1-5 may be set empirically, for example, or may be set by an experimental method, which is not described herein again.
Output light from the laser 1-2 is output to the acousto-optic modulator 1-4 through the first circulator 1-7, and a pulse light sequence modulated by the acousto-optic modulator 1-4 is amplified by the first erbium-doped fiber amplifier 1-8 and then injected into an optical fiber to be tested through the second circulator 1-9.
The output light wavelength of the main laser 1-1 is, for example, 1550.09 nm. Each light pulse in the pulsed light sequence has a width of, for example, 20ns and a peak power of, for example, 1W.
The slave laser 1-2 is, for example, a semiconductor laser.
The electro-optical modulator 1-3 is used for loading the microwave signal output by the arbitrary waveform generator onto the light wave to perform frequency modulation.
The acousto-optic modulator 1-4 is for modulating the continuous light output from the laser 1-2 into pulsed light.
As shown in fig. 1, the laser light modulated by the electro-optical modulator 1-3 enters the first circulator 1-7 from the first port a1 of the first circulator 1-7, is output from the second port a2 of the first circulator 1-7 and is input to the second circulator 1-2 as injection light, and the laser light output from the laser 1-2 enters the first circulator 1-7 from the second port a2 of the first circulator 1-7, wherein it is then output from the third port a3 of the first circulator 1-7 to the acousto-optical modulator 1-4.
The arbitrary function generator 1-6 is used for generating a preset square wave signal and outputting the signal to the acousto-optic modulator 1-4. The predetermined square wave signal may be set empirically, for example, or may be set experimentally, which is not described herein.
Where the output light frequency from laser 1-2 varies with the frequency of the injected light. In other words, when the frequency of injected light is f0At an output light frequency f0(ii) a When the frequency of injected light becomes f1At the same time, the output light frequency also becomes f1(ii) a When the frequency of injected light is f2When the frequency of the corresponding output light is also changed to f2(ii) a Etc., and the output power from laser 1-2 remains constant.
Backward Rayleigh scattering echo signals in the optical fiber to be detected are output to a second erbium-doped optical fiber amplifier 1-10 through a second circulator 1-9, and the backward Rayleigh scattering echo signals are amplified by the second erbium-doped optical fiber amplifier 1-10 and then detected by a photoelectric detector 1-11.
As an example, the above-mentioned phase-sensitive OTDR based on frequency-spatial domain matching and injection locking technique may further include a filter, for example, disposed between the second erbium-doped fiber amplifier 1-10 and the photodetector 1-11, for filtering out spontaneous emission noise of the second erbium-doped fiber amplifier 1-10.
Exemplary method
The embodiment of the invention also provides a phase-sensitive OTDR measuring method based on the frequency-space domain matching and injection locking technology, which is realized based on the phase-sensitive OTDR based on the frequency-space domain matching and injection locking technology; the measuring method comprises the following steps: inputting a first pulsed light sequence generated by the pulsed light sequence generation device into the echo signal detection device at a first transmitting time, and receiving a first backward Rayleigh scattering echo signal corresponding to the first pulsed light sequence through the photoelectric detector at a first receiving time, wherein the first pulsed light sequence comprises n detection light pulses with preset frequencies; n is a positive integer; inputting a second pulsed light sequence generated by the pulsed light sequence generation device into the echo signal detection device at a second transmitting time, and receiving a second backward Rayleigh scattering echo signal corresponding to the second pulsed light sequence through the photoelectric detector at a second receiving time, wherein the second pulsed light sequence comprises the n detection light pulses with the predetermined frequency; wherein the second transmission time is subsequent to the first transmission time; the first backward rayleigh scattering echo signal comprises a backward rayleigh scattering echo signal of each probe light pulse in the first pulse light sequence at each position of the optical fiber to be measured, and the second backward rayleigh scattering echo signal comprises a backward rayleigh scattering echo signal of each probe light pulse in the second pulse light sequence at each position of the optical fiber to be measured; obtaining a first frequency domain-space domain characteristic diagram of the first backward Rayleigh scattering echo signal and a second frequency domain-space domain characteristic diagram of the second backward Rayleigh scattering echo signal; the first frequency domain-space domain characteristic diagram and the second frequency domain-space domain characteristic diagram take the position on the optical fiber to be detected as a first dimensional coordinate, the frequency of the detected light pulse as a second dimensional coordinate, and the signal intensity or the signal amplitude value received by the photoelectric detector as a third dimensional coordinate; selecting a reference data area with a preset size from the first frequency domain-space domain characteristic diagram, determining a matching data area corresponding to the reference data area from the second frequency domain-space domain characteristic diagram, and calculating the displacement of the reference data area and the matching data area on a second dimensional coordinate so as to determine the frequency delay between the first frequency domain-space domain characteristic diagram and the second frequency domain-space domain characteristic diagram according to the displacement; and calculating the temperature variation or the strain variation of the optical fiber to be detected according to the frequency delay.
Fig. 2 schematically illustrates an exemplary process flow 200 of a phase-sensitive OTDR measurement method based on frequency-space domain matching and injection locking techniques, according to an embodiment of the present disclosure.
As shown in fig. 2, in step S210, a first pulse light sequence generated by the pulse light sequence generating device is input to the echo signal detecting device at a first transmitting time, and a first backward rayleigh scattered echo signal corresponding to the first pulse light sequence is received by the photodetectors 1-11 at a first receiving time, wherein the first pulse light sequence includes n detecting light pulses with predetermined frequencies; n is a positive integer.
In step S220, a second pulsed light sequence generated by the pulsed light sequence generation device is input to the echo signal detection device at a second transmission time, and a second backward rayleigh scattering echo signal corresponding to the second pulsed light sequence is received by the photodetectors 1 to 11 at a second reception time, wherein the second pulsed light sequence includes n detected light pulses of a predetermined frequency.
The n predetermined frequencies are, for example, n frequencies between the frequency f1 and the frequency f2, and are arranged in order from small to large or from large to small, for example, that is, the pulses in the first and second pulse light sequences are emitted in order from small to large or from large to small. n is for example 50, 100 or another integer. The spacing between each two adjacent frequencies of the n predetermined frequencies is, for example, the same or may also be at least partially different.
For example, the n predetermined frequencies may be 100 frequencies from 5MHz to 500MHz, and the interval between two adjacent frequencies is 5MHz, for example, the n predetermined frequencies may be 5MHz, 10MHz, 15MHz, …, and 500 MHz.
Wherein the second transmission time is after the first transmission time; the first backward Rayleigh scattering echo signal comprises a backward Rayleigh scattering echo signal of each probe light pulse in the first pulse light sequence on each position of the optical fiber to be measured, and the second backward Rayleigh scattering echo signal comprises a backward Rayleigh scattering echo signal of each probe light pulse in the second pulse light sequence on each position of the optical fiber to be measured.
In step S230, a first frequency domain-space feature map of the first backward rayleigh scattering echo signal and a second frequency domain-space feature map of the second backward rayleigh scattering echo signal are obtained; the first frequency domain-space domain characteristic diagram and the second frequency domain-space domain characteristic diagram take the position on the optical fiber to be detected as a first dimensional coordinate, the frequency of the detected light pulse as a second dimensional coordinate, and the signal intensity or the signal amplitude value received by the photoelectric detectors 1-11 as a third dimensional coordinate. For example, the first, second, and third coordinates may be represented by an X coordinate, a Y coordinate, and a Z coordinate in an XYZ coordinate system, respectively.
The position on the optical fiber to be measured corresponding to the received backward rayleigh scattering echo signal (such as the first or second backward rayleigh scattering echo signal) can be determined according to the following method: for each pulse in the first pulse light sequence and the second pulse light sequence, the transmission time of the pulse is known and is denoted as t0The duration corresponding to the back Rayleigh scattered echo signal of the pulse received by the photodetector 1-11 is, for example, from t1To t2(i.e., from t)1The backward Rayleigh scattering echo signal of the pulse is received at the beginning of the moment t2The moment reception ends), t is set1The signal strength (or signal amplitude) of the signal received at a time) As the starting position of the optical fiber to be measured, t2The signal strength (or signal amplitude) received at that time is taken as the end point position (e.g., the fiber length L) of the fiber position to be measured. If the starting point position of the optical fiber position to be measured is taken as 0 point, the position of the optical fiber to be measured
Where c represents the transmission speed of light in the optical fiber.
In step S240, a reference data region of a predetermined size is selected in the first frequency-domain spatial feature map.
As an example, the reference data region is, for example, data points in a neighborhood of a predetermined size of a first location point preset in the first frequency-domain spatial signature.
In step S250, a matching data region corresponding to the reference data region is determined in the second frequency domain-spatial domain feature map.
As an example, step S250 may be implemented by steps S310-S330 shown in fig. 3, for example.
The processing of steps S310-S330 described above is described in conjunction with fig. 4.
Fig. 4 shows a schematic diagram of a frequency domain-spatial domain matching method. The left graph in FIG. 4 shows the results of sweeping the fiber along the line at a certain temperature or strain value (as an example of a first frequency-domain-spatial-signature), and the right graph shows the results of sweeping with a change in temperature or strain (as an example of a second frequency-domain-spatial-signature). That is, the left graph and the right graph in fig. 4 respectively show the echo signals of the probe lights with multiple frequencies at different temperatures or strain values at two times.
It should be noted that, in fig. 4, the first frequency domain-space characteristic diagram and the second frequency domain-space characteristic diagram are represented in the form of two-dimensional diagrams, that is, in fig. 4, the abscissa represents the position on the optical fiber to be measured, the ordinate represents the frequency of the detection light pulse, and the signal intensity or signal amplitude received by the photodetectors 1 to 11 is represented by image brightness or gray scale (i.e., different signal intensities or signal amplitudes are represented as points with different brightness or different gray scale in fig. 4).
For example, assume that the coordinates of the preset first position point are (x)P，yP，zP) That is, the first dimension and the second dimension of the predetermined first position point are (x)P，yP) Assuming a predetermined size neighborhood as the point (x)P，yP) Z as a centreW×tWRectangle of size (wherein, ZWIs the size in the first dimension, tWAs a dimension in a second dimension). In other words, the predetermined first position point (x)P，yP) Is a first-dimension coordinate
Second dimension coordinate within range
The area consisting of data within the range. As shown in fig. 4, M in the first frequency domain-spatial domain feature map (left map) represents a reference data region.
In step S310, in the second frequency domain-spatial domain feature map (as shown in the right diagram of fig. 4), a data region formed by data points in a neighborhood of a predetermined size of a second position point having the same first-dimensional coordinate as the preset first position point is used as a data region to be matched.
The initial position of the second position point selected in the second frequency-space feature map may be any point (x) having the same first-dimensional coordinates as the first position point in the first frequency-space feature mapp，y'p) That is, the first dimension coordinate of the initial position of the second position point is equal to the first dimension coordinate x of the first position pointpAnd a second-dimensional coordinate y 'of the initial position of the second position point'pMay be different from or the same as the second-dimensional coordinate yP of the first position point. Thus, the first-dimension coordinate in the data area to be matched, namely the second frequency domain-space domain characteristic diagram
Second dimension coordinate within range
The area S is composed of data within the range.
In step S320, the data area S to be matched is moved along a second coordinate axis (i.e., the frequency axis in fig. 4) of the second frequency domain-spatial domain feature map, a difference matrix between the data area to be matched and the reference data area obtained by each movement in the moving process is obtained, and a sum of squares of all elements of the difference matrix obtained each time is calculated. That is, after the initial position of the second position point is selected in the second frequency domain-spatial domain feature map, the second position point is moved in a manner that the first-dimensional coordinate of the second position point is unchanged and the second-dimensional coordinate is changed, so that the data area to be matched after each movement is obtained, and further the corresponding difference matrix is obtained.
The manner of moving the data region S to be matched along the second coordinate axis of the second frequency domain-spatial domain feature map (i.e., the frequency axis in fig. 4) may be implemented in various ways.
For example, the data area S to be matched is moved along one side of the frequency axis (e.g. the upper side in fig. 4), the step size of each movement is a preset value (which may be set according to an empirical value, or determined by an experimental method, etc.), when the image boundary is moved, the data area S to be matched is moved along the other side of the frequency axis (e.g. the lower side in fig. 4) back to the initial position, and the step size of each movement is still the preset value until the boundary is moved. One step at a time, the disparity matrix described above is obtained and the sum of the squares of all the elements of the disparity matrix is calculated.
Still alternatively, the data area S to be matched may be sequentially moved (along the frequency axis) from one side boundary to the other side boundary by a preset step length, and the above-mentioned disparity matrix is obtained and the sum of squares of all elements of the disparity matrix is calculated each time the data area S is moved by one step length.
In step S330, a difference matrix corresponding to the difference matrix when the sum of squares of all elements of the difference matrix in the moving process is minimum is determined, and a data area to be matched corresponding to the difference matrix is used as a matching data area.
For example, assuming that the whole moving process moves 100 times in total to obtain 100 difference matrices, the difference matrix with the smallest sum of squares of all elements in the 100 difference matrices is selected, and the data area S to be matched corresponding to the difference matrix is used as the matching data area.
In step S260, the displacement of the reference data region and the matching data region on the second coordinate is calculated to determine the frequency delay between the first frequency-space characteristic map and the second frequency-space characteristic map according to the displacement.
The displacement of the reference data area and the matching data area on the second-dimensional coordinate may be calculated according to the distance between the respective center points (or according to other methods), for example, the center point of the reference data area is (x)P，yP) The position of the center point of the matching data area is (x)P，y'P) The displacement amount of the reference data area and the matching data area on the second-dimensional coordinate is y'P-yP. That is, the frequency delay is equal to y'P-yP。
Then, in step S270, the temperature change amount or the strain change amount of the optical fiber under test is calculated based on the frequency delay. The temperature variation or the strain variation is a temperature variation or a strain variation within a measurement time, that is, a temperature variation or a strain variation of the optical fiber to be measured from a first transmission time to a second transmission time.
As an example, in step S270, the strain variation Δ ∈ of the optical fiber under test may be calculated according to formula one, for example.
The formula I is as follows:
in formula one, Δ v represents the frequency delay, v represents the fundamental frequency of the light wave, pεDenotes the elasto-optic coefficient, Δ ε denotes the amount of change in strain, where v and pεIs a known constant, KεIndicating strain systemNumber, Kε＝-1+pε。
Further, as an example, in step S270, the temperature change amount Δ T of the optical fiber under test may be calculated according to the second formula, for example.
The formula II is as follows:
in the second formula, Δ v represents frequency delay, v represents fundamental frequency of light wave, ξ represents thermo-optic coefficient, α represents thermal expansion coefficient, Δ T represents temperature change amount, wherein ξ and α are known constants,
KTdenotes the temperature coefficient, KT＝-(ξ+α)。
As is apparent from the above description, in the measurement method of the embodiment of the present invention, the demodulation of data employs a frequency-space domain matching technique. When demodulating the temperature or strain variation value at a certain position, selecting data points in the neighborhood of the left and right space at the position of the left image in fig. 4 as a template matrix M (i.e. a reference data area), moving a rectangular area S at the same position in the right image in fig. 4 along a frequency axis, subtracting elements of a corresponding matrix S in the moving process to obtain a difference matrix, calculating the sum of squares of all elements of the difference matrix, recording the moving amount of the corresponding matrix S when the sum of squares is minimum, and determining the frequency delay amount of the left and right images according to the moving amount so as to demodulate the temperature or strain variation.
The method for demodulating data by using the two-dimensional image matching method has better stability and noise tolerance relative to a mode of averaging a plurality of spatial position points. As shown in fig. 5A, data at fiber positions 10.5m to 11.5m are selected for demodulation, and the signal strength at the position of 11m changes with time as shown in fig. 5B, so that the signal-to-noise ratio is low. The data demodulation (to obtain the frequency delay) is performed on the multiple position coordinate averaging and two-dimensional image matching algorithms by using the one-dimensional cross-correlation algorithm, and the experimental result is shown in fig. 5C, so that the demodulation performance of the image matching algorithm is far superior to that of the one-dimensional cross-correlation algorithm. Wherein, the 1D method in fig. 5C refers to the above one-dimensional cross-correlation algorithm, and the 2D method refers to the above two-dimensional image matching algorithm.
Moreover, while the operations of the method of the invention are depicted in the drawings in a particular order, this does not require or imply that the operations must be performed in this particular order, or that all of the illustrated operations must be performed, to achieve desirable results. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step execution, and/or one step broken down into multiple step executions.
While the spirit and principles of the invention have been described with reference to several particular embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, nor is the division of aspects, which is for convenience only as the features in such aspects may not be combined to benefit. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims (5)
1. The method for measuring the phase-sensitive OTDR based on the frequency-space domain matching and the injection locking technology is characterized in that the method is realized based on the phase-sensitive OTDR based on the frequency-space domain matching and the injection locking technology;
the phase-sensitive OTDR based on the frequency-space domain matching and injection locking technology comprises a pulse light sequence generating device and an echo signal detecting device;
the pulse light sequence generating device comprises a master laser (1-1), a slave laser (1-2), an electro-optic modulator (1-3), an acousto-optic modulator (1-4), an arbitrary waveform generator (1-5), an arbitrary function generator (1-6) and a first circulator (1-7);
the echo signal detection device comprises a first erbium-doped fiber amplifier (1-8), a second circulator (1-9), a second erbium-doped fiber amplifier (1-10) and a photoelectric detector (1-11);
the output laser of the main laser (1-1) is modulated by the electro-optical modulator (1-3), and the modulated laser is injected into the slave laser (1-2) through the first circulator (1-7), wherein the frequency of the modulation signal of the electro-optical modulator (1-3) is changed in a step mode, and the modulation signal is generated by the arbitrary waveform generator (1-5);
the output light of the slave laser (1-2) is output to the acousto-optic modulator (1-4) through the first circulator (1-7), and a pulse light sequence modulated by the acousto-optic modulator (1-4) is amplified by the first erbium-doped fiber amplifier (1-8) and then injected into an optical fiber to be tested through the second circulator (1-9); wherein the arbitrary function generator (1-6) is used for generating a preset square wave signal and outputting the signal to the acousto-optic modulator (1-4);
backward Rayleigh scattering echo signals in the optical fiber to be detected are output to the second erbium-doped optical fiber amplifier (1-10) through the second circulator (1-9), and the backward Rayleigh scattering echo signals are amplified by the second erbium-doped optical fiber amplifier (1-10) and then detected by the photoelectric detector (1-11);
the measuring method comprises the following steps:
inputting a first pulsed light sequence generated by the pulsed light sequence generation device into the echo signal detection device at a first transmitting time, and receiving a first backward Rayleigh scattering echo signal corresponding to the first pulsed light sequence through the photoelectric detector (1-11) at a first receiving time, wherein the first pulsed light sequence comprises n detection light pulses with preset frequency; n is a positive integer;
inputting a second pulsed light sequence generated by the pulsed light sequence generation device into the echo signal detection device at a second transmitting time, and receiving a second backward Rayleigh scattering echo signal corresponding to the second pulsed light sequence through the photoelectric detector (1-11) at a second receiving time, wherein the second pulsed light sequence comprises the n detection light pulses with the preset frequency;
wherein the second transmission time is subsequent to the first transmission time; the first backward rayleigh scattering echo signal comprises a backward rayleigh scattering echo signal of each probe light pulse in the first pulse light sequence at each position of the optical fiber to be measured, and the second backward rayleigh scattering echo signal comprises a backward rayleigh scattering echo signal of each probe light pulse in the second pulse light sequence at each position of the optical fiber to be measured;
obtaining a first frequency domain-space domain characteristic diagram of the first backward Rayleigh scattering echo signal and a second frequency domain-space domain characteristic diagram of the second backward Rayleigh scattering echo signal; the first frequency domain-space domain characteristic diagram and the second frequency domain-space domain characteristic diagram take the position on the optical fiber to be detected as a first dimensional coordinate, the frequency of the detected light pulse as a second dimensional coordinate, and the signal intensity or the signal amplitude value received by the photoelectric detector (1-11) as a third dimensional coordinate;
selecting a reference data region of a predetermined size in the first frequency-domain-spatial-domain feature map,
determining a matching data region corresponding to the reference data region in the second frequency domain-spatial domain characteristic diagram,
calculating the displacement of the reference data region and the matching data region on a second dimensional coordinate to determine the frequency delay between the first frequency domain-space domain characteristic diagram and the second frequency domain-space domain characteristic diagram according to the displacement;
and calculating the temperature variation or the strain variation of the optical fiber to be detected according to the frequency delay.
2. The method for measuring phase-sensitive OTDR based on frequency-space domain matching and injection locking technique according to claim 1, characterized in that said phase-sensitive OTDR based on frequency-space domain matching and injection locking technique further comprises a filter, said filter is disposed between said second erbium-doped fiber amplifier (1-10) and said photodetector (1-11), for filtering the spontaneous emission noise of said second erbium-doped fiber amplifier (1-10).
3. The method for phase-sensitive OTDR measurement based on frequency-spatial domain matching and injection locking technique according to claim 1 or 2, characterized in that said reference data region comprises data points in the neighborhood of a predetermined size of a preset first location point in said first frequency-spatial domain signature;
the step of determining the matching data region corresponding to the reference data region in the second frequency domain-spatial domain feature map comprises the following steps:
in the second frequency domain-spatial domain characteristic diagram, a data area formed by data points in a preset size neighborhood of a second position point which is the same as the first-dimension coordinate of the preset first position point is used as a data area to be matched;
moving the data area to be matched along a second dimensional coordinate axis of the second frequency domain-spatial domain characteristic diagram, obtaining a difference matrix between the data area to be matched and the reference data area, which is obtained by moving each time in the moving process, and calculating the square sum of all elements of the difference matrix obtained each time;
and determining a difference matrix corresponding to the minimum sum of squares of all elements of the difference matrix in the moving process, and taking a data area to be matched corresponding to the difference matrix as the matched data area.
4. The method for measuring phase-sensitive OTDR based on frequency-space domain matching and injection locking technique according to claim 1 or 2, characterized in that the step of calculating the temperature variation or strain variation of the fiber under test comprises:
calculating the strain variation of the optical fiber to be measured according to the following formula:
where Δ v denotes the frequency delay, v denotes the fundamental frequency of the light wave, pεRepresenting the elasto-optic coefficient, Δ ε representing the amount of change in strain, KεRepresenting the strain coefficient.
5. The method for phase-sensitive OTDR measurement based on frequency-space domain matching and injection locking technique according to claim 1 or 2,
calculating the temperature variation of the optical fiber to be measured according to the following formula:
where Δ v denotes a frequency delay, v denotes a fundamental frequency of an optical wave, and ξ denotes a thermo-optical systemNumber, α denotes the coefficient of thermal expansion,. DELTA.T denotes the amount of change in temperature, KTIndicating the temperature coefficient.
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