CN110926510B - A method and device for solving phase signal based on auxiliary light to reduce phase unwinding limitation of Φ-OTDR - Google Patents
A method and device for solving phase signal based on auxiliary light to reduce phase unwinding limitation of Φ-OTDR Download PDFInfo
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- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
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- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
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Abstract
The invention provides a phase signal solving method and a phase signal solving device for reducing phi-OTDR phase unwrapping limit based on auxiliary light, wherein main detection pulse light and auxiliary detection pulse light which has the same period and pulse width as the main detection pulse light are alternately injected into phi-OTDR, but has a certain frequency difference, signals obtained by coherent detection are respectively subjected to phase demodulation, after the difference is made between the statistical phase of each subsequent point of a reference point and the statistical phase of the reference point, the differential phases wrapped by the main detection pulse light and the auxiliary detection pulse light are arranged according to a time sequence, the differential phases of the main detection pulse light are separated after the composite pulse sequence is unwrapped, the phase change is calculated by the difference in a time domain, and after the correct unwrapping phase is identified by means of the linear characteristic of the phase change, the accurate demodulation of acceleration exceeding the phase unwrapping limit can be realized.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a phase signal solving method and device for reducing phi-OTDR phase unwrapping limitation based on auxiliary light.
Background
Along with the rapid development of national economy, the laying of oil and gas pipelines in China is longer and longer, and the monitoring difficulty is higher and higher; the mileage built by the high-speed railway varies day by day, and the real-time requirement of monitoring is higher and higher; the length of the bridge is longer and longer, the total number of the bridges is more and more, and the detection precision requirement is stricter and stricter. In all of the above, the monitoring means is required to have the characteristics of distribution, long distance and real-time performance.
Phase optical time domain reflectometry (Φ -OTDR) is a device for event detection based on back-rayleigh scattered light generated in an optical fiber. When a highly coherent laser pulse is injected into the fiber, the light pulse produces rayleigh scattered light as it travels along the fiber, with the back rayleigh scattered light returning to the fiber injection port being received by a photodetector. Because the detection light source is highly coherent, the time domain curve demodulated from the electrical signal output by the detector is speckle-like. If there is no disturbance event on the fiber, the speckle-like time domain curves corresponding to different pulses do not change. However, if a disturbance occurs somewhere on the fiber, the speckle shape of the curve changes. Because time and position have approximate linear relation, we can determine the position corresponding to the event by only finding out the position of the speckle shape change through carrying out differential operation on time domain curves of different pulses. The detection distance of the phase optical time domain reflectometer can reach dozens of kilometers or even hundreds of kilometers, and the dynamic state of the whole tested object along the line can be monitored at an operation terminal only by laminating and laying the optical fiber, the pipeline, the rail, the bridge and the like together. Therefore, phase optical time domain reflectometry has gained tremendous application in these areas.
The change of the speckle-shaped time domain curve of the phase optical time domain reflectometer can well reflect the occurrence of an external event, and because the amplitude of the curve and the event are not in a linear relation, the quantitative information of the event cannot be obtained by carrying out differential operation on the time domain curve between different pulses. In road and bridge monitoring, if quantitative information of bridge abnormal conditions is known, a deep assessment and prediction can be performed on the bridge, and the same is true for the rails. Fortunately, there is a linear relationship between the phase change of the phase optical time domain reflectometer and the intensity of the external perturbation event. Researchers can realize quantitative measurement of the phase optical time domain reflectometer by various detection and demodulation modes such as digital coherence, direct detection, quadrature demodulation, Hilbert transform and the like. In the implementation process of the quantitative demodulation, the phase is basically obtained through the arctan operation. And the initial phase obtained by the arctangent operation is coiled and wound in the range of [ -pi, pi ], and the phase unwrapping algorithm is required to be utilized for unwrapping. However, the phase unwrapping algorithm has a very harsh condition, i.e. the absolute difference between adjacent samples of the phase signal is less than pi. In a single-frequency optical phi-OTDR system in a coherent detection mode, the sampling rate of the system can be increased by increasing the frequency of pulse emission, so that the absolute difference is reduced. However, there is an upper limit to the frequency of transmission of the pulses, limited by the length of the fiber. When the pulse transmission frequency is increased to this upper limit, if the absolute difference is still larger than pi, the single-frequency optical Φ -OTDR system will not be able to correctly implement phase unwrapping. Therefore, the invention provides a phase signal solving method and device for reducing phi-OTDR phase unwrapping limitation based on auxiliary light, which breaks the limitation that the absolute difference in a single-frequency optical phi-OTDR system is less than pi, and realizes the improvement of a measurement range.
Disclosure of Invention
The purpose of the invention is as follows: in response to the above problem, in an auxiliary optical Φ -OTDR system, the phases of both frequency components are random along the length of the fiber, and at some locations, the phase of one optical frequency component can be inserted exactly between the phases of adjacent pulses of the other optical frequency component. Thus, when the newly combined phase sequence is phase unwrapped, the phase difference between adjacent sampling points corresponding to the phase unwrapping algorithm is reduced. Therefore, the invention provides a phase signal solving method and device for reducing phi-OTDR phase unwrapping limitation based on auxiliary light.
The technical scheme is as follows: in order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a phase signal solving method for reducing phi-OTDR phase unwrapping limitation based on auxiliary light introduces auxiliary detection pulse light into a phi-OTDR system, and the frequency difference of the main detection pulse light relative to reference light is f1The frequency difference of the introduced auxiliary detection pulse light relative to the reference light is f2And f is1Is not equal to f2Electric signals obtained by coherent detection
The steps of data processing are as follows:
step one, component separation: respectively with a centre frequency f1And f2Two band-pass filters extract two intermediate frequency signals ID1And ID2If the sequences of the main detection pulse light and the auxiliary detection pulse light are respectively k1And k2And the number of the two is M, the data sequence collected by a single pulse is j, and the number of the collected data is N, the intermediate frequency signal can be further expressed as
And
k1，k2is an integer;
step two, quadrature demodulation: for two intermediate frequency signals ID1And ID2Respectively carrying out orthogonal demodulation to respectively obtain the statistical phase phi without unwrapping1(k1J) and phi2(k2,j)；
Step three, phase difference: selecting a fiber position number j before a disturbance eventRUsing the non-noise static position of the reference point as a reference point, and calculating the non-unwrapped statistical phase phi of each point behind the reference pointi(ki,j)|i＝1,2Minus the un-unwrapped statistical phase phi of the reference pointi(ki,jR)|i＝1,2To obtain differential phase without unwrapping
And j isR∈[j]，j＞jR；
Step four, odd-even interpolation: differential phase psi without unwrapping1(k1X) and the differential phase phi of the unwound phase phi2(k2X) merge into a new sequence in pulse natural timing, namely:
step five, phase unwrapping: unwrapping psi (k, x) for each fiber position point x according to a phase unwrapping algorithm to obtain a differential phase theta (k, x), wherein the unwrapping step comprises the following steps:
step six, single-frequency extraction: the differential phase θ (k, x) after the unwrapping is calculated as follows:
extracting the unwrapped differential phase theta generated by the main detection pulse light1(k1,x)；
Step seven, time domain difference making: the extracted differential phase theta1(k1X) according to
Determining the phase change beta of the main detection pulse light in the phase light time domain reflectometer1(k1,x)；
Step eight, solving to obtain a signal: change of phase by beta1(k1X) projection onto beta1-selecting the sampling position number x closest to both sides of the event area in the x plane in the area where the phase change varies linearly along the length of the fiberAAnd xBThe phase signal beta of the disturbance event is determined according to the following formulaN(k1)：
βN(k1)＝β1(k1,xB)-β1(k1,xA)。
In addition, the invention also discloses a device of a phase signal solving method based on auxiliary light to reduce phi-OTDR phase unwrapping limitation, which comprises the following steps: a laser LD, a first coupler OC1, a second coupler OC2, a first acousto-optic modulator AOM1, a second acousto-optic modulator AOM2, a third coupler OC3, an erbium-doped Fiber amplifier EDFA, a Circulator, a sensing Fiber, a fourth coupler OC4, a balanced photodetector BPD, a voltage amplifier VA, a data acquisition card DAQ, a first driver1, a second driver2, a pulse signal generator PG and a computer PC;
the laser LD is connected with the first coupler OC 1;
the first coupler OC1 is connected with the second coupler OC2 and the fourth coupler OC4 at the same time;
the first acousto-optic modulator AOM1 is simultaneously connected with the second coupler OC2, the third coupler OC3 and the first driver 1;
the second acousto-optic modulator AOM2 is connected to the second coupler OC2, the third coupler OC3 and the second driver2 at the same time;
the erbium-doped fiber amplifier EDFA is simultaneously connected with the third coupler OC3 and the Circulator;
the pulse signal generator PG is simultaneously connected with the first driver1, the second driver2 and the data acquisition card DAQ;
the Circulator is simultaneously connected with the sensing optical Fiber and the fourth coupler OC 4;
the balanced photodetector BPD is simultaneously connected with the fourth coupler OC4 and the voltage amplifier VA;
and the data acquisition card DAQ is simultaneously connected with the voltage amplifier VA and the computer PC.
Further, the output splitting ratio of the second coupler OC2 is 50: 50.
Further, the pulse signal generator PG may transmit the same pulse width and the same pulse period to the first driver1 and the second driver2, but the pulse interval between different drivers may be arbitrary.
Further, if the frequency shift amounts of the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2 are f respectively1And f2The maximum frequency of the external disturbance signal is fHThen the bandwidth of the balanced photodetector is at least: f. ofB＝max{f1+fH,f2+fHAnd the sampling rate of the data acquisition card is at least fBTwice as much.
Has the advantages that: compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:
the phase signal obtained by solving by the method can effectively break through the limit of the phase unwrapping algorithm limit condition in the traditional single-frequency optical phi-OTDR system, and the acceleration measurement range of the phase optical time domain reflectometer is improved.
Drawings
FIG. 1 is a schematic process diagram of an assisted optical phi-OTDR quantitative measurement;
FIG. 2 is a schematic view of an experimental verification device;
FIG. 3600 Hz display of phase change on the phase change-fiber length plane for signal loading (a) a conventional single-frequency optical phase optical time domain reflectometer, (b) an auxiliary light based phase optical time domain reflectometer;
FIG. 4 is a solution of the phase signal;
FIG. 5 solution for wide-range tuning of the loading signal.
Detailed Description
The technical scheme of the invention is further explained in detail by combining the attached drawings:
it will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
In the coherent detection type phase optical time domain reflectometer, the phase at the subsequent position of the optical fiber includes information on the change of the phase at the previous position. When a disturbance event acts on the optical fiber, the phase change after the disturbance area is often a phase signal reflecting quantitative information of the disturbance event. The phase change after the perturbation region remains constant along the length of the fiber neglecting laser frequency drift and other noise. This property is not changed by changes in external disturbances for physically present phase changes. However, the appearance of the phase change we can see is solved from the amplitude signal we detect. In solving for the phase, once the physical phase signal is out of the range of [ -pi ], it is necessary to unwrap the wrapped phase. Unfortunately, using a phase unwrapping algorithm must satisfy the condition that the absolute value of the phase difference between adjacent sample points is less than pi. This condition is called the limit condition of the phase unwrapping algorithm. Under the influence of the condition, the measurement range of the phase optical time domain reflectometer on signals such as a sound field and the like is greatly limited.
In a phase optical time domain reflectometer based on single frequency light, the solution of the phase change can go through a relatively complex process. Firstly, obtaining the most original non-unwrapped statistical phase of an intermediate frequency signal obtained by coherent detection in an orthogonal demodulation mode, then selecting a reference point in a static area before a disturbance event, then subtracting the non-unwrapped statistical phase of the reference point from the non-unwrapped statistical phase of each sampling point after the reference point to obtain the non-unwrapped differential phase of the phase optical time domain reflectometer, at the moment, spreading the wrapped differential phase by using a phase unwrapping algorithm, then taking the average value of the unwrapped differential phases generated by all pulses participating in calculation as a reference phase, and subtracting the reference phase from the unwrapped differential phase generated by each pulse to obtain the phase change of the phase optical time domain reflectometer. Obviously, the phase change is not intertwined. Then two noiseless points are taken at two sides next to the disturbance event area, and the phase changes of the two points are differentiated, so that the phase signal corresponding to the disturbance event can be obtained.
The premise for correctly solving the phase signal is that the limit condition of the phase unwrapping algorithm must be satisfied, otherwise, in the static region after the disturbance event, we cannot find the correct phase change. The refractive index profile along the length of the fiber is not uniform, and therefore, even the statistical phase and the differential phase of the static region are randomly distributed along the length of the fiber. And because the differential phase which is not unwound is solved when the phase change is solved, and then the phase change is solved after the unwinding, the phase change when the phase unwinding algorithm fails is also distributed in a mess way. The situation changes after the introduction of the auxiliary light.
The introduced auxiliary light is pulse light which has the same period and the same pulse width but has a certain frequency difference with the main detection pulse light. The auxiliary detection pulse light and the main detection pulse light appear alternately in time sequence. The differential phases of the main detection pulse light and the auxiliary detection pulse light in the length direction of the optical fiber are randomly distributed. The difference in frequency between the two probe lights causes a certain random difference between the differential phases of the two probe lights. The result of this difference is that the differential phases generated by the auxiliary probe pulse light are inserted in time sequence at some positions between the differential phases generated by the adjacent pulses of the main probe pulse light. When the external disturbance amplitude becomes large, the absolute difference of the differential phase between adjacent pulses also increases for the main detection pulse light, and if only the un-unwrapped differential phase generated by the main detection pulse light is unwrapped, the resulting phase change may be disordered in distribution along the length direction of the optical fiber because the limit condition is not satisfied. However, after introducing the auxiliary probe pulse light, if the unwrapping process is performed for a newly combined pulse sequence, then some positional limit conditions may be met. At these positions, the differential phase of the main detection pulse light or the auxiliary detection pulse light is expanded to the correct value. If the unwrapped differential phase corresponding to the main detection pulse light at the positions is extracted to solve the phase change, the phase change after the disturbance event area can well reflect the disturbance event. For other positions, the finally calculated phase change may not be related to the disturbance information because the limit condition is not satisfied, and at these positions, there is no regularity between the two un-unwound differential phases at different positions, so that the calculated phase change is also irregularly distributed in the length direction of the optical fiber. On the other hand, since the integration of the frequency difference of the two probe lights along the length direction of the optical fiber is relatively slow, the change between the two states is generally not fast, whether for the point where the limit condition is satisfied or for the point where the limit condition is not satisfied. Then along the direction of travel of the laser light in the fiber is divided into several regions, some regions being points where the limit condition is met and some regions being unsatisfied. For the area satisfying the limit condition, the phase change of the optical fiber is the same as the property of a single-frequency optical phase optical time domain reflectometer, and the phase change after the disturbance event area is linearly changed along the length direction of the optical fiber. If we plot the phase change of the main detection pulse light obtained by extraction solution on the plane of phase change-optical fiber length, we can easily identify the position satisfying the limit condition according to the linear characteristic of the correctly solved phase change. At the positions, two sampling position serial number points closest to two sides of a disturbance event area are further selected, and then phase changes of main detection pulse light of the two position points are differentiated to obtain a phase signal of an auxiliary light phi-OTDR detection disturbance event.
Our inventive embodiments will be explained based on the above physical and signal processing ideas.
The experimental setup illustrated in fig. 2 is the hardware implementation of the embodiment, which is a phase optical time domain reflectometer employing coherent detection with the introduction of auxiliary light. The laser LD is a highly coherent light source with a linewidth below 100Hz, the first coupler OC1 splits the light emitted by the laser into two 90:10 portions, 90% of the light going up as signal light and 10% of the light going down as intrinsic reference light. The upper path light is divided into two paths of signal light with equal intensity after passing through the second coupler OC 2. The two paths of signal light are respectively and alternately modulated by an acousto-optic modulator AOM1 and an acousto-optic modulator AOM2, the frequency shift of the detection pulse light modulated by AOM1 is 40MHz, and the frequency shift of the detection pulse light modulated by AOM2 is 80 MHz. The frequency-shifted light of 40MHz is used as the main detection pulse light, and the frequency-shifted light of 80MHz is used as the auxiliary detection pulse light. The time sequence of the double-frequency optical pulse train is controlled by a pulse signal generator PG through drivers driver1 and driver2, the width of two paths of detection pulse light is 200ns, the repetition frequency is 50kHz, the minimum distance of auxiliary detection pulse light relative to the main detection pulse is 9us, and the auxiliary detection pulse light and the main detection pulse light are combined into a path of double-frequency optical pulse train through a third coupler OC 3. After being amplified by EDFA with the current of 201mA, the amplified product is injected into a test optical fiber by a circulator, and a piezoelectric ceramic PZT is loaded at a position about 1.25km away from an optical fiber injection port.
The PZT is wound with about 10m of optical fibre and its drive voltage is supplied by a signal generator, which simulates the generation of a sound field signal, from which the phase signal to be solved in this embodiment is also excited. Rayleigh scattered light returning from the optical fiber enters a fourth coupler OC4 through a Circulator, meanwhile, local reference light enters the other input port of the fourth coupler at the same time, the splitting ratio of the fourth coupler is 50:50, the output port of the fourth coupler is directly connected with a photoelectric balance detector BPD, the BPD directly converts photocurrent into a voltage signal, the voltage signal is sent to a data acquisition card DAQ in a computer PC after being amplified by 10 times through a broadband amplifier VA, the data acquisition card is controlled by software written by Labview, and the sampling rate of the data acquisition card is set to 312.5 MSa/s.
Wherein, the trigger signal of the pulse signal generator to the data acquisition card on the PC is synchronous with the modulation signal to the driver 1.
After a light path is built and debugged, a 5V 600Hz sinusoidal driving signal is loaded to the PZT to generate a sound field and further generate a phase signal. Collecting data to obtain electric signal
In the case of a data acquisition card,
is a discretized digital expression. Can be combined with
Further expressed as
Wherein, if k1Is a natural sequence of main probe pulses, k2Is a natural sequence of auxiliary probe pulses, then k1、k2And k1×2Satisfy the relationship
k1，k2Is an integer, and the time interval corresponding to the adjacent integer is the period 20us of the main detection pulse. j is a single probeThe sampling number of the sampling sequence of the data acquisition card in the range of the pulse action time is N, and the distance delta d between adjacent sampling points meets the requirement
Wherein c is the speed of light in vacuum, n is the average refractive index of the optical fiber, and S is the sampling rate of the data acquisition card. In the following description, only the pulse sequence and the number of sampling points are described, and the conversion is automatically performed in accordance with the above-described relationship when the time in the pulse sequence direction and the length of the optical fiber are involved, and the description thereof is omitted. In the present invention, the term "optical fiber length" as a physical quantity means a distance from any point on an optical fiber to an optical fiber injection port.
The data acquisition card acquires digital signals, which is the last step of coherent detection, and then the data is all subjected to digital processing, wherein the processing process is as follows.
Step one, component separation: AOM1 and AOM2 are acousto-optic modulators of 40MHz and 80MHz frequency-shifted components, respectively, so that the electrical signal
In while containing f140MHz and f2At an intermediate frequency of 80MHz, a Filter Design in the MATLAB tool kit was used&A40 MHz band-pass filter and an 80MHz band-pass filter are respectively designed for Analysis Tool, the pass band gain is 1, and the pass band bandwidth is 2 MHz.
Because the designed digital band-pass filter substitutes the parameters of the sampling rate, the designed filter is directly called the filter2 function in MATLAB, and the electric signal E can be separated into two paths of intermediate frequency signals I corresponding to 40MHz and 80MHz frequency shift lightD1And ID2If the number of the main detection pulse light and the number of the auxiliary detection pulse light are both 1000, the intermediate frequency signal can be further expressed as
And
and k is1，k2And j is an integer.
Step two, quadrature demodulation: for the intermediate frequency signal of 40MHz, respectively multiplying by the sine value and cosine value corresponding to 40MHz to obtain I component and Q component, passing the I component and Q component through a low-pass filter with gain of 1 and bandwidth of 5MHz, and then dividing the I component passing through the low-pass filter by the Q component to obtain the initial non-unwrapped statistical phase phi of the frequency-shifted light of 40MHz1(k1J) using the same method to obtain the initial unwrapped statistical phase phi corresponding to the 80MHz shifted light2(k2,j)。
Step three, phase difference: in order to eliminate instability introduced by a driving clock of an acousto-optic modulator and the like, a position with the serial number j is selected from the position of the optical fiber before a disturbance event areaRThe noiseless static position of 380 is taken as a reference point, and then the unwrapped statistical phase phi of points j > 380 after the reference pointi(ki,j)|i＝12Minus the un-unwrapped statistical phase phi of the reference pointi(ki,jR)|i＝1,2Obtaining the differential phase of the phase optical time domain reflectometer
Therefore, the problem of phase research of the absolute position on the optical fiber is converted into the problem of phase difference between two position points on the optical fiber, and the change of the phase difference along with the increase of the pulse sequence is the phase change of the phase optical time domain reflectometer caused by an external disturbance event.
Step four, odd-even interpolation: differential phase psi without unwrapping1(k1X) and the differential phase phi of the unwound phase phi2(k2And x) recombining. For pulse sequence k1And k2Recombination, k1The sequences are arranged in a new sequence as odd sequences, k2The sequences are arranged into even numbered sequences in the new sequence, and the unwrapped differential phase ψ (k, x) resulting in a new combined pulse sequence is:
step five, phase unwrapping: unwrapping psi (k, x) for each fiber position point x according to a phase unwrapping algorithm to obtain a differential phase θ (k, x), wherein the unwrapping comprises the following basic steps:
it is the focus of the present invention to unwrap the un-unwrapped differential phase ψ (k, x) to obtain a correctly unwrapped differential phase.
Step six, single-frequency extraction: based on the calculated unwrapped differential phase θ (k, x), according to:
extracting the differential phase of the odd sequence to obtain the unwrapped differential phase theta generated by the main detection pulse light1(k1,x)。
Step seven, time domain difference making: the extracted differential phase theta1(k1X) according to:
calculating the phase change beta of the main detection pulse light in the phase light time domain reflectometer1(k1And x), the results are shown in fig. 3 (b).
Meanwhile, for comparison, the phase change produced by a single-frequency optical phase optical time domain reflectometer under the same vibration event is also plotted in fig. 3 (a). The phase change in fig. 3(a) is cluttered after the vibration event region, due to the limit condition of the phase unwrapping algorithm not being satisfied. Therefore, we cannot find the final phase signal from fig. 3 (a). In fig. 3(b), the phase change after the vibration event region is disordered in some regions, and regularly distributed along the length direction of the optical fiber in some regions, and the phase change of the regularly distributed regions correctly reflects the influence of the vibration event on the phase of the phase optical time domain reflectometer.
Step eight, solving signals, and selecting the position serial numbers x which are closest to two sides of the event area on the positions of which the phase change linearly changes along the length direction of the optical fiber in the (b) of the graph 3A3350 and xB3630, then by the formula βN(k1)：
βN(k1)＝β1(k1,xB)-β1(k1,xA)
The phase signal is obtained as shown in fig. 4.
The phase signal in fig. 4 corresponds to 1000 times of main detection pulse light, that is, the phase signal includes 1000 data points, and two adjacent values of the 1000 data points are subjected to difference processing to obtain 999 absolute values. Of these 999 differences, 180 were greater than π, with the largest being 3.7154. This shows that our method effectively breaks through the limit of the limit condition of the phase unwrapping algorithm.
Further, we varied the frequency and amplitude of the PZT sinusoidal drive signal, and the results are shown in fig. 5. In fig. 5, two bars indicate that phase unwrapping can be simultaneously achieved by a conventional single-frequency optical phase optical time domain reflectometer and an auxiliary optical phase optical time domain reflectometer based on the present invention, a single bar indicates that phase unwrapping can only be achieved by the auxiliary optical phase optical time domain reflectometer, and no bar indicates that both methods cannot achieve correct phase unwrapping. As can be seen from fig. 5, compared with the conventional single-frequency optical phase optical time domain reflectometer, the auxiliary optical phase optical time domain reflectometer based on the present invention can achieve quantitative measurement of a signal with a higher frequency and a larger amplitude, that is, increase of the measurement range is achieved.
Claims (5)
1. A phase signal solving method for reducing phi-OTDR phase unwrapping limitation based on auxiliary light is characterized in that auxiliary detection pulse light is introduced into a phi-OTDR system, and the frequency difference of main detection pulse light relative to reference lightIs f1The frequency difference of the introduced auxiliary detection pulse light relative to the reference light is f2And f is1Is not equal to f2Electric signals obtained by coherent detection
The steps of data processing are as follows:
step one, component separation: respectively with a centre frequency f1And f2Two band-pass filters extract two intermediate frequency signals ID1And ID2If the sequences of the main detection pulse light and the auxiliary detection pulse light are respectively k1And k2And the number of the two is M, the data sequence collected by a single pulse is j, and the number of the collected data is N, the intermediate frequency signal can be further expressed as
And
k1，k2is an integer;
step two, quadrature demodulation: for two intermediate frequency signals ID1And ID2Respectively carrying out orthogonal demodulation to respectively obtain the statistical phase phi without unwrapping1(k1J) and phi2(k2,j)；
Step three, phase difference: selecting the serial number of the optical fiber position as j from the data sequence j before the disturbance eventRUsing the non-noise static position of the reference point as a reference point, and calculating the non-unwrapped statistical phase phi of each point behind the reference pointi(ki,j)|i＝1,2Minus the un-unwrapped statistical phase phi of the reference pointi(ki,jR)|i＝1,2To obtain differential phase without unwrapping
And j > jR；
Step four, odd-even interpolation: differential phase psi without unwrapping1(k1X) and the differential phase phi of the unwound phase phi2(k2X) merge into a new sequence in pulse natural timing, namely:
step five, phase unwrapping: unwrapping psi (k, x) for each fiber position point x according to a phase unwrapping algorithm to obtain a differential phase theta (k, x), wherein the unwrapping step comprises the following steps:
step six, single-frequency extraction: calculating the differential phase theta (k, x) after the unwrapping according to the following formula:
extracting the unwrapped differential phase theta generated by the main detection pulse light1(k1,x)；
Step seven, time domain difference making: the extracted differential phase theta1(k1X) according to:
determining the phase change beta of the main detection pulse light in the phase light time domain reflectometer1(k1,x)；
Step eight, solving to obtain a signal: change of phase by beta1(k1X) projection onto beta1-selecting the sampling position number x closest to both sides of the event area in the x plane in the area where the phase change varies linearly along the length of the fiberAAnd xBThe phase signal beta of the disturbance event is determined according to the following formulaN(k1)：
βN(k1)＝β1(k1,xB)-β1(k1,xA)。
2. An apparatus for implementing the method for solving a phase signal based on auxiliary optical reduced Φ -OTDR phase unwrapping constraints of claim 1, characterized in that it comprises: a laser LD, a first coupler OC1, a second coupler OC2, a first acousto-optic modulator AOM1, a second acousto-optic modulator AOM2, a third coupler OC3, an erbium-doped Fiber amplifier EDFA, a Circulator, a sensing Fiber, a fourth coupler OC4, a balanced photodetector BPD, a voltage amplifier VA, a data acquisition card DAQ, a first driver1, a second driver2, a pulse signal generator PG and a computer PC;
the laser LD is connected with the first coupler OC 1;
the first coupler OC1 is connected with the second coupler OC2 and the fourth coupler OC4 at the same time;
the first acousto-optic modulator AOM1 is simultaneously connected with the second coupler OC2, the third coupler OC3 and the first driver 1;
the second acousto-optic modulator AOM2 is connected to the second coupler OC2, the third coupler OC3 and the second driver2 at the same time;
the erbium-doped fiber amplifier EDFA is simultaneously connected with the third coupler OC3 and the Circulator;
the pulse signal generator PG is simultaneously connected with the first driver1, the second driver2 and the data acquisition card DAQ;
the Circulator is simultaneously connected with the sensing optical Fiber and the fourth coupler OC 4;
the balanced photodetector BPD is simultaneously connected with the fourth coupler OC4 and the voltage amplifier VA;
and the data acquisition card DAQ is simultaneously connected with the voltage amplifier VA and the computer PC.
3. The apparatus of claim 2 wherein the output split ratio of the second coupler OC2 is 50: 50.
4. The apparatus of claim 2, wherein the pulse width and the pulse period of the pulse signal generator PG to the first driver1 and the second driver2 are consistent, and the pulse interval between different drivers is arbitrary.
5. The apparatus of claim 2, wherein if the frequency shift amount of the first acousto-optic modulator AOM1 and the second acousto-optic modulator AOM2 is f respectively1And f2The maximum frequency of the external disturbance signal is fHThen the bandwidth of the balanced photodetector is at least fB＝max{f1+fH,f2+fHAnd the sampling rate of the data acquisition card is at least fBTwice as much.
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| CN111735527B (en) * | 2020-06-01 | 2022-03-29 | 哈尔滨工业大学 | Optical fiber distributed vibration sensing method based on time domain phase calculation |
| CN113701793B (en) * | 2021-08-09 | 2022-05-06 | 南京大学 | A Non-hardware Phase Locking Method in Phase-Sensitive Optical Time Domain Reflectometry |
| CN113852416B (en) * | 2021-09-23 | 2023-09-01 | 西北大学 | Phase demodulation method and device with fading noise identification and elimination |
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| CN115333913B (en) * | 2022-10-17 | 2023-03-24 | 中国科学技术大学 | Phase demodulation method and device for phase sensitive optical time domain reflectometer |
| CN116337244A (en) * | 2023-04-10 | 2023-06-27 | 常州工学院 | A Method of Extracting Φ-OTDR Phase Signal Based on Triple Noise Reduction |
| CN116907627B (en) * | 2023-09-13 | 2023-12-19 | 之江实验室 | Optical path difference auxiliary-based large dynamic range distributed phase sensing method and device |
Citations (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102628698A (en) * | 2012-04-06 | 2012-08-08 | 中国科学院上海光学精密机械研究所 | Distributed optical fiber sensor and information demodulating method |
| CN102645268A (en) * | 2012-04-26 | 2012-08-22 | 中国科学院上海光学精密机械研究所 | Optical frequency division multiplexing phase-sensitive optical time domain reflectometer |
| CN105067103A (en) * | 2015-08-31 | 2015-11-18 | 上海交通大学 | Vibration detection device and method based on optical frequency domain reflectometer |
| CN106052842A (en) * | 2016-08-05 | 2016-10-26 | 上海交通大学 | Distributed Fiber Optic Vibration Sensing System and Its Demodulation Method with Fading Noise Cancellation |
| CN106248119A (en) * | 2016-07-14 | 2016-12-21 | 南京大学 | A distributed ultra-high-speed disturbance quantitative detection method and device |
| CN106595837A (en) * | 2015-10-20 | 2017-04-26 | 中兴通讯股份有限公司 | Processing method and device for coherent phase sensitive optical time domain reflectometer |
| CN207280479U (en) * | 2017-08-30 | 2018-04-27 | 中国电子科技集团公司第三十四研究所 | A kind of φ-OTDR quadrature phase demodulation systems |
| CN107990970A (en) * | 2017-11-03 | 2018-05-04 | 上海交通大学 | The method for eliminating the noise that declines in distribution type fiber-optic acoustic systems |
| CN109238321A (en) * | 2018-11-01 | 2019-01-18 | 哈尔滨工业大学 | Based on the relevant phase-sensitive optical time domain reflectometer of multifrequency time domain and measurement method |
| CN109297581A (en) * | 2018-08-31 | 2019-02-01 | 南京大学 | A Quadratic Phase Difference Measurement Method for Compensating Frequency Drift in Phase-Sensitive Optical Time Domain Reflectometers |
| CN110048765A (en) * | 2018-09-30 | 2019-07-23 | 南京大学 | A Method for Quantitative Measurement of Φ-OTDR Based on Overall Least Squares Fitting |
| CN110132397A (en) * | 2019-05-09 | 2019-08-16 | 南京大学 | A Method for Reducing Dead Zone Probability in Φ-OTDR System Based on Space Division Multiplexing |
| CN110132329A (en) * | 2019-05-08 | 2019-08-16 | 汕头大学 | Stress, temperature and vibration composite detection fiber optic sensor and signal processing method |
| CN110487308A (en) * | 2019-08-27 | 2019-11-22 | 南京大学 | A high-performance coherent detection type Φ-OTDR implementation system and method based on phase locking |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7947945B2 (en) * | 2008-02-29 | 2011-05-24 | Corning Incorporated | Fiber optic sensing system, method of using such and sensor fiber |
| US20130113629A1 (en) * | 2011-11-04 | 2013-05-09 | Schlumberger Technology Corporation | Phase sensitive coherent otdr with multi-frequency interrogation |
-
2019
- 2019-11-27 CN CN201911179878.5A patent/CN110926510B/en active Active
Patent Citations (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102628698A (en) * | 2012-04-06 | 2012-08-08 | 中国科学院上海光学精密机械研究所 | Distributed optical fiber sensor and information demodulating method |
| CN102645268A (en) * | 2012-04-26 | 2012-08-22 | 中国科学院上海光学精密机械研究所 | Optical frequency division multiplexing phase-sensitive optical time domain reflectometer |
| CN105067103A (en) * | 2015-08-31 | 2015-11-18 | 上海交通大学 | Vibration detection device and method based on optical frequency domain reflectometer |
| CN106595837A (en) * | 2015-10-20 | 2017-04-26 | 中兴通讯股份有限公司 | Processing method and device for coherent phase sensitive optical time domain reflectometer |
| CN106248119A (en) * | 2016-07-14 | 2016-12-21 | 南京大学 | A distributed ultra-high-speed disturbance quantitative detection method and device |
| CN106052842A (en) * | 2016-08-05 | 2016-10-26 | 上海交通大学 | Distributed Fiber Optic Vibration Sensing System and Its Demodulation Method with Fading Noise Cancellation |
| CN207280479U (en) * | 2017-08-30 | 2018-04-27 | 中国电子科技集团公司第三十四研究所 | A kind of φ-OTDR quadrature phase demodulation systems |
| CN107990970A (en) * | 2017-11-03 | 2018-05-04 | 上海交通大学 | The method for eliminating the noise that declines in distribution type fiber-optic acoustic systems |
| CN109297581A (en) * | 2018-08-31 | 2019-02-01 | 南京大学 | A Quadratic Phase Difference Measurement Method for Compensating Frequency Drift in Phase-Sensitive Optical Time Domain Reflectometers |
| CN110048765A (en) * | 2018-09-30 | 2019-07-23 | 南京大学 | A Method for Quantitative Measurement of Φ-OTDR Based on Overall Least Squares Fitting |
| CN109238321A (en) * | 2018-11-01 | 2019-01-18 | 哈尔滨工业大学 | Based on the relevant phase-sensitive optical time domain reflectometer of multifrequency time domain and measurement method |
| CN110132329A (en) * | 2019-05-08 | 2019-08-16 | 汕头大学 | Stress, temperature and vibration composite detection fiber optic sensor and signal processing method |
| CN110132397A (en) * | 2019-05-09 | 2019-08-16 | 南京大学 | A Method for Reducing Dead Zone Probability in Φ-OTDR System Based on Space Division Multiplexing |
| CN110487308A (en) * | 2019-08-27 | 2019-11-22 | 南京大学 | A high-performance coherent detection type Φ-OTDR implementation system and method based on phase locking |
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