CN114910191B - Self-calibration method of Brillouin optical time domain scattering system - Google Patents
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Abstract
The invention relates to a self-calibration method of a Brillouin optical time domain scattering system, which comprises a laser light source (31), a first coupler (32), an electro-optical modulator (33), an acousto-optic modulator (35), a first optical fiber amplifier (34), a second optical fiber amplifier (36), an arbitrary waveform generator (37), a sensing optical fiber (38), a second coupler (39), a photoelectric detection unit (40), a demodulation unit (42) and a reference section optical fiber (41), wherein the sensing optical fiber (38) comprises a sensing optical fiber first port (201) and a sensing optical fiber second port (202), and the reference section optical fiber (41) is arranged between the first optical fiber amplifier (34) and the sensing optical fiber first port (201); the self-calibration method measures the flight time of light traversing the whole section of optical fiber to be measured, calculates the change of the maximum gain frequency offset, and obtains the temperature information of each position of the optical fiber. The system and the method of the invention improve the long-term working stability of the long-distance BOTDA sensing system, increase the calibration function and minimize the extra hardware of the system.
Description
Technical Field
The invention belongs to the field of optical fiber sensing, and particularly relates to a Brillouin optical time domain scattering system and a self-calibration method.
Background
The brillouin optical time domain analysis distributed optical fiber sensing system (hereinafter referred to as BOTDA) is a widely used distributed optical fiber sensing system. The system injects pulse pump light and continuous probe light at two ends of the optical fiber respectively. When the frequency offset of the probe light with respect to the pump light is in a specific interval and the power is sufficiently large, the stimulated brillouin scattering effect existing in the optical fiber transfers the pump light energy to the probe light, thereby amplifying the probe light. The gain of the probe light varies with the frequency offset, with the maximum gain point being affected by the temperature and strain of the fiber. The BOTDA has long detection distance and high sensitivity, can realize full-distribution strain and temperature measurement, and has wide application in the fields of safety monitoring, state alarming and the like of tunnels, submarine cables, large-scale buildings and the like.
In the prior art, china patent 201610341294 discloses a Brillouin scattering signal processing method and a distributed optical fiber sensing system thereof, wherein the distributed optical fiber sensing system consists of a sensing optical fiber, a laser signal source, a circulator, a detection pulse optical path modulation module, a frequency shift reference optical path modulation module, a coherent detection unit and a data acquisition processing module, so that the relative variation of Brillouin frequency shift can be accurately obtained, a backward Brillouin scattering spectrum can be obtained, and a complete Brillouin scattering spectrum can be obtained. At present, in order to track the frequency offset change, before a BOTDA system starts to measure, the maximum gain frequency offset of different delays after one pulse pumping light emission is read as a reference frequency offset, the delays after the pulse pumping light enters an optical fiber to be measured are mapped onto space positions through the speed of light in the optical fiber, the reference frequency offset of different positions is obtained, and during measurement, the actual measurement maximum gain frequency offset and the reference frequency offset under the same delay are directly subjected to difference to obtain the frequency offset change. However, the equal light speed in the optical fiber is affected by environmental factors such as temperature and the like to some extent, the measurement and the reference frequency offset under the same time delay are measured at different moments, and the optical fibers at different positions possibly correspond to each other, and due to slight inconsistency of materials of the optical fibers, reference frequency offset values at the positions are different, extra errors are introduced when the difference calculation frequency offset changes, and the measurement precision is affected.
Disclosure of Invention
In view of the defects existing in the existing BOTDA system, the invention provides a Brillouin optical time domain scattering system and a self-calibration method. The system and the self-calibration method can improve the long-term working stability of the long-distance BOTDA sensing system, increase the calibration function and simultaneously minimize the extra hardware of the system.
In order to achieve the above object, the present invention adopts the following technical scheme:
The Brillouin optical time domain scattering system structurally comprises a laser light source, a first coupler, an electro-optical modulator, an acousto-optic modulator, a first optical fiber amplifier, a second optical fiber amplifier, an arbitrary waveform generator, a sensing optical fiber, a second coupler, a photoelectric detection unit, a demodulation unit and a reference section optical fiber, wherein the sensing optical fiber comprises a sensing optical fiber first port and a sensing optical fiber second port, and a reference section optical fiber is arranged between the first optical fiber amplifier and the sensing optical fiber first port;
The laser source emits laser to the first coupler to be split into detection light and pump light, the pump light is modulated into pulse pump light through the acousto-optic modulator, the pulse pump light is amplified through the second optical fiber amplifier and then transmitted to the second coupler, the pulse pump light passing through the second coupler enters the sensing optical fiber through the first port of the sensing optical fiber, and the pulse pump light propagates to the second port of the sensing optical fiber through the sensing optical fiber;
The detection light is modulated into continuous detection light after frequency shift through an electro-optical modulator, the continuous detection light is injected into the reference section optical fiber through a first optical fiber amplifier, the continuous detection light passing through the reference section optical fiber reaches a second port of a sensing optical fiber and then enters the sensing optical fiber, the continuous detection light propagates to the first port of the sensing optical fiber in the sensing optical fiber, the continuous detection light emitted from the first port of the sensing optical fiber enters an incident end of the second coupler, the second coupler outputs the separated continuous detection light to the photoelectric detection unit, and the photoelectric detection unit outputs a telecommunication signal to the demodulation unit;
the arbitrary waveform generator is respectively connected with the electro-optic modulator and the acousto-optic modulator, and provides two paths of electric signal output, one path of electric signal output is used for outputting a single-frequency rectangular signal to modulate the electro-optic modulator, and the other path of electric signal output is used for outputting a rectangular pulse signal to modulate the acousto-optic modulator.
In the brillouin optical time domain scattering system, the first optical fiber amplifier and the second optical fiber amplifier are erbium-doped optical fiber amplifiers.
In the Brillouin optical time domain scattering system, the frequency shift range of the electro-optical modulator and the acoustic optical modulator is 9GHz-13GHz.
In the brillouin optical time domain scattering system, the mode of calculating the maximum gain frequency offset in the demodulation unit is a frequency sweep method, the frequency shift quantity of a modulator is adjusted, the brillouin signal intensity under each frequency shift quantity value is obtained one by one, and the frequency shift quantity with the maximum intensity is selected as the maximum gain frequency offset.
In the Brillouin optical time domain scattering system, the total length of a sensing optical fiber is 100km, the length of a reference section optical fiber is 100m, and the environment where the reference section optical fiber is located is constant.
The method comprises the following steps of:
Step 51: before the measurement starts, the sensing optical fiber is temporarily connected to the reference section optical fiber, and the maximum gain frequency offset of the reference section optical fiber is obtained;
Step 52: before measurement starts, a sensing optical fiber is connected to obtain Brillouin gain spectrums and reference maximum gain frequency deviation f 0 (t) of the sensing optical fiber and the reference section optical fiber at each position, and the flight time of the light to-and-fro sensing optical fiber is recorded and recorded as reference delay t 0,ref;
Step 53: after the measurement is started, collecting Brillouin signals at each modulation frequency to obtain Brillouin gain spectrums at each position of a sensing optical fiber and a reference section optical fiber, measuring a current maximum gain frequency offset f N (t), setting the current measurement as Nth measurement, and recording the moment when the maximum gain frequency offset f N (t) of the reference section optical fiber appears, namely the flight time of the optical round trip sensing optical fiber at the moment, as a current reference delay t N,ref;
Step 54: correcting by using reference delay, and recording the delay of a certain data point to be measured at present as t N, wherein the delay of corresponding reference data is as follows:
That is, it can be considered that t 0 at the time of reference data acquisition and t N at the time of current measurement correspond to signals of the same length of optical fiber.
Step 55: the measured maximum gain frequency offset f N(tN) and the reference maximum gain frequency offsetSubtracting to obtain the current maximum gain frequency deviation change delta f N(tN), namely
Step 56: the temperature measurement is set to ΔT N (T), the value of the change in the current measured temperature from the reference temperature. Based on the properties of Brillouin scattering, deltaT N＝ΔfN/A, the temperature measurement results DeltaT N (T) of the current optical fiber positions are obtained. Where the proportionality coefficient a is determined by the fiber material and is a constant known prior to measurement.
In the step 51, a step of adjusting an arbitrary waveform generator to apply a modulation signal frequency to the electro-optical modulator with a step of 1MHz between 9 GHz and 13GHz, where the signal frequency is a frequency offset of the probe light relative to the pump light, collecting brillouin signals at each modulation frequency one by one, obtaining brillouin gain spectra of each position of the reference section optical fiber, and taking a maximum point of the gain as f (t) to be used as a maximum gain frequency offset of the reference section optical fiber.
In the step 52, before the measurement starts, a random waveform generator is adjusted to apply a modulation signal frequency to the electro-optical modulator at a step length of 1MHz between 9 GHz and 13GHz, the signal frequency is a frequency offset of the probe light relative to the pump light, brillouin signals at each modulation frequency are collected one by one, a brillouin gain spectrum and a reference maximum gain frequency offset f 0 (t) of each position of the sensing optical fiber and the reference section optical fiber are obtained, and the flight time of the light to and from the sensing optical fiber is recorded as a reference delay t 0,ref.
In the step 55, if the reference data is time domain sampled discretely, the reference data corresponds to no sampling pointDelay, selecting two or more data points nearest to each other before and after the moment, and obtaining the maximum gain frequency offset of the two nearest points approximately by using a linear interpolation method through an interpolation method
Based on the technical scheme, the long-distance Brillouin optical time domain analysis distributed optical fiber sensing system has the following technical advantages compared with the prior art:
1. The Brillouin optical time domain scattering system based on optical flight time has the advantages that the calibration function is added, and meanwhile, the extra hardware of the system is minimized, so that the system is ensured to remarkably improve the performance at controllable cost, and good competitiveness is maintained.
2. The self-calibration method of the Brillouin optical time domain scattering system based on the optical flight time continuously corrects the problem of inconsistent time delay between the measurement data and the reference data by using a calibration means, so that the reading error and the reading drift after long-term working of the BOTDA system are effectively reduced, and the self-calibration method has important significance for the long-term working stability of the long-distance BOTDA sensing system.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a brillouin optical time domain scattering system according to the present invention.
Fig. 2 is a flow chart of a self-calibration method of the brillouin optical time domain scattering system.
The reference numerals in the figures are:
31-laser light source, 32-first coupler, 33-electro-optic modulator, 35-acousto-optic modulator, 34-first optical fiber amplifier, 36-second optical fiber amplifier, 37-arbitrary waveform generator, 38-sensing optical fiber, 39-second coupler, 40-photoelectric detection unit, 42-demodulation unit, 41-reference section optical fiber, 201-sensing optical fiber first port, 202-sensing optical fiber second port;
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without any inventive effort, are intended to be within the scope of the invention.
Fig. 1 is a schematic structural diagram of a brillouin optical time domain scattering system according to the present invention. As shown in fig. 1, the present invention is a brillouin optical time domain scattering system, which comprises a laser light source 31, a first coupler 32, an electro-optical modulator 33, an acousto-optic modulator 35, a first optical fiber amplifier 34, a second optical fiber amplifier 36, an arbitrary waveform generator 37, a sensing optical fiber 38, a second coupler 39, a photoelectric detection unit 40, a demodulation unit 42 and a reference section optical fiber 41, wherein the sensing optical fiber 38 comprises a sensing optical fiber first port 201 and a sensing optical fiber second port 202, and the reference section optical fiber 41 is arranged between the first optical fiber amplifier 34 and the sensing optical fiber first port 201.
The laser light source 31 emits laser to the first coupler 32 to split the laser into probe light and pump light, the pump light is modulated into pulse pump light by the acousto-optic modulator 35, the pulse pump light is amplified by the second optical fiber amplifier 36 and then transmitted to the second coupler 39, the pulse pump light passing through the second coupler 39 enters the sensing optical fiber 38 through the sensing optical fiber first port 201, and the pulse pump light propagates to the sensing optical fiber second port 202 in the sensing optical fiber 38.
The above-mentioned detection light is frequency-shifted by the electro-optical modulator 33 and modulated into continuous detection light, the continuous detection light is injected into the reference section optical fiber 41 by the first optical fiber amplifier 34, the continuous detection light passing through the reference section optical fiber 41 reaches the second port 202 of the sensing optical fiber and then enters the sensing optical fiber 38, the continuous detection light propagates in the sensing optical fiber 38 to the first port 201 of the sensing optical fiber, the continuous detection light emitted from the first port 201 of the sensing optical fiber enters the incident end of the second coupler 39, the second coupler 39 outputs the separated continuous detection light to the photoelectric detection unit 40, and the photoelectric detection unit 40 outputs a telecommunication signal to the demodulation unit 42.
The arbitrary waveform generator 37 is connected to the electro-optical modulator 33 and the acousto-optic modulator 35, and the arbitrary waveform generator 37 provides two paths of electrical signal outputs, one path outputs a single-frequency rectangular signal to modulate the electro-optical modulator 33, and the other path outputs a rectangular pulse signal to modulate the acousto-optic modulator 35.
Compared with a typical BOTDA system, the system of the invention has the added hardware that a section of the reference section optical fiber with fixed environment is added before the injection of the detection light so as to receive the pulse pump light which propagates the whole section of the optical fiber to be detected. The system is calibrated in such a way that light propagates back and forth for the flight time of the whole length of optical fiber to be measured and the reference section of optical fiber. A reference section of optical fiber 41 is added before the continuous probe light is injected into the fiber under test, and the characteristic response of the section of optical fiber is used for calibrating the flight time of the pulsed probe light.
In the hardware composition of the system of the invention: the laser light source 31 provides continuous signal light, the second coupler 32 splits the light of the fourth laser light source 31 into upper detection light and lower pump light, the electro-optical modulator 33 shifts the frequency of the detection light by a certain value between 9 and 13GHz, and the first optical fiber amplifier 34 amplifies the frequency-shifted detection light; the acousto-optic modulator 35 generates pulse pumping light with the pulse width of 20-100ns, the second optical fiber amplifier 36 amplifies the pulse pumping light, the arbitrary waveform generator 37 provides two paths of electric signal output, the upper path is a single-frequency sine signal, the electro-optic modulator is modulated, the lower path is a rectangular pulse signal, the acousto-optic modulator is modulated, and the rectangular pulse repetition period is determined by a user according to the application scene.
The sensing optical fiber 38 has a total length of 100km and is provided with a sensing optical fiber first port 201 and a sensing optical fiber second port 202, wherein pulse pump light enters from the sensing optical fiber first port 201, continuous probe light enters from the sensing optical fiber second port 202, and the pulse pump light and the continuous probe light interact in transmission to generate a brillouin signal; the second coupler 39 couples the pulsed pump light into the sensing fiber first port 201 while separating the probe light exiting the sensing fiber first port 201 from the brillouin signal. The photodetection unit 40 outputs an electric signal whose voltage is proportional to the intensity of the detected light; the length of the reference section of optical fiber 41 is 100m, the environment is constant, the optical path is between the first optical fiber amplifier 34 and the first port 201 of the sensing optical fiber to be measured, and the characteristic brillouin signal is provided to calculate the light flight time of the current whole section of sensing optical fiber 38 to be measured. The demodulation unit 42 separates the voltage corresponding to the brillouin signal from the output of the photoelectric detection unit 40, analyzes and obtains the maximum gain frequency offset under each delay, measures the delay of the brillouin signal of the reference section, carries out delay self-correction, calculates the change of the maximum gain frequency offset, and finally obtains the temperature information of each position of the optical fiber.
When in measurement, the time of pumping pulse light injected into the first sensing optical fiber is taken as zero point, signal acquisition delay is defined, the delay can be divided into a direct current component of a unit length delay variation mean value and an alternating current component of delay variation fluctuation up and down on the mean value, the direct current component is calculated, the delay of each point of the current measurement is corrected, and the error of calculating the maximum gain frequency offset is minimized.
The general steps of measurement and signal calibration in this embodiment are shown in fig. 2. Wherein the "temperature measurement result" shows the difference between the temperature of each point of the optical fiber at the current measurement and the temperature at the reference measurement.
Step 51: the sensing fiber 38 is temporarily not accessed, and instead, a connecting wire with negligible length is accessed at both ports, i.e. the fiber to be measured has only the reference section fiber 41. And adjusting an arbitrary waveform generator to apply modulation signal frequency between 9 GHz and 13GHz to the electro-optical modulator by using a step length of 1MHz, wherein the signal frequency is the frequency offset of the probe light relative to the pumping light, collecting Brillouin signals at each modulation frequency one by one to obtain Brillouin gain spectrums at each position of the reference section optical fiber, and taking the maximum point of the gain as f (t) to be used as the maximum gain frequency offset of the reference section optical fiber. The reference section optical fiber 41 is in the BOTDA detection host or in a fixed environment where the detection host is located, and its brillouin maximum gain frequency offset does not change with time.
Step 52: the connecting wire of the previous step is removed and the sensing fiber 38 is accessed. Before the formal measurement starts, the brillouin gain spectrum and the reference maximum gain frequency offset f 0 (t) of each position of the sensing optical fiber and the reference section optical fiber are obtained in the same method as in step 51, and obviously, f 0 (t) should be terminated with the reference section optical fiber maximum gain frequency offset. The time when the maximum gain frequency offset of the reference section optical fiber appears at f 0 (t) is calculated, namely the flight time of the light to and from the sensing optical fiber 38 at the time is recorded as a reference delay t 0,ref. One calculation method is to correlate the reference segment fiber maximum gain frequency offset of step 51 with f 0 (t).
Step 53: after the measurement is started, adjusting the frequency of a modulation signal (namely, the frequency offset of the probe light relative to the pump light) applied to the electro-optical modulator 33 by the random waveform generator 37 in a step length of 1MHz between 9 GHz and 13GHz, collecting Brillouin signals at each modulation frequency one by one to obtain the Brillouin gain spectrums of each position of the sensing optical fiber and the reference section optical fiber, measuring the current maximum gain frequency offset f N (t), setting the current measurement as the Nth measurement, and calculating the reference delay t N,ref of the current measurement when the maximum gain frequency offset f N (t) of the reference section optical fiber appears, namely, the flight time of the optical round trip sensing optical fiber at the moment, similar to the step 52;
Step 54: correcting by using reference delay, and recording the delay of a certain data point to be measured at present as t N, wherein the delay of corresponding reference data is as follows:
Considering t 0 during reference data acquisition and t N during current measurement to correspond to signals of the same section of optical fiber;
Step 55: the measured maximum gain frequency offset f N(tN) and the reference maximum gain frequency offset Subtracting to obtain the current maximum gain frequency deviation change delta f N(tN), namelyIf the time domain sampling of the reference data is discrete, the reference data corresponds to no sampling pointDelay, selecting two or more data points nearest to each other before and after the moment, and obtaining the maximum gain frequency offset of the two nearest points approximately by using a linear interpolation method through an interpolation method
Step 56: the temperature measurement is set to ΔT N (T), the value of the change in the current measured temperature from the reference temperature. Based on the properties of Brillouin scattering, deltaT N＝ΔfN/A, the temperature measurement results DeltaT N (T) of the current optical fiber positions are obtained. Where the proportionality coefficient a is determined by the fiber material and is a constant known prior to measurement.
While the present invention has been described in detail and with reference to the embodiments thereof, it will be understood by those skilled in the art that modifications and improvements can be made based on the disclosure without departing from the spirit and scope of the invention.
Claims (7)
1. The self-calibration method of the Brillouin optical time domain scattering system is characterized in that the Brillouin optical time domain scattering system comprises a laser light source (31), a first coupler (32), an electro-optical modulator (33), an acousto-optic modulator (35), a first optical fiber amplifier (34), a second optical fiber amplifier (36), an arbitrary waveform generator (37), a sensing optical fiber (38), a second coupler (39), a photoelectric detection unit (40), a demodulation unit (42) and a reference section optical fiber (41), wherein the sensing optical fiber (38) comprises a sensing optical fiber first port (201) and a sensing optical fiber second port (202), and a reference section optical fiber (41) is arranged between the first optical fiber amplifier (34) and the sensing optical fiber first port (201);
The laser light source (31) emits laser to the first coupler (32) to be split into detection light and pump light, the pump light is modulated into pulse pump light through the acousto-optic modulator (35), the pulse pump light is amplified through the second optical fiber amplifier (36) and then transmitted to the second coupler (39), the pulse pump light passing through the second coupler (39) enters the sensing optical fiber (38) through the first port (201) of the sensing optical fiber, and the pulse pump light propagates to the second port (202) of the sensing optical fiber in the sensing optical fiber (38);
The detection light is modulated into continuous detection light after frequency shift through an electro-optical modulator (33), the continuous detection light is injected into the reference section optical fiber (41) through a first optical fiber amplifier (34), the continuous detection light passing through the reference section optical fiber (41) reaches a sensing optical fiber second port (202) and then enters the sensing optical fiber (38), the continuous detection light propagates to a sensing optical fiber first port (201) in the sensing optical fiber (38), the continuous detection light emitted by the sensing optical fiber first port (201) enters an incident end of the second coupler (39), the second coupler (39) outputs the separated continuous detection light to the photoelectric detection unit (40), and the photoelectric detection unit (40) outputs a telecommunication signal to the demodulation unit (42);
The arbitrary waveform generator (37) is respectively connected with the electro-optic modulator (33) and the acousto-optic modulator (35), the arbitrary waveform generator (37) provides two paths of electric signal output, one path outputs a single-frequency rectangular signal to modulate the electro-optic modulator (33), the other path outputs a rectangular pulse signal to modulate the acousto-optic modulator (35), the method obtains the maximum gain frequency offset under each delay through analysis by setting a reference section optical fiber (41), and measures the reference delay of the Brillouin signal of the reference section optical fiber, carries out delay self-correction, calculates the change of the maximum gain frequency offset to realize self calibration based on the Brillouin optical time domain analysis, and the method comprises the following steps:
Step 51: before the measurement starts, the sensing optical fiber (38) is temporarily not connected and the reference section optical fiber (41) is connected, and the maximum gain frequency offset of the reference section optical fiber (41) is obtained;
Step 52: before measurement starts, a sensing optical fiber (38) is connected to obtain Brillouin gain spectrums and reference maximum gain frequency deviation f 0 (t) of the sensing optical fiber (38) and the reference section optical fiber (41) at all positions, and the flight time of the light to-and-fro sensing optical fiber (38) is recorded and recorded as reference delay t 0ref;
Step 53: after the measurement is started, collecting Brillouin signals at each modulation frequency to obtain Brillouin gain spectrums at each position of a sensing optical fiber (38) and a reference section optical fiber (41), measuring a current maximum gain frequency offset f N (t), setting the current measurement as the Nth measurement, and marking the time when the maximum gain frequency offset f N (t) of the reference section optical fiber (41) appears, namely the flight time of the light to-and-fro sensing optical fiber (38) at the moment, as a current reference delay t N,ref;
Step 54: correcting by using reference delay, and recording the delay of a certain data point to be measured at present as t N, wherein the delay of corresponding reference data is as follows:
Considering t 0 during reference data acquisition and t N during current measurement to correspond to signals of the same section of optical fiber;
Step 55: the measured maximum gain frequency offset f N(tN) and the reference maximum gain frequency offset Subtracting to obtain the current maximum gain frequency deviation change delta f N(tN), namely
Step 56: the temperature measurement result is set as deltat N (T), namely the change value of the current measured temperature compared with the reference temperature, according to the characteristic of brillouin scattering, deltat N＝ΔfN/a, the temperature measurement result deltat N (T) of each position of the current optical fiber is obtained according to the delta T N＝ΔfN/a, wherein the proportionality coefficient a is determined by the optical fiber material and is a constant known before measurement.
2. The self-calibration method of a brillouin optical time domain scattering system according to claim 1, wherein in the step 51, between 9 GHz and 13GHz, a random waveform generator (37) is adjusted to apply a modulation signal frequency to an electro-optical modulator (33) with a step length of 1MHz, the signal frequency is a frequency offset of probe light relative to pump light, brillouin signals at each modulation frequency are collected one by one, a brillouin gain spectrum of each position of a reference section optical fiber (41) is obtained, and a maximum point of gain is recorded as f (t) and is taken as a maximum gain frequency offset of the reference section optical fiber (41).
3. The self-calibration method of a brillouin optical time domain scattering system according to claim 1, wherein in the step 52, before the measurement is started, an arbitrary waveform generator (37) is adjusted to apply a modulation signal frequency to an electro-optical modulator (33) in a step of 1MHz between 9 GHz and 13GHz, the signal frequency is a frequency offset of probe light relative to pump light, brillouin signals at each modulation frequency are collected one by one, a brillouin gain spectrum and a reference maximum gain frequency offset f 0 (t) at each position of a sensing optical fiber (38) and a reference section optical fiber (41) are obtained, and a flight time of light to and from the sensing optical fiber (38) is recorded as a reference delay t 0,ref.
4. The method according to claim 1, wherein in the step 55, if the reference data is time domain sampled discretely, no sampling point corresponds toIn the case of time delay, two or more data points which are nearest to each other before and after the moment are selected, and the data points are obtained by interpolation
5. A method of self-calibrating a brillouin optical time domain scattering system according to claim 1, wherein the first and second optical fibre amplifiers (34, 36) are erbium doped optical fibre amplifiers.
6. The self-calibration method of a brillouin optical time domain scattering system according to claim 1, wherein the frequency shift range of the electro-optical modulator (33) and the acousto-optic modulator (35) is 9GHz-13 GHz.
7. The self-calibration method of a brillouin optical time domain scattering system according to claim 1, wherein the mode of calculating the maximum gain frequency offset in the demodulation unit (42) is a sweep frequency method, the frequency shift amount of the modulator is adjusted, the brillouin signal intensity under each frequency shift amount is obtained one by one, and the frequency shift amount with the maximum intensity is selected as the maximum gain frequency offset.
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| CA3066988A1 (en) * | 2017-05-12 | 2018-11-15 | INDIAN INSTITUTE OF TECHNOLOGY MADRAS (IIT Madras) | System for simultaneous multi-point dynamic parameter measurement in distributed optical sensing, and methods thereof |
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| CA3066988A1 (en) * | 2017-05-12 | 2018-11-15 | INDIAN INSTITUTE OF TECHNOLOGY MADRAS (IIT Madras) | System for simultaneous multi-point dynamic parameter measurement in distributed optical sensing, and methods thereof |
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