Optical time domain reflectometry system based on frequency compensation of gas absorption spectrum and demodulation method

Abstract

The present invention provides an optical time domain reflectometry system and demodulation method based on gas absorption spectrum frequency compensation. The optical time domain reflectometry system includes: a φ-OTDR system light source, a chirped pulse signal modulation module, a first amplifier, a coupler, a gas chamber, a first detector, a circulator, an optical fiber to be tested, a second amplifier, a filter, and a second detector. The continuous laser signal of the φ-OTDR system light source is converted into a chirped modulated pulse signal by the chirped pulse signal modulation module. One signal of the chirped modulated pulse signal enters the gas chamber, and the first detector obtains the gas absorption spectrum based on the transmission signal of the gas chamber. The other signal enters the second port through the first port and enters the optical fiber to be tested. The optical fiber Rayleigh scattering signal enters the third port through the second port and is amplified by the second amplifier. The scattered signal amplified by the second amplifier is filtered by the filter and then obtained by the second detector. The present invention can solve the technical problem that the existing frequency-sweeping φ-OTDR system is affected by the frequency drift of the light source, resulting in insufficient measurement accuracy.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, and particularly relates to a light time domain reflection system and a demodulation method based on gas absorption spectrum frequency compensation. BACKGROUND

[0002] Distributed acoustics sensing (DAS) can sense and locate acoustic signals on a sensing optical fiber with a length of several kilometers, and has advantages of high sensitivity, high precision and dynamic measurement. In recent years, it has been widely used in the fields of structure health detection, vehicle tracking and seismic wave detection. Among various DAS schemes, the phase-sensitive optical time domain reflectometry (Phase-sensitivity Optical Time Domain reflectometry, Φ-OTDR) is one of the best measurement schemes. Researchers in various countries have proposed various technologies to improve the performance of the system, wherein the measurement distance is determined by the signal-to-noise ratio of the system, and long-distance distributed measurement can be achieved by means of coherent detection, high-extinction-ratio detection pulse and Raman signal amplification. The spatial resolution of the system is limited by the pulse width, and the scheme of using linear scanning pulse and matched filtering can achieve high spatial resolution measurement of centimeter level. The measurement time mainly depends on the pulse repetition frequency (i.e. the detection distance), and the compressed sensing technology of random pulse sampling can break through the Nyquist sampling theorem to realize high-frequency vibration signal measurement. The measurement accuracy of the system is mainly limited by the system noise and the accuracy of the demodulation algorithm, and the scattering enhanced optical fiber and various improved algorithms can ensure the demodulation accuracy of the signal. At the same time, various measurement schemes of the system have also been proposed and applied, including interferometer demodulation, heterodyne coherent detection, sweep scheme and chirped pulse, etc. The sweep scheme and chirped pulse scheme use frequency scanning of the optical pulse to construct the Rayleigh interference spectrum of the optical fiber to be measured, and determine the temperature / strain by the relative movement of the spectrum, which effectively avoids the demodulation error increase caused by the phase coherent fading of the coherent detection system.

[0003] The measurement accuracy of the system indicates the closeness of the measurement result to the true value, and directly reflects the performance of the system. The phase-sensitive ​​​​​​The system noise mainly comes from three parts, the laser phase noise, the laser frequency drift and the noise within the detection bandwidth, wherein the laser phase noise is determined by the laser line width, the wavelength drift of the laser is affected by the laser drive control, and the noise within the bandwidth comes from the extinction ratio of the pulse and the noise of the detector. In 2018, German researchers gave the measurement deviation caused by 24-hour laser phase drift through experiments, which was 120 nanostress or 13.4 millikelvin (Liehr S, Sven Münzenberger, Krebber K. Wavelength-scanning coherent OTDR for dynamic high strain resolution sensing [J]. Optics Express, 2018, 26(8): 10573). Therefore, it is necessary to eliminate The system light source needs a high-stability laser as the light source, and such light source is high in cost and has higher requirements for the use environment, which limits The system engineering practicability. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art.

[0005] According to an aspect of the present application, there is provided an optical time domain reflection system based on frequency compensation of gas absorption spectrum, comprising: a system light source, a chirp pulse signal modulation module, a first amplifier, a coupler, a gas chamber, a first detector, a circulator, a fiber to be measured, a second amplifier, a filter and a second detector, The continuous laser signal of the system light source is converted into a chirp modulation pulse signal by the chirp pulse signal modulation module, and the chirp modulation pulse signal is divided into two signals after the first amplifier and the coupler in turn. One signal enters the gas chamber to generate a transmission signal, and the first detector obtains a gas absorption spectrum according to the transmission signal. The other signal enters the second port of the circulator through the first port of the circulator, enters the fiber to be measured, and then enters the third port of the circulator through the second port. After the fiber Rayleigh scattering signal, it passes through the second amplifier and the filter in turn, and the second detector obtains a Rayleigh interference spectrum according to the filtered scattering signal.

[0006] Further, the chirp pulse signal modulation module comprises a signal generator and a semiconductor fiber amplifier, and the signal generator is connected with the system light source and the semiconductor fiber amplifier, and the signal generator controls the driving current of the system light source and provides a driving pulse signal for the semiconductor fiber amplifier; The continuous laser output of the system light source enters the semiconductor fiber amplifier to be converted into a chirp modulation pulse signal.

[0007] Further, the chirped pulse signal modulation module comprises a first electro-optical modulator, a second electro-optical modulator and an arbitrary waveform generator, the arbitrary waveform generator is connected with the first electro-optical modulator and the second electro-optical modulator respectively, the arbitrary waveform generator provides the chirped microwave signal for the first electro-optical modulator and provides the electrical pulse signal for the second electro-optical modulator; The continuous laser output of the system light source is subjected to the first electro-optical modulator to realize the chirped frequency modulation, and then is subjected to the second electro-optical modulator to realize the pulse modulation and is converted into the chirped modulation pulse signal.

[0008] Further, the coupler controls 5%-20% of the signal to enter the gas chamber, and the remaining signal enters the first port of the circulator.

[0009] Further, the optical time domain reflection system further comprises a driver, the driver is connected with the system light source to control the current and temperature of the system light source.

[0010] Further, the optical time domain reflection system further comprises an acquisition card, the acquisition card is connected with the first detector and the second detector respectively.

[0011] Further, the acquisition card is connected with the signal generator to realize the synchronization of the light source wavelength scanning, the pulse modulation and the signal acquisition.

[0012] Further, the acquisition card is connected with the arbitrary waveform generator to realize the synchronization of the light source wavelength scanning, the pulse modulation and the signal acquisition.

[0013] According to another aspect of the present application, a demodulation method of the optical time domain reflection system based on the frequency compensation of the gas absorption spectrum is provided, the demodulation method of the optical time domain reflection system based on the frequency compensation of the gas absorption spectrum realizes the phase demodulation by using the optical time domain reflection system based on the frequency compensation of the gas absorption spectrum.

[0014] Further, the demodulation method of the optical time domain reflection system based on the frequency compensation of the gas absorption spectrum comprises: based on the optical time domain reflection system based on the frequency compensation of the gas absorption spectrum, the continuous laser signal of the system light source is modulated into the chirped modulation pulse signal; the chirped modulation pulse signal is divided into two paths and enters the gas chamber and the measured optical fiber respectively; the gas absorption spectrum and the Rayleigh interference spectrum are acquired respectively; the frequency variation of the system light source and the frequency variation of the measured optical fiber are acquired according to the gas absorption spectrum and the Rayleigh interference spectrum respectively; the frequency variation of the measured optical fiber is subtracted from the frequency variation of the system light source, and the demodulation of the optical time domain reflection system is completed according to the difference value.

[0015] ​​The application discloses a gas absorption spectrum frequency compensation-based optical time domain reflection system and a demodulation method The continuous laser signal of the system light source is converted into a chirp modulation pulse signal and is divided into two paths, one path obtains a gas absorption spectrum through a gas chamber, and the other path obtains a Rayleigh interference spectrum through a to-be-measured optical fiber, the gas absorption spectrum is used for compensating the Rayleigh interference spectrum variation of the to-be-measured optical fiber, the frequency jitter of the light source is avoided to be demodulated into temperature / strain variation, high-precision and high-sensitivity temperature / strain demodulation is realized, and the measurement precision of the phase-OTDR system is improved. Compared with the prior art, the technical scheme of the application can solve the technical problem of insufficient measurement precision of the prior art frequency-sweeping system caused by the influence of the light source frequency drift. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings included to provide a further understanding of the embodiments of the application and constitute a part of the specification, illustrate the embodiments of the application and together with the text description serve to explain the principles of the application. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0017] Figure 1 A working principle schematic diagram of an inner modulation scheme of a gas absorption spectrum frequency compensation-based optical time domain reflection system according to a specific embodiment of the application is shown;

[0018] Figure 2 A working principle schematic diagram of an outer modulation scheme of a gas absorption spectrum frequency compensation-based optical time domain reflection system according to a specific embodiment of the application is shown;

[0019] Figure 3 A principle schematic diagram of a chirp pulse-based frequency compensation Rayleigh interference spectrum according to a specific embodiment of the application is shown;

[0020] Figure 4 A to-be-measured optical fiber Rayleigh interference spectrum based on chirp pulse strain demodulation according to a specific embodiment of the application is shown;

[0021] Figure 5 A strain position enlarged view of a part A of Figure 4 ;

[0022] Figure 6 A relative frequency shift obtained by cross-correlation according to a specific embodiment of the application is shown;

[0023] Figure 7 A gas absorption spectrum-based frequency compensation Rayleigh interference spectrum according to a specific embodiment of the application is shown; Light source frequency drift monitoring schematic diagram. DETAILED DESCRIPTION

[0024] It should be noted that the embodiments and features of the embodiments in the present application can be combined with each other in the case of no conflict. The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0025] It should be noted that the terms used herein are only intended to describe specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form, unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a reference to the presence of a feature, step, operation, device, component and / or combinations thereof.

[0026] Unless specifically stated otherwise, the relative arrangements of the components and steps illustrated in these embodiments and the numerical expressions and values are not limiting to the scope of the present application. It should be understood that the dimensions of the various parts shown in the drawings are not necessarily to scale. The techniques, methods, and devices known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered as part of the specification, if appropriate. In all examples shown and discussed herein, any specific value should be interpreted as merely an example, and not as a limitation. Therefore, other examples of the exemplary embodiments can have different values. It should be noted that similar reference numbers and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0027] As shown in Figure 1 and Figure 2 According to a specific embodiment of the present application, a gas absorption spectrum frequency compensation based optical time domain reflection system is provided, which comprises: a system light source, a chirp pulse signal modulation module, a first amplifier, a coupler, a gas chamber, a first detector, a circulator, a fiber to be measured, a second amplifier, a filter and a second detector, The continuous laser signal of the system light source is converted into a chirp modulation pulse signal by a chirp pulse signal modulation module, the chirp modulation pulse signal is divided into two signals after passing through a first amplifier and a coupler in sequence, one of the two signals generates a transmission signal after entering a gas chamber, and a first detector obtains a gas absorption spectrum according to the transmission signal, and the other signal enters a second port of the circulator through a first port of the circulator, enters the optical fiber, and then the Rayleigh scattering signal of the optical fiber enters a third port of the circulator through the second port of the circulator, and then passes through a second amplifier and a filter in sequence, and a second detector obtains a Rayleigh interference spectrum according to the filtered scattering signal.

[0028] By using the configuration mode, an optical time domain reflection system based on frequency compensation of gas absorption spectrum is provided, the optical time domain reflection system The continuous laser signal of the system light source is converted into a chirp modulation pulse signal, and then divided into two signals, one of the two signals obtains a gas absorption spectrum through a gas chamber, and the other signal obtains a Rayleigh interference spectrum through a measured optical fiber, the gas absorption spectrum is used to compensate the change of the Rayleigh interference spectrum of the measured optical fiber, the frequency jitter of the light source is demodulated into a temperature / strain change, high-precision and high-sensitivity temperature / strain demodulation is realized, and the measurement precision of the phase-OTDR system is improved.

[0029] As a specific embodiment of the present application, The system light source can use a distributed feedback laser (DFB laser). When the temperature of the laser changes or the driving current jitters, the wavelength of the light source will change, and the optical time domain reflection system of the present application can compensate the phase change in real time, effectively improve The demodulation system environment adaptability and enhance its engineering usability.

[0030] Further, in the present application, the chirp modulation pulse signal can be realized by an internal modulation scheme or an external modulation scheme, the internal modulation scheme controls the driving current by a signal generator, as shown in Figure 1 The external modulation scheme realizes the chirp pulse signal modulation by an arbitrary waveform generator and an electro-optic modulator (EOM), as shown in Figure 2 .

[0031] As a specific embodiment of the present application, as shown in Figure 1 In the internal modulation scheme, the chirp pulse signal modulation module includes a signal generator and a semiconductor fiber amplifier, the signal generator is connected with The system light source and the semiconductor fiber amplifier, the signal generator controls The driving current of the system light source, and provides a driving pulse signal for the semiconductor fiber amplifier; The continuous laser output of the system light source is converted into a chirped modulation pulse signal in the semiconductor fiber amplifier. The correspondence between the modulation current and the wavelength can be obtained by testing and calibrating the current-wavelength curve in advance, and the linear scanning of the laser can be realized by pre-calibrating the voltage curve.

[0032] As another specific embodiment of the present application, as shown in Figure 2 the external modulation scheme, the chirped pulse signal modulation module includes a first electro-optic modulator, a second electro-optic modulator, and an arbitrary waveform generator, the arbitrary waveform generator is connected with the first electro-optic modulator and the second electro-optic modulator respectively, the arbitrary waveform generator provides a chirped microwave signal for the first electro-optic modulator and an electrical pulse signal for the second electro-optic modulator; The continuous laser output of the system light source is converted into a chirped modulation pulse signal in the semiconductor fiber amplifier. The correspondence between the modulation current and the wavelength can be obtained by testing and calibrating the current-wavelength curve in advance, and the linear scanning of the laser can be realized by pre-calibrating the voltage curve.

[0033] In this embodiment, the arbitrary waveform generator can synchronize the output of the chirped microwave signal and the electrical pulse signal with the internal clock.

[0034] Further, in the present application, the coupler can be configured to control 1%-20% of the signal to enter the gas chamber, and the remaining signal to enter the first port of the circulator. The coupler can adjust the amount of signal allocated for the gas absorption spectrum and the Rayleigh interference spectrum of the fiber to be measured.

[0035] Further, in the present application, in order to realize the control of the laser parameters of the system light source, the configurable optical time domain reflection system further includes a driver, the driver is connected with the system light source to control the current and temperature of the system light source.

[0036] The wavelength selection of the laser is realized by controlling the current and temperature of the driver, and the driver controls the initial wavelength and power of the laser. Since the gas absorption spectrum is related to the energy level of the gas molecules, the initial wavelength of the laser should be near the gas absorption peak. The gas in the gas chamber can be selected from 12 C2H2, H 13 CN, 12 CO, 13 CO and combinations thereof. The above-mentioned gases are only some examples, but are not limited thereto.

[0037] In the present invention, to facilitate signal acquisition, the optical time-domain reflectometry system can be configured to also include an acquisition card, which is connected to the first and second detectors. The acquisition card can collect and record the electrical signals converted by the first and second detectors, respectively. As a specific embodiment of the present invention, channel 1 of the acquisition card can be connected to the first detector to obtain a gas absorption spectrum, while channel 2 can be connected to the second detector to obtain a Rayleigh interferometer spectrum based on chirped pulses.

[0038] Furthermore, the acquisition card can also be connected to a signal generator or arbitrary waveform generator to achieve synchronization of light source wavelength scanning, pulse modulation and signal acquisition.

[0039] As a specific embodiment of the present invention, both the first amplifier and the second amplifier can be erbium-doped fiber amplifiers. The first amplifier amplifies the peak power of the pulsed light to the order of hundreds of milliwatts, and the second amplifier amplifies the scattered signal to the order of microwatts.

[0040] Furthermore, the filter may be a tunable optical filter to filter out the spontaneous emission noise signal.

[0041] In the present invention, the key parameters of the optical time domain reflectometry system based on gas absorption spectrum frequency compensation include spatial resolution, measurement distance and measurement time, etc. The pulse width determines The spatial resolution of the system; the time interval between pulses determines the measurement distance of the system; the time interval between pulses determines the measurement time of the system. The system is similar, and the reference Rayleigh interference spectrum can be obtained by pre-frequency shifting to simulate temperature and strain changes, thereby improving its dynamic measurement range and demodulation accuracy. The frequency compensation scheme based on gas absorption spectroscopy is also applicable to frequency scanning. The demodulation system uses frequency scanning between pulses to achieve the measurement of gas absorption spectrum and Rayleigh interference spectrum.

[0042] The optical time domain reflectometry system based on gas absorption spectrum frequency compensation of the present invention utilizes gas absorption spectrum to measure in real time System light source frequency drift, synchronous correction The measurement results compensate for the measurement deviation caused by the frequency change of the light source, achieve high-precision and high-sensitivity dynamic measurement, improve the performance of the optical time domain reflectometry system and enhance its engineering adaptability.

[0043] Compared with the existing sweep frequency The optical time domain reflectometry system of the present invention has the following advantages:

[0044] (1) The optical time domain reflection system of the present application can realize high-precision and high-sensitivity temperature / strain measurement, and the frequency drift amount of the system light source is obtained in real time through gas absorption spectrum, the Rayleigh interference spectrum change of the measured optical fiber is compensated, and the frequency jitter of the light source is avoided to be demodulated as the temperature / strain change amount, thereby realizing high-precision and high-sensitivity temperature / strain demodulation.

[0045] (2) The optical time domain reflection system of the present application has high anti-interference ability, The system light source is usually a DFB fiber laser, when the temperature of the laser changes or the driving current jitters, the wavelength of the light source will change, the present application can effectively improve The environmental adaptability of the demodulation system, and enhance its engineering usability, at the same time, the gas absorption spectrum is determined by the energy level of the gas molecules, so when the gas composition and concentration are determined, the absorption spectrum pattern is not affected by the external environment, compared with other phase reference schemes, it has better anti-interference ability.

[0046] According to another aspect of the present application, a demodulation method of an optical time domain reflection system based on gas absorption spectrum frequency compensation is provided, which realizes phase demodulation by using the optical time domain reflection system based on gas absorption spectrum frequency compensation as described above.

[0047] Further, in the present application, the demodulation method of the optical time domain reflection system based on gas absorption spectrum frequency compensation comprises: The continuous laser signal of the system light source is modulated into a chirp modulation pulse signal, the chirp modulation pulse signal is divided into two paths and enters the gas chamber and the measured optical fiber respectively, and the gas absorption spectrum and the Rayleigh interference spectrum are obtained respectively; the frequency change of the system light source and the frequency change of the measured optical fiber are obtained according to the gas absorption spectrum and the Rayleigh interference spectrum respectively; The frequency change of the measured optical fiber is subtracted from The frequency change of the system light source, and the demodulation of the optical time domain reflection system is completed according to the difference value.

[0048] As a specific embodiment of the present application, the cross-correlation algorithm can be used to obtain The frequency change of the system light source and the frequency change of the measured optical fiber according to the gas absorption spectrum and the Rayleigh interference spectrum.

[0049] The demodulation method of the optical time domain reflection system based on gas absorption spectrum frequency compensation of the present application uses the gas absorption spectrum to measure The frequency change of the system light source in real time, synchronously corrects The measurement result of the measured optical fiber, and compensates the measurement deviation caused by the frequency change of the light source. Compared with the existing The system avoids demodulating the light source frequency drift into temperature / strain changes, and the gas absorption spectrum has ultra-high stability, which improves the system's anti-interference ability. The solution based on the gas absorption spectrum phase compensation of the present invention is also applicable to frequency sweep pulses. Demodulation system.

[0050] The principle of frequency-compensated Rayleigh interferometry spectroscopy based on chirped pulses is as follows: Figure 3 As shown, the chirped pulse frequency is linearly modulated from v4 to v1, and the different frequencies have the same amplitude when entering the fiber under test. At time t, the pulsed light Rayleigh scattered signal E(t) returns from z1 to z3; at time t+Δt, the pulsed light Rayleigh scattered signal E(t+Δt) returns from z2 to z4. When Δt is very small, the distances from z1 to z2 and from z3 to z4 are negligible compared to the distance from z2 to z3, and the scattered signal can be considered to return from z2 to z3. However, at time t, the pulsed light frequency is v3 to v1, and at time t+Δt, the pulsed light frequency is v4 to v2, achieving a sweep of the optical frequency at the same location.

[0051] At this time, when the external environment remains unchanged, E(t)≠E(t+Δt); however, when the external environment causes the optical phase to change, there is a certain moment t+Δt such that E(t)=E(t+Δt). Therefore, the demodulation formula for strain and temperature is similar to that of the frequency sweep scheme. The frequency change is restored by using the temporal translation of the interference pattern, and the corresponding strain and temperature changes are obtained respectively. and Among them, δv is the chirp frequency variation range; τ p is the chirp period, δv / τ p is the chirp frequency change rate; Δt is the temporal translation of the interference pattern; Δv is the frequency change equivalent to the spectral shift; v0 is the initial frequency of the laser; Δε is the strain change; and ΔT is the temperature change.

[0052] Obtain Rayleigh interferometry spectra in the time and space domains such as Figure 4 and Figure 5 As shown, according to Figure 5 It can be seen that strain / temperature causes the signal to move in the time domain / space domain, that is, in the frequency domain. Using the chirp frequency slope (frequency variation range / chirp pulse width) and the system sampling rate, the signal movement Δv in frequency is obtained through cross-correlation operation. m , compensate for the frequency change caused by strain change Δε and temperature change ΔT, and restore the Rayleigh interference spectrum, where the relative movement of the Rayleigh interference spectrum can determine the frequency shift amount through the cross-correlation algorithm.

[0053]

[0054] Among them, K ε is the strain coefficient; K Tis the temperature coefficient.

[0055] The change in light frequency Δv m The frequency change caused by temperature and strain, as well as the jitter of the light source frequency, causes system measurement errors. The optical time domain reflectometry analysis based on gas absorption spectrum frequency compensation of the present invention is used to obtain the frequency change Δv caused by temperature / strain and light source jitter using the Rayleigh interference spectrum of the optical fiber to be measured. m ,like Figure 6 As shown; the frequency change Δv caused by the light source jitter is demodulated by the gas absorption spectrum, as shown Figure 7 As shown. The difference between the two is Δv m -Δv, real-time compensation eliminates the influence of light source frequency jitter, and realizes high-precision temperature / strain measurement of phase-OTDR system.

[0056] The present invention is The high-sensitivity measurement system provides a high-precision demodulation solution, using the gas absorption spectrum to compensate for light source frequency drift in real time, with the following advantages:

[0057] (1) The system can achieve high-precision demodulation of temperature strain and obtain the frequency drift of the light source in real time through gas absorption spectrum frequency measurement, thus avoiding the traditional The influence of light source drift during long-term operation can be compensated to achieve high-precision and high-sensitivity measurement.

[0058] (2) It has high anti-interference ability, can obtain the frequency drift of the light source in real time, and has strong robustness. The optical time domain reflection system based on gas absorption spectrum frequency compensation can avoid the influence of the wavelength fluctuation of the system light source, so it has high engineering practicality. At the same time, the gas absorption spectrum is determined by the energy level of the gas molecules. Therefore, when the gas composition and concentration are determined, its absorption spectrum is not affected by the external environment. Compared with other phase reference schemes, it has better anti-interference ability.

[0059] (3) This solution has strong adaptability and is simple, and can be used in other systems that require light source wavelength drift monitoring.

[0060] In order to have a further understanding of the present invention, the following Figures 1 to 7 The demodulation method of the optical time domain reflectometry system based on gas absorption spectrum frequency compensation of the present invention is described in detail. The following embodiments take acetylene gas in the gas chamber as an example.

[0061] The demodulation method of the optical time domain reflectometry system based on gas absorption spectrum frequency compensation of the present invention adopts the following method: Figure 1 or Figure 2 The optical time domain reflectometry system shown implements the demodulation.

[0062] The driver controls the current and temperature of the distributed feedback laser and adjusts the initial wavelength and power of the continuous laser. The initial wavelength of the laser is near the main absorption peak of acetylene gas at 1529.62nm or other main peak positions.

[0063] When using Figure 1 In the internal modulation scheme shown, the signal generator controls the driving current of the distributed feedback laser and provides a driving pulse signal for the semiconductor fiber amplifier. The continuous laser output of the distributed feedback laser enters the semiconductor fiber amplifier and is converted into a chirped modulated pulse signal.

[0064] When using Figure 2 In the external modulation scheme shown, the arbitrary waveform generator provides a chirped microwave signal to the first electro-optical modulator and an electrical pulse signal to the second electro-optical modulator; the continuous laser output of the distributed feedback laser is chirped frequency modulated by the first electro-optical modulator, and then converted into a chirped modulated pulse signal by pulse modulation by the second electro-optical modulator.

[0065] The chirp-modulated pulse signal is divided into two signals after passing through the first amplifier and coupler in sequence. One signal, 10%, enters the gas chamber, and the first detector obtains the gas absorption spectrum. The other signal, 90%, enters the second port through the first port of the circulator and enters the optical fiber to be tested. The optical fiber Rayleigh scattering signal enters the third port through the second port of the circulator, and then passes through the second amplifier and filter, and the Rayleigh interference spectrum is obtained by the second detector.

[0066] The acquisition card is connected to the first detector, the second detector, and the signal generator or the arbitrary waveform generator respectively, so as to realize the synchronization of light source wavelength scanning, pulse modulation and signal acquisition.

[0067] The frequency change Δv of the distributed feedback laser and the frequency change Δv of the optical fiber to be tested are obtained respectively by using the cross-correlation algorithm based on the gas absorption spectrum and the Rayleigh interference spectrum. m , the difference between the two is Δv m -Δv, real-time compensation eliminates the influence of light source frequency jitter, and realizes high-precision temperature / strain measurement of phase-OTDR system.

[0068] In summary, the present invention provides an optical time domain reflectometry system and demodulation method based on gas absorption spectrum frequency compensation. The continuous laser signal of the system light source is converted into a chirped modulated pulse signal and then divided into two paths. One path obtains the gas absorption spectrum through the gas chamber, and the other path obtains the Rayleigh interference spectrum through the optical fiber to be tested. The gas absorption spectrum is used to compensate for the changes in the Rayleigh interference spectrum of the optical fiber to be tested, avoiding the demodulation of the light source frequency jitter into temperature / strain changes, achieving high-precision and high-sensitivity temperature / strain demodulation, and improving the measurement accuracy of the phase-OTDR system.

[0069] In addition, it should be noted that the use of the terms "first", "second" and the like does not denote any order, quantity, combination or the like, but is merely intended to distinguish between different parts, and therefore cannot be understood as limiting the scope of protection of the present application.

[0070] The preferred embodiments of the present application have been described above with the purpose of illustrating the principles of the present application, and should not be construed in a limiting sense. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. An optical time domain reflectometry system based on gas absorption spectrum frequency compensation, characterized in that: The optical time domain reflectometer system includes: a φ-OTDR system light source, a chirped pulse signal modulation module, a first amplifier, a coupler, an air chamber, a first detector, a circulator, an optical fiber to be tested, a second amplifier, a filter, and a second detector. The continuous laser signal of the φ-OTDR system light source is converted into a chirped modulated pulse signal by the chirped pulse signal modulation module. The chirped modulated pulse signal is divided into two signals after passing through the first amplifier and the coupler in sequence. One signal generates a transmission signal after entering the air chamber. The first detector obtains a gas absorption spectrum based on the transmission signal. The other signal enters the second port of the circulator through the first port of the circulator and enters the optical fiber to be tested. The optical fiber Rayleigh scattering signal enters the third port of the circulator through the second port and then passes through the second amplifier and the filter in sequence. The second detector obtains a Rayleigh interference spectrum based on the filtered scattering signal.

2. The optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to claim 1, characterized in that: The chirped pulse signal modulation module includes a signal generator and a semiconductor optical fiber amplifier. The signal generator is connected to the φ-OTDR system light source and the semiconductor optical fiber amplifier respectively. The signal generator controls the driving current of the φ-OTDR system light source and provides a driving pulse signal for the semiconductor optical fiber amplifier. The continuous laser output of the light source of the φ-OTDR system enters the semiconductor optical fiber amplifier and is converted into the chirped modulated pulse signal.

3. The optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to claim 1, characterized in that: The chirped pulse signal modulation module includes a first electro-optical modulator, a second electro-optical modulator and an arbitrary waveform generator, wherein the arbitrary waveform generator is connected to the first electro-optical modulator and the second electro-optical modulator respectively, and the arbitrary waveform generator provides a chirped microwave signal for the first electro-optical modulator and an electrical pulse signal for the second electro-optical modulator; The continuous laser output of the light source of the φ-OTDR system is chirped frequency modulated by the first electro-optical modulator, and then pulse modulated by the second electro-optical modulator to be converted into the chirped modulated pulse signal.

4. The optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to any one of claims 1 to 3, characterized in that: The coupler controls 1%-20% of the signal to enter the gas chamber, and the remaining signal enters the first port of the circulator.

5. The optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to any one of claims 1 to 3, characterized in that: The optical time domain reflectometry system further includes a driver connected to the φ-OTDR system light source to control the current and temperature of the φ-OTDR system light source.

6. The optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to claim 1, characterized in that: The optical time domain reflectometry system further includes an acquisition card, which is connected to the first detector and the second detector respectively.

7. The optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to claim 2, characterized in that: The acquisition card is connected to the signal generator to achieve synchronization of light source wavelength scanning, pulse modulation and signal acquisition.

8. The optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to claim 3, characterized in that: The acquisition card is connected to the arbitrary waveform generator to achieve synchronization of light source wavelength scanning, pulse modulation and signal acquisition.

9. A demodulation method for an optical time domain reflectometry system based on gas absorption spectrum frequency compensation, characterized in that: The demodulation method of the optical time domain reflectometry system uses the optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to any one of claims 1 to 8 to achieve phase demodulation.

10. The demodulation method of the optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to claim 9, characterized in that: The demodulation method of the optical time domain reflectometry system based on gas absorption spectrum frequency compensation includes: Modulating the continuous laser signal of the light source of the φ-OTDR system into a chirped modulated pulse signal based on the optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to any one of claims 1 to 8; The chirp modulated pulse signal is divided into two paths and enters the gas chamber and the optical fiber to be tested respectively, so as to obtain the gas absorption spectrum and the Rayleigh interference spectrum respectively; respectively obtaining frequency changes of the light source of the φ-OTDR system and the frequency changes of the optical fiber to be tested according to the gas absorption spectrum and the Rayleigh interference spectrum; The frequency change of the optical fiber to be tested is subtracted from the frequency change of the light source of the φ-OTDR system, and the demodulation of the optical time domain reflection system is completed according to the difference.

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