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

Abstract

The invention provides an optical time domain reflection system and demodulation method based on gas absorption spectrum frequency compensation, and the system comprises a phi-OTDR system light source, a chirped pulse signal modulation module, a first amplifier, a coupler, a gas chamber, a first detector, a circulator, a to-be-detected optical fiber, a second amplifier, a filter, and a second detector. A continuous laser signal of a phi-OTDR system light source is converted into a chirp modulation pulse signal through a chirp pulse signal modulation module, one path of the chirp modulation pulse signal enters a gas chamber, a first detector obtains a gas absorption spectrum according to a transmission signal of the gas chamber, and the other path of the chirp modulation pulse signal enters a second port through a first port and enters an optical fiber to be detected; an optical fiber Rayleigh scattering signal enters the third port through the second port and then is amplified by the second amplifier; and a scattering signal amplified by the second amplifier is filtered by the filter and then is obtained by the second detector. According to the invention, the technical problem that the existing sweep frequency phi-OTDR system is influenced by the frequency drift of the light source, so that the measurement precision is insufficient can be solved.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to an optical time domain reflection system and a demodulation method based on gas absorption spectrum frequency compensation. Background Art

[0002] Distributed acoustic sensing (DAS) can sense and locate acoustic signals on kilometers of sensing optical fibers. It has the advantages of high sensitivity, high precision and dynamic measurement. In recent years, it has been widely used in structural health detection, vehicle tracking and seismic wave detection. Among various DAS solutions, phase-sensitivity optical time domain reflectometry (PTDR) is the most popular. ) is one of the best measurement solutions. Researchers from various countries have proposed a variety of technologies to improve System performance, where the measured distance is determined by The signal-to-noise ratio of the system determines that long-distance distributed measurement can be achieved through coherent detection, high extinction ratio detection pulses, and Raman signal amplification; The spatial resolution of the system is limited by the pulse width. The linear scanning pulse and matched filtering scheme can achieve centimeter-level high spatial resolution measurement. The measurement time mainly depends on the pulse repetition rate (i.e., the detection distance). The compressed sensing technology of random pulse sampling can break through the Nyquist sampling theorem and 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. Scattering-enhanced optical fiber and various improved algorithms can ensure the demodulation accuracy of the signal. System measurement schemes have also been proposed and applied, including interferometer demodulation, heterodyne coherent detection, frequency sweeping scheme and chirped pulse. The frequency sweeping scheme and chirped pulse scheme use the frequency sweep of optical pulses 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 coherent detection. The demodulation error caused by the phase coherent fading of the system increases.

[0003] The measurement accuracy of the system indicates how close the measurement result is to the true value, which directly reflects the performance of the system. System noise mainly comes from three parts: laser phase noise, laser frequency drift and noise within the detection bandwidth. The laser phase noise is determined by the laser linewidth, the laser wavelength drift is affected by the laser drive control, and the noise within the bandwidth comes from the pulse extinction ratio and the noise of the detector. In 2018, German researchers conducted experiments and found that the measurement deviation caused by 24-hour laser phase drift is 120 nanostrain 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, eliminating System light source jitter requires a high-stability laser as the light source, but such light sources are expensive and have higher requirements on the use environment, limiting Practical application of systems engineering. Summary of the invention

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

[0005] According to one aspect of the present invention, an optical time domain reflectometry system based on gas absorption spectrum frequency compensation is provided, the optical time domain reflectometry system comprising: The system comprises a 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 system light source is converted into a chirp modulated pulse signal by a chirp pulse signal modulation module. The chirp modulated pulse signal is divided into two signals after passing through the first amplifier and the coupler in sequence. One signal enters the gas chamber to generate a transmission signal. The first detector obtains the 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 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 passes through the second amplifier and the filter in sequence. The second detector obtains the Rayleigh interference spectrum according to the filtered scattering signal.

[0006] Furthermore, the chirped pulse signal modulation module includes a signal generator and a semiconductor optical fiber amplifier, and the signal generator is respectively connected to The system light source is connected to the semiconductor fiber amplifier and controlled by the signal generator. The driving current of the system light source and the driving pulse signal for the semiconductor optical fiber amplifier; The continuous laser output of the system light source enters the semiconductor fiber amplifier and is converted into a chirp modulated pulse signal.

[0007] Further, the chirped pulse signal modulation module includes a first electro-optical modulator, a second electro-optical modulator and an arbitrary waveform generator, 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 provides an electrical pulse signal for the second electro-optical modulator; The continuous laser output of the system light source is chirped through the first electro-optic modulator to achieve frequency modulation, and then converted into a chirped modulated pulse signal through the second electro-optic modulator to achieve pulse modulation.

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

[0009] Furthermore, the optical time domain reflectometer system also includes a driver. System light source connection to control The current and temperature of the system's light sources.

[0010] Furthermore, the optical time domain reflectometry system also includes an acquisition card, which is connected to the first detector and the second detector respectively.

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

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

[0013] According to another aspect of the present invention, a demodulation method of an optical time domain reflectometry system based on gas absorption spectrum frequency compensation is provided. The demodulation method of an optical time domain reflectometry system uses the optical time domain reflectometry system based on gas absorption spectrum frequency compensation as described above to realize phase demodulation.

[0014] Furthermore, the demodulation method of the optical time domain reflectometry system based on gas absorption spectrum frequency compensation includes: based on the optical time domain reflectometry system based on gas absorption spectrum frequency compensation as described above, The continuous laser signal of the system light source is modulated into a chirp modulated pulse signal; the chirp modulated pulse signal is divided into two paths and enters the gas chamber and the optical fiber to be tested respectively; the gas absorption spectrum and the Rayleigh interference spectrum are obtained respectively; according to the gas absorption spectrum and the Rayleigh interference spectrum, the The frequency change of the system light source and the frequency change of the optical fiber to be tested; The frequency change of the system light source is subtracted and the demodulation of the optical time domain reflectometer system is completed based on the difference.

[0015] Applying the technical solution of the present invention, an optical time domain reflectometry system and a demodulation method based on gas absorption spectrum frequency compensation are provided. The continuous laser signal of the system light source is converted into a chirp 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 Rayleigh interference spectrum changes of the optical fiber to be tested, avoiding demodulating the frequency jitter of the light source into temperature / strain changes, achieving high-precision and high-sensitivity temperature / strain demodulation, and improving the measurement accuracy of the phase-OTDR system. Compared with the prior art, the technical solution of the present invention can solve the existing frequency scanning in the prior art. The system is affected by the frequency drift of the light source, resulting in insufficient measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 A schematic diagram showing the working principle of a modulation scheme in an optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to a specific embodiment of the present invention is shown;

[0018] Figure 2 A schematic diagram showing the working principle of an external modulation scheme of an optical time domain reflectometry system based on gas absorption spectrum frequency compensation according to a specific embodiment of the present invention is shown;

[0019] Figure 3 A schematic diagram of the principle of frequency-compensated Rayleigh interference spectroscopy based on chirped pulses provided according to a specific embodiment of the present invention is shown;

[0020] Figure 4 The figure shows the Rayleigh interference spectrum of the optical fiber to be tested based on chirped pulse strain demodulation provided according to a specific embodiment of the present invention;

[0021] Figure 5 for Figure 4 A magnified view of the strain position at local A;

[0022] Figure 6 The relative frequency shift obtained by cross-correlation solution according to a specific embodiment of the present invention is shown;

[0023] Figure 7 The gas absorption spectrum provided according to the specific embodiment of the present invention is shown. Schematic diagram of light source frequency drift monitoring. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present invention. Meanwhile, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0027] like Figure 1 and Figure 2 As shown, according to a specific embodiment of the present invention, an optical time domain reflectometry system based on gas absorption spectrum frequency compensation is provided, and the optical time domain reflectometry system includes: The system comprises a 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 system light source is converted into a chirp modulated pulse signal by a chirp pulse signal modulation module. The chirp modulated pulse signal is divided into two signals after passing through the first amplifier and the coupler in sequence. One signal enters the gas chamber to generate a transmission signal. The first detector obtains the gas absorption spectrum according to the transmission signal. The other signal 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 passes through the second amplifier and the filter in sequence. The second detector obtains the Rayleigh interference spectrum according to the filtered scattering signal.

[0028] By using this configuration, an optical time domain reflectometry system based on gas absorption spectrum frequency compensation is provided. The continuous laser signal of the system light source is converted into a chirp 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.

[0029] As a specific embodiment of the present invention, The system light source can use a distributed feedback laser (DFBLaser). When the laser temperature changes or the driving current jitters, it will cause the wavelength of the light source to change. The optical time domain reflection system of the present invention can compensate for the phase change in real time, effectively improving Improve the environmental adaptability of the demodulation system and enhance its engineering usability.

[0030] Furthermore, in the present invention, the chirp modulated pulse signal can be implemented by an internal modulation scheme or an external modulation scheme. The internal modulation scheme controls its driving current by a signal generator, such as Figure 1 The external modulation scheme realizes chirped pulse signal modulation through an arbitrary waveform generator and an electro-optical modulator (EOM), as shown in Figure 2 shown.

[0031] As a specific embodiment of the present invention, Figure 1 As shown in the internal modulation scheme, the chirped pulse signal modulation module includes a signal generator and a semiconductor optical fiber amplifier. The signal generator is respectively connected to The system light source is connected to the semiconductor fiber amplifier and controlled by the signal generator. The driving current of the system light source and the driving pulse signal for the semiconductor optical fiber amplifier; The continuous laser output of the system light source enters the semiconductor fiber amplifier and is converted into a chirped modulated pulse signal. The corresponding relationship 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 achieved by pre-calibrating the voltage curve.

[0032] As another specific embodiment of the present invention, Figure 2 As shown, in the external modulation scheme, the chirped pulse signal modulation module includes a first electro-optical modulator, a second electro-optical modulator and an arbitrary waveform generator, the arbitrary waveform generator is connected to the first electro-optical modulator and the second electro-optical modulator respectively, the arbitrary waveform generator provides a chirped microwave signal for the first electro-optical modulator, and provides an electrical pulse signal for the second electro-optical modulator; The continuous laser output of the system light source is chirped through the first electro-optic modulator to achieve frequency modulation, and then converted into a chirped modulated pulse signal through the second electro-optic modulator to achieve pulse modulation.

[0033] In this embodiment, the arbitrary waveform generator can utilize an internal clock to synchronously output a chirped microwave signal and an electrical pulse signal.

[0034] Furthermore, in the present invention, a 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 be used to adjust the signal amount allocated to the gas absorption spectrum and the Rayleigh interference spectrum of the optical fiber to be measured.

[0035] Furthermore, in the present invention, in order to achieve The system light source laser parameter control, configurable optical time domain reflectometry system also includes a driver, the driver and System light source connection to control The current and temperature of the system's light sources.

[0036] The wavelength selection of the laser is achieved by controlling the current and temperature of the driver, which controls the initial wavelength and power of the laser. Since the absorption wavelength of 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 as 12 C2H2、H 13 CN, 12 CO, 13 CO and combinations thereof, etc. The above gas selections are only some examples listed, but are not limited thereto.

[0037] In the present invention, in order to facilitate signal acquisition, the optical time domain reflectometry system can be configured to further include an acquisition card, which is connected to the first detector and the second detector respectively. The acquisition card can respectively collect and record the electrical signals converted by the first detector and the second detector. As a specific embodiment of the present invention, it can be set to obtain a gas absorption spectrum through the acquisition card channel 1 connected to the first detector, and channel 2 connected to the second detector to obtain a Rayleigh interference spectrum based on a chirped pulse.

[0038] Furthermore, the acquisition card can also be connected to a signal generator or an 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 pulse 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 adopt an adjustable optical filter to filter out the spontaneous radiation 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 reflection 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 change of light source frequency, realize high-precision and high-sensitivity dynamic measurement, improve the performance of the optical time domain reflection 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 reflectometry system of the present invention can achieve high-precision and high-sensitivity temperature / strain measurement, obtain the system light source frequency drift in real time through the gas absorption spectrum, compensate for the Rayleigh interference spectrum change of the optical fiber to be measured, avoid demodulating the light source frequency jitter into temperature / strain changes, and achieve high-precision and high-sensitivity temperature / strain demodulation;

[0045] (2) The optical time domain reflectometry system of the present invention has a high anti-interference capability. The system light source is usually a DFB fiber laser. When the laser temperature changes or the driving current jitters, the wavelength of the light source will change. The present invention can effectively improve the phase by real-time compensation through gas absorption spectrum. The environmental adaptability of the demodulation system enhances its engineering usability. At the same time, the gas absorption spectrum is determined by the energy level of 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.

[0046] According to another aspect of the present invention, a demodulation method of an optical time domain reflectometry system based on gas absorption spectrum frequency compensation is provided. The demodulation method of an optical time domain reflectometry system uses the optical time domain reflectometry system based on gas absorption spectrum frequency compensation as described above to realize phase demodulation.

[0047] Further, in the present invention, the demodulation method of the optical time domain reflectometry system based on gas absorption spectrum frequency compensation includes: based on the optical time domain reflectometry system based on gas absorption spectrum frequency compensation as described above, The continuous laser signal of the system light source is modulated into a chirp modulated pulse signal. The chirp modulated pulse signal is divided into two paths and enters the gas chamber and the optical fiber to be tested respectively to obtain the gas absorption spectrum and the Rayleigh interference spectrum respectively. The frequency change of the system light source and the frequency change of the optical fiber to be tested; The frequency change of the system light source is subtracted and the demodulation of the optical time domain reflectometer system is completed based on the difference.

[0048] As a specific embodiment of the present invention, the gas absorption spectrum and the Rayleigh interference spectrum can be respectively obtained by using a cross-correlation algorithm. The frequency change of the system light source and the frequency change of the optical fiber under test.

[0049] The demodulation method of 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 changes, synchronous correction The measurement results of the optical fiber to be tested compensate for the measurement deviation caused by the change of the light source frequency. The system avoids demodulating the light source frequency drift into temperature / strain changes. At the same time, 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 in the figure, the chirped pulse frequency is linearly modulated from v4 to v1, and different frequencies have the same amplitude when entering the optical fiber to be tested. At time t, the pulse light Rayleigh scattering signal E(t) returns from z1 to z3; at time t+Δt, the pulse light Rayleigh scattering signal E(t+Δt) returns from z2 to z4. When Δt is very small, the distance from z1 to z2 and the distance from z3 to z4 can be ignored compared to the distance from z2 to z3, and the scattering signal can be regarded as returning from z2 to z3. However, at time t, the pulse light frequency is v3 to v1, and at time t+Δt, the pulse light frequency is v4 to v2, realizing the scanning of the optical frequency at the same position.

[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 moment t+Δt such that E(t)=E(t+Δt). Therefore, the demodulation formula for strain and temperature is similar to the formula for 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 It includes both the frequency change caused by temperature and strain and the jitter of the light source frequency, which 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 the 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 measure the temperature / strain of the optical fiber to be tested, thus achieving 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 reflectometry 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 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 scheme has strong adaptability and is simple, and can be used in other systems that require light source wavelength drift monitoring.

[0060] In order to further understand 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 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 chirp 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 the second electro-optical modulator to realize pulse modulation.

[0065] The chirp modulated pulse signal is divided into two signals after passing through the first amplifier and the 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 respectively connected to the first detector and the second detector, and the signal generator or the arbitrary waveform generator, 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 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 a demodulation method based on gas absorption spectrum frequency compensation. The continuous laser signal of the system light source is converted into a chirp 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 terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An optical time domain reflectometry system based on gas absorption spectrum frequency compensation, characterized in that: The optical time domain reflectometry system comprises: 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 enters the air chamber and generates a transmission signal. 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 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 passes through the second amplifier and the filter in sequence. The second detector obtains a Rayleigh interference spectrum according to 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, wherein the signal generator is connected to the φ-OTDR system light source and the semiconductor optical fiber amplifier respectively, and 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 provides 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 through the first electro-optical modulator to achieve frequency modulation, and then converted into the chirped modulated pulse signal through the second electro-optical modulator to achieve pulse modulation.

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 4, characterized in that: The optical time domain reflectometry system further includes a driver, which is 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, and the acquisition card 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 of 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 as described in any one of claims 1 to 8 to realize 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 comprises: 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 as described in 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; According to the gas absorption spectrum and the Rayleigh interference spectrum, respectively obtain the frequency change of the light source of the φ-OTDR system and the frequency change of the optical fiber to be tested; 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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