Optical time domain reflection system and demodulation method based on narrow-band filter frequency compensation

Abstract

The invention provides an optical time domain reflection system and demodulation method based on narrow-band filter frequency compensation, in the optical time domain reflection system, 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; a chirp modulation pulse signal is divided into two paths of signals after passing through a first amplifier and a coupler in sequence, one path of signal generates a transmission signal after passing through a first narrow-band filter, a first detector obtains a transmission spectrum of the narrow-band filter according to the transmission signal, and the other path of signal enters a second port of the circulator through a first port of the circulator and enters an optical fiber to be detected; an optical fiber Rayleigh scattering signal enters the third port of the circulator through the second port and then sequentially passes through the second amplifier and the second filter, and the second detector obtains a Rayleigh interference spectrum according to the filtered scattering signal. The technical problem that in the prior art, due to the fact that an existing sweep frequency phi-OTDR system is affected by light source frequency drift, 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 narrowband filter frequency compensation. Background Art

[0002] Distributed fiber optic sensing technology uses optical fiber as both a transmission medium and a sensing unit to achieve continuous distributed temperature, strain, and acoustic wave measurements along the fiber. On this basis, the phase-sensitive optical time domain reflectometry system (Phase-sensitivity Optical Time Domain reflectometry, ) has the advantages of high sensitivity, fast response speed and low cost, and has great application value in the fields of civil structure health monitoring and perimeter security. Sensing schemes can be divided into two categories according to the detection method, coherent detection and direct detection. Coherent detection obtains the beat frequency signal of the Rayleigh scattered signal and the local optical signal, and demodulates the measured parameter through phase change. The phase demodulation methods include orthogonal (IQ), Hilbert transform and other phase demodulation methods, which have better signal-to-noise ratio than direct detection. The direct detection scheme directly obtains the interference spectrum of the Rayleigh scattered signal, and can realize phase demodulation based on 3×3 coupler and phase generated carrier, but has high requirements on device consistency and modulator working point respectively. The other type uses the optical frequency scanning method, which uses the optical frequency change to compensate for the phase change caused by temperature / strain, and realizes quantitative measurement of temperature / strain. Compared with the phase demodulation scheme, the frequency scanning scheme can avoid the influence of phase coherence attenuation to a limited extent, and realize distributed high-precision phase-sensitive optical time domain reflectometry measurement.

[0003] Phase-sensitive optical time-domain reflectometry systems sense changes in the external environment by detecting phase changes in Rayleigh scattered signals in optical fibers. The noise disturbances in the detection system can also be misinterpreted as the measured parameter. The main noises include laser phase noise, laser frequency drift, and noise within the detection bandwidth. Laser phase noise is determined by the laser linewidth, laser wavelength drift is affected by laser drive control, and noise within the bandwidth comes from the extinction ratio of the pulse and the noise of the detector. The above noises limit In view of the influence of light source frequency drift, Nanjing University of Aeronautics and Astronautics proposed to compensate for laser frequency drift based on active optical frequency scanning technology. The cross-correlation operation of the curve is used to find the magnitude and direction of the frequency drift of the light source, and the feedback is used to control the laser output so that The optical frequency remains stable, and the laser wavelength drift noise is ultimately suppressed (Wang Xu, Liu Minhan, Yu Miao, et al. Analysis and Improvement of Digital Orthogonal Demodulation Algorithm of Phase-Sensitive Optical Time Domain Reflectometry System [J]. Chinese Laser, 2017, 44(12): 269-275). In the experiment, 10s of data were recorded, 100 cross-correlation curves were obtained, and the drift of the light source was observed by the drift of the cross-correlation peak. During this period, the light source drifted by 6.4MHz. However, the active optical frequency scanning method assumes that the external vibration signal only exists in a limited area of ​​the optical fiber. When the temperature or environment of the optical fiber to be tested changes as a whole, the compensation scheme cannot obtain the drift of the light source. In addition, multiple acquisitions are required when actively compensating the light source frequency, which reduces the system sampling rate and increases the amount of data processing, limiting the system's indicators in terms of sampling rate and processing speed. Therefore, a simpler and more practical method is used to eliminate The error caused by the drift of the system light source becomes This is one of the key issues that the system needs to solve. 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 narrowband filter frequency compensation is provided, the optical time domain reflectometry system comprising: A system light source, a chirped pulse signal modulation module, a first amplifier, a coupler, a first narrowband filter, a first detector, a circulator, an optical fiber to be tested, a second amplifier, a second 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 a first amplifier and a coupler in sequence. One signal generates a transmission signal after passing through a first narrowband filter. The first detector obtains a narrowband filter transmission 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 a second amplifier and a second filter in sequence. The second detector obtains a 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 1%-20% of the signal to enter the first narrowband filter, and the remaining signal enters the first port of the circulator.

[0009] Furthermore, the first narrowband filter is a Fabry-Perot cavity type narrowband filter constructed by dual fiber gratings.

[0010] 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.

[0011] Furthermore, the optical time domain reflectometry system also includes an acquisition card, which is connected to the first detector and the second detector respectively.

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

[0013] Furthermore, the acquisition card is connected to an arbitrary waveform generator to achieve synchronization of light source wavelength scanning, pulse modulation and signal acquisition.

[0014] According to another aspect of the present invention, a demodulation method of an optical time domain reflectometry system based on narrowband filter frequency compensation is provided, wherein the demodulation method of the optical time domain reflectometry system adopts the optical time domain reflectometry system based on narrowband filter frequency compensation as described above to realize phase demodulation.

[0015] Furthermore, the demodulation method of the optical time domain reflectometry system based on narrowband filter frequency compensation includes: based on the optical time domain reflectometry system based on narrowband filter 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 first narrowband filter and the optical fiber to be tested respectively, and the narrowband filter transmission spectrum and the Rayleigh interference spectrum are obtained 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.

[0016] The technical solution of the present invention provides an optical time domain reflectometry system and a demodulation method based on narrowband filter 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 is passed through the first narrowband filter to obtain the narrowband filter transmission spectrum, and the other path is passed through the optical fiber to be tested to obtain the Rayleigh interference spectrum. The narrowband filter transmission spectrum is used to compensate for the Rayleigh interference spectrum change of the optical fiber to be tested, avoiding demodulating the light source frequency drift 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

[0017] 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.

[0018] Figure 1 A schematic diagram showing the working principle of a modulation scheme in an optical time domain reflectometry system based on narrowband filter frequency compensation provided in a specific embodiment of the present invention is shown;

[0019] Figure 2 A schematic diagram showing the working principle of an external modulation scheme of an optical time domain reflectometry system based on narrowband filter frequency compensation provided in a specific embodiment of the present invention is shown;

[0020] 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;

[0021] 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;

[0022] Figure 5 It shows the specific embodiment provided according to the present invention Figure 4 A magnified view of the strain position at local A;

[0023] Figure 6 The relative frequency shift obtained by cross-correlation solution according to a specific embodiment of the present invention is shown;

[0024] Figure 7 The transmission spectrum of the narrow-band filter provided according to the specific embodiment of the present invention is shown. Schematic diagram of light source frequency drift monitoring. DETAILED DESCRIPTION

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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 narrowband filter frequency compensation is provided, and the optical time domain reflectometry system includes: A system light source, a chirped pulse signal modulation module, a first amplifier, a coupler, a first narrowband filter, a first detector, a circulator, an optical fiber to be tested, a second amplifier, a second 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 a first amplifier and a coupler in sequence. One signal generates a transmission signal after passing through a first narrowband filter. The first detector obtains a narrowband filter transmission 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 a second amplifier and a second filter in sequence. The second detector obtains a Rayleigh interference spectrum according to the filtered scattering signal.

[0029] By using this configuration, an optical time domain reflection system based on narrowband filter 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 is passed through the first narrowband filter to obtain the narrowband filter transmission spectrum, and the other path is passed through the optical fiber to be tested to obtain the Rayleigh interference spectrum. The narrowband filter transmission spectrum is used to compensate for the Rayleigh interference spectrum changes of the optical fiber to be tested, avoiding the demodulation of the light source frequency drift into temperature / strain changes, achieving high-precision and high-sensitivity temperature / strain demodulation, and improving the measurement accuracy of the phase-OTDR system.

[0030] 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.

[0031] Furthermore, in the present invention, the chirp spectrum needs to cover the first narrowband filter, and 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 through 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.

[0032] 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.

[0033] 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.

[0034] In this embodiment, the arbitrary waveform generator can utilize an internal clock to synchronously output a chirped microwave signal and an electrical pulse signal.

[0035] Furthermore, in the present invention, the coupler can be configured to control 1%-20% of the signal to enter the first narrowband filter, 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 narrowband filter transmission spectrum and the Rayleigh interference spectrum of the optical fiber to be measured.

[0036] As a specific embodiment of the present invention, the first narrowband filter can be a Fabry-Perot cavity (FP) type narrowband filter constructed by dual fiber gratings (FBGs). Its transmission spectrum width can reach about 30MHz, which is much smaller than that of fiber gratings and Brillouin spectrum based on chirp signals, and can ensure the measurement accuracy of light source drift.

[0037] 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 light source. The wavelength selection of the laser is achieved by controlling its current and temperature through the driver, which controls the initial wavelength and power of the laser.

[0038] 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 the narrowband filter transmission spectrum through the acquisition card channel 1 connected to the first detector, and the channel 2 is connected to the second detector to obtain the Rayleigh interference spectrum based on the chirped pulse.

[0039] 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.

[0040] 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.

[0041] Furthermore, the second filter may be a tunable optical filter to filter out the spontaneous radiation noise signal.

[0042] In the present invention, based on the narrowband filter transmission spectrum frequency compensation The key parameters of the system include spatial resolution, measurement distance and measurement time. 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 frequency drift compensation scheme based on transmission spectrum is also applicable to frequency scanning The demodulation system uses frequency scanning between pulses to measure the transmission spectrum of narrow-band filters and Rayleigh interference spectrum.

[0043] The optical time domain reflectometry system based on narrowband filter frequency compensation of the present invention uses a narrowband filter to measure the frequency change of the light source of the phase-OTDR system in real time, and synchronously corrects the measurement result of the optical fiber to be tested by the phase-OTDR, thereby compensating for the measurement deviation caused by the frequency change of the light source. Compared with the existing phase-OTDR system, it avoids demodulating the frequency drift of the light source into the temperature / strain change, and improves the anti-interference ability of the system. The solution based on narrowband filter frequency compensation is also applicable to the frequency sweep pulse phase-OTDR demodulation system.

[0044] Compared with the existing sweep frequency The optical time domain reflectometry system of the present invention has the following advantages:

[0045] (1) The optical time domain reflectometry system of the present invention can achieve high-precision and high-sensitivity temperature / strain measurement, obtain the frequency drift of the light source in real time through the transmission spectrum of the narrow-band filter, correct the measurement results of the optical fiber to be tested, avoid demodulating the frequency drift of the light source into the temperature / strain change, and achieve high-precision and high-sensitivity temperature / strain demodulation;

[0046] (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 compensates the phase in real time through the transmission spectrum of the narrowband filter, which can effectively improve Improve the environmental adaptability of the demodulation system and enhance its engineering usability.

[0047] According to another aspect of the present invention, a demodulation method of an optical time domain reflectometry system based on narrowband filter frequency compensation is provided. The demodulation method of an optical time domain reflectometry system uses the optical time domain reflectometry system based on narrowband filter frequency compensation as described above to realize phase demodulation.

[0048] Further, in the present invention, the demodulation method of the optical time domain reflectometry system based on narrowband filter frequency compensation includes: based on the optical time domain reflectometry system based on narrowband filter 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 first narrowband filter and the optical fiber to be tested respectively, and the narrowband filter transmission spectrum and the Rayleigh interference spectrum are obtained 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.

[0049] As a specific embodiment of the present invention, the narrow-band filter transmission 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.

[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, through 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 T is 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 high-precision optical time domain reflectometry analysis based on narrow-band transmission 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 narrow-band transmission 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 provides a high-precision demodulation solution for a phase-OTDR high-sensitivity measurement system, and uses a narrow-band filter transmission spectrum to compensate for the light source frequency drift in real time, which has the following advantages:

[0057] (1) The system can achieve high-precision demodulation of temperature and strain, measure the frequency of the transmission spectrum through a narrow-band filter, obtain the frequency drift of the light source in real time, avoid the influence of the drift of the traditional phase-OTDR light source, compensate for the temperature / strain measurement results of the optical fiber to be tested, and 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 the frequency compensation of the transmission spectrum of the narrow-band filter can avoid the influence of the wavelength fluctuation of the system light source, so it has high engineering practicality;

[0059] (3) The present invention has strong adaptability and a simple solution, 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 narrowband filter frequency compensation of the present invention is described in detail.

[0061] The demodulation method of the optical time domain reflectometry system based on narrowband filter 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.

[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 with 10% enters the first narrowband filter, and the first detector obtains the transmission spectrum of the narrowband filter. The other signal with 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 the second 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 to achieve synchronization of light source wavelength scanning, pulse modulation and signal acquisition.

[0067] According to the narrowband filter transmission spectrum and Rayleigh interference spectrum, 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. 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 narrowband filter 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 is passed through the first narrow-band filter to obtain the narrow-band filter transmission spectrum, and the other path is passed through the optical fiber to be tested to obtain the Rayleigh interference spectrum. The narrow-band filter transmission spectrum is used to compensate for the Rayleigh interference spectrum changes of the optical fiber to be tested, avoiding the demodulation of the light source frequency drift 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 narrowband filter 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, a first narrowband filter, a first detector, a circulator, an optical fiber to be tested, a second amplifier, a second 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 passing through the first narrowband filter. The first detector obtains a narrowband filter transmission 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 second 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 narrowband filter 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 a chirp modulated pulse signal.

3. The optical time domain reflectometry system based on narrowband filter 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 a chirped modulated pulse signal through the second electro-optical modulator to achieve pulse modulation.

4. The optical time domain reflectometry system based on narrowband filter 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 first narrowband filter, and the remaining signal enters the first port of the circulator.

5. The optical time domain reflectometry system based on narrowband filter frequency compensation according to any one of claims 1 to 4, characterized in that: The first narrowband filter is a Fabry-Perot cavity type narrowband filter constructed by dual fiber gratings.

6. The optical time domain reflectometry system based on narrowband filter frequency compensation according to claim 1, 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.

7. The optical time domain reflectometry system based on narrowband filter 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.

8. The optical time domain reflectometry system based on narrowband filter 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.

9. The optical time domain reflectometry system based on narrowband filter 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.

10. A demodulation method for an optical time domain reflectometry system based on narrowband filter frequency compensation, characterized in that: The demodulation method of the optical time domain reflectometry system uses the optical time domain reflectometry system based on narrowband filter frequency compensation as described in any one of claims 1 to 9 to realize phase demodulation.

11. The demodulation method of an optical time domain reflectometry system based on narrowband filter frequency compensation according to claim 10, characterized in that: The demodulation method of the optical time domain reflection system based on narrowband filter frequency compensation comprises: based on the optical time domain reflection system based on narrowband filter frequency compensation as described in any one of claims 1 to 9, modulating the continuous laser signal of the φ-OTDR system light source into a chirped modulated pulse signal, the chirped modulated pulse signal is divided into two paths and enters the first narrowband filter and the optical fiber to be tested respectively, and the narrowband filter transmission spectrum and the Rayleigh interference spectrum are respectively obtained; the frequency change of the φ-OTDR system light source and the frequency change of the optical fiber to be tested are respectively obtained according to the narrowband filter transmission spectrum and the Rayleigh interference spectrum; the frequency change of the optical fiber to be tested is subtracted from the frequency change of the φ-OTDR system light source, and the demodulation of the optical time domain reflection system is completed according to the difference.

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