Optical time domain reflectometry system based on narrowband filter frequency compensation and demodulation method

Abstract

The application provides an optical time domain reflection system and a demodulation method based on narrow-band filter frequency compensation, in the optical time domain reflection system, a continuous laser signal of a light source of a phi-OTDR system is converted into a chirp modulation pulse signal through 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 turn, one signal generates a transmission signal after passing through a first narrow-band filter, a first detector obtains a narrow-band filter transmission spectrum according to the transmission signal, the other signal enters a second port of a circulator through a first port of the circulator, enters a fiber to be measured, a fiber Rayleigh scattering signal enters a third port of the circulator through the second port, and then passes through a second amplifier and a second filter in turn, and a second detector obtains a Rayleigh interference spectrum according to the filtered scattering signal. The application can solve the technical problem that the existing sweep frequency phi-OTDR system in the prior art is affected by light source frequency drift, resulting in insufficient measurement accuracy.

Description

TECHNICAL FIELD

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

[0002] Distributed optical fiber sensing technology uses optical fiber as both transmission medium and sensing unit to realize continuous distributed temperature, strain and acoustic wave measurement along the optical fiber. On this basis, the phase-sensitive optical time domain reflection 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 civil structure health monitoring and perimeter security. Existing 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 Rayleigh scattering signal and local light signal, and demodulates the measured parameters through phase change. The phase demodulation method includes quadrature (IQ), Hilbert transform and other phase demodulation methods, which has better signal-to-noise ratio than direct detection. The direct detection scheme directly obtains the interference spectrum of Rayleigh scattering signal, and can realize phase demodulation based on 3x3 coupler and phase generated carrier, but it has high requirements for device consistency and modulator operating point, respectively. Another type uses optical frequency scanning method to compensate 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 decay to a certain extent, and realize distributed high-precision phase-sensitive optical time domain reflection sensing measurement.

[0003] The phase-sensitive optical time domain reflection system detects the phase change of Rayleigh scattering signal in the optical fiber to perceive the change of external environment, and the noise disturbance of the detection system will also be demodulated as the measured parameters. The main noises include laser phase noise, laser frequency drift and noise within the detection bandwidth. The laser phase noise is determined by the linewidth of the laser, the wavelength drift of the laser is affected by the driving control of the laser, and the noise within the bandwidth comes from the extinction ratio of the pulse and the noise of the detector. The above noises limit the overall sensing performance of the sensing system. In view of the influence of the frequency drift of the light source, Nanjing University of Aeronautics and Astronautics proposes to compensate the frequency drift of the laser based on the active optical frequency scanning method, to obtain the size and direction of the frequency drift of the light source through the active frequency scanning technology and curve cross-correlation operation, and to feedback control the output of the laser so that The optical frequency is kept stable, and the wavelength drift noise of the laser is finally suppressed (Wang X, Liu M, Yu M, et al. Analysis and improvement of digital quadrature demodulation algorithm for phase-sensitive optical time domain reflectometry system[J]. Chinese Journal of Lasers, 2017, 44(12): 269-275). In the experiment, 10s of data are recorded, 100 cross-correlation curves are obtained, and the drift of the cross-correlation peak is used to observe the drift of the light source. The light source drifts by 6.4MHz in this period of time. However, the active optical frequency scanning method assumes that the external vibration signal only exists in the limited area of the optical fiber. When the temperature or the overall environment of the measured optical fiber changes, the compensation scheme cannot obtain the drift of the light source. Moreover, when the active compensation of the light source frequency is needed, multiple acquisitions are required, which reduces the sampling rate of the system and increases the data processing amount, thereby limiting the indicators of the system 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, which is one of the key problems to be solved by the system. SUMMARY

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

[0005] According to one aspect of the present application, an optical time domain reflectometry system based on narrowband filter frequency compensation is provided, which comprises: a system light source, a chirp pulse signal modulation module, a first amplifier, a coupler, a first narrowband filter, a first detector, a circulator, a measured optical fiber, a second amplifier, a second filter and a second detector, the continuous laser signal of the system light source is converted into a chirp modulation pulse signal through the chirp pulse signal modulation module, the chirp modulation pulse signal is divided into two signals after the first amplifier and the coupler, one signal generates a transmission signal after passing through the first narrowband filter, and the first detector obtains the narrowband filter transmission spectrum according to the transmission signal, and the other signal enters the second port of the circulator through the first port of the circulator, enters the measured optical fiber, and 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 second filter in turn, and the second detector obtains the 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, 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] ​Furthermore, 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 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-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.

[0008] Furthermore, 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 reflection system also includes a driver, the driver and System light source connection to control The current and temperature of the system's light sources.

[0011] Furthermore, the optical time domain reflectometry system further 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. 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 implement 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 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 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 reflectometry system is completed based on the difference.

[0016] The application provides an optical time domain reflection system and a demodulation method based on narrow-band filter frequency compensation. 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 passes through a first narrow-band filter to obtain a narrow-band filter transmission spectrum, and the other path passes through a to-be-measured optical fiber to obtain a Rayleigh interference spectrum. The Rayleigh interference spectrum change of the to-be-measured optical fiber is compensated by using the narrow-band filter transmission spectrum, the frequency drift of the light source is avoided from being 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. Compared with the prior art, the technical scheme of the application can solve the technical problem of insufficient measurement precision of the prior art phase-OTDR system caused by the influence of the frequency drift of the light source. The system is affected by the frequency drift of the light source, and the measurement precision is insufficient. BRIEF DESCRIPTION OF DRAWINGS

[0017] 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, 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.

[0018] Figure 1 Fig. 1 shows a working principle diagram of an internal modulation scheme of an optical time domain reflection system based on narrow-band filter frequency compensation according to a specific embodiment of the application;

[0019] Figure 2 Fig. 2 shows a working principle diagram of an external modulation scheme of an optical time domain reflection system based on narrow-band filter frequency compensation according to a specific embodiment of the application;

[0020] Figure 3 Fig. 3 shows a principle diagram of a frequency compensation Rayleigh interference spectrum based on a chirp pulse according to a specific embodiment of the application;

[0021] Figure 4 Fig. 4 shows a to-be-measured optical fiber Rayleigh interference spectrum based on a chirp pulse strain demodulation according to a specific embodiment of the application;

[0022] Figure 5 Fig. 5 shows a partial A strain position enlargement of Fig. 4 according to a specific embodiment of the application; Figure 4

[0023] Figure 6 Fig. 6 shows a cross-correlation solution of relative frequency shift according to a specific embodiment of the application;

[0024] ​Figure 7 Fig. 8 shows a schematic diagram of a narrow-band filter transmission spectrum based optical time domain reflectometry system according to an embodiment of the present application; Fig. 9 shows a schematic diagram of a light source frequency drift monitoring according to an embodiment of the present application. DETAILED DESCRIPTION

[0025] It should be noted that the embodiments and features of the embodiments in the present application can be combined if there is no conflict. The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. The description of the at least one example 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 of ordinary skill in the art without creative labor fall within the scope of the present application.

[0026] 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 the terms "comprise" and / or "include" as used in the specification indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0027] Unless otherwise specifically stated, the relative arrangements of parts and steps, numerical expressions, and numerical values set forth in the examples herein are not intended to limit the scope of the application. At the same time, it should be understood that the sizes of the various parts shown in the drawings are not drawn in proportion. 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 in appropriate circumstances. In all examples shown and discussed herein, any specific value should be interpreted as merely exemplary, and not as a limitation. Therefore, other examples of exemplary embodiments can have different values. It should be noted that similar reference numbers and letters represent similar items in the following drawings, so that once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0028] As shown in Figs. 1 and 2, according to an embodiment of the present application, a narrow-band filter transmission spectrum based optical time domain reflectometry system is provided, which comprises: Figure 1 and Figure 2 As shown in Figs. 1 and 2, according to an embodiment of the present application, a narrow-band filter transmission spectrum based optical time domain reflectometry system is provided, which comprises: a system light source, a chirp pulse signal modulation module, a first amplifier, a coupler, a first narrow-band filter, a first detector, a circulator, a fiber to be measured, a second amplifier, a second 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, the chirp modulation pulse signal is divided into two signals in sequence after passing through the first amplifier and the coupler, one of the two signals generates a transmission signal after passing through the first narrowband filter, and the first detector obtains a narrowband filter transmission spectrum according to the transmission signal, and the other signal enters the second port of the circulator through the first port of the circulator, enters the optical fiber to be measured, and the Rayleigh scattering signal of the optical fiber enters the third port of the circulator through the second port, then passes through the second amplifier and the second filter in sequence, and the second detector obtains a Rayleigh interference spectrum according to the filtered scattering signal.

[0029] By using the configuration mode, an optical time domain reflection system based on narrowband filter frequency compensation is provided, the optical time domain reflection system converts the continuous laser signal of the system light source into a chirp modulation pulse signal, and divides the chirp modulation pulse signal into two signals, one of the two signals obtains a narrowband filter transmission spectrum through the first narrowband filter, and the other signal obtains a Rayleigh interference spectrum through the optical fiber to be measured, the narrowband filter transmission spectrum is used to compensate the change of the Rayleigh interference spectrum of the optical fiber to be measured, the frequency drift of the light source is avoided to be demodulated into the temperature / strain change, high-precision and high-sensitivity temperature / strain demodulation is realized, and the measurement precision of the phase-OTDR system is improved. The continuous laser signal of the system light source is converted into a chirp modulation pulse signal, and the chirp modulation pulse signal is divided into two signals, one of the two signals obtains a narrowband filter transmission spectrum through the first narrowband filter, and the other signal obtains a Rayleigh interference spectrum through the optical fiber to be measured, the narrowband filter transmission spectrum is used to compensate the change of the Rayleigh interference spectrum of the optical fiber to be measured, the frequency drift of the light source is avoided to be demodulated into the temperature / strain change, high-precision and high-sensitivity temperature / strain demodulation is realized, and the measurement precision of the phase-OTDR system is improved.

[0030] As a specific embodiment of the present application, The system light source can adopt a distributed feedback laser (DFB laser). When the temperature of the laser changes or the driving current of the laser fluctuates, 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.

[0031] Further, in the present application, the chirp spectrum needs to cover the first narrowband filter, the chirp modulation pulse signal can be realized through an internal modulation scheme or an external modulation scheme, the internal modulation scheme controls the driving current through a signal generator, as shown in Figure 1 The external modulation scheme realizes the chirp pulse signal modulation through an arbitrary waveform generator and an electro-optic modulator (EOM), as shown in Figure 2 .

[0032] 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's light source enters a semiconductor fiber amplifier and is converted into a chirped modulated pulse signal. The relationship between the modulated current and wavelength can be determined by pre-calibrating the current-wavelength curve. This allows for linear scanning of the laser 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 to the first electro-optical modulator and an electrical pulse signal to the second electro-optical modulator. The continuous laser output of the system light source 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.

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

[0035] Furthermore, in the present invention, a 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 amount of signal 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 with dual fiber Bragg gratings (FBGs). Its transmission spectrum width can reach approximately 30 MHz, which is much smaller than that of fiber Bragg gratings and Brillouin spectroscopy based on chirped signals, ensuring the accuracy of light source drift measurement.

[0037] Furthermore, in the present invention, in order to achieve The system light source laser parameter control, configurable optical time domain reflection 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, 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 narrowband filter transmission spectrum, while channel 2 can be connected to the second detector to obtain a Rayleigh interferometer spectrum based on a chirped pulse.

[0039] Further, the acquisition card can also be connected with a signal generator or an arbitrary waveform generator to realize synchronization of wavelength scanning, pulse modulation and signal acquisition of the light source.

[0040] As a specific embodiment of the present application, the first amplifier and the second amplifier can both adopt an erbium-doped fiber amplifier. 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] Further, the second filter can adopt an adjustable optical filter to filter out the spontaneous emission noise signal.

[0042] In the present application, based on the transmission spectrum frequency compensation of the narrowband filter The key parameters of the system 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; and the time interval between pulses determines the measurement time of the system. The transmission spectrum frequency drift compensation scheme is also applicable to a frequency scanning demodulation system, which realizes the measurement of the transmission spectrum of the narrowband filter and the Rayleigh interference spectrum by using the frequency scanning between pulses.

[0043] The optical time domain reflection system based on the frequency compensation of the narrowband filter in the present application utilizes the narrowband filter to measure the frequency variation of the light source of the phase-OTDR system in real time, synchronously corrects the measurement results of the phase-OTDR to-be-measured optical fiber, and compensates for the measurement deviation caused by the frequency variation of the light source. Compared with the existing phase-OTDR system, the present application avoids demodulating the frequency drift of the light source into the temperature / strain variation, and improves the anti-interference ability of the system. The frequency compensation scheme based on the narrowband filter is also applicable to a frequency scanning pulse phase-OTDR demodulation system.

[0044] Compared with the existing frequency scanning measurement system, the optical time domain reflection system of the present application has the following advantages:

[0045] (1) The optical time domain reflection system of the present application can realize high-precision and high-sensitivity temperature / strain measurement. The amount of frequency drift of the light source is obtained in real time by the transmission spectrum of the narrowband filter, the measurement results of the to-be-measured optical fiber are corrected, the frequency drift of the light source is avoided to be demodulated into the temperature / strain variation, and high-precision and high-sensitivity temperature / strain demodulation is realized.

[0046] (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, and when the temperature of the laser changes or the driving current jitters, the wavelength of the light source will change, and the present application can effectively improve the wavelength stability of the system light source by transmitting the spectrum of the narrow-band filter in real time to compensate the phase The demodulation system is environmentally adaptable, and the engineering usability is enhanced.

[0047] According to another aspect of the present application, a demodulation method of an optical time domain reflection system based on narrow-band filter frequency compensation is provided, which implements phase demodulation by using the optical time domain reflection system based on narrow-band filter frequency compensation as described above.

[0048] Further, in the present application, the demodulation method of the optical time domain reflection system based on narrow-band filter frequency compensation comprises: based on the optical time domain reflection system based on narrow-band filter frequency compensation as described above, obtaining 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 a first narrow-band filter and a to-be-measured optical fiber respectively, and the narrow-band filter transmission spectrum and the Rayleigh interference spectrum are obtained respectively; the frequency variation of the system light source and the frequency variation of the to-be-measured optical fiber are obtained respectively according to the narrow-band filter transmission spectrum and the Rayleigh interference spectrum. The frequency variation of the system light source and the frequency variation of the to-be-measured optical fiber. The frequency variation of the system light source and the frequency variation of the to-be-measured optical fiber.

[0049] As a specific embodiment of the present application, the frequency variation of the system light source and the frequency variation of the to-be-measured optical fiber can be obtained respectively by using a cross-correlation algorithm according to the narrow-band filter transmission spectrum and the Rayleigh interference spectrum. The frequency variation of the system light source and the frequency variation of the to-be-measured optical fiber.

[0050] The principle of frequency compensation Rayleigh interference spectrum based on chirp pulse is as shown in Figure 3 The pulse light Rayleigh scattering signals E(t) and E(t+Δt) return from z1 to z3 and from z2 to z4 respectively at t and t+Δt. When Δt is very small, the distances from z1 to z2 and from z3 to z4 can be ignored compared with the distance from z2 to z3, and the scattering signals can be regarded as returning from z2 to z3. However, at t, the pulse light frequency is v3 to v1, and at t+Δt, the pulse light frequency is v4 to v2, which realizes the scanning of the light 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 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, 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 The frequency change caused by temperature and strain, as well as the jitter of the light source frequency, causes system measurement errors. The high-precision optical time domain reflectometry analysis based on narrowband 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 narrowband 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, utilizing a narrowband filter transmission spectrum to compensate for light source frequency drift in real time. This solution has the following advantages:

[0057] (1) The system can realize high-precision demodulation of temperature strain, measure the frequency of the transmitted spectrum through a narrow-band filter, obtain the frequency drift of the light source in real time, avoid the influence of the traditional phase-OTDR light source drift, compensate the temperature / strain measurement results of the to-be-measured optical fiber, and realize high-precision and high-sensitivity measurement;

[0058] (2) The system has high anti-interference capability, 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 transmitted spectrum of the narrow-band filter can avoid the influence of the wavelength fluctuation of the system light source, and therefore has high engineering practicability;

[0059] (3) The application has strong adaptability, and the scheme is simple, and can be used in other systems that need to monitor the wavelength drift of the light source.

[0060] In order to further understand the application, the following will be combined with Figures 1 to 7 The demodulation method of the optical time domain reflection system based on the frequency compensation of the narrow-band filter of the application will be described in detail.

[0061] The demodulation method of the optical time domain reflection system based on the frequency compensation of the narrow-band filter of the application is realized by using the optical time domain reflection system as shown in Figure 1 or Figure 2 .

[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 the inner modulation scheme as shown in Figure 1 is used, 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 to convert into a chirped modulation pulse signal.

[0064] When the outer modulation scheme as shown in Figure 2 is used, 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 distributed feedback laser is subjected to chirped frequency modulation through the first electro-optic modulator, and then subjected to pulse modulation through the second electro-optic modulator to convert into a chirped modulation pulse signal.

[0065] The chirp modulation pulse signal is divided into two signals after passing through the first amplifier and the coupler, one of which is 10% of the signal entering the first narrow-band filter, and the first detector obtains the narrow-band filter transmission spectrum, and the other is 90% of the signal entering the second port through the first port of the circulator, entering the optical fiber to be measured, and the Rayleigh scattering signal of the optical fiber enters the third port through the second port of the circulator, and then the second detector obtains the Rayleigh interference spectrum after passing through the second amplifier and the second filter.

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

[0067] According to the narrow-band filter transmission spectrum and the Rayleigh interference spectrum, the frequency change Delta v of the distributed feedback laser and the frequency change Delta v of the optical fiber to be measured are obtained by using the cross-correlation algorithm. m The difference between the two is Delta v m - Delta v, which can compensate for the influence of the frequency jitter of the light source in real time and realize high-precision temperature / strain measurement of the phase-OTDR system.

[0068] In summary, the application provides an optical time domain reflectometry system and a demodulation method based on narrow-band filter frequency compensation. The continuous laser signal of the system light source is converted into a chirp modulation pulse signal, which is divided into two paths, one of which passes through the first narrow-band filter to obtain the narrow-band filter transmission spectrum, and the other passes through the optical fiber to be measured to obtain the Rayleigh interference spectrum, and the narrow-band filter transmission spectrum is used to compensate for the change of the Rayleigh interference spectrum of the optical fiber to be measured, which avoids demodulating the frequency drift of the light source into the temperature / strain change, realizes high-precision and high-sensitivity temperature / strain demodulation, and improves the measurement accuracy of the phase-OTDR system.

[0069] In addition, it should be noted that the use of the terms "first", "second", etc. to define parts is only for the convenience of distinguishing the corresponding parts, and the above terms have no special meaning unless otherwise stated, and therefore cannot be understood as limiting the scope of protection of the application.

[0070] The above only describes the preferred embodiments of the application and is not intended to limit the application. Those skilled in the art can make various modifications and changes to the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the scope of protection of the application.

Claims

1. An optical time domain reflectometry system based on narrowband filter 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, 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 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 second 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 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. 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 a chirped 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 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 converted into a chirped modulated pulse signal by pulse modulation by the second electro-optical modulator.

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 with 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 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, which 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 according to 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 reflectometer system based on narrowband filter frequency compensation comprises: modulating a continuous laser signal of a φ-OTDR system light source into a chirped modulated pulse signal based on the optical time domain reflectometer system based on narrowband filter frequency compensation according to any one of claims 1 to 9; the chirped modulated pulse signal is divided into two paths and enters a first narrowband filter and an optical fiber to be tested respectively, and a narrowband filter transmission spectrum and a Rayleigh interference spectrum are obtained respectively; obtaining a frequency change of the φ-OTDR system light source and a frequency change of the optical fiber to be tested respectively based on the narrowband filter transmission spectrum and the Rayleigh interference spectrum; subtracting the frequency change of the optical fiber to be tested from the frequency change of the φ-OTDR system light source, and completing the demodulation of the optical time domain reflectometer system according to the difference.

Images