Optical time domain reflectometry system based on reference fiber phase compensation and demodulation method

Abstract

The application provides an optical time domain reflection system and a demodulation method based on reference optical fiber phase compensation, and the optical time domain reflection system comprises a signal generator, a distributed feedback laser, a semiconductor fiber amplifier, a first amplifier, a circulator, a second amplifier, a wave filter, a detector, a reference optical fiber and a to-be-measured optical fiber, and the continuous laser signal of the distributed feedback laser is converted into a pulse optical signal through the semiconductor fiber amplifier and is amplified through the first amplifier; the amplified pulse optical signal enters the second port of the circulator through the first port of the circulator, enters the reference optical fiber and the to-be-measured optical fiber in sequence, and after the optical fiber Rayleigh scattering signal enters the third port of the circulator through the second port, sequentially passes through the second amplifier and the filter, and the detector obtains the Rayleigh interference spectrum of the reference optical fiber and the to-be-measured optical fiber according to the filtered scattering signal. The application can solve the technical problem that the measurement precision of the traditional phase-OTDR system is insufficient due to the influence of the light source phase drift.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, and particularly to an optical time domain reflectometry system and a demodulation method based on reference fiber phase compensation. BACKGROUND

[0002] Distributed optical fiber sensing technology has been used in large infrastructure, geological disasters, geophysical exploration, Internet of Things and other fields, and the research has great economic and scientific value. Distributed optical fiber sensing technology mainly utilizes the nonlinear effects in optical fiber, including Rayleigh scattering, Brillouin scattering and Raman scattering, to form various types of distributed optical fiber sensing demodulation systems, which have different scene distributed optical fiber sensing monitoring capabilities. For high-sensitivity dynamic strain measurement, the optical time domain reflectometry (OTDR) based on Rayleigh scattering effect is one of the best measurement schemes.

[0003] The traditional phase-OTDR system uses a narrow linewidth high coherence light source to generate pulsed light, and directly detects the interference intensity between the backscattered Rayleigh signals in the pulse. Due to the random distribution of scattering points in the optical fiber, the interference signal has a jagged irregular shape. When the external environment and system are unchanged, the interference pattern is unchanged and has repeatability; when the external temperature or strain changes, the optical path between the scattering points changes, causing the phase of the scattered light to change, which affects the interference intensity of the perturbed position. However, the traditional phase-OTDR for direct signal intensity detection can only be used for qualitative measurement, and is used for intrusion, positioning, speed and vibration monitoring, and cannot obtain the change amount of temperature and strain. Further research has found that the main reason for the change of interference intensity is the change of phase difference of scattered light, so the amount of phase change can be determined through phase demodulation and frequency compensation scheme, and quantitative measurement of temperature and strain is realized. In the past decade, phase-OTDR for high-sensitivity quantitative measurement has been widely studied, and the main technologies include interferometer demodulation, heterodyne coherent detection, sweep scheme and chirped pulse, which have realized high-resolution strain / temperature measurement at the level of nanometer strain and millikelvin.

[0004] The high-sensitivity phase-OTDR demodulation system provides an effective solution for seismic wave, geological exploration and other acoustic wave detection. However, due to its high sensitivity, higher requirements are put forward for the stability of the measurement system. The phase shift of the light source system (including wavelength, initial phase, etc.) is one of the main error sources, which leads to the decrease of the absolute accuracy of measurement. In 2018, German researchers gave the measurement deviation caused by 24-hour laser phase shift through experiments, which is 120 nanometer strain 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). The error caused by jitter is about two orders of magnitude higher than the system resolution, so the laser phase shift seriously affects the system performance. The cost of ultra-stable light source is high, and it is still difficult to ensure the absolute stability of the light source wavelength / phase for a long time. Therefore, the measurement results of high-sensitivity phase-OTDR are more reported in the simulation test under laboratory conditions, and the light source wavelength shift problem still needs to be solved for engineering practicality. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the prior art.

[0006] According to one aspect of the present application, an optical time domain reflectometry system based on reference optical fiber phase compensation is provided, which comprises a signal generator, a distributed feedback laser, a semiconductor fiber amplifier, a first amplifier, a circulator, a second amplifier, a filter, a detector, a reference optical fiber and a to-be-measured optical fiber. The signal generator drives and controls the distributed feedback laser and the semiconductor fiber amplifier respectively. The continuous laser signal of the distributed feedback laser is converted into a pulse optical signal by the semiconductor fiber amplifier and is amplified by the first amplifier. The amplified pulse optical signal enters the second port of the circulator through the first port of the circulator, enters the reference optical fiber and the to-be-measured optical fiber in turn, 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 filter in turn. The detector obtains the Rayleigh interference spectrum of the reference optical fiber and the to-be-measured optical fiber according to the filtered scattering signal.

[0007] Further, the reference optical fiber is placed in a constant temperature environment and is in a relaxed state.

[0008] Further, the length of the reference optical fiber is at least 2 times the system spatial resolution, and the middle section of the reference optical fiber is taken as the phase compensation monitoring area.

[0009] Further, the measured length of the to-be-measured fiber is the difference between the system measurement distance and the length of the reference fiber.

[0010] Further, the first amplifier and the second amplifier are both erbium-doped fiber amplifiers.

[0011] Further, the optical time domain reflection system further comprises an acquisition card, the acquisition card being connected with the signal generator and the detector respectively.

[0012] Further, the signal generator synchronously drives the acquisition card to realize synchronization of the light source wavelength scanning, the pulse modulation and the signal acquisition.

[0013] According to another aspect of the present application, a demodulation method of an optical time domain reflection system based on reference fiber phase compensation is provided, which realizes phase demodulation by using the optical time domain reflection system based on reference fiber phase compensation as described above.

[0014] Further, the demodulation method of the optical time domain reflection system comprises: obtaining Rayleigh interference spectra of the reference fiber and the to-be-measured fiber respectively based on the optical time domain reflection system based on reference fiber phase compensation as described above; obtaining phase changes of the reference fiber and the to-be-measured fiber according to the Rayleigh interference spectra of the reference fiber and the to-be-measured fiber; and completing demodulation of the optical time domain reflection system based on the difference between the phase change of the to-be-measured fiber and the phase change of the reference fiber.

[0015] Further, the phase changes of the reference fiber and the to-be-measured fiber are obtained by performing cross-correlation operation according to the Rayleigh interference spectra of the reference fiber and the to-be-measured fiber.

[0016] By using the technical scheme of the present application, the optical time domain reflection system based on reference fiber phase compensation and the demodulation method are provided, the reference fiber and the to-be-measured fiber are connected in series in the optical time domain reflection system, Rayleigh interference spectra of the reference fiber and the to-be-measured fiber are obtained respectively, the system phase drift amount can be obtained in real time by using the reference fiber, the phase change of the to-be-measured fiber is compensated, the light source phase jitter is avoided to be demodulated into temperature / strain change amount, high-precision and high-sensitivity temperature / strain demodulation is realized, the environmental adaptability of the phase-OTDR system can be effectively improved, and the engineering usability thereof is enhanced. Compared with the prior art, the technical scheme of the present application can solve the technical problem of insufficient measurement precision of the traditional phase-OTDR system caused by the influence of light source phase drift. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. It is readily apparent to one skilled in the art that the accompanying drawings typically depict only some embodiments of the present application and therefore should not be considered as limiting the scope of the application, as there are many embodiments of the present application that can be derived from the present description.

[0018] Figure 1 A working principle schematic diagram of an optical time domain reflection system based on reference fiber phase compensation is shown according to a specific embodiment of the present application;

[0019] Figure 2 A Rayleigh interference spectrum of a fiber to be measured is shown according to a specific embodiment of the present application;

[0020] Figure 3 A Rayleigh interference spectrum of a reference fiber is shown according to a specific embodiment of the present application;

[0021] Figure 4 A working principle schematic diagram of an optical time domain reflection system based on reference fiber phase compensation is shown according to a specific embodiment of the present application; Figure 3 A partial enlarged schematic diagram of DETAILED DESCRIPTION

[0022] It should be noted that the embodiments and features of the embodiments in the present application can be combined with each other without conflict. The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not intended to limit the present application and its application or use in any way. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0023] It should be noted that the terms used herein are only intended to describe specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a feature, step, operation, device, component and / or combination thereof.

[0024] The relative arrangement of parts and steps, numerical expressions, and numerical values set forth in the examples herein are not meant to limit the scope of the present application unless otherwise specifically stated. It is to be understood that the drawings are not necessarily to scale as the dimensions of the parts shown are for the purpose of illustration and description only and not to limit the scope of the application. 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 description. In all examples shown and discussed herein, any specific value should be interpreted as merely an example and not a limitation. Thus, other examples of the example embodiments can have different values. It should be noted that like reference numerals and letters refer to like items in the several views of the drawings, and, as such, further discussion of such items is not necessary in the subsequent views.

[0025] As Figure 1 shown, according to a specific embodiment of the present application, a phase-OTDR system based on reference fiber phase compensation is provided, which comprises a signal generator, a distributed feedback laser (DFB laser), a semiconductor optical amplifier (SOA), a first amplifier, a circulator, a second amplifier, a filter, a detector, a reference fiber and a fiber to be measured, the signal generator drives and controls the distributed feedback laser and the semiconductor optical amplifier respectively; the continuous laser signal of the distributed feedback laser is converted into a pulsed optical signal by the semiconductor optical amplifier and is amplified by the first amplifier; the amplified pulsed optical signal enters the second port of the circulator through the first port of the circulator, enters the reference fiber and the fiber to be measured in turn, and the fiber Rayleigh scattering signal enters the third port of the circulator through the second port, and then passes through the second amplifier and the filter in turn, and the detector obtains the Rayleigh interference spectrum of the reference fiber and the fiber to be measured according to the filtered scattering signal.

[0026] By using such a configuration, a phase-OTDR system based on reference fiber phase compensation is provided, which obtains the Rayleigh interference spectrum of the reference fiber and the fiber to be measured by connecting the reference fiber and the fiber to be measured in series, can obtain the system phase drift in real time through the reference fiber, compensate for the phase change of the fiber to be measured, avoids demodulating the light source phase jitter into the temperature / strain change, realizes high-precision and high-sensitivity temperature / strain demodulation, and can effectively improve the environmental adaptability of the phase-OTDR system and enhance its engineering usability.

[0027] Further, in the present application, the signal generator controls the driving voltage of the distributed feedback laser, the driving voltage is proportional to the laser modulation current, 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 is realized by pre-calibrating the voltage curve.

[0028] In addition, the signal generator provides a driving pulse signal for the semiconductor fiber amplifier.

[0029] Further, in the present application, the reference fiber can be placed in a constant temperature environment and in a relaxed state.

[0030] As a specific embodiment of the present application, the first amplifier and the second amplifier can both be erbium-doped fiber amplifiers.

[0031] Further, the filter can be an adjustable optical filter to filter out the spontaneous emission noise signal.

[0032] In addition, in the present application, the optical time domain reflectometry system further comprises a data acquisition card, which is connected with the signal generator and the detector, respectively.

[0033] In the present application, the key parameters of the optical time domain reflectometry system based on reference fiber phase compensation include spatial resolution, measurement distance and measurement time, etc.

[0034] The optical time domain reflectometry system based on reference fiber phase compensation in the present application uses the reference fiber to measure the phase drift of the phase-OTDR system in real time, and synchronously corrects the measurement result of the fiber under test.

[0035] 1) The optical time domain reflectometry system of the present application can realize high-precision and high-sensitivity temperature / strain measurement.

[0036] 2) The optical time domain reflection system of the present application has high anti-interference capability. The light source of the phase-OTDR system is usually a DFB fiber laser. When the temperature of the laser changes or the driving current fluctuates, the wavelength of the light source will change. The present application can effectively improve the environmental adaptability of the phase-OTDR demodulation system and enhance its engineering usability by compensating the phase of the reference optical fiber in real time.

[0037] 3) The optical time domain reflection system of the present application does not increase the complexity of the hardware system and is suitable for all types of phase-OTDR systems, including interferometer demodulation, heterodyne coherent detection, sweep frequency scheme and chirp pulse scheme. The reference optical fiber can be connected in series with the optical fiber to be measured, and it does not increase the hardware complexity of the phase-OTDR system.

[0038] According to another aspect of the present application, a demodulation method of an optical time domain reflection system based on reference optical fiber phase compensation is provided, which realizes phase demodulation by using the optical time domain reflection system based on reference optical fiber phase compensation as described above.

[0039] Further, in the present application, the demodulation method of the optical time domain reflection system based on reference optical fiber phase compensation comprises: obtaining Rayleigh interference spectra of the reference optical fiber and the optical fiber to be measured respectively based on the optical time domain reflection system based on reference optical fiber phase compensation as described above; obtaining phase changes of the reference optical fiber and the optical fiber to be measured according to the Rayleigh interference spectra of the reference optical fiber and the optical fiber to be measured; and completing the demodulation of the optical time domain reflection system based on the difference value by subtracting the phase change of the optical fiber to be measured from the phase change of the reference optical fiber.

[0040] As a specific embodiment of the present application, the phase changes of the reference optical fiber and the optical fiber to be measured can be obtained by cross-correlation operation according to the Rayleigh interference spectra of the reference optical fiber and the optical fiber to be measured.

[0041] In the present application, the phase change of the reference optical fiber is the system phase drift, and the phase change of the optical fiber to be measured is the phase change caused by temperature / strain and light source jitter. By subtracting the phase change of the reference optical fiber from the phase change of the optical fiber to be measured, the demodulation result without system influence can be obtained, which avoids demodulating the system phase jitter as the temperature / strain measurement value and improves the measurement accuracy of the phase-OTDR system.

[0042] In the sweep frequency phase-OTDR system, the phase change caused by the external environment is compensated by using the change of the optical frequency, that is, the phase change is determined by the shift amount of the Rayleigh interference spectrum in frequency. The amplitude E of the interference signal obtained at the detector is R (t,Δv) is the superposition of N signals within half the width of the pulse, which is analyzed by using the following one-dimensional pulse response model:

[0043]

[0044] Among them, r i is the reflectivity of the i-th scattering point; E0 is the incident light field intensity; α is the fiber loss; τ i is the time delay of the i-th scattering point, that is, the time from incident to detector reception, τ i =2nz i / c, c is the speed of light in vacuum; z i The position of the i-th scattering point, n is the refractive index of the optical fiber; v0 is the laser carrier frequency; Δv is the change in frequency compared to the first pulse light; τ d is the pulse width; rect() is the pulse function,

[0045] The detector output power is the square of the modulus of the measured superimposed signal, which can be divided into two parts, the DC component and the AC component:

[0046] I(t,Δv)=|E R (t,Δv)| 2 =I DC +I AC

[0047]

[0048]

[0049] DC component I DC It is the linear superposition of the signal strength of each scattering point. However, the DC component is meaningless for interferometric phase measurement, and an AC detection scheme is usually used to filter out the DC component. AC middle represents the phase difference between the i-th scattering point and the k-th scattering point, τ k is the time delay of the kth scattering point, The AC component makes the intensity of the Rayleigh scattering signal jagged, that is, the intensity fluctuates, and is sensitive to phase changes caused by external temperature and strain. m The phase change caused by the strain change Δε and the temperature change ΔT is compensated to restore the Rayleigh interference spectrum, where the relative movement of the Rayleigh interference spectrum can be determined by the frequency shift through the cross-correlation algorithm.

[0050]

[0051] Among them, K ε is the gauge factor; Δτ ik is the time difference between the i-th scattering point and the k-th scattering point; τ ik is the time difference between the i-th scattering point and the k-th scattering point; K Tis the temperature coefficient.

[0052] The change in light frequency Δv m It includes both phase changes caused by temperature and strain, and phase jitter of the system, which causes system measurement errors. The high-precision optical time domain reflectometry based on phase compensation of the present invention is used to obtain the phase change Δv caused by temperature / strain and light source jitter using the Rayleigh interferometer spectrum of the optical fiber to be measured. m , the phase change Δv caused by the light source jitter is demodulated by the reference fiber, and the difference Δv is calculated. m -Δv, real-time compensation of the difference eliminates the influence of system phase jitter, avoids demodulating system phase jitter into temperature / strain measurement values, and realizes high-precision temperature / strain measurement of the phase-OTDR system.

[0053] The demodulation method for an optical time-domain reflectometry system uses a reference fiber to measure phase changes in a phase-OTDR system in real time, synchronously correcting the phase-OTDR measurement results for the fiber under test, thereby compensating for measurement deviations caused by light source phase changes. By measuring the phase of the reference fiber, the system phase drift is acquired in real time, avoiding the effects of conventional phase-OTDR phase noise and long-term light source drift. This compensates for the temperature and strain measurements of the fiber under test, avoiding the effects of fluctuations in the system light source wavelength, and achieving high-precision and high-sensitivity measurements. This method offers strong robustness and high engineering practicality.

[0054] In order to have a further understanding of the present invention, the following Figures 1 to 4 The demodulation method of the optical time domain reflectometry system based on reference fiber phase compensation of the present invention is described in detail.

[0055] The demodulation method of the optical time domain reflectometry system based on reference fiber phase compensation of the present invention adopts the following method: Figure 1 The optical time domain reflectometry system shown in the figure realizes phase demodulation. First, the Rayleigh interference spectra of the reference fiber and the fiber under test are obtained respectively; the phase changes of the reference fiber and the fiber under test are obtained by performing cross-correlation operation based on the Rayleigh interference spectra of the reference fiber and the fiber under test. Figure 2 The Rayleigh interferometer spectrum of the optical fiber under test is shown. The relative shift of the spectrum is caused by temperature / strain and system phase jitter. Figure 3 The Rayleigh interference spectrum of the reference optical fiber is shown in the figure, and the partially enlarged figure is shown in the figure. Figure 4 As shown, the relative shift of its spectrum is caused by the system phase jitter.

[0056] The demodulation of the optical time domain reflectometry system is completed based on the difference between the phase change of the optical fiber to be tested and the phase change of the reference optical fiber.

[0057] In summary, the present application provides an optical time domain reflectometry system and a demodulation method based on reference optical fiber phase compensation, the optical time domain reflectometry system acquires Rayleigh interference spectrum of the reference optical fiber and the to-be-measured optical fiber by being connected in series, can acquire the system phase shift amount in real time through the reference optical fiber, compensates the phase change of the to-be-measured optical fiber, avoids demodulating the light source phase jitter into temperature / strain change amount, realizes high-precision and high-sensitivity temperature / strain demodulation, and can effectively improve the environmental adaptability of the phase-OTDR system and enhance the engineering usability thereof.

[0058] In addition, it should be noted that the use of the terms "first", "second", etc. to define parts only facilitates the differentiation of 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 present application.

[0059] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Various modifications and changes can be made by those skilled in the art based on the principles and spirit of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An optical time domain reflectometry system based on reference fiber phase compensation, characterized in that: The optical time domain reflectometry system includes: a signal generator, a distributed feedback laser, a semiconductor fiber amplifier, a first amplifier, a circulator, a second amplifier, a filter, a detector, a reference fiber, and a fiber to be tested. The signal generator drives and controls the distributed feedback laser and the semiconductor fiber amplifier respectively; the continuous laser signal of the distributed feedback laser is converted into a pulsed light signal by the semiconductor fiber amplifier and amplified by the first amplifier; the amplified pulsed light signal enters the second port of the circulator through the first port of the circulator, and successively enters the reference fiber and the fiber to be tested; the fiber Rayleigh scattering signal enters the third port of the circulator through the second port, and then passes through the second amplifier and the filter in sequence. The detector obtains the Rayleigh interference spectrum of the reference fiber and the fiber to be tested based on the filtered scattering signal.

2. The optical time domain reflectometry system based on reference fiber phase compensation according to claim 1, characterized in that: The reference optical fiber is placed in a constant temperature environment and is in a relaxed state.

3. The optical time domain reflectometry system based on reference fiber phase compensation according to claim 1, characterized in that: The length of the reference optical fiber is at least twice the spatial resolution of the system, and the middle section of the reference optical fiber is used as the phase compensation monitoring area.

4. The optical time domain reflectometry system based on reference fiber phase compensation according to any one of claims 1 to 3, characterized in that: The measured length of the optical fiber to be measured is the difference between the system measurement distance and the length of the reference optical fiber.

5. The optical time domain reflectometry system based on reference fiber phase compensation according to claim 1, characterized in that: The first amplifier and the second amplifier both use erbium-doped fiber amplifiers.

6. The optical time domain reflectometry system based on reference fiber phase compensation according to any one of claims 1 to 4, characterized in that: The optical time domain reflectometry system further includes an acquisition card, which is connected to the signal generator and the detector respectively.

7. The optical time domain reflectometry system based on reference fiber phase compensation according to claim 6, characterized in that: The signal generator synchronously drives the acquisition card to realize synchronization of light source wavelength scanning, pulse modulation and signal acquisition.

8. A demodulation method for an optical time domain reflectometry system based on reference fiber phase compensation, characterized in that: The demodulation method of the optical time domain reflectometry system uses the optical time domain reflectometry system based on reference fiber phase compensation according to any one of claims 1 to 7 to realize phase demodulation.

9. The demodulation method of an optical time domain reflectometry system based on reference fiber phase compensation according to claim 8, characterized in that: The demodulation method of the optical time domain reflectometry system includes: Obtaining Rayleigh interference spectra of the reference fiber and the fiber to be tested respectively based on the optical time domain reflectometry system based on reference fiber phase compensation according to any one of claims 1 to 7; Obtaining phase changes of the reference optical fiber and the optical fiber to be tested according to the Rayleigh interference spectra of the reference optical fiber and the optical fiber to be tested; The phase change of the optical fiber to be tested is subtracted from the phase change of the reference optical fiber, and the demodulation of the optical time domain reflectometry system is completed based on the difference.

10. The demodulation method of an optical time domain reflectometry system based on reference fiber phase compensation according to claim 9, characterized in that: A cross-correlation operation is performed based on the Rayleigh interference spectra of the reference optical fiber and the optical fiber to be tested to obtain the phase changes of the reference optical fiber and the optical fiber to be tested.

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