Phi-OTDR and BOTDR fused ultra-long-distance multi-parameter sensing system and working method thereof

Abstract

The invention discloses a phi-OTDR and BOTDR fused ultra-long-distance multi-parameter sensing system and a working method thereof, relates to the technical field of optical fiber measurement, and is used for solving the problem of simultaneous measurement of multiple parameters in long-distance sensing. The system comprises a narrow linewidth light source, an optical fiber coupler, an acoustic optical modulator, a semiconductor optical amplifier, a random scrambler, a Raman laser, a circulator, a polarization beam splitter, a delay optical fiber, a wavelength division multiplexer, an erbium-doped optical fiber, a signal generator, an electro-optical modulator, a microwave generator, a fiber bragg grating, a photoelectric balance detector, a data acquisition card and the like. According to the invention, the phi-OTDR and the BOTDR of a coherent detection structure are fused, the extinction ratio of detection pulse light is improved through modulator cascade connection, and simultaneous measurement of ultra-long-distance temperature, strain and vibration parameters is realized under the assistance of bidirectional Raman amplification and remote pump amplification technologies; the system is high in fusion degree, low in cost and high in practicability, and has important application significance in the monitoring fields of ultra-long distance invasion, pipeline leakage, high-voltage transmission lines and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber measurement, and particularly relates to an ultra-long-distance multi-parameter sensing system integrating Φ-OTDR and BOTDR and a working method thereof. Background Art

[0002] Phase-sensitive optical time-domain reflectometer (Φ-OTDR) is a dynamic monitoring means based on optical fiber sensing. Its core principle is to accurately capture and analyze external environmental vibrations by analyzing the dynamic change information of backward Rayleigh scattered light in the sensing optical fiber. Under the condition of no external disturbance, the backward Rayleigh scattering signal presents a steady-state characteristic, and its amplitude and phase do not change significantly with time; when a vibration event occurs at a certain point along the optical fiber, the scattered light at this position will generate a dynamic phase fluctuation due to the instantaneous disturbance of the refractive index or mechanical deformation of the optical fiber. By comparing the differences in scattered signals at adjacent times (time-domain differential operation) and combining time-frequency analysis techniques (such as short-time Fourier transform), the system can quickly lock the position coordinates where the vibration occurs and accurately extract key parameters such as vibration frequency and intensity. Compared with traditional vibration sensing technologies, Φ-OTDR has significant advantages such as fast real-time response ability, ultra-high sensitivity detection performance, and full-region coverage monitoring. Currently, it has been applied in large-scale engineering in scenarios such as security perimeter monitoring, oil and gas pipeline safety monitoring, and high-voltage cable condition monitoring.

[0003] Brillouin optical time domain reflectometry (BOTDR) is a distributed sensing technology based on the Brillouin scattering effect in optical fibers, mainly used for long-distance and full-distributed temperature and strain measurements. Its core technology relies on the linear relationship between the frequency shift of Brillouin scattered light and the external physical quantities (temperature, strain) suffered by the optical fiber, and has advantages such as high precision, anti-electromagnetic interference, and no need to pre-install sensors. It is widely used in fields such as infrastructure health monitoring, energy pipeline safety assessment, and geological disaster warning.

[0004] However, Φ-OTDR is based on phase-sensitive detection of Rayleigh scattering, has extremely high sensitivity and fast response ability to dynamic disturbances (such as vibrations and instantaneous strains), but can only measure relative phase changes and cannot directly obtain absolute temperature or static strain information; BOTDR is based on the linear relationship between Brillouin frequency shift and temperature / strain, can measure the absolute temperature and static strain along the optical fiber, the spatial resolution is usually at the meter level, and the monitoring distance can reach more than 100 kilometers, but the sampling rate is low and it is difficult to capture high-frequency dynamic events. Summary of the Invention

[0005] In view of the above problems, the present invention proposes an ultra-long-distance multi-parameter sensing system integrating Φ-OTDR and BOTDR and its working method.

[0006] According to one aspect of the present invention, an ultra-long-distance multi-parameter sensing system integrating Φ-OTDR and BOTDR is proposed. The system includes a narrow-linewidth light source 1, a first optical fiber coupler 2, a second optical fiber coupler 3, an acousto-optic modulator 4, a first semiconductor optical amplifier 5, a random polarization scrambler 6, a third optical fiber coupler 7, a second semiconductor optical amplifier 8, a first circulator 11, a signal generator 17, an electro-optic modulator 18, a microwave generator 19, a second circulator 20, a fiber Bragg grating 21, a fourth optical fiber coupler 22, a photoelectric balanced detector 23, and a data acquisition card 24;

[0007] Among them, the optical signal output end of the narrow-linewidth light source 1 is connected to the optical signal input end of the first optical fiber coupler 2, and the two optical signal output ends of the first optical fiber coupler 2 are respectively connected to the input end of the second optical fiber coupler 3 and the input end of the electro-optic modulator 18;

[0008] The two optical signal output ends of the second optical fiber coupler 3 are respectively connected to the input end of the acousto-optic modulator 4 and the input end of the first semiconductor optical amplifier 5. The output end of the first semiconductor optical amplifier 5 is connected to the input end of the random polarization scrambler 6. The output ends of the acousto-optic modulator 4 and the random polarization scrambler 6 are respectively connected to the input end of the third optical fiber coupler 7. The output end of the third optical fiber coupler 7 is connected to the input end of the second semiconductor optical amplifier 8. The output end of the second semiconductor optical amplifier 8 is connected to the first optical signal port 11-1 of the first circulator 11. The second optical signal port 11-2 of the first circulator 11 is connected to the fiber group to be measured;

[0009] The output end of the electro-optic modulator 18 is connected to the first optical signal port 20-1 of the second circulator 20, and the output end of the microwave generator 19 is connected to the microwave signal loading end of the electro-optic modulator 18. The second optical signal port 20-2 of the second circulator 20 is connected to the fiber Bragg grating 21. The third optical signal port 11-3 of the first circulator 11 and the third optical signal port 20-3 of the second circulator 20 are respectively connected to the input end of the fourth optical fiber coupler 22. The output end of the fourth optical fiber coupler 22 is connected to the optical signal input end of the photoelectric balanced detector 23. The electrical signal output end of the photoelectric balanced detector 23 is connected to the electrical signal input end of the data acquisition card 24;

[0010] The microwave signal output end of the signal generator 17 is respectively connected to the microwave signal loading end of the first semiconductor optical amplifier 5, the microwave signal loading end of the acousto-optic modulator 4, and the trigger signal input end of the data acquisition card 24.

[0011] Further, the optical fiber group to be measured includes: a first Raman amplifier 9, a second Raman amplifier 10, a first polarization beam splitter 12, a delay optical fiber 13, a wavelength division multiplexer 14, a first erbium-doped optical fiber 15, a second erbium-doped optical fiber 16, a third Raman amplifier 25, a fourth Raman amplifier 26, and a second polarization beam splitter 27; a first optical fiber to be measured, a second optical fiber to be measured, a third optical fiber to be measured, and a fourth optical fiber to be measured;

[0012] Among them, the second optical signal port 11-2 of the first circulator 11 is connected to one end of the first optical fiber to be measured, and the other end of the first optical fiber to be measured is connected to the first port 14-1 of the wavelength division multiplexer 14; the output ends of the first Raman amplifier 9 and the second Raman amplifier 10 are respectively connected to the input end of the first polarization beam splitter 12, the output end of the first polarization beam splitter 12 is connected to one end of the delay optical fiber 13, the other end of the delay optical fiber 13 is connected to the second port 14-2 of the wavelength division multiplexer 14, the third port 14-3 of the wavelength division multiplexer 14 is connected to one end of the second optical fiber to be measured, the other end of the second optical fiber to be measured is connected to one end of the first erbium-doped optical fiber 15, the other end of the first erbium-doped optical fiber 15 is connected to one end of the third optical fiber to be measured, and the other end of the third optical fiber to be measured is connected to one end of the second erbium-doped optical fiber 16; the other end of the second erbium-doped optical fiber 16 is connected to one end of the fourth optical fiber to be measured, and the other end of the fourth optical fiber to be measured is connected to the output end of the second polarization beam splitter 27; the output ends of the third Raman amplifier 25 and the fourth Raman amplifier 26 are respectively connected to the input end of the second polarization beam splitter 27.

[0013] Further, the output power range of the narrow linewidth light source 1 is 10 mW to 40 mW, and the wavelength range is 1549 nm to 1551 nm.

[0014] Further, the coupling ratio of the first optical fiber coupler 2 is 90:10 or 80:20 or 70:30, the coupling ratio range of the second optical fiber coupler 3 is 50:50, the coupling ratio range of the third optical fiber coupler 7 is 50:50, and the coupling ratio range of the fourth optical fiber coupler 22 is 50:50.

[0015] Further, the extinction ratio range of the first semiconductor optical amplifier 5 is 40 dB to 60 dB, and the extinction ratio range of the second semiconductor optical amplifier 8 is 40 dB to 60 dB; the frequency shift range of the acousto-optic modulator 4 is 300 MHz - 600 MHz, and the extinction ratio range is 40 dB to 60 dB.

[0016] Further, the output optical power ranges of the first Raman amplifier 9, the second Raman amplifier 10, the third Raman amplifier 25, and the fourth Raman amplifier 26 are all 300 mW to 1000 mW, and the central wavelength ranges are 1470 nm to 1490 nm; the central wavelength range of the fiber Bragg grating 21 is 1549 nm to 1551 nm, and the bandwidth is 0.12 nm; the detection bandwidth range of the optoelectronic balanced detector 23 is 100 MHz to 1 GHz.

[0017] According to another aspect of the present invention, a working method of an ultra-long-distance multi-parameter sensing system integrating Φ-OTDR and BOTDR is proposed. The working method is implemented based on the above-mentioned ultra-long-distance multi-parameter sensing system integrating Φ-OTDR and BOTDR; the working method includes:

[0018] The continuous optical signal output by the narrow-linewidth light source 1 is divided into two paths by the first fiber coupler 2: the first upper branch and the first lower branch;

[0019] The continuous optical signal of the first upper branch is divided into two paths again by the second fiber coupler 3: the second upper branch and the second lower branch; the continuous optical signal of the second upper branch is modulated into an optical pulse signal by the acousto-optic modulator 4, and the continuous optical signal of the second lower branch is modulated into an optical pulse signal by the first semiconductor optical amplifier 5, and then the polarization state of the light is perturbed by the random polarization scrambler 6; the optical pulse output by the acousto-optic modulator 4 and the optical pulse output by the random polarization scrambler 6 are coupled together by the third fiber coupler 7, and then amplified by the second semiconductor optical amplifier 8, and then enter the first optical signal port of the first circulator 11, and enter the fiber optic cable to be measured through the second optical signal port of the first circulator 11;

[0020] The continuous optical signal of the first lower branch is phase-modulated by the electro-optic modulator 18, then filtered by the fiber Bragg grating 21 through the second optical signal port of the second circulator 20, and then output from the third optical signal port of the second circulator 20, and enters the fourth fiber coupler 22 for mixing together with the backward Rayleigh scattering and Brillouin scattering optical signals returned from the fiber optic cable to be measured output from the third optical signal port of the first circulator 11, and then is photoelectrically converted by the optoelectronic balanced detector 23, and the output photocurrent is processed and recorded by extracting the envelope through the data acquisition card 24;

[0021] The microwave generator 19 is used to provide a microwave modulation signal for the electro-optic modulator 18; the signal generator 17 is used to provide a driving signal for the first semiconductor optical amplifier 5, a modulation signal for the acousto-optic modulator 4, and a trigger signal for the data acquisition card 24.

[0022] Further, the working method further includes: the optical signal output from the second optical signal port of the first circulator 11 enters the first optical fiber to be measured; the laser beams output from the first Raman amplifier 9 and the second Raman amplifier 10 are polarization split by the first polarization beam splitter 12, then pass through the delay optical fiber 13, and the laser beam coming out of the delay optical fiber 13 and the optical signal entering the first optical fiber to be measured enter the wavelength division multiplexer 14 together for beam combination; the beam-combined optical signal enters the second optical fiber to be measured, and the tail end of the second optical fiber to be measured is sequentially connected to the first erbium-doped optical fiber 15, the third optical fiber to be measured, the second erbium-doped optical fiber 16, and the fourth optical fiber to be measured; the laser beams output from the third Raman amplifier 25 and the fourth Raman amplifier 26 are polarization split by the second polarization beam splitter 27 and then enter the fourth optical fiber to be measured to amplify the signal at the tail end; the erbium-doped optical fiber is used to realize remote pumping amplification of the detection optical pulse signal.

[0023] Further, the optical signal entering the optical fiber group to be measured from the second optical signal port of the first circulator 11 is expressed as follows:

[0024]

[0025] where t represents the optical wave propagation time; A4 represents the amplitude of the optical pulse signal E3(t) modulated by the second semiconductor optical amplifier 8; A2 is the amplitude of the optical pulse signal E1(t) modulated by the acousto-optic modulator 4; f is the output frequency of the narrow linewidth light source 1; Δf is the frequency shift of the acousto-optic modulator 4; is the initial output phase of the narrow linewidth light source 1; rect is the rectangular function; T1 is the width of the optical pulse signal E1(t) modulated by the acousto-optic modulator 4; A3 is the amplitude of the optical pulse signal E2(t) modulated by the first semiconductor optical amplifier 5; T2 is the width of the optical pulse signal E2(t) modulated by the first semiconductor optical amplifier 5, τ is the time delay between the optical pulse signal E2(t) and the optical pulse signal E1(t), and τ is greater than the maximum value of T1 and T2; T3 is the width of the optical pulse signal E3(t) modulated by the second semiconductor optical amplifier 8, and T3 > (T2 + T1 + τ);

[0026] The backward Rayleigh scattering optical signal E R (t) and the Brillouin scattering optical signal E B (t) are respectively expressed as follows:

[0027]

[0028] where A(t) is the amplitude of the backward Rayleigh scattering optical signal, is the phase of the backward Rayleigh scattering optical signal; A B (t) is the amplitude of the Brillouin scattering optical signal, f B is the Brillouin frequency shift, is the phase of the Brillouin scattering optical signal.

[0029] Furthermore, the peak optical power at any position of the fiber under test in the fiber group to be measured is expressed as:

[0030] P R (L) = exp{-g eff P0[(1 - R).e -αrd (e -αrL - 1) - R(e -αrL - 1)] / α r -α R L}

[0031] Among them, α r and α R respectively represent the transmission loss of the Raman pump light and the transmission loss of the signal light; g eff is the effective gain coefficient; P0 is the total output power of the first Raman amplifier 9, the second Raman amplifier 10, the third Raman amplifier 25, and the fourth Raman amplifier 26; d is the total length of all fibers under test; L is the position of the fiber under test; R is the percentage of the sum of the output powers of the first Raman amplifier 9 and the second Raman amplifier 10 in the total power P0, 0 < R < 1;

[0032] The effective output power of the optoelectronic balanced detector 23 is: P H = 2G 2 P R P L

[0033] Among them, G is the responsivity of the optoelectronic balanced detector 23, P R is the power of the backward Rayleigh scattering optical signal, and P L is the power of the eigen-optical signal input from the third optical signal port of the second circulator 20 to the fourth fiber coupler 22.

[0034] The beneficial technical effects of the present invention are:

[0035] The present invention proposes an ultra-long-distance multi-parameter sensing system integrating Φ-OTDR and BOTDR. By cascading an acousto-optic modulator, a first semiconductor optical amplifier, and a second semiconductor optical amplifier, the extinction ratio of the detection pulse optical signal in the system is improved, avoiding the continuous leakage of continuous light caused by low-duty-cycle pulsed light in the ultra-long sensing distance system, thereby deteriorating the signal-to-noise ratio and spatial resolution ability of the system. In addition, the cascading of multiple modulators replaces the erbium-doped fiber amplifier in the traditional system, avoiding the continuous generation of ASE noise. A first Raman amplifier, a second Raman amplifier, a third Raman amplifier, and a fourth Raman amplifier are used to form bidirectional Raman amplification, and remote pumping is provided for the first erbium-doped fiber and the second erbium-doped fiber to form remote pumping amplification, thereby realizing ultra-long-distance sensing and eliminating relay power supply, which is convenient for flexible application in the field of ultra-long-distance monitoring. Multi-frequency continuous reference light is used to perform beat frequency in different frequency bands with the Rayleigh scattering signal and the Brillouin scattering signal in the optical fiber respectively. Further, signals in different frequency bands can be analyzed in the digital domain, and temperature, strain, and vibration parameters along the sensing optical fiber can be obtained simultaneously.

[0036] The present invention realizes the high integration of the system, effectively saves the detection and acquisition costs, breaks through the limitations of single technology, realizes the integrated perception of "dynamic tracking + static diagnosis", and has important application value in the fields of smart cities, energy security, geological disaster warning, etc., especially suitable for scenarios that require both real-time response and long-term stability monitoring. Brief Description of the Drawings

[0037] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features, and advantages of the exemplary embodiments of the present invention will become readily understood. In the drawings, several embodiments of the present invention are shown in an exemplary rather than restrictive manner, wherein:

[0038] Figure 1 It is a schematic structural diagram of an ultra-long-distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to the present invention.

[0039] Figure 2 It is a simulation result diagram of the Raman amplified scattered optical signal in the embodiment of the present invention.

[0040] Figure 3 It is an experimental result diagram of the Brillouin frequency shift in the embodiment of the present invention.

[0041] Figure 4 It is an experimental result diagram of the Rayleigh scattered optical signal in the embodiment of the present invention. Detailed Embodiments

[0042] The principles and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are provided only to enable those skilled in the art to better understand and then implement the present invention, rather than limiting the scope of the present invention in any way. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to be able to fully convey the scope of the present disclosure to those skilled in the art.

[0043] The frequency bands of Rayleigh scattering (Φ-OTDR) and Brillouin scattering (BOTDR) are different (the Brillouin frequency shift is about 10 - 11 GHz). Using these characteristics, the Rayleigh scattering signal and the Brillouin scattering signal can be well separated. Φ-OTDR and BOTDR are two core technologies in the field of fiber optic sensing, respectively based on the Rayleigh scattering and Brillouin scattering effects, with different physical characteristics and application scenarios. With the growth of the demand for long-distance infrastructure monitoring (such as oil and gas pipelines, high-speed railway tracks, submarine cables, etc.), a single sensing technology is difficult to meet the requirements of multi-parameter, high-precision, and full-distributed monitoring. By fusing Φ-OTDR and BOTDR, not only can the same sensing fiber and part of the optical path (such as lasers, couplers) be shared, reducing the hardware complexity, but also the advantages of both can be fully utilized to achieve the combination of dynamic and static, multi-parameter collaborative sensing, and improve the comprehensive performance of the system; the fusion of the two can cover the monitoring requirements of dynamic and static parameters: Φ-OTDR is used to capture vibration or deformation events in real time, and BOTDR provides environmental temperature compensation and long-term structural health assessment, forming a collaborative mechanism of "dynamic trigger + static calibration".

[0044] Therefore, an embodiment of the present invention proposes an ultra-long-distance multi-parameter sensing system that fuses Φ-OTDR and BOTDR, such as Figure 1 shown, the system includes: a narrow linewidth light source 1, a first fiber coupler 2, a second fiber coupler 3, an acousto-optic modulator 4, a first semiconductor optical amplifier 5, a random polarization scrambler 6, a third fiber coupler 7, a second semiconductor optical amplifier 8, a first Raman amplifier 9, a second Raman amplifier 10, a first circulator 11, a first polarization beam splitter 12, a delay fiber 13, a wavelength division multiplexer 14, a first erbium-doped fiber 15, a second erbium-doped fiber 16, a signal generator 17, an electro-optic modulator 18, a microwave generator 19, a second circulator 20, a fiber Bragg grating 21, a fourth fiber coupler 22, a photoelectric balanced detector 23, a data acquisition card 24, a third Raman amplifier 25, a fourth Raman amplifier 26, a second polarization beam splitter 27; the fiber under test includes a first fiber under test, a second fiber under test, a third fiber under test, and a fourth fiber under test;

[0045] Among them, the optical signal output end of the narrow linewidth light source 1 is connected to the optical signal input end of the first optical fiber coupler 2, and the two optical signal output ends of the first optical fiber coupler 2 are respectively connected to the input end of the second optical fiber coupler 3 and the input end of the electro-optic modulator 18; the two optical signal output ends of the second optical fiber coupler 3 are respectively connected to the input end of the acousto-optic modulator 4 and the input end of the first semiconductor optical amplifier 5, the output end of the first semiconductor optical amplifier 5 is connected to the input end of the random polarization scrambler 6, the output ends of the acousto-optic modulator 4 and the random polarization scrambler 6 are respectively connected to the input end of the third optical fiber coupler 7, the output end of the third optical fiber coupler 7 is connected to the input end of the second semiconductor optical amplifier 8, and the output end of the second semiconductor optical amplifier 8 is connected to the first optical signal port 11-1 of the first optical circulator 11;

[0046] The second optical signal port 11-2 of the first optical circulator 11 is connected to the first optical fiber under test, the other end of the first optical fiber under test is connected to the first port 14-1 of the wavelength division multiplexer 14, the output ends of the first Raman amplifier 9 and the second Raman amplifier 10 are respectively connected to the input end of the first polarization beam splitter 12, the output end of the first polarization beam splitter 12 is connected to the delay optical fiber 13, the delay optical fiber 13 is connected to the second port 14-2 of the wavelength division multiplexer 14, the third port 14-3 of the wavelength division multiplexer 14 is connected to the second optical fiber under test, the other end of the second optical fiber under test is connected to the first erbium-doped optical fiber 15, the other end of the first erbium-doped optical fiber 15 is connected to the third optical fiber under test, the other end of the third optical fiber under test is connected to the second erbium-doped optical fiber 16, the other end of the second erbium-doped optical fiber 16 is connected to the fourth optical fiber under test, the other end of the fourth optical fiber under test is connected to the output end of the second polarization beam splitter 27, and the output ends of the third Raman amplifier 25 and the fourth Raman amplifier 26 are respectively connected to the input end of the second polarization beam splitter 27;

[0047] The output end of the electro-optic modulator 18 is connected to the first optical signal port 20-1 of the second optical circulator 20, the output end of the microwave generator 19 is connected to the microwave signal loading end of the electro-optic modulator 18, the second optical signal port 20-2 of the second optical circulator 20 is connected to the fiber Bragg grating 21, the third optical signal port 11-3 of the first optical circulator 11 and the third optical signal port 20-3 of the second optical circulator 20 are respectively connected to the input end of the fourth optical fiber coupler 22, the output end of the fourth optical fiber coupler 22 is connected to the optical signal input end of the photoelectric balanced detector 23, and the electrical signal output end of the photoelectric balanced detector 23 is connected to the electrical signal input end of the data acquisition card 24;

[0048] The microwave signal output end of the signal generator 17 is respectively connected to the microwave signal loading end of the first semiconductor optical amplifier 5, the microwave signal loading end of the acousto-optic modulator 4, and the trigger signal input end of the data acquisition card 24.

[0049] In this embodiment, preferably, the output power range of the narrow linewidth light source 1 is 10 mW to 40 mW, and the wavelength range is 1549 nm to 1551 nm. Specifically, the output power of the narrow linewidth light source 1 is 20 mW, and the wavelength is 1550.214 nm.

[0050] In this embodiment, preferably, the coupling ratio of the first optical fiber coupler 2 is 90:10 or 80:20 or 70:30, the coupling ratio of the second optical fiber coupler 3 is 50:50, the coupling ratio of the third optical fiber coupler 7 is 50:50, and the coupling ratio of the fourth optical fiber coupler 22 is 50:50.

[0051] In this embodiment, preferably, the extinction ratio range of the first semiconductor optical amplifier 5 is 40 dB to 60 dB, and the extinction ratio range of the second semiconductor optical amplifier 8 is 40 dB to 60 dB; the frequency shift range of the acousto-optic modulator 4 is 300 MHz - 600 MHz, and the extinction ratio range is 40 dB to 60 dB. Specifically, the frequency shift of the acousto-optic modulator 4 is 400 MHz, and the extinction ratio is 45 dB.

[0052] In this embodiment, preferably, the output optical power ranges of the first Raman amplifier 9, the second Raman amplifier 10, the third Raman amplifier 25, and the fourth Raman amplifier 26 are all 300 mW to 1000 mW, and the center wavelength ranges are 1470 nm to 1490 nm; specifically, the output optical power of the first Raman amplifier 9 is 500 mW, the center wavelength is 1480 nm, the output optical power of the second Raman amplifier 10 is 500 mW, the center wavelength is 1480 nm, the output optical power of the third Raman amplifier 25 is 500 mW, the center wavelength is 1480 nm, and the output optical power of the fourth Raman amplifier 26 is 500 mW, the center wavelength is 1480 nm.

[0053] In this embodiment, preferably, the center wavelength range of the fiber Bragg grating 21 is 1549 nm to 1551 nm, and the bandwidth is 0.12 nm; the detection bandwidth range of the optoelectronic balanced detector 23 is 100 MHz to 1 GHz. Specifically, the center wavelength of the fiber Bragg grating 21 is 1549.782 nm, and the bandwidth is 0.1 nm. The detection bandwidth of the optoelectronic balanced detector 23 is 1 GHz.

[0054] Another embodiment of the present invention proposes a working method for an ultra-long-distance multi-parameter sensing system that combines Φ-OTDR and BOTDR. The working method is implemented based on an ultra-long-distance multi-parameter sensing system that combines Φ-OTDR and BOTDR described in the above embodiment; the working method includes:

[0055] The continuous optical signal with a central wavelength of 1550 nm output by the narrow linewidth light source 1 is divided into two paths by the first fiber coupler 2: the first upper branch and the first lower branch; the continuous optical signal of the first upper branch coming out of the first fiber coupler 2 is divided into two paths by the second fiber coupler 3: the second upper branch and the second lower branch; the continuous optical signal of the second upper branch coming out of the second fiber coupler 3 is modulated into an optical pulse signal by the acousto-optic modulator 4, and the continuous optical signal of the second lower branch coming out of the second fiber coupler 3 is modulated into an optical pulse signal by the first semiconductor optical amplifier 5. The optical signal coming out of the first semiconductor optical amplifier 5 is depolarized by the random depolarizer 6. The optical pulse at the output end of the acousto-optic modulator 4 and the optical pulse at the output end of the random depolarizer 6 are coupled together by the third fiber coupler 7 and then amplified by the second semiconductor optical amplifier 8; the optical signal output by the second semiconductor optical amplifier 8 enters the first optical signal port of the first optical circulator 11 and enters the first fiber under test from the second optical signal port of the first optical circulator 11;

[0056] The lasers with a central wavelength of 1480 nm output by the first Raman amplifier 9 and the second Raman amplifier 10 pass through the first polarization beam splitter 12, and then the lasers coming out after passing through the delay fiber 13 enter the second port of the wavelength division multiplexer 14. The optical signal coming out of the first fiber under test enters the first port of the wavelength division multiplexer 14. After passing through the wavelength division multiplexer 14, the above two kinds of lasers enter the second fiber under test together. The tail end of the second fiber under test is connected to the first erbium-doped fiber 15 to realize remote pumping amplification of the detected optical pulse signal; the tail end of the first erbium-doped fiber 15 is successively connected to the third fiber under test, the second erbium-doped fiber 16, and the fourth fiber under test to meet the requirements of long-distance detection; the lasers with a central wavelength of 1480 nm output by the third Raman amplifier 25 and the fourth Raman amplifier 26 are connected to the fourth fiber under test through the second polarization beam splitter 27 to realize amplification of the tail end signal;

[0057] The continuous optical signal of the first lower branch coming out of the first fiber coupler 2 is phase-modulated by the electro-optic modulator 18, then injected into the fiber Bragg grating 21 for filtering through the second optical signal port of the second optical circulator 20, and then output from the third optical signal port of the second optical circulator 20; then it enters the fourth fiber coupler 22 together with the backward Rayleigh scattering and Brillouin scattering optical signals returned from the fiber under test output from the third optical signal port of the first optical circulator 11 for mixing, and is photoelectrically converted by the photoelectric balanced detector 23. The output photocurrent extracts the envelope through the data acquisition card 24 and is processed and recorded;

[0058] The microwave generator 19 is used to provide a microwave modulation signal for the electro-optic modulator 18; the signal generator 17 is used to provide a driving signal for the first semiconductor optical amplifier 5, a modulation signal for the acousto-optic modulator 4, and a trigger signal for the data acquisition card 24.

[0059] Due to the different frequency bands of Rayleigh scattering and Brillouin scattering, the electro-optic modulator 18 can modulate the continuous optical signal of the first lower branch output from the first optical fiber coupler 2. After mixing through the fourth optical fiber coupler 22, the signals of temperature and vibration can be captured and extracted. Finally, the extracted temperature and vibration signals are subjected to time-frequency conversion to complete the positioning of the vibration information along the sensing system, the characterization of the frequency information, and the capture of the temperature change information along the sensing system.

[0060] Further, the single-frequency continuous light output by the narrow-linewidth light source 1 is set as E(t):

[0061]

[0062] where A1 is the amplitude of the single-frequency continuous light. E(t) is modulated by the acousto-optic modulator 4 into an optical pulse signal E1(t) and a frequency shift of Δf is generated:

[0063]

[0064] where t is the optical wave propagation time, A2 is the amplitude of the optical pulse signal E1(t), rect is the rectangular function, T1 is the width of the optical pulse signal E1(t); f is the output frequency of the narrow-linewidth light source 1, Δf is the frequency shift of the acousto-optic modulator 4, is the initial phase of the output of the narrow-linewidth light source 1.

[0065] The single-frequency continuous light E(t) output by the narrow-linewidth light source 1 is modulated by the first semiconductor optical amplifier 5 into an optical pulse signal E2(t):

[0066]

[0067] where A3 is the amplitude of the optical pulse signal E2(t), T2 is the width of the optical pulse signal E2(t), τ is the time delay between the optical pulse signal E2(t) and the optical pulse signal E1(t), and τ > max(T1, T2).

[0068] The optical pulse signal E2(t) modulated by the first semiconductor optical amplifier 5 passes through the random polarization scrambler 6 and is combined with the optical pulse signal E1(t) modulated by the acousto-optic modulator 4 through the third optical fiber coupler 7 to obtain E c (t):

[0069]

[0070] E c (t) is further modulated by the second semiconductor optical amplifier 8 into an optical pulse signal E3(t) and is injected into the optical fiber through the first circulator 11:

[0071]

[0072] Among them, A4 represents the amplitude of the optical pulse signal E3(t); T3 is the width of the optical pulse signal E3(t), and T3 > (T2 + T1 + τ).

[0073] Assume that the reference optical signal after being modulated by the electro-optic modulator 18 is E L (t), the reference optical signal after being filtered by the fiber Bragg grating 21 is E K (t), the backward Rayleigh scattering optical signal is E R (t), and the Brillouin scattering optical signal is E B (t):

[0074]

[0075]

[0076] Among them, A5 is the amplitude of the continuous optical wave with frequency f after being modulated by the electro-optic modulator 18, A m and f m are the amplitude and frequency of the modulation signal output by the microwave generator 19; B is the amplitude of the reference optical signal; A(t) is the amplitude of the backward Rayleigh scattering optical signal, A B (t) is the amplitude of the Brillouin scattering optical signal, f B is the Brillouin frequency shift, is the phase of the backward Rayleigh scattering optical signal, is the phase of the Brillouin scattering optical signal.

[0077] The backward Rayleigh scattering optical signal E R (t) and the Brillouin scattering optical signal E B (t) are respectively frequency-mixed with the reference optical signal E K (t) by the fourth fiber coupler 22. Due to the limitation of the detector response frequency, only the beat signal |f K -f B | of the reference optical signal E m -f B | and the reference optical signal E K (t) and the backward Rayleigh scattering optical signal E R (t) can be detected. The beat signals of the data collected by the data acquisition card 24 are respectively filtered and demodulated, so as to realize the simultaneous measurement of Rayleigh scattering and Brillouin scattering. The beat signal of the backward Rayleigh scattering optical signal and the beat signal of the Brillouin scattering optical signal should satisfy the following formula:

[0078] Δf > |f m -f B |

[0079] Further, the output power distributions of the first Raman amplifier 9, the second Raman amplifier 10, the third Raman amplifier 25, and the fourth Raman amplifier 26 are as follows:

[0080] P R (L) = exp{-g eff P0[(1 - R).e -αrd (e -αrL -1) - R(e -αrL -1)] / α r -α R L}

[0081] Among them, P R (L) is the peak optical power at position L in the fiber to be measured; α r and α R respectively represent the transmission loss of the Raman pump light and the transmission loss of the signal light; g eff is the effective gain coefficient; P0 is the total output power of the first Raman amplifier 9, the second Raman amplifier 10, the third Raman amplifier 25, and the fourth Raman amplifier 26; d is the total length of the fiber to be measured; R is the percentage of the sum of the output powers of the first Raman amplifier 9 and the second Raman amplifier 10 in the total power P0, and 0 < R < 1.

[0082] The effective output power of the optoelectronic balance detector 23 in the system is P H :

[0083] P H = 2G 2 P R P L

[0084] Among them, G is the responsivity of the optoelectronic balance detector 23, P R is the power of the backward Rayleigh scattered light signal, and P L is the power of the intrinsic optical signal input from the third optical signal port of the second circulator 20 to the fourth fiber coupler 22. P H is much greater than the output power of the direct detection system

[0085] Further, the technical effects of the present invention are verified through experiments.

[0086] Figure 2 is the simulation result diagram of the Raman amplified scattered light signal. As Figure 2 shown, when the optical power of the laser pulse remains unchanged, the power of the Rayleigh scattered light returning in the fiber gradually decays with the sensing distance, and with the increase of the Raman pump optical power, the power of the Rayleigh scattered light in the fiber will also increase accordingly, thereby increasing the sensing distance and realizing Raman pump light amplification.

[0087] Figure 3It is a graph of the experimental results of Brillouin frequency shift. As Figure 3 shown, on a 275-kilometer sensing optical fiber, the Brillouin scattering frequency shift spectrum diagram obtained by analyzing the returned Brillouin scattering optical signal. Based on the linear relationship between Brillouin frequency shift and temperature / strain, the absolute temperature and static strain along the optical fiber can be measured.

[0088] Figure 4 It is a graph of the experimental results of Rayleigh scattering optical signal. As Figure 4 shown, on a 275-kilometer sensing optical fiber, the Rayleigh signal amplitude diagram obtained by analyzing the returned Rayleigh scattering optical signal. By analyzing the dynamic change information of the backward Rayleigh scattering light in the sensing optical fiber, the accurate capture and analysis of external environmental vibration can be realized.

[0089] The present invention proposes an ultra-long-distance multi-parameter sensing system integrating Φ-OTDR and BOTDR and its working method. By cascading multiple modulators, the extinction ratio of the detection pulse optical signal in the fusion system is improved, avoiding the continuous leakage of continuous light caused by low-duty-cycle pulse light in the ultra-long sensing distance system, thereby deteriorating the signal-to-noise ratio and spatial resolution ability of the system. In addition, the cascading of multiple modulators replaces the erbium-doped fiber amplifier in the traditional system, avoiding the continuous generation of ASE noise. The ultra-long-distance sensing is realized by using bidirectional Raman amplification and remote pumping technology, and at the same time, relay power supply is eliminated, which is convenient for flexible application in the field of ultra-long-distance monitoring. Multiple-frequency continuous reference light is used to beat with the Rayleigh scattering signal and Brillouin scattering signal in the optical fiber in different frequency bands, and the signals in different frequency bands are analyzed in the digital domain to obtain the temperature, strain and vibration parameters along the sensing optical fiber at the same time. The present invention realizes the high integration of the system, effectively saves the detection and acquisition costs, and realizes the integrated perception of "dynamic tracking + static diagnosis", which has important application value in the fields of smart city, energy security, geological disaster warning, etc., especially in the scenarios that take into account real-time response and long-term stability monitoring.

[0090] Although the spirit and principles of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the specific embodiments disclosed, and the division of each aspect does not mean that the features in these aspects cannot be combined for benefit. This division is only for the convenience of expression. The present invention aims to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR, characterized in that: It comprises a narrow linewidth light source (1), a No. 1 optical fiber coupler (2), a No. 2 optical fiber coupler (3), an acousto-optic modulator (4), a No. 1 semiconductor optical amplifier (5), a random polarization scrambler (6), a No. 3 optical fiber coupler (7), a No. 2 semiconductor optical amplifier (8), a No. 1 circulator (11), a signal generator (17), an electro-optic modulator (18), a microwave generator (19), a No. 2 circulator (20), a fiber Bragg grating (21), a No. 4 optical fiber coupler (22), a photoelectric balance detector (23), and a data acquisition card (24); The optical signal output end of the narrow linewidth light source (1) is connected to the optical signal input end of the first optical fiber coupler (2), and the two optical signal output ends of the first optical fiber coupler (2) are respectively connected to the input end of the second optical fiber coupler (3) and the input end of the electro-optic modulator (18); The two optical signal output ends of the second optical fiber coupler (3) are respectively connected to the input end of the acousto-optic modulator (4) and the input end of the first semiconductor optical amplifier (5), the output end of the first semiconductor optical amplifier (5) is connected to the input end of the random polarization scrambler (6), the output end of the acousto-optic modulator (4) and the output end of the random polarization scrambler (6) are respectively connected to the input end of the third optical fiber coupler (7), the output end of the third optical fiber coupler (7) is connected to the input end of the second semiconductor optical amplifier (8), the output end of the second semiconductor optical amplifier (8) is connected to the first optical signal port (11-1) of the first circulator (11), and the second optical signal port (11-2) of the first circulator (11) is connected to the optical fiber group to be tested; The output end of the electro-optic modulator (18) is in communication with the first optical signal port (20-1) of the second circulator (20), and the output end of the microwave generator (19) is in communication with the microwave signal loading end of the electro-optic modulator (18); the second optical signal port (20-2) of the second circulator (20) is in communication with the fiber Bragg grating (21); the third optical signal port (11-3) of the first circulator (11) and the third optical signal port (20-3) of the second circulator (20) are respectively in communication with the input end of the fourth optical fiber coupler (22); the output end of the fourth optical fiber coupler (22) is in communication with the optical signal input end of the photoelectric balance detector (23), and the electrical signal output end of the photoelectric balance detector (23) is in communication with the electrical signal input end of the data acquisition card (24); The microwave signal output end of the signal generator (17) is respectively connected to the microwave signal loading end of the first semiconductor optical amplifier (5), the microwave signal loading end of the acousto-optic modulator (4), and the trigger signal input end of the data acquisition card (24).

2. The ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to claim 1, characterized in that: The optical fiber group to be tested comprises: a No. 1 Raman amplifier (9), a No. 2 Raman amplifier (10), a No. 1 polarization beam splitter (12), a delay optical fiber (13), a wavelength division multiplexer (14), a No. 1 erbium-doped optical fiber (15), a No. 2 erbium-doped optical fiber (16), a No. 3 Raman amplifier (25), a No. 4 Raman amplifier (26), and a No. 2 polarization beam splitter (27); a No. 1 optical fiber to be tested, a No. 2 optical fiber to be tested, a No. 3 optical fiber to be tested, and a No. 4 optical fiber to be tested; The second optical signal port (11-2) of the first circulator (11) is connected to one end of the first optical fiber to be tested, and the other end of the first optical fiber to be tested is connected to the first port (14-1) of the wavelength division multiplexer (14); the output end of the first Raman amplifier (9) and the output end of the second Raman amplifier (10) are respectively connected to the input end of the first polarization beam splitter (12), the output end of the first polarization beam splitter (12) is connected to one end of the delay optical fiber (13), the other end of the delay optical fiber (13) is connected to the second port (14-2) of the wavelength division multiplexer (14), and the third end of the wavelength division multiplexer (14) is connected to the input end of the first polarization beam splitter (12). The port (14-3) is connected to one end of the No. 2 optical fiber to be tested, the other end of the No. 2 optical fiber to be tested is connected to one end of the No. 1 erbium-doped optical fiber (15), the other end of the No. 1 erbium-doped optical fiber (15) is connected to one end of the No. 3 optical fiber to be tested, and the other end of the No. 3 optical fiber to be tested is connected to one end of the No. 2 erbium-doped optical fiber (16); the other end of the No. 2 erbium-doped optical fiber (16) is connected to one end of the No. 4 optical fiber to be tested, and the other end of the No. 4 optical fiber to be tested is connected to the output end of the No. 2 polarization beam splitter (27); the output end of the No. 3 Raman amplifier (25) and the output end of the No. 4 Raman amplifier (26) are respectively connected to the input end of the No. 2 polarization beam splitter (27).

3. An ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to claim 1 or 2, characterized in that: The narrow linewidth light source (1) has an output power range of 10 mW to 40 mW and a wavelength range of 1549 nm to 1551 nm.

4. The ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to claim 1 or 2, characterized in that: The coupling ratio of the first optical fiber coupler (2) is 90:10 or 80:20 or 70:30, the coupling ratio range of the second optical fiber coupler (3) is 50:50, the coupling ratio range of the third optical fiber coupler (7) is 50:50, and the coupling ratio range of the fourth optical fiber coupler (22) is 50:

50.

5. The ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to claim 1 or 2, characterized in that: The extinction ratio range of the first semiconductor optical amplifier (5) is 40dB-60dB, and the extinction ratio range of the second semiconductor optical amplifier (8) is 40dB-60dB; the frequency shift range of the acousto-optic modulator (4) is 300MHz-600MHz, and the extinction ratio range is 40dB-60dB.

6. The ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to claim 2, characterized in that: The output optical power ranges of the No. 1 Raman amplifier (9), the No. 2 Raman amplifier (10), the No. 3 Raman amplifier (25) and the No. 4 Raman amplifier (26) are all 300 mW to 1000 mW, and the central wavelength range is 1470 nm to 1490 nm; the central wavelength range of the fiber Bragg grating (21) is 1549 nm to 1551 nm, and the bandwidth is 0.12 nm; the detection bandwidth range of the photoelectric balance detector (23) is 100 MHz to 1 GHz.

7. A working method of an ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR, characterized in that: The working method is implemented based on an ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to any one of claims 1 to 6; the working method comprises: The continuous optical signal output by the narrow linewidth light source (1) is divided into two paths by a first optical fiber coupler (2): a first upper branch and a first lower branch; The continuous optical signal of the first upper branch is divided into two paths again through the second optical fiber coupler (3): the second upper branch and the second lower branch; the continuous optical signal of the second upper branch is modulated into an optical pulse signal through the acousto-optic modulator (4), and the continuous optical signal of the second lower branch is modulated into an optical pulse signal through the first semiconductor optical amplifier (5), and then the polarization state of the light is scrambled through the random polarization scrambler (6); the optical pulse output by the acousto-optic modulator (4) and the optical pulse output by the random polarization scrambler (6) are coupled together through the third optical fiber coupler (7), and then optically amplified through the second semiconductor optical amplifier (8), and then enter the first optical signal port of the first circulator (11), and enter the optical fiber group to be tested through the second optical signal port of the first circulator (11); The continuous optical signal of the first lower branch is phase modulated by an electro-optic modulator (18), injected into a fiber Bragg grating (21) for filtering via the second optical signal port of the second circulator (20), then outputted from the third optical signal port of the second circulator (20), and mixed with the backward Rayleigh scattered and Brillouin scattered optical signals returned by the optical fiber group to be tested and outputted from the third optical signal port of the first circulator (11) by entering the fourth optical fiber coupler (22), then photoelectrically converted by a photoelectric balanced detector (23), and the outputted photocurrent is extracted through a data acquisition card (24) for envelope processing and recording; The microwave generator (19) is used to provide a microwave modulation signal for the electro-optic modulator (18); the signal generator (17) is used to provide a driving signal for a semiconductor optical amplifier (5), a modulation signal for the acousto-optic modulator (4), and a trigger signal for the data acquisition card (24).

8. The working method of the ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to claim 7, characterized in that: The working method also includes: The optical signal output from the second optical signal port of the first circulator (11) enters the first optical fiber to be tested; the laser light output from the first Raman amplifier (9) and the second Raman amplifier (10) is polarized and split through the first polarization beam splitter (12), and then passes through the delay optical fiber (13). The laser light output from the delay optical fiber (13) and the optical signal entering the first optical fiber to be tested enter the wavelength division multiplexer (14) for beam combination; the beam combined optical signal enters the second optical fiber to be tested, and the tail end of the second optical fiber to be tested is connected to the first erbium-doped optical fiber (15), the third optical fiber to be tested, the second erbium-doped optical fiber (16), and the fourth optical fiber to be tested in sequence; the laser light output from the third Raman amplifier (25) and the fourth Raman amplifier (26) is polarized and split through the second polarization beam splitter (27), and then enters the fourth optical fiber to be tested to achieve amplification of the tail end signal; wherein the erbium-doped optical fiber is used to achieve remote pump amplification of the detection optical pulse signal.

9. The working method of the ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to claim 8, characterized in that: The optical signal entering the optical fiber group to be tested from the second optical signal port of the first circulator (11) is expressed as follows: Wherein, t represents the propagation time of the light wave; A4 represents the amplitude of the optical pulse signal E3(t) modulated by the second semiconductor optical amplifier (8); A2 represents the amplitude of the optical pulse signal E1(t) modulated by the acousto-optic modulator (4); f represents the output frequency of the narrow linewidth light source (1); Δf represents the shift frequency of the acousto-optic modulator (4); is the output initial phase of the narrow linewidth light source (1); rect is a rectangular function; T1 is the width of the optical pulse signal E1(t) modulated by the acousto-optic modulator (4); A3 is the amplitude of the optical pulse signal E2(t) modulated by the first semiconductor optical amplifier (5); T2 is the width of the optical pulse signal E2(t) modulated by the first semiconductor optical amplifier (5); τ is the time delay between the optical pulse signal E2(t) and the optical pulse signal E1(t), τ is greater than the maximum value of T1 and T2; T3 is the width of the optical pulse signal E3(t) modulated by the second semiconductor optical amplifier (8), and T3>(T2+T1+τ); The backscattered light signal E returned by the optical fiber group under test R (t), Brillouin scattered light signal E B (t) are respectively expressed as follows: Where A(t) is the amplitude of the backscattered Rayleigh light signal, is the phase of the backscattered Rayleigh light signal; A B (t) is the amplitude of the Brillouin scattered light signal, f B is the Brillouin frequency shift, is the phase of the Brillouin scattered light signal.

10. The working method of the ultra-long distance multi-parameter sensing system integrating Φ-OTDR and BOTDR according to claim 9, characterized in that: The peak optical power at any position of the optical fiber to be tested in the optical fiber group to be tested is expressed as: P R (L)=exp{-g eff P0[(1-R).e -αrd (and -αrL -1)-R(e -αrL -1)] / α r -α R L} Among them, α r and α R represent the transmission loss of Raman pump light and signal light respectively; g eff is the effective gain coefficient; P0 is the total output power of the first Raman amplifier (9), the second Raman amplifier (10), the third Raman amplifier (25), and the fourth Raman amplifier (26); d is the total length of all the optical fibers to be tested; L is the position of the optical fiber to be tested; R is the percentage of the sum of the output powers of the first Raman amplifier (9) and the second Raman amplifier (10) in the total power P0, 0<R<1; The effective output power of the photoelectric balance detector (23) is: P H =2G 2 P R P L Wherein, G is the responsivity of the photoelectric balance detector (23), P R is the power of the backscattered Rayleigh light signal, P L It is the power of the intrinsic optical signal input to the fourth optical fiber coupler (22) from the third optical signal port of the second circulator (20).

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