High-spatial-resolution multi-parameter fusion type distributed optical fiber sensing system

Abstract

The invention discloses a high-spatial-resolution multi-parameter fusion type distributed optical fiber sensing system, and the system comprises a light source module which is used for providing a light source for the whole sensing system, and generating two branches of laser output; the pulse generation module is used for generating pulsed light by using the first light branch; the first optical fiber circulator is used for transmitting the pulsed light and scattered light returned from the sensing optical fiber; the scattered light separation module is used for receiving the scattered light returned by the first optical fiber circulator and separating the scattered light into Brillouin scattered light and Rayleigh scattered light; the local oscillation light generation module is used for generating BOTDR local oscillation light and # imgabs0 # local oscillation light by utilizing the second optical branch; the coherent detection module is used for carrying out coherent detection on Brillouin scattered light and BOTDR local oscillation light and carrying out coherent detection on Rayleigh scattered light and # imgabs1 # local oscillation light so as to obtain corresponding electric signals; and the data acquisition device is used for acquiring the corresponding electric signal. The spatial resolution index of the method reaches 1m or even better.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber sensing, and in particular relates to a high spatial resolution multi-parameter fusion type distributed optical fiber sensing system. Background Art

[0002] In industries such as oil and gas and civil engineering, conventional technologies can only achieve point measurements, which is difficult to meet development needs. Distributed fiber optic sensing (DFOS) systems have shown great potential due to their high sensitivity, stable performance, weak electromagnetic interference, low signal loss, and adaptability to harsh environments. They can achieve real-time online monitoring of large-scale sensor networks. Common DOFS mainly includes phase-sensitive optical time domain reflectometry Distributed acoustic sensing technology (DAS) based on Raman optical time domain reflectometry (ROTDR) distributed temperature sensing technology (DTS) based on Brillouin optical time domain reflectometry / analysis (BOTDR / A) distributed strain sensing technology (DSS). Traditional DFOS technology mainly uses single scattering technology, and the measured parameters are also limited. In practical applications, multiple systems are usually required to monitor multiple parameters, which significantly increases the cost and complexity of the measurement system and becomes an obstacle to the application and promotion of DFOS systems.

[0003] With the development of technology, researchers have used the common technologies between different types of DFOS technologies to complement each other, making multi-parameter distributed fiber optic sensing that integrates multiple mechanisms possible. Compared with multi-parameter sensing methods that use multiple systems and multiple optical cables, the fused DFOS system has a higher degree of integration, can use fewer optical cables, and has significant cost advantages; however, the current fused DFOS cannot meet the requirements of typical applications in the oil and gas and civil engineering industries in terms of spatial resolution. Summary of the invention

[0004] The purpose of the present invention is to provide a high spatial resolution multi-parameter fusion distributed optical fiber sensing system to solve the problems raised in the background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A high spatial resolution multi-parameter fusion distributed optical fiber sensing system, comprising:

[0007] The light source module is used to provide light source for the entire sensing system and generate two-branch laser output;

[0008] A pulse generating module, used for generating pulse light by using the first optical branch;

[0009] A first optical fiber circulator is arranged between the pulse generating module and the sensing optical fiber and is used for transmitting the pulse light and the scattered light returned from the sensing optical fiber;

[0010] A scattered light separation module, connected to the first optical fiber circulator, for receiving the scattered light returned by the first optical fiber circulator, and separating the scattered light into Brillouin scattered light and Rayleigh scattered light;

[0011] The local oscillator light generation module is used to generate the BOTDR local oscillator light and Local oscillator light;

[0012] The coherent detection module is connected to the scattered light separation module and the local oscillator light generation module to respectively separate the Brillouin scattered light from the BOTDR local oscillator light and the Rayleigh scattered light from the Coherent detection of local oscillator light to obtain the corresponding electrical signal;

[0013] The data acquisition device is connected to the coherent detection module and is used to obtain the corresponding electrical signal.

[0014] Preferably, the light source module comprises:

[0015] Narrow linewidth laser, used to generate narrow linewidth laser light source;

[0016] The first optical fiber coupler is connected to the narrow line width laser and is used to divide the laser light generated by the narrow line width laser into two optical branches.

[0017] Preferably, the pulse generating module comprises:

[0018] A signal generator, used for providing a radio frequency signal;

[0019] an electro-optic modulator, whose radio frequency port is connected to the signal generator and is used to frequency modulate the laser signal based on the radio frequency signal;

[0020] an acousto-optic modulator, connected to the photoelectric modulator, and having a radio frequency port connected to a signal generator, for pulse modulating the frequency-modulated laser signal based on the radio frequency signal to generate pulsed light;

[0021] A polarization controller, connected to the AOM, for controlling the polarization state of the pulse;

[0022] The first optical amplifier is connected to the polarization controller and is used to adjust the power of the output pulse to meet the threshold requirement of scattered light generation.

[0023] Preferably, the local oscillator light generation module comprises:

[0024] The second optical fiber coupler is used to divide the optical signal of the second optical branch into two sub-branches, wherein the first sub-branch is the BOTDR local oscillator light and the second sub-branch is Local oscillator light;

[0025] The optical frequency shifter is arranged on the first sub-branch and is used for frequency shifting of the laser of the first sub-branch to generate frequency-shifted BOTDR local oscillator light.

[0026] Preferably, the optical frequency shifter is an electro-optic modulator.

[0027] Preferably, the scattered light separation module comprises:

[0028] A second optical amplifier, used to increase the light intensity of the scattered light;

[0029] a second optical fiber circulator connected to the second optical amplifier to receive the enhanced scattered light;

[0030] A fiber grating filter is connected to the second optical circulator and transmits Rayleigh scattered light and reflects Brillouin scattered light for the scattered light;

[0031] The second optical circulator is also connected to the coherent detection module, and the reflected Brillouin scattered light is transmitted to the coherent detection module via the second optical circulator.

[0032] Preferably, the second optical amplifier is an erbium-doped fiber amplifier.

[0033] Preferably, the coherent detection module comprises:

[0034] The first detector performs heterodyne detection on the frequency-shifted BOTDR local oscillator light and the Brillouin scattered light to obtain corresponding electrical signals;

[0035] An electrical filter, connected to the first detector, for filtering and amplifying the electrical signal;

[0036] The second detector, The local oscillator light and the Rayleigh scattered light are heterodyned and then detected heterodyne to obtain the corresponding electrical signal;

[0037] Preferably, the first detector is a balanced photodetector, and the second detector is a polarization diversity detector.

[0038] Preferably, the first optical amplifier is an erbium-doped fiber amplifier.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention can complete the real-time online monitoring of temperature, strain and vibration parameters of a large-scale sensor network, and when the sensing distance is on the order of 10 km, the spatial resolution index can reach 1 m or even better. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1It is a schematic structural diagram of a high spatial resolution multi-parameter fusion distributed optical fiber sensing system according to an embodiment of the present invention.

[0042] Figure 2 It is a schematic diagram of the spectrum of modulation and reception of the present invention.

[0043] Figure 3 Schematic diagram of the pulse generation principle of the system of the present invention.

[0044] Markings in the figure: 101, narrow linewidth laser, 102, first fiber coupler, 201, signal generator, 202, electro-optic modulator, 203, acousto-optic modulator, 204, polarization controller, 205, first optical amplifier, 301, first fiber circulator, 401, sensing fiber, 501, second fiber coupler, 502, optical frequency shifter, 601, second optical amplifier, 602, second fiber circulator, 603, fiber grating filter, 701, first detector, 702, second detector, 703, electric filter, 801, data acquisition device. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0046] Figure 1 The schematic diagram of the structure of the high spatial resolution multi-parameter fusion distributed optical fiber sensing system of the present invention is shown.

[0047] Reference Figure 1 , the optical fiber sensing system comprises:

[0048] The light source module is used to provide light source for the entire sensing system and generate two-branch laser output;

[0049] A pulse generating module, used for generating pulse light by using the first optical branch;

[0050] A first optical fiber circulator is arranged between the pulse generating module and the sensing optical fiber and is used for transmitting the pulse light generated by the pulse generating module and the scattered light returned from the sensing optical fiber;

[0051] A scattered light separation module, connected to the first optical fiber circulator, for receiving the scattered light returned by the first optical fiber circulator, and separating the scattered light into Brillouin scattered light and Rayleigh scattered light;

[0052] The local oscillator light generation module is used to generate the BOTDR local oscillator light and Local Oscillator

[0053] The coherent detection module is connected to the scattered light separation module and the local oscillator light generation module to respectively separate the Brillouin scattered light from the BOTDR local oscillator light and the Rayleigh scattered light from the Coherent detection of local oscillator light to obtain the corresponding electrical signal;

[0054] The data acquisition device is connected to the coherent detection module and is used to obtain the corresponding electrical signal.

[0055] Specifically, the light source module includes a narrow linewidth laser and a first fiber coupler, the output end of the narrow linewidth laser is connected to the input end of the first fiber coupler, the first output port of the first fiber coupler is directly connected to the pulse generation module, the output laser of the narrow linewidth laser is branched into two optical branches through the first fiber coupler, wherein the first optical branch is connected to the pulse generation module; the second output port of the first fiber coupler is connected to the local oscillator light generation module to generate two local oscillator lights, including BOTDR local oscillator light, Local oscillator light.

[0056] Specifically, the local oscillator light generation module includes a second optical fiber coupler and an optical frequency shifter. The optical frequency shifter is an optoelectronic modulator. The second optical branch is divided into two sub-branches by the second optical fiber coupler, wherein the first sub-branch is input to the optical frequency shifter, and then the BOTDR local oscillator light after frequency shifting is output; the second sub-branch is directly output, that is, the non-frequency shifted local oscillator light. Local oscillator light.

[0057] Specifically, the pulse generation module includes an electro-optic modulator, an acousto-optic modulator, a polarization controller and a first optical amplifier. The first optical amplifier uses an erbium-doped fiber amplifier. The first output port of the first fiber coupler is connected to the input port of the electro-optic modulator. The electro-optic modulator, the acousto-optic modulator, the polarization controller and the first optical amplifier are connected end to end in sequence. The radio frequency ports of the electro-optic modulator and the acousto-optic modulator are connected to a signal generator. The signal from the signal generator performs frequency modulation and pulse modulation on the laser in the first optical branch to generate pulse light. The polarization controller is used to control the polarization state of the pulse, and can realize technologies such as polarization fading suppression. The first optical amplifier is used to adjust the power of the output pulse to meet the threshold requirements for scattered light generation. The output port of the first optical amplifier is connected to the first port of the first optical fiber circulator, the second port of the first optical fiber circulator is connected to the sensing optical fiber, and the third port of the first optical fiber circulator is connected to the scattered light separation module. After the pulse light enters the sensing optical fiber, scattered light will be generated. The scattered light includes Rayleigh scattered light and Brillouin scattered light. The generated scattered light is returned through the first optical fiber circulator and input into the scattered light separation module.

[0058] In this embodiment, the electro-optic modulator and the acousto-optic modulator are combined to generate high-quality pulses with high extinction ratio and steep rising edge. Since the bandwidth of the electro-optic modulator can reach the order of 10 GHz and the rising edge is better than 1 ns, it can be used to generate pulse signals that are close to rectangular and have narrow pulse widths. In addition, the larger bandwidth also provides richer spectrum resources, which can realize technologies such as frequency division multiplexing and chirped pulses. The acousto-optic modulator has a higher extinction ratio than the electro-optic modulator, which can usually reach more than 50 dB, which can effectively improve the signal-to-noise ratio of the scattered signal and improve the accuracy of parameter measurement.

[0059] Specifically, the scattered light separation module includes a second optical amplifier, a second optical fiber circulator, and a fiber grating filter. The input port of the second optical amplifier is connected to the third port of the first optical fiber circulator, the first port of the second optical fiber circulator is connected to the output end of the second optical amplifier, the second port of the second optical fiber circulator is connected to the input end of the fiber grating filter, the output end of the fiber grating filter is connected to the coherent detection module, and the third port of the second optical fiber circulator is also connected to the coherent detection module; after the scattered light returns from the first optical fiber circulator, the light intensity is increased by the first optical amplifier, and then the Brillouin scattered light is filtered out by the second optical fiber circulator and the fiber grating filter, and the light transmitted through the fiber grating filter is Rayleigh scattered light.

[0060] Specifically, the coherent detection module includes a first detector, an electrical filter, and a second detector. The first detector is a balanced photodetector, and the second detector is a polarization diversity detector. The output port of the optical frequency shifter is connected to the first input port of the first detector, and the third port of the second optical fiber circulator is connected to the second input port of the first detector. The Brillouin scattered light and the frequency-shifted BOTDR local oscillator light are used as inputs of the first detector to perform heterodyne detection to obtain corresponding electrical signals. The electrical filter is connected to the output port of the first detector to filter and amplify the electrical signal. The second output port of the second optical coupler is connected to the first input port of the second detector, and the output port of the fiber grating filter is connected to the second input port of the second detector to receive the Rayleigh scattered light and the non-frequency-shifted local oscillator light. The local oscillator light is used as the input of the second detector for heterodyne detection to obtain the corresponding electrical signal.

[0061] The data acquisition device respectively acquires the electrical signals output by the first detector and the second detector for subsequent signal demodulation, and obtains temperature strain information and vibration information from the first detector and the second detector respectively.

[0062] Figure 2The schematic diagram of the modulation and reception spectrum is shown to illustrate the principle of separating Rayleigh scattered light and Brillouin scattered light in the scattered light in the spectrum. In this embodiment, the scattered light separation module has separated the Rayleigh scattered light and the Brillouin scattered light, but due to the limited isolation of the fiber grating filter, it is impossible to achieve complete separation, so further separation is required in the spectrum. Figure 2 As shown in Figure 2, after the laser of the first optical branch passes through the electro-optic modulator and the acousto-optic modulator to generate pulsed light, the frequency of the pulsed light produces a frequency shift of Δf1 relative to the output frequency of the laser, as shown in Figure (b). After the second fiber coupler, the laser of the first sub-branch passes through the optical frequency shifter to generate a frequency shifted BOTDR local oscillator frequency of Δf BFS +Δf1-Δf2, as shown in Figure (d); the laser of the second sub-branch is directly connected to the second detector, and the local oscillator frequency is consistent with the laser output, as shown in Figure (c). The scattered light includes Brillouin scattered light and Rayleigh scattered light. The frequency of Rayleigh scattered light is consistent with the incident light, so the frequency is still Δf1; the frequency of Brillouin scattered light will produce a magnitude of Δf with the frequency of the incident light. BFS The frequency difference is Δf. Since Brillouin scattered light has two types: Stokes light and anti-Stokes light, the frequency is BFS ±Δf1, Figure (e) shows Δf BFS +Δf1 situation.

[0063] In the coherent detection module, Rayleigh scattered light and non-frequency shifted The frequency spectrum after heterodyne beat frequency detection is shown in Figure (f), where the frequency of Rayleigh signal is Δf1 and the frequency of Brillouin scattered light is Δf BFS , due to the Brillouin scattering frequency difference Δf BFS The frequency of the Rayleigh scattered light is about 10 GHz, so the Rayleigh scattered signal is within the detection bandwidth of the detector, while the Brillouin scattered signal is outside the detection bandwidth of the detector. The residual Brillouin scattered light in the Rayleigh scattered light can be ignored, and the effective detection of the Rayleigh scattered signal is achieved. The Brillouin scattered light and the frequency-shifted BOTDR local oscillator light are subjected to heterodyne beat frequency detection. The spectrum after heterodyne beat frequency detection is shown in Figure (g). The frequency of the Brillouin scattered light is Δf2, and the frequency of the Rayleigh signal is Δf BFS -Δf2, at this time, the Brillouin scattering signal is within the detection bandwidth of the detector, while the Rayleigh scattering signal is outside the detection bandwidth of the detector. The influence of the residual Rayleigh scattering light in the Brillouin scattering light can be ignored, thus achieving effective detection of the Brillouin scattering signal.

[0064] Figure 3 The schematic diagram of the optical pulse generation principle for achieving high spatial resolution in the system of the present invention is shown. Figure 3 , Frequency division multiplexing technology is used to achieve high spatial resolution. The specific method is to divide each pulse with a pulse width of T into N sub-pulses with a pulse width of Δt, and each sub-pulse has a different frequency. Figure 3 Taking N=3 as an example, the frequencies of the three sub-pulses are f1, f2, and f3 respectively. In the demodulation process, digital bandpass filters with center frequencies of f1, f2, and f3 are used to filter out each sub-pulse and demodulate each one. The width of the total pulse in this design is different from that of the conventional The average power of the optical pulse will not be reduced, and the spatial resolution of the system is the spatial resolution corresponding to the sub-pulse width Δt. When the number of sub-pulses is N, the spatial resolution can be increased by N times. BOTDR uses differential pulse pair technology to achieve high spatial resolution. The principle of this technology is to use a pair of pulses with a small difference in pulse width to perform two measurements respectively, and then differentiate the results of the two measurements to obtain an equivalent high spatial resolution corresponding to the difference in pulse pair width. In the present invention, since BOTDR and The same set of optical pulses is used, so a pair of consecutive optical pulses is regarded as a pair of differential pulses, where the pulse width of the first optical pulse is set to T, and the pulse width of the second optical pulse is set to T+τ, so as to achieve a differential pulse width of τ. In the second pulse width τ part, the frequency is set to 0, and the influence of the extra pulse time τ can be removed by a digital bandpass filter. For , the effective pulse width is still T.

[0065] By combining Rayleigh scattering and Brillouin scattering, The distributed vibration / acoustic wave measurement is realized by using the BOTDR technology, and the distributed temperature and strain measurement is realized by using the composite frequency division multiplexing and differential pulse pairing technology in the modulation and demodulation design to realize the strain, temperature and vibration detection with high spatial resolution.

Claims

1. A high spatial resolution multi-parameter fusion distributed optical fiber sensing system, characterized in that: include: The light source module is used to provide light source for the entire sensing system and generate two-branch laser output; A pulse generating module, used for generating pulse light by using the first optical branch; A first optical fiber circulator is arranged between the pulse generating module and the sensing optical fiber and is used for transmitting the pulse light and the scattered light returned from the sensing optical fiber; A scattered light separation module, connected to the first optical fiber circulator, for receiving the scattered light returned by the first optical fiber circulator, and separating the scattered light into Brillouin scattered light and Rayleigh scattered light; The local oscillator light generation module is used to generate the BOTDR local oscillator light and Local oscillator light; The coherent detection module is connected to the scattered light separation module and the local oscillator light generation module to respectively separate the Brillouin scattered light from the BOTDR local oscillator light and the Rayleigh scattered light from the Coherent detection of local oscillator light to obtain the corresponding electrical signal; The data acquisition device is connected to the coherent detection module and is used to obtain the corresponding electrical signal.

2. A high spatial resolution multi-parameter fusion distributed optical fiber sensing system as claimed in claim 1, characterized in that: The light source module comprises: Narrow linewidth laser, used to generate narrow linewidth laser light source; The first optical fiber coupler is connected to the narrow line width laser and is used to divide the laser light generated by the narrow line width laser into two optical branches.

3. A high spatial resolution multi-parameter fusion distributed optical fiber sensing system as claimed in claim 1, characterized in that: The pulse generation module comprises: A signal generator, used for providing a radio frequency signal; an electro-optic modulator, whose radio frequency port is connected to the signal generator and is used to frequency modulate the laser signal based on the radio frequency signal; an acousto-optic modulator, connected to the photoelectric modulator, and having a radio frequency port connected to a signal generator, for pulse modulating the frequency-modulated laser signal based on the radio frequency signal to generate pulsed light; A polarization controller, connected to the AOM, for controlling the polarization state of the pulse; The first optical amplifier is connected to the polarization controller and is used to adjust the power of the output pulse to meet the threshold requirement of scattered light generation.

4. A high spatial resolution multi-parameter fusion distributed optical fiber sensing system as claimed in claim 1, characterized in that: The local oscillator light generation module comprises: The second optical fiber coupler is used to divide the optical signal of the second optical branch into two sub-branches, wherein the first sub-branch is the BOTDR local oscillator light and the second sub-branch is Local oscillator light; The optical frequency shifter is arranged on the first sub-branch and is used for frequency shifting of the laser of the first sub-branch to generate frequency-shifted BOTDR local oscillator light.

5. A high spatial resolution multi-parameter fusion distributed optical fiber sensing system as claimed in claim 4, characterized in that: The optical frequency shifter is an electro-optic modulator.

6. A high spatial resolution multi-parameter fusion distributed optical fiber sensing system as claimed in claim 1, characterized in that: The scattered light separation module comprises: A second optical amplifier, used to increase the light intensity of the scattered light; a second optical fiber circulator connected to the second optical amplifier to receive the enhanced scattered light; A fiber grating filter is connected to the second optical circulator and transmits Rayleigh scattered light and reflects Brillouin scattered light for the scattered light; The second optical circulator is also connected to the coherent detection module, and the reflected Brillouin scattered light is transmitted to the coherent detection module via the second optical circulator.

7. A high spatial resolution multi-parameter fusion distributed optical fiber sensing system as claimed in claim 6, characterized in that: The second optical amplifier is an erbium-doped fiber amplifier.

8. The high spatial resolution multi-parameter fusion distributed optical fiber sensing system according to claim 1, characterized in that: The coherent detection module comprises: The first detector performs heterodyne detection on the frequency-shifted BOTDR local oscillator light and the Brillouin scattered light to obtain corresponding electrical signals; An electrical filter, connected to the first detector, for filtering and amplifying the electrical signal; The second detector, The local oscillator light and the Rayleigh scattered light are heterodyned and then detected to obtain the corresponding electrical signal.

9. A high spatial resolution multi-parameter fusion distributed optical fiber sensing system as claimed in claim 8, characterized in that: The first detector is a balanced photodetector, and the second detector is a polarization diversity detector.

10. The high spatial resolution multi-parameter fusion distributed optical fiber sensing system according to claim 3, characterized in that: The first optical amplifier is an erbium-doped fiber amplifier.

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