Fusion type distributed optical fiber vibration sensing system with broadband response

Abstract

The invention discloses a fusion type distributed optical fiber vibration sensing system with broadband response, which is suitable for high-precision acoustic signal measurement and spatial position positioning. The system comprises an acoustic measurement unit, a position measurement unit and a data acquisition synchronous control module which are respectively used for acquiring high-frequency vibration information and positioning low-frequency signals, has the sensing capabilities of wide band, high resolution and high signal-to-noise ratio, and realizes signal synchronization by adopting phase-locked control and high-sampling-rate data acquisition, so that the accuracy of signal synchronization is improved. And the signal stability and the signal-to-noise ratio are improved through polarization control and filtering design. The method supports frequency feature extraction, accurate identification and spatial positioning of the vibration event, and is suitable for pipeline structure monitoring, fault diagnosis and other engineering application scenes in a complex environment.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a fusion-type distributed optical fiber vibration sensing system with wide-band response. Background Art

[0002] my country is experiencing rapid development in the construction of large-scale infrastructure, such as underground pipeline transmission systems, rail transit, and large bridges. Monitoring the health of these ultra-long-distance, large-scale infrastructure during their service life is crucial to ensuring public safety and extending their service life. Existing monitoring technologies must not only detect faults promptly and accurately locate the incident, but also identify the fault type based on the inherent frequency characteristics of the vibration signal, thereby achieving comprehensive sensing of vibration events.

[0003] Currently, distributed vibration sensing systems based on optical time-domain reflectometry (OTDR) meet the requirements of long-distance monitoring to a certain extent. However, their frequency response range is limited by the monitoring distance, often exhibiting spectrum folding, making it difficult to accurately detect high-frequency vibration events. Meanwhile, fiber-optic distributed vibration sensing systems based on interferometry, while offering the advantage of wideband response, suffer from weak vibration localization capabilities, hindering their widespread application in practical engineering projects.

[0004] Based on the above-mentioned deficiencies of the existing technology, there is an urgent need to develop a fiber optic interferometry measurement system and detection method that can not only achieve high-precision acoustic signal and position information measurement, but also have broadband sensing capabilities and low real-time computing load, so as to meet the actual needs of large-scale infrastructure health monitoring. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a fusion-type distributed optical fiber vibration sensing system with a wide-band response, which can simultaneously achieve high-precision acoustic signal and position information measurement, and adopt phase-locked technology and dedicated sampling frequency to reduce the real-time computing load, improve the signal-to-noise ratio and signal demodulation accuracy.

[0006] The present invention adopts the following technical solution: a fusion-type distributed optical fiber vibration sensing system with wide-band response, comprising: a position measurement unit, an acoustic measurement unit, and a data acquisition synchronization control module.

[0007] The position measurement unit includes: a first laser, a first coupler, a first acousto-optic modulator, a first erbium-doped fiber amplifier, a first photodetector, a first circulator, and a second coupler;

[0008] The acoustic measurement unit includes: a second laser, a second acousto-optic modulator, a second erbium-doped fiber amplifier, a second photodetector, a third coupler, a Faraday rotator, a second circulator, a polarization controller, and a fourth coupler;

[0009] The data acquisition synchronization control module includes: a dual-channel data acquisition card and a phase-locked control circuit. The dual-channel data acquisition card simultaneously outputs a reference clock and a trigger signal, which are respectively input into the first and second acousto-optic modulators, and synchronized with the first and second acousto-optic modulators through the phase-locked control circuit;

[0010] The position measurement unit and the acoustic measurement unit are used to locate low-frequency signals and collect high-frequency vibration signals, respectively, and inject them into the sensing optical fiber through a wavelength division multiplexer; a bandpass filter is provided at the end of the sensing optical fiber and connected to a Faraday rotation mirror for sensing light reflection.

[0011] Preferably, the position measurement unit generates a laser signal using a first laser, which is separated into a first reference light and a first detection light by a first coupler; the first detection light is frequency-shift modulated by a first acousto-optic modulator to form a pulsed light, which is amplified by a first erbium-doped fiber amplifier and then injected into the sensing fiber through a wavelength division multiplexer;

[0012] The bandpass filter at the end of the sensing optical fiber is used to block the Faraday rotator mirror at the end in the position measurement unit, thereby avoiding the interference of Fresnel reflection on the position sensing signal; and returns the back Rayleigh scattered light generated by the pulse light, which enters the second coupler through the first circulator to interfere with the first reference light and is received by the first photodetector.

[0013] Preferably, the acoustic measurement unit generates a laser signal using a second laser, which is divided into a second reference light and a second detection light by a third coupler; the second detection light is modulated by a second acousto-optic modulator, amplified by a second erbium-doped fiber amplifier, and injected into the sensing fiber through a wavelength division multiplexer; the sensing light in the sensing fiber is reflected by a bandpass filter and a Faraday rotator mirror, and then enters the interference path of the fourth coupler through a second circulator;

[0014] The second reference light passes through the circulator and the vibration isolation structure and is injected into the reference optical fiber with a length corresponding to that of the sensing optical fiber. It is reflected by the second Faraday rotator. The reflected light passes through the circulator and is adjusted by the polarization controller before returning to the fourth coupler. It interferes with the sensing light and is received by the second photodetector.

[0015] Preferably, the polarization controller is used to adjust the polarization states of the sensing light and the reference light to make the polarization states consistent, thereby improving the signal-to-noise ratio and phase demodulation accuracy of the intermediate frequency interference signal.

[0016] Preferably, the dual-channel data acquisition card has a sampling rate of 160MSa / s, outputs a 10MHz reference clock and trigger signal, obtains 40MHz and 200MHz drive signals through frequency multiplication, respectively drives the second and first acousto-optic modulators in the acoustic and position measurement units, and synchronously acquires the interference signals of the position measurement unit and the acoustic measurement unit, performs high-precision demodulation through a high sampling rate, and realizes synchronization of laser modulation and signal acquisition.

[0017] The phase-locked control circuit adopts a phase-locked control method synchronized with the acousto-optic modulator. When the sampling rate f s With the intermediate frequency signal frequency f C When a specific proportional relationship exists, a simplified phase demodulation algorithm can be used.

[0018] Preferably, in the position measurement unit, the first laser uses a continuous wave laser with a central wavelength of 1561.40 nm and a linewidth of 3.7 kHz. The light source is divided into a first reference light and a first detection light through a 90:10 first coupler. The first detection light generates pulsed light through a first acousto-optic modulator with a modulation frequency of 200 MHz.

[0019] Preferably, in the acoustic measurement unit, the second laser uses a continuous wave laser with a central wavelength of 1550.12 nm and a linewidth of 3.7 kHz. The light source is divided into a second reference light and a second detection light through a 50:50 third coupler, and the second detection light is frequency shift modulated by a second acousto-optic modulator with a frequency modulation frequency of 40 MHz.

[0020] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0021] 1. The fusion-type distributed optical fiber vibration sensing system of the present invention realizes high-precision acoustic signal measurement and position information measurement simultaneously, which can meet the requirements of high spatial resolution and wide-band response in engineering applications. It can realize accurate identification and positioning of vibration events according to the natural frequency characteristics of vibration signals, effectively improving the recognition rate of vibration events.

[0022] 2. The present invention achieves high-precision clock synchronization and signal drive between modules by adopting phase-locked synchronization technology and dedicated sampling frequency, effectively reducing the real-time computing load; through polarization control and vibration isolation design, the high signal-to-noise ratio and stability of the interference signal are guaranteed. At the same time, a matching filter is installed at the end of the measuring optical fiber to avoid the interference of Fresnel reflection on the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the optical path diagram of the fusion-type distributed optical fiber vibration sensing system of the present invention;

[0024] Figure 2 This is a spatiotemporal distribution diagram of the vibration area according to an embodiment of the present invention;

[0025] Figure 3 This is a time domain diagram of a vibration signal according to an embodiment of the present invention;

[0026] Figure 4 This is the vibration signal spectrum diagram of the present invention. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the application are further described in detail below with reference to the accompanying drawings. The described embodiments are only part of the embodiments involved in the present invention. All non-innovative embodiments based on this embodiment by other researchers in the field are within the scope of protection of the present invention.

[0028] In one embodiment of the present invention, a fusion-type distributed optical fiber vibration sensing system with wide frequency response is provided. Figure 1 As shown, it includes: a position measurement unit, an acoustic measurement unit, and a data acquisition synchronization control module.

[0029] Specifically, the position measurement unit includes: a first laser, a first coupler, a first acousto-optic modulator, a first erbium-doped fiber amplifier, a first photodetector, a first circulator, and a second coupler;

[0030] an acoustic measurement unit, comprising: a second laser, a second acousto-optic modulator, a second erbium-doped fiber amplifier, a second photodetector, a third coupler, a Faraday rotator mirror, a second circulator, a polarization controller, and a fourth coupler;

[0031] The data acquisition synchronization control module includes: a dual-channel data acquisition card and a phase-locked control circuit.

[0032] In this embodiment, the acoustic measurement unit uses a continuous wave (CW) laser with a central wavelength of 1550.12 nm and a line width of 3.7 kHz as a light source through a second laser.

[0033] The light source is split into reference and probe light by a 50:50 third coupler (OC3). The probe light is modulated at 40 MHz by a second acousto-optic modulator (AOM2). The modulated signal is amplified by a second erbium-doped fiber amplifier (EDFA2) and injected into the sensing fiber via a wavelength division multiplexer (WDM).

[0034] Then, the optical signal in the sensing fiber passes through a bandpass filter (BPF) matched to the central wavelength, is reflected by the Faraday rotator mirror (FRM1), and enters the fourth coupler (OC4) through the second circulator (Cir2).

[0035] It should be noted that the use of a Faraday rotator at the end of the optical path can automatically compensate for the optical fiber polarization distortion and improve the stability of the signal.

[0036] Furthermore, the reference light is transmitted through the circulator and injected into a path corresponding to the fiber length, and is reflected by the second Faraday rotator (FRM2). The reflected light passes through the circulator and is adjusted by the polarization controller (PC) before returning to the 2×2 fourth coupler (OC4), where it interferes with the reference light and is finally detected by the second photodetector (BPD2).

[0037] During the detection process, the PC must be adjusted to ensure that the polarization states of the sensing light and reference light are consistent, thereby improving the signal-to-noise ratio (SNR) of the intermediate frequency signal and the accuracy of signal demodulation. In addition, the reference section uses an isolation box as a vibration isolation structure to effectively isolate external vibrations and reduce environmental noise.

[0038] In this embodiment, the position measurement unit uses a first laser, a continuous wave laser with a central wavelength of 1561.40 nm and a line width of 3.7 kHz as a light source.

[0039] The light source is split into reference light and probe light by a 90:10 first coupler (OC1); then, the probe light is shift-modulated by a 200MHz first acousto-optic modulator (AOM1) to generate pulsed light.

[0040] The pulsed light is further amplified by the first erbium-doped fiber amplifier (EDFA1) and injected into the sensing fiber through a wavelength division multiplexer.

[0041] It should be noted that since a 1560.00 nm bandpass filter is connected to the end of the sensing fiber, the sensing light cannot pass through the filter to reach the Faraday rotator at the end, thereby avoiding the influence of Fresnel reflection at the end of the fiber on the signal analysis of the position sensing unit.

[0042] Furthermore, the backscattered Rayleigh light generated by the pulsed light in the link passes through the first circulator (Cir1), interferes with the reference light in the 2×2 second coupler (OC2), and is finally detected by the first photodetector (BPD1).

[0043] In this embodiment, the data acquisition synchronization control module uses a phase-locked model to achieve synchronization between the data acquisition card (DAQ) and each acousto-optic modulator (AOM).

[0044] Preferably, this embodiment is equipped with a dual-channel DAQ to ensure that the relative time error between the position measurement unit and the acoustic measurement unit modules is controlled at the picosecond level.

[0045] Furthermore, a 10MHz reference clock and trigger signal are simultaneously output from the DAQ. The 10MHz reference clock signal is first multiplied to generate a 40MHz drive signal, which is then multiplied again to generate a 200MHz signal, ensuring that the relative time error between modules is controlled within the picosecond range.

[0046] A 40MHz drive signal is input to AOM2, providing continuous frequency modulation for the acoustic measurement module. A 200MHz trigger signal is input to AOM1, achieving excellent wave-cutting performance. This converts the probe light in the acoustic measurement module into pulses with a pulse width of 32ns and a frequency of 2kHz.

[0047] At the same time, the data acquisition synchronization control module uses a dedicated sampling frequency to shorten data processing time. When the sampling rate fs and the intermediate frequency signal frequency fc have a specific multiplication relationship as shown in the following formula, a simplified phase demodulation algorithm can be used to reduce the IQ demodulation amount, thereby reducing the real-time computing load and improving signal demodulation accuracy:

[0048]

[0049] In this embodiment, the DAQ sampling rate is preferably 160MSa / s, the AOM in the acoustic measurement unit is 40MHz, and the AOM in the position measurement unit is 200MHz, both of which meet the proportionality requirements. By implementing IQ demodulation at this specific sampling rate, the system's real-time computational load is significantly reduced, thus meeting the requirements of engineering applications.

[0050] Furthermore, the reference fiber link in the data acquisition and synchronization control module was placed in a soundproof box, and a 20kHz sine wave signal was applied to the PZT at the end of the fiber. The vibration position precisely corresponded to the single-mode fiber located at 20330m.

[0051] The space-time diagram of the vibration area is as follows Figure 2 As shown in the figure, a vibration stripe is shown at 20330 meters, and its frequency is consistent with the applied signal. According to the sensing principle of the sound sensing module, the characteristics of the interference signal can be captured at the same time.

[0052] When a 20kHz vibration signal is applied to the PZT, time domain interference signals are generated within a 3ms interval. The detailed view of these interference signals is shown in Figure 2. Figure 3 The corresponding 20kHz frequency spectrum can be directly demodulated using Fourier transform.

[0053] Therefore, the vibration sensing system proposed in this embodiment successfully demodulates the 20 kHz vibration event occurring over a 20 km optical fiber distance.

[0054] In order to further verify the reliability of the vibration sensing system of this embodiment, a series of high-frequency vibration tests were performed using frequencies of 5kHz to 50kHz. The spectrum of the vibration signal is shown in FIG. Figure 4As shown, it is demonstrated that the vibration sensing system of this embodiment can realize accurate recognition and positioning of vibration events according to the natural frequency characteristics of the vibration signal, thereby effectively improving the recognition rate of vibration events.

[0055] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A fusion-type distributed optical fiber vibration sensing system with broadband response, characterized in that: include: Position measurement unit, acoustic measurement unit, data acquisition synchronization control module; The position measurement unit includes: a first laser, a first coupler, a first acousto-optic modulator, a first erbium-doped fiber amplifier, a first photodetector, a first circulator, and a second coupler; The acoustic measurement unit includes: a second laser, a second acousto-optic modulator, a second erbium-doped fiber amplifier, a second photodetector, a third coupler, a Faraday rotator, a second circulator, a polarization controller, and a fourth coupler; The data acquisition synchronization control module includes: a dual-channel data acquisition card and a phase-locked control circuit. The dual-channel data acquisition card simultaneously outputs a reference clock and a trigger signal, which are respectively input into the first and second acousto-optic modulators, and synchronized with the first and second acousto-optic modulators through the phase-locked control circuit; The position measurement unit and the acoustic measurement unit are used to locate low-frequency signals and collect high-frequency vibration signals, respectively, and inject them into the sensing optical fiber through a wavelength division multiplexer; a bandpass filter is provided at the end of the sensing optical fiber and connected to a Faraday rotation mirror for sensing light reflection.

2. The fusion-type distributed optical fiber vibration sensing system with wide-band response according to claim 1, characterized in that: The position measurement unit uses a first laser to generate a laser signal, which is separated into a first reference light and a first detection light by a first coupler; the first detection light is frequency-shift modulated by a first acousto-optic modulator to form a pulse light, which is amplified by a first erbium-doped fiber amplifier and then injected into the sensing fiber through a wavelength division multiplexer.

3. The fusion-type distributed optical fiber vibration sensing system with wide-band response according to claim 2, characterized in that: The bandpass filter at the end of the sensing optical fiber is used to block the Faraday rotator mirror at the end in the position measurement unit, thereby avoiding the interference of Fresnel reflection on the position sensing signal; and returns the back Rayleigh scattered light generated by the pulse light, which enters the second coupler through the first circulator to interfere with the first reference light and is received by the first photodetector.

4. The fusion-type distributed optical fiber vibration sensing system with broadband response according to claim 1, characterized in that: The acoustic measurement unit uses a second laser to generate a laser signal, which is divided into a second reference light and a second detection light through a third coupler; the second detection light is modulated by a second acousto-optic modulator, amplified by a second erbium-doped fiber amplifier, and injected into the sensing fiber through a wavelength division multiplexer; the sensing light in the sensing fiber is reflected by a bandpass filter and a Faraday rotator mirror, and then enters the interference path of the fourth coupler through a second circulator.

5. The fusion-type distributed optical fiber vibration sensing system with broadband response according to claim 4, characterized in that: The second reference light passes through the circulator and the vibration isolation structure and is injected into the reference optical fiber with a length corresponding to that of the sensing optical fiber, and is reflected by the second Faraday rotator. The reflected light passes through the circulator and is adjusted by the polarization controller and then returns to the fourth coupler, where it interferes with the sensing light and is received by the second photodetector.

6. The fused distributed optical fiber vibration sensing system with broadband response according to claim 5, characterized in that: In the acoustic measurement unit, the polarization controller is used to adjust the polarization states of the sensing light and the reference light to make the polarization states consistent, thereby improving the signal-to-noise ratio and phase demodulation accuracy of the intermediate frequency interference signal.

7. The fusion-type distributed optical fiber vibration sensing system with broadband response according to claim 1, characterized in that: The dual-channel data acquisition card has a sampling rate of 160MSa / s and outputs a 10MHz reference clock and trigger signal. By frequency multiplication, 40MHz and 200MHz drive signals are obtained to drive the second and first acousto-optic modulators in the acoustic and position measurement units, respectively. The interference signals of the position measurement unit and the acoustic measurement unit are collected synchronously, and high-precision demodulation is performed through high sampling rate to achieve synchronization of laser modulation and signal collection.

8. The fusion-type distributed optical fiber vibration sensing system with broadband response according to claim 7, characterized in that: The phase-locked control circuit adopts a phase-locked control method synchronized with the acousto-optic modulator. When the sampling rate f s With the intermediate frequency signal frequency f C When the following proportional relationship exists, a simplified phase demodulation algorithm is used: Here, k can be any positive integer.

9. The fusion-type distributed optical fiber vibration sensing system with wide-band response according to claim 1, characterized in that: In the position measurement unit, the first laser uses a continuous wave laser with a central wavelength of 1561.40 nm and a linewidth of 3.7 kHz. The light source is divided into a first reference light and a first detection light by a 90:10 first coupler. The first detection light is generated into pulsed light by a first acousto-optic modulator with a modulation frequency of 200 MHz.

10. The fusion-type distributed optical fiber vibration sensing system with wide-band response according to claim 1, characterized in that: In the acoustic measurement unit, the second laser uses a continuous wave laser with a central wavelength of 1550.12 nm and a linewidth of 3.7 kHz. The light source is divided into a second reference light and a second detection light by a 50:50 third coupler. The second detection light is frequency-shift modulated by a second acousto-optic modulator with a frequency modulation frequency of 40 MHz.

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