CN-116878639-B - Distributed optical fiber acoustic wave sensor

CN116878639BCN 116878639 BCN116878639 BCN 116878639BCN-116878639-B

Abstract

The invention provides a distributed optical fiber acoustic wave sensor which comprises a narrow linewidth laser, a pulse optical modulator, an erbium-doped optical fiber amplifier, a circulator, a filter, a photoelectric detector, an analog-to-digital converter, a demodulation system and a fluorescent optical fiber, wherein fluorescent substances are doped in the fiber core of the fluorescent optical fiber, the narrow linewidth laser emits continuous laser and then is modulated into pulse light, the pulse light enters the circulator through a first port and is injected into the fluorescent optical fiber through a second port after passing through the erbium-doped optical fiber amplifier, the pulse light excites the fluorescent substances to generate fluorescence, the fluorescence returned along the fluorescent optical fiber forms fluorescence return light, the pulse light injected into the fluorescent optical fiber generates backward Rayleigh scattered light, and the fluorescence return light and the backward Rayleigh scattered light beat frequency in the fluorescent optical fiber to form beat frequency signals. The distributed optical fiber acoustic wave sensor provided by the invention realizes coherent detection based on a structure similar to a direct detection method, does not need a frequency shifting device and a coupler, simplifies the device structure and improves the sensor quality.

Inventors

ZHANG YUCHENG
GUO ZHONGJIA
ZHANG XIAODONG
LI XIAOHUI

Assignees

北京云智矿安科技有限公司

Dates

Publication Date: 20260512
Application Date: 20230707

Claims (10)

1. A distributed fiber optic acoustic wave sensor, comprising: the device comprises a narrow linewidth laser, a pulse light modulator, an erbium-doped fiber amplifier, a circulator, a filter, a photoelectric detector, an analog-to-digital converter, a demodulation system and a fluorescent fiber; fluorescent substances are doped in the fiber cores of the fluorescent fibers; The circulator has a first port, a second port, and a third port; The narrow linewidth laser emits continuous laser, the continuous laser is modulated into pulse light after passing through the pulse light modulator, and the pulse light enters the circulator through the first port after passing through the erbium-doped fiber amplifier and is injected into the fluorescent fiber through the second port; The pulse light injected into the fluorescent optical fiber excites the fluorescent substance to generate fluorescence, and the fluorescence returned along the fluorescent optical fiber forms fluorescence return light; the pulse light injected into the fluorescent optical fiber generates backward Rayleigh scattered light; the fluorescence return light and the backward Rayleigh scattered light beat in the fluorescence optical fiber to form a beat signal, and an external sound wave signal is coupled into the beat signal to form a modulated beat signal; The modulation beat frequency signal enters the filter through the third port to filter noise, and then is converted into an electric signal by the photoelectric detector, the electric signal is converted into a digital signal by the analog-to-digital converter, and the demodulation system demodulates the digital signal to obtain an external sound wave signal.
2. The distributed optical fiber acoustic wave sensor of claim 1, wherein the fluorescent substance comprises neodymium ions, europium ions, and samarium ions.
3. The distributed optical fiber acoustic wave sensor of claim 1, wherein the fluorescent substance comprises a fluorescent dye comprising a rhodamine series dye.
4. The distributed optical fiber acoustic wave sensor of claim 1, wherein the fluorescent substance is uniformly distributed in the fiber core.
5. The distributed optical fiber acoustic wave sensor of claim 1, wherein the material of the core comprises a polymeric material.
6. The distributed fiber optic acoustic wave sensor of claim 1 wherein the photodetector comprises a balanced photodetector.
7. The distributed optical fiber acoustic wave sensor according to claim 1, wherein the narrow linewidth laser is configured to continuously output a single frequency laser having a linewidth not exceeding 1MHz.
8. The distributed optical fiber acoustic wave sensor of claim 1, wherein the pulsed optical modulator comprises an electro-optic modulator, an acousto-optic modulator, or a semiconductor optical amplifier.
9. The distributed optical fiber acoustic wave sensor of claim 1, wherein the fluorescence forms homodyne interference with the pulsed light.
10. The distributed optical fiber acoustic wave sensor of claim 1, wherein the fluorescence forms heterodyne interference with the pulsed light.

Description

Distributed optical fiber acoustic wave sensor Technical Field The invention relates to the technical field of optical fiber sensing, in particular to a distributed optical fiber acoustic wave sensor. Background The distributed optical fiber acoustic sensor (DAS) has the advantages of being good in electromagnetic interference resistance, concealment, corrosion resistance, insulation and the like, has the advantages of being capable of realizing dynamic strain distribution, quantitative detection, simple in structure, long in detection distance, high in adaptation degree to complex terrains, free of external field power supply and the like, and is widely applied to various national defense and industrial fields such as perimeter security, resource exploration, petroleum and natural gas pipeline detection, communication line detection and the like. A distributed optical fiber acoustic wave sensing system based on a phase sensitive optical time domain reflectometry (phi-OTDR) technology utilizes the phase change of backward Rayleigh scattered light in optical fiber transmission to realize the distributed measurement and restoration of acoustic wave signals. Generally, a distributed optical fiber vibration sensor (DVS) can only detect the position of a vibration event on the whole optical fiber link, but cannot quantitatively measure the amplitude and phase of vibration, and the DAS can also realize real-time, multi-point and quantitative detection of the amplitude and phase of an acoustic wave signal besides the advantage of DVS, so that the size and frequency of acoustic wave information can be further demodulated, and the DAS has wider application prospect. Referring to fig. 1, the early DAS adopts a direct detection method, and continuous light emitted from a narrow linewidth laser NLL is modulated into pulsed light by an acousto-optic modulator AOM. The pulse light enters the sensing optical fiber SF through the circulator C after being amplified by the erbium-doped optical fiber amplifier EDFA. The pulse light generates backward Rayleigh scattered light in the sensing optical fiber SF, the sound wave signal emitted by the sound source is coupled into the backward Rayleigh scattered light to form a modulation signal, the modulation signal is transmitted to the photoelectric detector PD through the circulator C to be converted into an electric signal, the electric signal is processed through the analog-to-digital converter ADC to obtain a digital signal, and then the demodulation system DS (Demodulation System) demodulates the digital signal to obtain the position, amplitude, frequency and phase information of the sound wave. The modulation principle of the acoustic wave signal on the backward Rayleigh scattered light is that when the acoustic wave signal acts on the sensing optical fiber SF, the length and the refractive index of the optical fiber at the position are changed according to Hooke's law, the photoelastic effect of the optical fiber and the like, so that the optical path of the light wave transmitted at the position is changed, and finally the intensity of the backward Rayleigh scattered light is changed due to the interference effect. During demodulation, the change of the intensity of the backward Rayleigh scattering light is analyzed, so that the information of the sound wave can be obtained. In order to improve the signal-to-noise ratio, a later-developed coherent detection method introduces local reference light on the basis of a direct detection method, and the principle of the method is that backward Rayleigh scattered light and the local reference light with fixed frequency difference are subjected to beat frequency to form beat frequency signals, and then a demodulation system extracts amplitude, phase and frequency information of sound wave signals from the beat frequency signals. Referring to fig. 2, the principle of the distributed optical fiber acoustic wave sensor based on heterodyne modulation is that continuous light emitted by a narrow linewidth laser NLL is divided into two paths by a first coupler OC1, one path is used as a local reference light LO to enter a second coupler OC2, the other path is used as a detection light, the detection light enters a sensing optical fiber SF after passing through an acousto-optic modulator AOM and an erbium-doped optical fiber amplifier EDFA to generate backward rayleigh scattering light coupled with an acoustic wave signal, the detection light is subjected to frequency shift processing by a waveform generator WG (waveform generator) to enable the detection light and the local reference light to have a fixed frequency difference, beat frequencies are generated in the local reference light LO and the backward rayleigh scattering light in the second coupler OC2 to form a beat frequency signal, the beat frequency signal is converted into an electrical signal by a photoelectric detector PD and is processed by an analog-digital converter ADC to