Distributed fibre sensing system and vibration detection and positioning method therefor

Patent metadata

Field	Value
Publication number	US-10989587-B2
Application number	US-201616322259-A
Country	US
Kind code	B2
Filing date	Aug 26, 2016
Priority date	Aug 25, 2016
Publication date	Apr 27, 2021
Grant date	Apr 27, 2021

Abstract

A distributed fibre sensing system and a vibration detection and positioning method therefor are disclosed. The system comprises: a signal generating module, a light source module, an optical frequency comb generating module, a frequency sweeping and pulse generating module, an optical circulator, a sensing fibre, an interference module, a photoelectric conversion module and a detection and position module. The method comprises: obtaining a plurality of Rayleigh backscattering signals of the sensing fibre; performing a fading elimination processing on the Rayleigh backscattering signals, thereby obtaining a plurality of averaged Rayleigh backscattering signals of non-interference fading and polarization fading; performing a phase processing on the averaged Rayleigh backscattering signals, thereby obtaining phase variance curves; and determining a vibration point according to variances in the phase variance curves, and finally obtaining a position and a vibration waveform of the vibration point.

First claim

The invention claimed is:

1. A distributed fibre sensing system comprising:
a signal generating module including (i) a signal generator configured to output a swept radio frequency pulse sequence and a single-frequency sinusoidal wave signal, (ii) a first radio frequency signal amplifier configured to amplify the swept radio frequency pulse sequence, and (iii) a second radio frequency signal amplifier configured to amplify the single-frequency sinusoidal wave signal;
an optical frequency comb generating module connected to the second radio frequency signal amplifier to receive the amplified single-frequency sinusoidal wave signal;
a frequency sweeping and pulse generating module connected to the first radio frequency signal amplifier to receive the amplified swept radio frequency pulse sequence;
a light source module connected to the optical frequency comb generating module;
an optical circulator;
a sensing fibre;
an interference module connected to the optical circulator;
a photoelectric conversion module connected to the interference module; and
a detection and position module connected to the photoelectric conversion module, wherein:
an ultra-narrow-linewidth laser generated by the light source module is split into a detection light path and a reference light path which are then output to the optical frequency comb generating module and the interference module, respectively;
the optical frequency comb generating module inputs an optical frequency comb signal to the frequency sweeping and pulse generating module, and the frequency sweeping and pulse generating module outputs an amplified swept-frequency optical probe pulse string which is then input into the sensing fibre through the optical circulator;
a Rayleigh backscattering light generated by the sensing fibre is input to the interference module through the optical circulator and mixed with a reference light at the interference module to generate a mixed optical signal, and the mixed optical signal is input into the photoelectric conversion module;
the photoelectric conversion module converts the mixed optical signal into an electric signal, and inputs the electric signal to the detection and position module for detection and positioning of a vibration point.

2. The distributed fibre sensing system according to claim 1 , wherein:
the first radio frequency signal amplifier and the second radio frequency signal amplifier are connected to two output channels of the signal generator respectively;
one channel of the signal generator repeatedly outputs a swept radio frequency pulse sequence, and the other channel outputs a single-frequency sinusoidal wave signal, the swept radio frequency pulse sequence comprises: a plurality of swept radio frequency pulse signals with equal time interval, same pulse width, and different and non-overlapped sweeping ranges.

3. The distributed fibre sensing system according to claim 2 , wherein
the product of the time interval and the number of swept radio frequency pulse signals is equal to the round trip time of light in the sensing fibre.

4. The distributed fibre sensing system according to claim 1 , wherein:
the light source module comprises a narrow-linewidth fibre laser device, a fibre coupler and a polarization controller which are connected in sequence;
the fibre coupler has a split ratio of 90:10.

5. The distributed fibre sensing system according to claim 1 , wherein:
the optical frequency comb generating module comprises a DC voltage source and an optical modulator;
the DC voltage source adjusts a DC bias voltage input into the optical modulator and generates the optical frequency comb signal.

6. The distributed fibre sensing system according to claim 1 , wherein
the frequency sweeping and pulse generating module comprises an acousto-optic modulator or a single-sideband modulator and an erbium-doped fibre amplifier which are connected to each other.

7. A vibration detection and positioning method based on the system according to claim 1 , comprising:
generating a plurality of digital band-pass filters with different frequency bands without any overlapping by the detection and position module, and performing digital filtering on original data segments from a plurality of swept-frequency optical probe pulses, thereby obtaining a plurality of Rayleigh backscattering signals of the sensing fibre;
performing a fading elimination processing on the Rayleigh backscattering signals, thereby obtaining a plurality of averaged Rayleigh backscattering signals of non-interference fading and polarization fading;
performing a phase processing on the averaged Rayleigh backscattering signals, thereby obtaining phase variance curves; and
determining a vibration point according to variances in the phase variance curves, and finally obtaining a position and a vibration waveform of the vibration point.

8. The vibration detection and positioning method according to claim 7 , wherein
the Rayleigh backscattering signals are obtained by the following method:
generating the plurality of digital band-pass filters with different frequency bands without any overlapping by the detection and position module;
dividing the original data segments from the plurality of swept-frequency optical probe pulses into sub-data segments, the number of which is equal to that of the digital band-pass filters;
and then performing a cross-correlation operation on the sub-data segments and the corresponding digital matched filters, thereby obtaining a set of Rayleigh backscattering signals of the sensing fibre.

9. The vibration detection and positioning method according to claim 7 , wherein
the fading elimination processing includes: taking a conjugate of one Rayleigh backscattering signal as a reference value, multiplying another of Rayleigh backscattering signals with the reference value, thereby obtaining a set of Rayleigh backscattering signals whose phases close to zero; and averaging the Rayleigh backscattering signals whose phases close to zero, thereby obtaining averaged Rayleigh backscattering signals without interference fading and polarization fading.

10. The vibration detection and positioning method according to claim 7 , wherein
the phase processing includes: taking a phase term of each averaged Rayleigh backscattering signal as a phase curve; delaying the phase curve, making a difference between the phase curves before and after a time shift to obtain a differential phase curve; and finding the variance of the differential phase curve, thereby obtaining the phase variance curve.

11. The vibration detection and positioning method according to claim 7 , wherein:
the determination of the vibration point includes setting a point on the phase variance curve as the vibration point, the set point having a variance on the phase variance curve greater than 0.02;
the position of the vibration point on the sensing fibre is z=c′k 0 t s /2, c′ is a propagation speed of light in the sensing fibre, t s is a sampling rate of the detection and position module, and k 0 is an index value corresponding to the vibration point;
the vibration point has a vibration waveform which is a new sequence composed of differential phases at the vibration point in a differential phase curve.

Assignees

• Univ Shanghai Jiaotong
• Neubrex Co Ltd

Inventors

• He Zuyuan
• Liu Qingwen
• Chen Dian
• Fan Xinyu

Classifications

• G01D5/35358

  using backscattering to detect the measured quantity · CPC title

• G01H9/004 Primary

  using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125) · CPC title

• G01D5/35306

  using an interferometer arrangement · CPC title