Distributed fiber optic acoustic detection device

• US 10,429,234 B2
• Filed: 01/21/2015
• Issued: 10/01/2019
• Est. Priority Date: 01/21/2015
• Status: Active Grant

• Current Assignee: Neubrex Co., Ltd.
• Original Assignee: Neubrex Co., Ltd.
• Inventors: Nishiguchi, Kenichi, Kishida, Kinzo, Li, Che-Hsien
• Primary Examiner(s): Caputo, Lisa M
• Assistant Examiner(s): Miller, Rose M
• Application Number:
  US15/542,588
• Publication Number:
  US 20170356793A1
• Time in Patent Office: 1,714 Days
• Field of Search: 73643, 73655
• CPC Class Codes: G01H 9/002 for representing acoustic field distribution sonar systems for imaging G01S7/56, G01S15/89; acoustic holography G03H3/00
• CPC Class Codes: G01H 9/006 the vibrations causing a variation in the relative position of the end of a fibre and another element
• CPC Class Codes: G01V 1/001 Acoustic presence detection
• CPC Class Codes: G01V 1/226 Optoseismic systems
• CPC Class Codes: G01V 1/42 using generators in one well and receivers elsewhere or vice versa G01V1/52 takes precedence

Abstract

A distributed fiber optic acoustic detection device employs a novel distributed acoustic detection method using a phase noise cancelling distributed acoustic sensing (PNC-DAS) technique.

Claims

1. A distributed fiber optic acoustic detection device that measures a distribution state of an acoustic wave by utilizing backscattered light disturbance due to strain of an optical fiber caused by the acoustic wave, the distributed fiber optic acoustic detection device comprising:

a laser light source;

a pulse generator for shaping laser light emitted from the laser light source into an optical pulse, to inject into an optical fiber the optical pulse as a prove optical pulse for acoustic detection;

a delay circuit for delaying the laser light to be injected into the pulse generator for the pulse generator to inject a delayed optical pulse as a replica optical pulse of the prove optical pulse for acoustic detection;

a switching circuit for switching injection of the laser light into the pulse generator between directly and via the delay circuit;

a detector for detecting Rayleigh backscattered light returning to an input end of the optical fiber after backscattered in the optical fiber, to extract an intermediate frequency signal from the detected signal; and

a signal processor for processing the intermediate frequency signal extracted by the detector to convert the processed signal into a baseband signal,

wherein during acoustic measurement,

the prove optical pulse and the replica optical pulse are repeatedly injected one after another as an odd-numbered prove pulse and an even-numbered prove pulse, respectively, into the optical fiber at constant time intervals by the switching action of the switching circuit, and the signal processor processes the intermediate signal that is obtained by subtracting a Rayleigh backscattered signal responsive to an odd-numbered optical pulse from a Rayleigh backscattered signal responsive to the next even-numbered optical pulse.

2. The distributed fiber optic acoustic detection device of claim 1, further comprising:

modulator for modulating the optical pulse launched from the pulse generator and

a demodulator for demodulating Rayleigh backscattered light responsive to the optical pulse modulated by the modulator,

wherein the modulator modulates the optical pulse using a given code sequence to inject the modulated optical pulse into the optical fiber, and the demodulator demodulates Rayleigh backscattered light caused by the modulated optical pulse.

3. The distributed fiber optic acoustic detection device of claim 1, wherein the detector is any one of a polarization diversity heterodyne detector for performing a heterodyne detection using as a reference light a laser light frequency-shifted from the laser light emitted from the laser light source by the frequency shifter, a homodyne detector using as a reference light a frequency-unshifted laser light emitted from the laser light source, and a interferometer configured with m×

m optical couplers without using both of the foregoing two kinds of reference light, where m is a natural number of three or more.

4. The distributed fiber optic acoustic detection device of claim 1, wherein the constant time interval is longer than a value calculated by dividing a value twice the length of the optical fiber by a value of a group velocity of the laser light in the optical fiber.

5. The distributed fiber optic acoustic detection device of claim 1, wherein a linewidth of the laser light of the laser light source is 100 kHz or more.

6. The distributed fiber optic acoustic detection device of claim 1, wherein the phase of an output signal of the signal processor is spatially differentiated and the phase is unwrapped into a continuous phase.