Distributed acoustic sensing with Michelson interferometer demodulation

Xiaohui Liu,Gangding Peng,Hongzhong Wang,Ying Shang,Wenan Zhao,Chang Wang,Chen Wang

doi:10.1007/s13320-017-0363-y

Abstract

The distributed acoustic sensing (DAS) has been extensively studied and widely used. A distributed acoustic sensing system based on the unbalanced Michelson interferometer with phase generated carrier (PGC) demodulation was designed and tested. The system could directly obtain the phase, amplitude, frequency response, and location information of sound wave at the same time and measurement at all points along the sensing fiber simultaneously. Experiments showed that the system successfully measured the acoustic signals with a phase-pressure sensitivity about–148 dB (re rad/μPa) and frequency response ripple less than 1.5 dB. The further field experiment showed that the system could measure signals at all points along the sensing fiber simultaneously.

Highlights

Distributed acoustic sensing (DAS) is a novel technology which offers the capability of measurement at thousands of points simultaneously, using a simple and unmodified optical fiber as the sensing element
The amplified light passes through an isolator and is injected into a Michelson interferometer which consists of a 2×2 coupler, a phase modulator (PM), and two Faraday rotation mirrors (FRMs)
An optical fiber distributed acoustic sensing system based on the unbalanced Michelson interferometer and phase generated carrier (PGC) demodulation is demonstrated

Summary

Introduction

Distributed acoustic sensing (DAS) is a novel technology which offers the capability of measurement at thousands of points simultaneously, using a simple and unmodified optical fiber as the sensing element. Compared with conventional point sensors, DAS needs no special reflectors or fiber Bragg gratings in its optical path, which greatly reduces the operation difficulty in field test It can measure thousands of continuous points along the sensing fiber and form acoustic or seismic imaging. The DAS system operates according to a radar-style process: it sends a series of pulses into the fiber and records the return of the naturally occurring scattered signal against time One representative of this backscattered sensing is phase sensitive optical time domain reflectometer (φ-OTDR), which inputs a narrow line-width laser to the sensing fiber and monitors the phase changes of Rayleigh backscattered lights [6,7,8,9]. Experiments showed that the system could successfully acquire the acoustic signal information, including the location, frequency, amplitude, and phase, at all points along the sensing fiber simultaneously

System design

Lab experiments

Field experiments