Dual Michelson interferometers for distributed vibration detection

Abstract

A distributed fiber optic vibration sensor is described, in which two Michelson interferometers are used as phase detectors and two 3×3 couplers are deployed to demodulate the time-varying phase change caused by vibration. The two interferometers are separated by four wavelength division multiplexers. The position of the vibration is obtained by signal correlation, which can be used as a perimeter security sensor to locate the intruder. The experimental results with a 4012 m fiber sensor are discussed.

Fibre Bragg Grating-Based Cascaded Acoustic Sensors for Potential Marine Structural Condition Monitoring

“…The majority of optical fibre acoustic sensors to date have been based on interferometric configurations such as using Mach-Zahnder [8], Michelson [9], Fabry-Perrot [10] or Sagnac [11] techniques. Recently, distributed feedback (DFB) fibre lasers have been applied to this field (and their use has been reported elsewhere [12]).…”

Advanced fiber-optic acoustic sensors

“…Their preliminary works marked the beginning of fiber-optic acoustic sensing that, since then, continued to be developed. Currently, numerous works in this field can be found, many of these following interferometric configurations such as Mach-Zehnder [4], Michelson [5], Sagnac [6], and Fabry-Pérot [7], while others explore the possibilities offered by fiber Bragg grating (FBG) sensors [8]. A comprehensive review paper in this area until 2008 was written by Graham et al [9], and another work comparing three different types of fiber-optic acoustic sensors was published in 2010 [10].…”

A distributed fiber vibration sensor utilizing dispersion induced walk-off effect in a unidirectional Mach-Zehnder interferometer

“…For distributed optical fiber sensing systems demonstrated so far, a large number of signals are acquired and processed in order to obtain a reasonable signal to noise ratio (SNR), so the acquisition time is typically on the order of few minutes. They fall into two categories, one is based on optical fiber interferometers [1][2][3][4][5][6][7][8][9][10] and the other is based on optical backscattering [11][12][13][14][15].…”

“…In order to obtain the vibration location of distributed optical fiber sensor system, either modified optical interferometer structures are adopted or two kinds of optical interferometer structures are merged together, such as incorporating an MZI with a Sagnac loop [3], modified Sagnac/MZI [4], twin Sagnac interferometers [5,6], merged Sagnac-Michelson interferometers [7], dual Michelson interferometers [8], dual MZIs [9] and scanning MZI [10]. Due to the differences between correlated signals in separate interferometers caused by noises or changes of polarization states, both the spatial resolution and measurement range for twin optical interferometer structures are limited.…”

“…Due to the differences between correlated signals in separate interferometers caused by noises or changes of polarization states, both the spatial resolution and measurement range for twin optical interferometer structures are limited. A 40m spatial resolution over 6km sensing fiber has been achieved using a Sagnac-Michelson interferometer [7], and a 102m spatial resolution over 4012m fiber has been achieved using a dual Michelson interferometer structure [8]. These systems cannot be used for long distance, high spatial resolution and high vibration frequency applications.…”