Interferometer based on strongly coupled multi-core optical fiber for accurate vibration sensing

Abstract

We report on the use of a simple interferometer built with strongly-coupled core optical fiber for accurate vibration sensing. Our multi-core fiber (MCF) is designed to mode match a standard single-mode optical fiber (SMF). The interferometer consists of a low insertion loss SMF-MCF-SMF structure where only two super-modes interfere. The polymer coating of the MCF was structured and the interferometer was sandwiched between a flat piece and a V-groove. In this manner our device is highly sensitive to force with sensitivity reaching -4225 pm/N. To make the MCF interferometer sensitive to vibrations the flat piece was allowed to move, thus, its periodic movements exert cyclic localized pressure on the MCF which makes the interference pattern to shift periodically. Our sensors can be used to monitor vibrations in a broad frequency range with the advantage that the measurements are unaffected by temperature changes.

Robust in-fiber spatial interferometer using multicore fiber for vibration detection

“…In conclusion, we have proposed and demonstrated a simple and efficient optical fiber vibration sensor based on in-fiber spatially integrated Michelson interferometer using weakly coupled MCF. Vibration sensing with high sensitivity, high SNR and large frequency response range up to 12 kHz has been achieved, which is much higher than the values that are measured by the sensors that are made of strongly coupled MCF [10,11]. The dependence of MI performance on the selection of core pairs has been experimentally compared, and it turns out that MIs constructed using any two cores are able to retrieve the correct vibration frequency in the case of small vibration amplitude.…”

“…Therefore, by monitoring the variation of output power of the MI over time, the vibration frequency can be obtained. It must be pointed out that the other reported interferometric vibrations sensors that are fabricated by either splicing or tapering are essentially based on the principle of light interference between different optical modes (including super-modes) within a single optical path in the fiber [3,[9][10][11][12]. However, different from previously reported interferometric vibrations sensors, the proposed MCF based in-fiber spatially integrated MI is fabricated by using two independent cores of a single fiber, where two completely separate optical paths are employed to construct the interferometer, and independent light coupling between the cores of MCF and the SMFs is enabled by the fan-in coupler.…”

“…It normally requires a wavelength scanning light source to demodulate the Bragg reflection wavelength, so the detectable frequency range is usually quite limited. In addition, modal interferometers which are fabricated by splicing different kinds of fibers have also been demonstrated [9][10][11][12]. However, the concern is that this kind of sensors has bad mechanical strength due to splicing.…”

Pendulum-Type Hetero-Core Fiber Optic Accelerometer for Low-Frequency Vibration Monitoring

“…There have been a variety of fiber optic sensors developed for smart structures by use of Brillouin scattering [15,16], fiber Bragg grating (FBG) [17][18][19][20][21][22][23][24], and optical interferometer [25,26]. Minardo et al introduced distributed fiber optic temperature and strain sensors using Brillouin optical timedomain analysis (BOTDA) into railway infrastructures and succeeded to dynamically monitor strain distribution due to train passage [15].…”

Novel accelerometer realized by a polarization-maintaining photonic crystal fiber for railway monitoring applications

“…Recently, in the effort to achieve high performance accelerometers, specialty optical fibers including PCFs [15] have been proposed, providing a new direction for improvement and exploration rather than merely focusing on the mechanical design. Villatoro et al in 2017, proposed a strongly coupled multicore fiber to measure vibrations with a very high sensitivity of −4225 pm/N, which may be useful for acoustic measurements [23] even though, high accelerations were not demonstrated. Rong et al reported a highly sensitive accelerometer through FBG inscription in a special double-clad fiber consisting of a low-index dip in the center of the fiber core [24].…”