Interrogation Sensing Scheme Based on a Figure-of-Eight Fiber Loop Mirror

Abstract

A fiber optic interrogation sensor scheme based on a "figure-of-eight" configuration created from a single directional 3 × 3 fiber optic coupler is proposed. Two loops are formed in each arm and one of them contains the sensing head and the other is used as reference signal. A theoretical study based on Jones matrix analysis of this fiber loop mirror combination is reported. The optical configuration is tested as an interrogation scheme for a fiber strain sensor where the spectral response arises from the combination of the reference signal modulated by the sensor signal. The strain sensor configuration shows a phase sensitivity of 6.7 ± 4.38 × 10 −2 mrad/µstrain by linear regression.Index Terms-Fiber interferometer, figure-of-eight, highlybirefringent fiber, optical fiber sensor, strain sensor.

High-birefringence fiber loop mirror sensor using a WDM fused fiber coupler

“…However, for a large range of strain measurement it is expected to present a sinusoidal response typical of the pattern fringe obtained by the sensing head. This response was observed in the literature concerning the use of two FLMs concatenated [9] or in figure-eight configuration [11]. Despite the maxima of transmissivity being fixed, the minima have a measurable shift.…”