A novel active continuous-wave FLRD strain sensor based on frequency-shifted interferometry

Abstract

ABSTRACT An active continuous-wave fiber loop ringdown strain sensor based on frequency-shifted interferometry is presented and experimentally investigated. By measuring the decay rate of the continuous light in the ringdown loop (RDL), the sensor achieves strain measurement without optical pulsation and rapid detection. A bidirectional erbium-doped fiber amplifier is embedded in the loop to form an active fiber RDL, to compensate the inherent loop loss. The strain sensor head was built by splicing a segment of normal graded index multimode fiber (MMF) into the RDL composed of single-mode fiber. In this configuration, the core-cladding mode conservation and insertion loss of the MMF changes with the strain applied, making it possible to detect different levels of strains. The proposed device was tested with the strains in the range from 0 to 2.25 mϵ, which exhibits a linear response with a sensitivity of 0.29 km-1·mϵ-1, with a measurement resolution of 22 mϵ.