FBG-based dynamic strain sensors demodulated by self-mixing interferometry: Improving strain measurement resolution

A fiber optic strain sensor has been devised based on the use of optical feedback or self-mixing interference within the cavity of a single-longitudinal-mode laser as a novel fiber Bragg grating interrogation scheme for strain measurement in the domain of structural health monitoring. The entire sensor device thus simply consists of a laser diode with an integrated photodiode coupled to a fiber Bragg grating under strain. The feasibility of demodulating the induced small wavelength shifts of fiber Bragg gratings under dynamic mechanical loading by self-mixing interferometry has been experimentally verified with strain gauges. This current investigation further reports new work to improve the accuracy of the measured strains. Measurement resolution, defined by the distance between two consecutive peaks from the optical fringes, has been improved from 10 με to 6 με by increasing the fiber gauge length.