Fiber-Bragg-Grating Based Single Axial Mode Fabry-Perot Interferometer and Its Strain and Acceleration Sensing Applications

Abstract

Based on a rigorous mode theory and considering the wavelength dispersion of fiber Bragg grating (FBG), the conditions necessary for FBG-based Fabry-Perot interferometer (BFPI) to operate in single axial mode (SM) were investigated, as an extension of phase-shifted FBG, by analytical formulas and numerical simulation. Following the theoretical results, SM-BFPI of very narrow bandpass was designed and fabricated. Using that, the first of its kind to our knowledge, SM-BFPI-based WDM distributed (four-points) strain sensing was demonstrated which had a point-like ultrahigh spatial resolution of 2.1 mm and very high strain precision of <;0.8 με . Using a specially designed acceleration pick-up and a path-imbalance Mach-Zehnder interferometer for wavelength interrogation, a fully automatic SM-BFPI accelerometer, capable of giving ultrahigh performance, was developed. The performance of the accelerometer, with a very high sensitivity of 0.5 mGal in 0.1-200 Hz for 0-±980 Gal, is superior to that of electric servo-type accelerometer. To enable the accelerometer to exactly work in the field, the interrogator was stabilized against ambient temperature changes and mechanical disturbances by means of a compensation technique, using the constant wavelength of a reference SM-BFPI. In the course of the experimental study, particular attention has been paid to performance comparison with FBG sensors, much improvement against them having been demonstrated.