Microwave-photonic optical fiber interferometers for wavelength interrogation of fiber Bragg grating sensors with high sensitivity and a tunable dynamic range.

Abstract

We propose and demonstrate a new, to the best of our knowledge, microwave interference-based scheme with high sensitivity and tunable measurement range, which is realized by a Mach-Zehnder interferometer (MZI). A chirped fiber Bragg grating and single-mode fiber serve as the two unbalanced arms of the RF interferometer. The induced differential chromatic dispersion transfers the wavelength shift of the fiber Bragg gratings to the change of the RF phase difference between the two interferometric carriers, which ultimately leads to the variation of the RF signal intensity. The phase sensitivity can be improved by adjusting the power ratio of the two beams in the interferometer and coarse adjustment of the optical variable delay line (OVDL). The OVDL is also employed to tune the measurement range of the system by adjusting the time delay difference between the two arms of the MZI. The system effectively solves the problem of unavoidable attenuation of the sensitivity of the optical carrier-based microwave interferometry system caused by the change of phase difference due to the change of measurement parameters, avoiding the mutual constraint between the measurement range and high sensitivity.