The fiber optic Sagnac interferometer and its sensing application

The fiber optic Sagnac interferometer which comprise of a broadband source, a fiber optic coupler and special sensing fiber has great application potentiality. The characteristic of output spectrum was investigated and high precision polarization maintaining fiber (PMF) beat-length measurement was achieved. Hydrogen concentration and pressure sensor with PM photonic crystal fiber was demonstrated. A spectrum interrogation methods based on absolution phase interrogation were proposed.