Phase interrogation algorithm with high resolution for hybrid Sagnac interferometers

A phase interrogation algorithm with high resolution for the measurement of the polarization nonreciprocal phase-shift of hybrid Sagnac interferometers is proposed. Taking wavenumber instead of wavelength as the function variable, the output spectrum is a standard cosine spectrum function. The frequency, interference order and relative phase of this spectrum function can be obtained after Fourier transform and inverse Fourier transform. And then the measurement of the polarization nonreciprocal phase-shift of hybrid Sagnac interferometers can be realized with high resolution and a large rangement. A typical hybrid Sagnac interferometer based polarization maintaining fibrer (PMF) temperature sensor is built and the absolute phase is determined with proposed algorithm. Experiments show that less than 0.1℃ temperature resolution is realized and the temperatures from room temperature to 900℃ can be measured with a good linearity.