Fibre-optic Sagnac interferometer as sensor of the SOP changes

Abstract

The fiber-optic Sagnac interferometer (FOSI) has many useful applications begin from gyro up to wide range of sensors for measurement of different physical quantities. In this paper a new its application as a sensor of the state of polarization (SOP) changes is presented. The optical part of system is based on minimum gyro configuration, however a high level polarizer is replaced by specialized polarization filter with 3dB extinction ratio. The coherence and Jones matrix formalism for the system description were applied. Utilized in the system a fiber-optic phase modulator allow measuring the SOP changes by comparison appropriate harmonic amplitudes of the output signal. Additionally, two dead ends of the FOSI are used for system stabilization as well as an input intensity control. This system is dedicated for easy and active stabilization of the SOP in the fiber-optic devices where the polarization fading is a main disadvantage.