Distributed Polarization Characteristic Testing for Optical Closed Loop of Sagnac Interferometer

Distributed polarization characteristic of Sagnac optical closed loop that composed of two polarizing devices- polarization maintaining fiber coil and Y-waveguide, can directly affect the performance of fiber optic sensors. Several existing methods are applicable for only one device testing at a time, the efficiency is therefore relatively low and the connection quality between devices is unavailable. In this paper, the Sagnac optical closed loop is split into semi-closed loop (SCL) and full-closed loop (FCL) structures. The transmission behavior of polarized optical signal is fully analyzed, and the information of polarization mode crosstalk is positioned and extracted accurately. By conducting one test of SCL and FCL respectively utilizing white light interferometry, the distributed polarization characteristic of both optical devices and connection points can be entirely obtained. The testing results of optical closed loop are highly consistent with single device test and the difference is less than 0.2dB. A good testing stability is demonstrated through ten repeat measurements and the fluctuation is almost around 0.1dB. We believe that the proposed testing method is capable of promoting the assembly of high-performance Sagnac interferometer and the development of fiber optic sensors.