Polarization Stability of a Double-Loop Interferometer Based on a Planar 3×3 Coupler

An interferometer with double loops based on a planar 3×3 coupler is proposed. The main factors that cause the instability of the polarization state are obtained by theoretical analysis and experiment. Furthermore, the stability of the polarization state is described quantitatively by the time-varying vector of polarization. Using these effective measures, interference with a stable polarization state at all times is achieved.