High-isolation polarization-independent optical circulator coupled with single-mode fibers

A high-isolation polarization-independent optical circulator is reported. The goal is to provide a simple structure that sharply diminishes the degradation on the isolation caused by imperfection of polarization separation in the polarizing beam splitters. The circulator structure is almost the same as that of a conventional circulator except that a birefringent plate is added to each port to achieve high isolation. The effectiveness of the added birefringent plate has been confirmed by calculation and experiment. Insertion loss and isolation of the fabricated circulator coupled with single-mode fibers have been measured to be <1.0 dB and >29.9 dB, respectively, for 1.299 μm wavelength light. A loss ratio over 28.9 dB has been realized