HIGH-ISOLATION POLARIZATION-INDEPENDENT OPTICAL CIRCULATOR

A high-isolation polarization-independent optical circulator is reported. The new circulator structure can sharply reduce isolation dependency on both the rotation error of a rotator and on extinction ratio of a polarizing beam splitter. As a result, the circulator has high isolation over a wide wavelength and temperature range. A 4-port circulator coupled with single-mode fibers is fabricated. Its measured insertion loss and isolation are < 1.8 and > 31.5 dB, respectively. Consequently, loss ratio of over 29.7 dB has been realized. The isolation which is free from reflections is measured to be > 45.1 dB. It is confirmed that the wavelength range for this kind of isolation over 40-dB is very wide; the measured range is wider than the measurement system limit of 90 nm.