High-isolation polarization-insensitive N-port optical circulator

A polarization-insensitive N-port optical circulator is proposed. A four-port and a six-port circulator are assembled and their characteristics are measured. Experiments demonstrate that the circulators have a low insertion loss (</=1.3 dB), a high isolation level (>/=65.0 dB), and a high return loss (>/=61.3 dB) for any polarization state of input light.