High-isolation polarization-insensitive optical circulator for advanced optical communication systems

An optical circulator configuration that does not use polarization beam-splitters (PBSs) is described. Birefringent crystals (BCs) are used instead of PBSs to achieve a high-isolation polarization-insensitive optical circulator. The use of BCs simplifies fabrication. A conceptual configuration and two concrete structures are proposed. The prototype optical circulator was tested and exhibited over 60 dB of isolation in the wavelength range of 70 nm around 1550 nm. The insertion loss is under 1.5 dB and fluctuates only 0.2 dB with changes in the polarization state