Polarization diversity circuit based on silica waveguides and photonic crystal waveplates for a 4×4 silicon optical switch

We propose a compact polarization diversity circuit for a silicon waveguide device. It consists of silica waveguides and photonic crystal waveplates, and can convert input light with various polarization states into two output light signals with the same polarization. Setting these circuits at the front and rear of two silicon optical switches, the polarization dependence in the switch can be dramatically suppressed. We fabricated polarization diversity circuits for a 4×4 silicon optical switch and realized a polarization insensitive 4×4 optical switch. The polarization dependent loss was reduced to 1.1 dB and the polarization dependent crosstalk was less than −17 dB.