Polarization Independent Optical Isolator in Sagnac-Type Configuration

We propose a polarization-independent optical isolator that does not use walk-off between the two orthogonal polarizations. The design is based on two Faraday rotators in combination with two half-wave plates in a closed, Sagnac-interferometer-like configuration. An experimental prototype is tested successfully under variation of the input light polarization state with isolation level between 43 dB and 50 dB for all input polarizations (linear, circular, or elliptical).