A polarization independent optical device is provided wherein the device has two optical paths that include one or more birefringent crystals, a electrically controllable rotator, and a fixed waveplate. The device may operate as a switch, attenuator, coupler, or polarization mode dispersion compensator....http://www.google.com.au/patents/US6594063?utm_source=gb-gplus-sharePatent US6594063 - Birefringent optical device
