Automatic endless polarization control with integrated-optical Ti:LiNbO(3) polarization transformers

In coherent-optical transmission systems continuous or endless polarization matching between the superposed beams must be ensured. We describe a practical closed-loop polarization-control system with two integrated-optical retarders acting as polarization transformers. They have variable retardations and variable eigenmodes, i.e., adjustable birefringence magnitude and orientation as in a Babinet-Soleil compensator. In theory, one retarder would be sufficient. However, a second device is added to correct nonideal behavior of the first. The intensity losses during polarization control are less than 0.15 dB.