ABSTRACT
Fixed or adjustable polarization transformers have been known for many decades and are typically used to convert a well-defined input state of polarization (SOP) of a quasi-monochromatic light beam into another well-defined output SOP. Optical polarization controllers, on the other hand, are relatively new and were developed for a substantially more difficult task, namely to transform an unknown and even time-varying input SOP continuously and automatically into a prescribed output SOP. Such adaptive polarization transformation is often referred to as automatic polarization stabilization or automatic polarization control. The need for automatic polarization controllers arose with the introduction of single-mode optical fibers in telecommunication systems and in optical sensors. The lithium niobate polarization controller is designed to emulate the polarization transformations of a combination cascade of five independently rotatable zero-order quarter-wave plates. The maximum speed of the polarization controller is limited by the electrical bandwidth of the individual electrode sections.
