Endless polarization control algorithm using adjustable linear retarders with fixed axes

New designs are presented for polarization-transforming elements equivalent to rotating quarter-wave plates and rotating half-wave plates. These are constructed from sequences of adjustable linear retarders with fixed retardation axes, such as liquid-crystal cells (untwisted nematic) and electrooptical modulators. Then, a new endless polarization control algorithm is proposed and demonstrated. The variable linear retarders in this endless polarization controller operate over a finite range of retardance without any reset or unwinding procedure. This endless algorithm can produce all possible sequences of continuous polarization state transformations.

I. Introduction

Controlling the state of polarization (SOP) in optical fibers has long been an active research topic with many papers published in the last 20 years [1]– [7]. This research dealt with both devices for polarization control, e.g., fiber squeezers [3], [4], [6], liquid crystals [7], rotating waveplates [1], or waveguide devices such as LiNbO₃ [3], [5], [6], [8], and algorithms for polarization control, i.e., number of devices and driving algorithms. The principal objective of these algorithms was to provide a polarization controller (PC) with unlimited transformation ranges. This property of being able to generate an arbitrary sequence of continuously varying polarization states is referred to as endlessness.