Variable delay device for an optical component such as a polarization mode dispersion compensator

Abstract

A variable delay device of the type used to correct for polarization mode dispersion in a signal transmitted over an optical communications system. In an exemplary embodiment, the variable delay device uses a plurality of polarization rotators and delay elements aligned in series and alternating with one another. The polarization rotators map the fast polarization mode component of the incoming optical signal to the slow axes of one or more delay elements, to achieve a desired pattern of relative incremental delays which total the initial differential delay being compensated. The delay elements may have uniform or non-uniform incremental delay values, and the polarization rotators may be selectively actuated to achieve the desired pattern of delay values corresponding to the intended total delay. Examples of suitable delay devices include waveguides having relatively high differential group delay characteristics associated with two orthogonal axes compared with conventional single-mode transmission fiber, and examples of suitable polarization rotators include twisted nematic liquid crystal (TNLC) or ferroelectric liquid crystal (FLC) cells which rotate the polarization mode components of the optical signal by 90° when actuated.