Variable optical attenuator

Abstract

The invention relates to a variable optical attenuator utilizing a variable polarization rotator, preferably in the form of a liquid crystal cell, positioned between two birefringent elements, preferably in the form of two similar birefringent crystals. The first birefringent element splits a beam light into orthogonally polarized sub-beams, which are passed through the liquid crystal cell, thereby undergoing a desired polarization rotation. The second birefringent element recombines only a portion of each of the first and second sub-beams providing the desired amount of light as an output beam. To minimize insertion loss, a first lens is positioned between the first birefringent element and the liquid crystal cell, and a second lens is positioned between the liquid crystal cell and the second birefringent crystal. Ideally the liquid crystal cell is positioned a focal length away from the first lens, whereby both the first and second sub-beams enter the liquid crystal cell at the same point of entry, thereby minimizing polarization dependent loss (PDL) due to any anisotropy in the liquid crystal.

Dependencies are inferred from the claim text.