Voltage-controlled optical fiber coupler using a layer of low-refractive-index liquid crystal with positive dielectric anisotropy

Abstract

A variable fiber directional coupler is made using liquid crystal as the intermediate cladding layer between two side-polished optical fibers. A nematic liquid crystal with low refractive index and positive dielectric anisotropy is used. An ac electric field is applied to the liquid crystal by applying a voltage across two parallel electrode stripes on the two sides of the fibers. The electric field rotates the molecular orientations and changes the refractive index of the liquid crystal. The coupling ratio between the two fibers is then controlled by the applied voltage. The dependence of the coupling ratio on the applied voltage is studied for various light wavelengths, including a continuous variable range between 1.272 mu m and 1.310 mu m.