VOLTAGE-CONTROLLED OPTICAL-FIBER COUPLER USING A LAYER OF LOW-REFRACTIVE-INDEX LIQUID-CRYSTAL WITH POSITIVE DIELECTRIC ANISOTROPY

A variable fiber directional coupler is made using liquid crystal as t he intermediate cladding layer between two side-polished optical fiber s. A nematic liquid crystal with low refractive index and positive die lectric anisotropy is used. An ac electric field is applied to the liq uid crystal by applying a voltage across two parallel electrode stripe s on the two sides of the fibers. The electric field rotates the molec ular orientations and changes the refractive index of the liquid cryst al. The coupling ratio between the two fibers is then controlled by th e applied voltage. The dependence of the coupling ratio on the applied voltage is studied for various light wavelengths, including a continu ous variable range between 1.272 mu m and 1.310 mu m.