A zero-gap electro-optic directional coupler switch in nematic liquid crystal

A guided-wave optical routing/switching device using nematic liquid crystals has been investigated in terms of its modal properties and electro-optic control. The basic component is a nematic liquid crystal cell, where anchoring films (either Teflon, silica or Nylon) are deposited to obtain the correct planar molecular orientation. Patterned electrodes are realized on the quartz substrates of the cell for the application of an external electric field. By properly tailoring the electrode widths, a voltage-controlled channel waveguide can be induced within the liquid crystal (LC) layer and allow bimodal propagation for a chosen wavelength of operation. A slight change in the applied voltage modifies the phase velocity of the two propagating modes, resulting in a relative phase shift along the direction of propagation and, consequently, in a voltage-controlled interference at the output. The investigated geometry appears to be a versatile and fully electro-optic switch, whose bias can be optimally tuned for operation at any wavelength of interest.