Photonic Switches Based on Liquid Crystal Electro-optical Waveguides

We present an overview on a class of photonic devices based on a nematic liquid crystal (NLC) infiltrated in confined geometries acting as a core of optical waveguides. This approach allows to obtain switchable waveguide devices by exploiting the combination of electrooptic effect of the NLC characterized by an attracting low driving voltage characteristic and high extinction ratio. In switchable LC optical waveguides in SiO2/Si V-groove an on-off ratio of over 40 dB has been experimentally demonstrated by applying a square-wave voltage with an amplitude of only 8 V. In addition we report the design photonic devices based on NLC infiltrated in polydimethylsiloxane (PDMS) channels, named LC:PDMS waveguides, for flexible photonic integrated circuits The minimization of the free energy in the NLC core waveguides computed by means of finite elements allows to derive the refractive index profile, which is implemented in a BPM algorithm to design a large variety of switchable and tuneable photonic devices. As an example a 2 × 2 optical switch made of a zero-gap electro-optical controlled directional coupler is able to switch light from one waveguide to a second one with an extinction ratio of 16 dB by applying a voltage of just 1.62V to coplanar electrodes. Light remains in the same waveguide with an extinction ratio of about 18 dB with a voltage of 1.76 V. Recent results will be also reported on simulation studies of the NLC ordering in PDMS channels under an electric field between coplanar electrodes by a Monte Carlo approach.