Ricerc@Sapienza

The use of liquid crystals (LC) as cladding in optical switching applications enables large phase shifts with low power consumption, due to the possibility of changing the orientation of
LC’s molecules by applying an external electric field. As a result, variations of such a driving electric field, leads to changes in the effective refractive index of the LC and, consequently, in the optical phase at the output of such waveguides. Establishing an appropriate molecular organization inside the cells is thus fundamental for the function and optimization of such devices.

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.

We present photonic devices based on a nematic liquid crystals (NLC) infiltrated in polydimethylsiloxane (PDMS) channels, named LC:PDMS waveguides, for flexible photonic integrated circuits. A simulation study of the NLC ordering and possible defects under an electric field between coplanar gold electrodes has been carried out by a Monte Carlo approach.