Liquid crystals embedded in poly(dimethylsiloxane) photonic devices: modeling and fabrication issues

Liquid crystals (LC) can be successfully adopted as waveguides for photonic devices and optofluidic systems, while poly(dimethylsiloxane) (PDMS) is a cheap and easy to implement soft material which allows the making of any geometry. Modelization and making of several LC embedded in PDMS photonic devices are presented in this work. The theoretical study of the waveguides’ inner structure was performed by Monte Carlo simulations of the molecular ordering inside the microchannel. Calculations were based on a Lebwhol-Lasher (LL) lattice spin model to emulate the LC cell by imposing homeotropic boundary conditions at each channel considering also the effect of an applied electric field. A comparison will be carried out with modeling based on the minimization of Oseen Frank free energy including both elastic and dielectric terms by using finite elements implemented in COMSOL Multiphysics® software platform. These modelling were used to optimize a 2x2 optical switch, based on a zero-gap electro-optical controlled directional coupler, which allows the switching of light among the waveguides with an extinction ratio of 16 dB, by applying only 1.62 V at near infrared wavelengths. A second device was also studied and designed consisting in a multimodal interferometer (MMI) acting as an optical multi/demultiplexer operating at wavelengths of 980 nm and 1550 nm. In this case an extinction ratio of 11.5 dB can be reached for both wavelengths with a device’s length of just 495 μm. The optimized design of a tunable optical ring resonator as a filter or a true delay line will be also shown.