Liquid Crystals for nanophotonic applications

Research Area: Heterogeneous Integration with Silicon Photonics

Main Researcher: Wout De Cort

Silicon-on-insulator is an ideal material for passive waveguide components. However, for active functions that require nonlinearities or electrooptic effects the material properties are relatively weak. In nanophotonic waverguides a significant fraction of the light is in the surrounding air. If the air is replaced with a material with very strong electrooptic or nonlinear properties, like Liquid Crystal, active functions can be implemented in SOI.
We explore the possibilities to add a Liquid crystal cladding to SOI nanophotonic waveguides. To do this, we fabricate aLC cell, not unlike those used in displays, but where one glass contact plate is replaced by an SOI waveguide component. The other plate of the cell is a thin glass plate with a gold contact and a polyimide alignment layer. The plates are joined with two stripes of glue and the distance is well controlled with spacers suspended in the glue. Once mounted, the cell is filled with liquid crystal with cappilary forces.
We have measured the change in refractive index in a 3micron wide SOI ridge waveguide. Here, the effect is not very strong, because only a small fraction of the light is in the cladding. Still, we can observe the effect when we measure the transmission of a Fabry-Perot cavity formed by the facets. The results is very close to the predicted theoretical values.

This research is in collaboration with the Liquid Crystal & Photonics Group

Other people involved:

• Wout De Cort

Related Research Projects

• IAP-V: PHOTON (Photons and Photonics : from basic physics to system concepts)