Optical Multistability in High-Q Nonlinear Photonic Crystal Nanoresonators

Abstract

Photonic crystals are prime candidates for photonic integrated circuit applications, for instance in the field of optical telecommunications and optical computing. In this thesis we experimentally investigate the optical nonlinear behavior of single and coupled nanoresonators on a waveguide in a photonic crystal membrane. Photonic crystal resonators typically have small mode volume and high quality factor, which optimizes the optical nonlinearity crucial for active photonic devices. Our photonic crystal is designed for near-infrared light (~1550nm). Thermo-optical nonlinearity is the dominating nonlinearity in these InGaP photonic crystal waveguides. We measure the thermo-optical timescale in the system and find that the decay time of a mode is related to its mode profile. Additionally, we present a nonlinear mode mapping technique to measure the mode profile. We use an out-of-plane blue pump beam to spatially scan the surface of the photonic crystal and probe the mode. The pump light is absorbed and serves as a local heat source. Nonlinear effects, caused by free carrier absorption of infrared input light, significantly improve the resolution with respect to linear mode map techniques. This provides a non-invasive far-field imaging technique. Lastly, we look at two coupled nanocavities that give rise to optical multistability in the nonlinear regime. We investigate the phase space of the system by exciting the system with a puls of the out-of-plane pump beam. It turns out the pump pulse triggers a state change that remains stable after the pump is turned off. In this way we, find different energy branches of the multistable system, where the position of the pump pulse determines the thermo-optical state the system stabilizes in. Using this effect we demonstrate a programmable multistable all-optical switch, where we walk through the multistable phase space of the system, addressing several thermo-optical stable states in the system by lowering or raising the internal energy of the hybridized cavities.