Design of mechanically-tunable photonic crystal split-beam nanocavity.

Abstract

Photonic crystal split-beam nanocavities allow for ultra-sensitive optomechanical transductions but are degraded due to their relatively low optical quality factors. We have proposed and experimentally demonstrated a new type of one-dimensional photonic crystal split-beam nanocavity optimized for an ultra-high optical-quality factor. The design is based on the combination of the deterministic method and hill-climbing algorithm. The latter is the simplest and most straightforward method of the local search algorithm that provides the local maximum of the chosen quality factors. This split-beam nanocavity is made up of two mechanical uncoupled cantilever beams with Bragg mirrors patterned onto it and separated by a 75-nm air gap. Experimental results emphasize that the quality factor of the second-order TE mode can be as high as 1.99×10(4). Additionally, one beam of the device is actuated in the lateral direction with the aid of a NEMS actuator, and the quality factor maintains quite well even if there is a lateral offset up to 64 nm. Potentially promising applications, such as sensitive optomechanical torque sensor, local tuning of Fano resonance, all-optical-reconfigurable filters, etc., are foreseen.