Optical Force on Dielectric Nanorods Coupled to a High-Q Photonic Crystal Nanocavity

It is of particular importance to bridge nanophotonics and nanomechanics by utilizing near-field-induced gradient forces to manipulate dielectric objects. On the basis of the finite-difference time-domain method, we theoretically study nanocavity-resonator-induced optical forces on different dielectric nanorods. The optical system consists of a nanorod which is optically coupled to a photonic crystal slab with a predesigned L3 nanocavity that has a resonant mode of high-quality factor Q approximate to 10(4) and small modal volume 0.1 mu m(3). Tunable attractive and repulsive (bipolar) optical forces on the nanorod are discovered, which crucially depend on the size of the nanorod and its separation from the slab. The magnitude of the force is revealed to be on the order of 10(3) pN with source irradiance I = 10 mW/mu m(2) for a nanorod of size around 200 x 100 x 100 nm(3) at a separation d = 100 nm. The results are compared with those by the Rayleigh scattering approximation, which suggests that the optical force is dominated by the gradient force due to the strong local field around the nanocavity. We further demonstrate the optomechanical stability of the system. Such a system provides a promising integrated on-chip platform for all-optical operation of nanomechanical devices.