A hybrid photonic-plasmonic cavity design for optical force enhancement

We theoretically study hybrid photonic-plasmonic modes in a composite structure in which a silicon microdisk is vertically coupled to a metal microdisk. Benefitting from the low-loss property of whispering gallery modes and the strong field localization of plasmonic modes, the hybrid modes hold potential advantages over conventional photonic or plasmonic devices, in particular toward optical force enhancement. The composite structure enables a significant power enhancement in the hybrid mode, and the optical gradient force reaches as high as 48 pN/W for a single polystyrene nanoparticle with a radius of 5 nm. Since the enhanced gradient force pulls the nanoparticles into the area with the strongest electromagnetic field, this composite device is beneficial to nanoparticle detection with low noise and fast response.