Hybrid photonic–plasmonic mode for refractometer and nanoparticle trapping

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 sensing and nanoparticle trapping. In the refractometer application, a high figure of merit exceeding 200 can be obtained in 1550 nm wavelength band. In the nanoparticle trapping, the composite structure enables a significant power enhancement in the hybrid mode, and the 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.