Design of a half-ring plasmonic tweezers for environmental monitoring

An integrated near-field plasmonic tweezers, based on two gold half-ring elements, is proposed. The device consists of a silicon-on-insulator (SOI) waveguide on which two symmetric half-ring-shaped elements are deposited. The SOI waveguide, having dimensions 500 × 220 nm, enables single mode light propagation at 1.55 μm. The structure of the half-ring plasmonic tweezers exhibits up to five design parameters: inner radius ri, outer radius re, gap g, height h and angle ϑ. Gold permittivity is modeled by means of a Drude equation. The trapping performance is investigated by evaluating the optical force exerted on a nanoparticle having a radius of 25 nm, together with the stiffness and the trapping potential. Simulation results show that stable trapping is achieved for an input power as low as 27 mW at 1.55 μm, with a stiffness of −4.06 fN mW−1 nm−1.