Splitting and unidirectional excitation of surface plasmon polaritons by two uniform metallic nanoslits with a nanocavity antenna

A tunable splitter and source of surface plasmon polaritons (SPPs) is proposed. The structure is composed of two Ag films, with two uniform nanoslits fabricated in the lower Ag film and lying above is a movable Ag film. By changing the horizontal position of the top Ag film, the splitting ratio of the SPPs varies periodically based on SPP interference. The field distribution of the structure is investigated by using the finite-difference time-domain (FDTD) method. The period obtained by the FDTD agrees well with the Fabry–Pérot cavity model. When the SPP splitting ratio is large (or small), our structure acts as a low noise SPP source. Compared with other SPP sources, our model possesses better directionality.