Designing binary nanoslit structures for simultaneously achieving high unidirectivity and high intensity of surface plasmon polaritons

Abstract

We propose an approach for designing binary nanoslit structures (BNSs) in the case of back-side illumination to simultaneously control the propagation direction of surface plasmon polaritons (SPPs) and enhance their electric field intensities. In this approach, the geometrical parameters of two unit nanoslits of BNSs are first designed with the proposed SPP interference models, and then the number and the spatial arrangement of designed nanoslits are optimized to increase the electric field intensity and the unidirectivity of the SPPs produced by BNSs. We numerically demonstrate that under the back-side illumination condition, a BNS designed by the proposed approach can produce the SPPs whose extinction ratio is about 2420 and electric field intensity is enhanced by a factor of about 7.3, which is significantly larger than the electric field intensities of the SPPs produced by reference grating couplers under the same illumination condition.