Excitation of direction-tunable surface plasmon polaritons by using a rectangular array of silver nanodisks.

Use of dipole-like localized surface plasmons (LSPs) induced on a rectangular array of silver nanodisks to excite directional surface plasmon polaritons (SPPs) on a flat silver film is demonstrated. By modifying the spectral resonance of the LSPs, an effective coupling of the incident light into the SPPs has been achieved at operational wavelength of λ = 628 nm. The maximum SPP intensity exceeds 25% of the incident intensity. Meanwhile, owing to the angle-dependent spatial distribution of the LSPs and the constructive interference between columns or rows of the array, the excited SPPs are supported to propagate in two orthogonal channels with a width of 1756 nm. Moreover, the propagation of the SPPs is tunable by rotating the polarization direction of the incident light between angles of 0 and π/2. This approach of launching direction-tunable SPPs shows great potential in applications of integrated plasmonic circuits.