Asymmetric Plasmonic Nanoshells as Subwavelength Directional Nanoantennas and Color Nanorouters: A Multipole Interference Approach

Asymmetric plasmonic nanoshells (ANs), consisting of an off-center dielectric core and a metallic shell, are proposed as subwavelength directional nanoantennas, when coupled to a localized source of electromagnetic radiation. Unidirectional emission and color routing are obtained at multiple wavelengths and for different subwavelength AN geometries and sizes. ANs are capable of 2 orders of magnitude directional emission enhancements and of forward-backward directional gains as large as 30 dB. The obtained results are straightforwardly interpreted in terms of interference phenomena in coherent multipole sums.