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.