Dielectric nanoantenna as an efficient and ultracompact demultiplexer for surface waves

TL;DR

This paper introduces a simple, low-loss dielectric nanoantenna made of silicon that efficiently and directionally launches and demultiplexes surface waves with high spectral resolution, suitable for compact photonic circuits.

Contribution

The work presents a novel dielectric nanoantenna design that achieves high efficiency, spectral resolution, and reconfigurability without complex lithography, outperforming plasmonic counterparts.

Findings

Demonstrated directional launching of surface waves with high front-to-back ratio

Achieved spectral demultiplexing with less than 50 nm wavelength difference

Reconfigurable operational range by varying silicon sphere diameter

Abstract

Nanoantennas for highly efficient excitation and manipulation of surface waves at nanoscale are key elements of compact photonic circuits. However, previously implemented designs employ plasmonic nanoantennas with high Ohmic losses, relatively low spectral resolution, and complicated lithographically made architectures. Here we propose an ultracompact and simple dielectric nanoantenna (silicon nanosphere) allowing for both directional launching of surface plasmon polaritons on a thin gold film and their demultiplexing with a high spectral resolution. We show experimentally that mutual interference of magnetic and electric dipole moments supported by the dielectric nanoantenna results in opposite propagation of the excited surface waves whose wavelengths differ by less than 50 nm in the optical range. Broadband reconfigurability of the nanoantennas operational range is achieved simply by varying the diameter of the silicon sphere. Moreover, despite subwavelength size ($<\lambda/3$) of the proposed nanoantennas, they demonstrate highly efficient and directional launching of surface waves both in the forward and backward directions with the measured front-to-back ratio having a contrast of almost two orders of magnitude within a 50 nm spectral band. Our lithography-free design has great potential as highly efficient, low-cost, and ultracompact demultiplexer for advanced photonic circuits.