Surface Plasmon Polariton Unidirectional Nano-Launcher Based on the Strong Coupling Effects in an Asymmetric Optical Slot Nanoantenna Pair

We investigate the strong coupling effects in asymmetric optical slot nanoantenna pairs (AOSNPs) consisting of two parallelly positioned optical slot nanoantennas with different lengths and propose a surface plasmon polariton (SPP) unidirectional nano-launcher based on the strongly coupled AOSNPs (SCAOSNPs). Two subradiant modes can be excited in the SCAOSNPs, which originate from the hybridizations of the dipolar plasmon resonant modes in the two slot antennas. The subradiant modes give rise to large phase difference and nearly equal near-field electric field amplitudes between the two slot antennas, which can be used for unidirectional SPP launching and enable an ultra-compact nano-launcher. An extinction ratio up to 246 is achieved in the calculation via an SCAOSNP with a footprint of 170 nm by 260 nm on the surface of the gold film. The ultra-small footprint and tunable working wavelength enable the SCAOSNP important applications in future optical circuits and on-chip plasmonic devices.