Experimental demonstration of low-loss optical waveguiding at deep sub-wavelength scales

Abstract

Emerging communication applications call for a road map towards nanoscale photonic components and systems. Although metal-based nanostructures theoretically offer a solution to enable nanoscale photonics, the key demonstration of optical modes with deep sub-diffraction-limited confinement and significant propagation distances has not been experimentally achieved because of the trade-off between optical confinement and metallic losses. Here we report the first experimental demonstration of truly nanoscale guided waves in a metal-insulator-semiconductor device featuring low-loss and broadband operation. Near-field scanning optical microscopy reveals mode sizes down to 50×60 nm2 at visible and near-infrared wavelengths propagating more than 20 times the vacuum wavelength. Interference spectroscopy confirms that the optical mode hybridization between a surface plasmon and a dielectric mode concentrates the hybridized mode inside a nanometre thin gap. This nanoscale waveguide holds promise for next generation on-chip optical communication systems that integrate light sources, modulators or switches, nonlinear and quantum optics. © 2011 Macmillan Publishers Limited. All rights reserved.