Plasmonic candle: towards efficient nanofocusing with channel plasmon polaritons

Abstract

Channel plasmon polaritons (CPPs) propagating along the bottom of V-grooves cut into a metal were recently shown to exhibit strong confinement combined with low propagation loss, a feature that makes this guiding configuration very promising for the realization of ultracompact photonic components. Here, we present a comprehensive study of radiation nanofocusing with CCPs propagating along subwavelength metal grooves that are terminated with various types of tapers of different lengths. Tapered V-grooves are fabricated in a gold film using a focused ion beam milling technique, with the tapering being realized by gradually decreasing the groove width and/or depth (in different way for different structures), and characterized at telecom wavelengths with a collection scanning near-field optical microscope. Efficient CPP nanofocusing is directly demonstrated featuring a field intensity enhancement of up to ∼130 for optimal taper configurations. Experimental observations are found to be concurrent with three-dimensional finite-difference time-domain electromagnetic simulations, predicting the possibility of reaching an intensity enhancement of ∼1200 and opening thereby exciting perspectives for practical applications of CPP nanofocusing.