Numerical analysis of coupled wedge plasmons in a structure of two metal wedges separated by a gap

Abstract

This paper presents the results of the numerical finite-difference time-domain analysis of a strongly localized anti-symmetric plasmon, coupled across a nano-gap between two identical metal wedges. Dispersion, dissipation, field structure, and existence conditions of such coupled wedge plasmons are determined and investigated on an example of the fundamental coupled mode. It is shown that in the general case there exist three critical wedge angles and a critical gap width (separation between the wedge tips). If the gap width is larger than the critical separation, then the anti-symmetric wedge plasmons can exist only in the ranges between the first and the second critical angles, and between the third critical angle and 180o. If the gap width is smaller or equal to the critical separation, then the third and the second critical angles merge, leaving only one interval of wedge angles within which the anti-symmetric coupled wedge plasmons can exist. The effect of rounded wedge tips is also investigated and is shown to be similar to that of different wedge angles. Feasibility of using these plasmons for the design of efficient sub-wavelength waveguides is discussed.