Finite element analysis of waveguide mode coupling through a sub-structured metallic flat lens Rafa l Kasztelanic a and Rafa l Koty´ nski a a Department of Information Optics, Faculty of Physics, University of Warsaw Pasteura 7, 02-093 Warsaw, Poland; ABSTRACT In this paper we present a numerical analysis of a planar or sub-structured metallic flat lens for mode coupling between a pair of waveguides. The analysis of periodically sub-structured silver coupler is based on the finite element model of the device. The uniform and infinite double layered silver coupler is also considered, and is modelled with the transfer matrix method. The study is focused on minimising propagation losses and optimising the coupling coefficient, which is calculated from the transfer properties of the lens for a Gaussian distribution of the modal fields. The analysis reveals the importance of the periodic nanostructure of the silver layers for reaching a coupling efficiency which is higher than could be obtained with uniform layers or with air. Keywords: superlens, mode coupling, surface plasmon polaritons 1. INTRODUCTION Experimental validation of near-field superlensing 1, 2 together with the earlier works demonstrating transparency in metallic stacks 3 opened new possibilities for using metallic nanostructures in photonic applications. Various physical mechanisms are involved in the operation of layered lenses, including the negative refraction predicted by Veselago, 4 negative refraction in photonic crystals, 5 plasmon assisted evanescent wave enhancement proposed by Pendry, 6 resonant tunnelling, 7 or tunnelling in the canalisation regime. 8 The application of superlenses seems most direct and promissing for the resolution enhancement in the lithographic techniques, 1, 2 as well as resolution improvement of SNOM microscopy. 9, 10 Send correspondence to R. Kasztelanic, kasztel@igf.fuw.edu.pl, ph. +48.22.5546885 Figure 1. a) The scheme of the modeled single and double layer sub-structured metallic flat lens for mode coupling between a pair of single mode waveguides. The distance between fibres is 40nm. b) magnified view of the double layer coupler; c) magnified view of the single layer coupler. Metamaterials III, edited by Nigel P. Johnson, Ekmel Özbay, Nikolay I. Zheludev, Richard W. Ziolkowski Proc. of SPIE Vol. 6987, 698727, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.786381 Proc. of SPIE Vol. 6987 698727-1 2008 SPIE Digital Library -- Subscriber Archive Copy