Abstract
We find the conditions for the existence of trapped modes in planar periodic particle arrays. Confined excitations of TE and TM symmetry are observed in symmetric environments, originating in lattice resonances that are signalled by the onset of new diffraction beams. This mechanism of mode formation is shown to be inhibited by the presence of a dielectric interface in an asymmetric configuration. Modes can still exist above a threshold finite distance from the interface. Both rigorous numerical simulation and analytical modeling are used to elucidate the origin and systematics of this unexpected difference in the behavior of trapped modes in self-standing and supported particle arrays.
Highlights
The visible and near-infrared optical properties of individual nanoparticles have recently attracted considerable interest, partly triggered by the increasing degree of control over size, composition, and morphology for structures ranging from a few nanometers to several microns, and produced by colloidal chemistry [1] and epitaxy [2] or via lithography [3]
We find the conditions for the existence of trapped modes in planar periodic particle arrays
We investigate the conditions for the existence of trapped modes in planar periodic arrays of small particles
Summary
The visible and near-infrared optical properties of individual nanoparticles have recently attracted considerable interest, partly triggered by the increasing degree of control over size, composition, and morphology for structures ranging from a few nanometers to several microns, and produced by colloidal chemistry [1] and epitaxy [2] (bottom-up approach) or via lithography [3] (top-down). Nanoparticle assemblies offer additional ways of manipulating optical fields that have been exploited to realize interesting phenomena such as light waveguiding [6, 7] and narrowing of plasmon bands [8, 9, 10], relying on the existence of confined modes in periodic particle arrays. The main finding of this work is that these divergences disappear when the particles are sitting in an asymmetric environment, for example, near the interface between two dielectric materials, so that the long-range interaction is suppressed The exception to this rule is the perfect-conductor surface, for which TM excitations are still present in an array supported on it, TE modes are not allowed in this case. Received 31 Jul 2009; revised 18 Sep 2009; accepted 18 Sep 2009; published 2 Oct 2009 12 October 2009 / Vol 17, No 21 / OPTICS EXPRESS 18827
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