## 1. Introduction

[2] Metamaterials are artificially constructed structures, which possess extraordinary electromagnetic properties not found in natural materials. One of the most comprehensively studied examples is a material having negative refractive index [*Shelby et al.*, 2001], which can lead to the design of perfect lens with a subwavelength resolution [*Pendry*, 2000] leading to potential novel imaging systems. To sustain subwavelength imaging, the evanescent electromagnetic fields have to be preserved on their passage from the source to the focal point. In conventional materials, however, these fields decay exponentially. It has been shown [*Pendry*, 2000] that the evanescent field components are directly involved in the image formation, when metamaterials with negative refraction are used in a lens configuration.

[3] However, metamaterials with negative refraction have inherent limitations in terms of high loss and frequency dispersion [*Smith et al.*, 2004; *Podolskiy and Narimanov*, 2005] which, combined with the design complexity (especially at optical frequencies), make practical implementation of them limited. A promising alternative, in order to exploit the near fields at optical frequencies in a controlled fashion, can be found in the rapidly emerging research area of plasmonics [*Barnes et al.*, 2003; *Maier*, 2007]. The plasmons are surface waves confined to the interface between noble metals and surrounding air and occur at the IR and visible frequency regimes, where most metals appear to have negative permittivity. It has been shown that a nanolens, in order to achieve subwavelength resolution, can be constructed with the desired property of lossless plasmonic transfer of the near-field information [*Ono et al.*, 2005; *Kawata et al.*, 2008].

[4] The complexity of simulating such a device leads to a significantly increased numerical simulation time using a conventional dispersive finite difference time domain (FDTD) code; this is due to the large number of cells required to model a three-dimensional (3-D) device with subwavelength features. In this paper, a parallel 3-D dispersive FDTD technique is applied. The convergence and the accuracy of the simulation is improved with an additional spatial averaging scheme applied to the dispersive FDTD algorithm [*Zhao et al.*, 2007]. The combination of dispersion and spatial averaging in a parallel FDTD scheme is unique, leading to a useful numerical tool in the growing research field of plasmonics. The issue of symmetry is explored, which is shown to have a direct result at the time taking the fields to reach their steady state. The numerical convergence in the modeling of symmetric and nonsymmetric nanolenses is thoroughly studied and interesting results are obtained. Finally, note that the parallel FDTD method is proved to be a very useful numerical tool to explore very complicated electromagnetic structures, whose complexity would otherwise lead to prohibitively long simulation times on a single processor computer. Conformal parallel FDTD techniques can also be used to reduce the required spatial resolution. However, late time instabilities and increased complexity of the FDTD algorithm may affect the robustness of the proposed numerical simulation tool.