Recently, the investigation and design of metamaterials have attracted considerable attention. Metamaterials are artificially engineered periodic structures that possess desirable electromagnetic properties that cannot be found in naturally occurring materials. For instance, metamaterials allow one to create negative permittivity and/or permeability, and consequently a negative refractive index to construct the so-called left-handed material (LHM, or negative index material) [1]. LHMs can be used to build a perfect lens [2], through which subwavelength imaging with unlimited resolutions can be achieved. Potential applications of metamaterials in optical frequencies 84include optical cloaking structures for reducing scattering cross sections [3], optical hyperlens for simultaneous subwavelength image transmission and magnification [4], plasmonic waveguides for highly efficient light transmission [5], and plasmon solar cells for enhancing light scattering and absorption.