Enhancement of Plasmon Propagation Length Using Metamaterials
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0964-R01-08
Enhancement of Plasmon Propagation Length Using Metamaterials David Brandon McNeil, Arkadii Krokhin, and Arup Neogi Physics, University of North Texas, 211 Avenue A, Denton, TX, 76203
ABSTRACT We propose using a strongly anisotropic dielectric as a substrate for a thin metallic film along the boundary of which surface plasmon excitations may propagate. We show that the propagation range of surface plasmons is increased if the substrate is a birefringent dielectric crystal with a properly oriented optical axis. The increase of the propagation range depends on the degree of anisotropy, and, consequently, it turns out to be small for substrates of natural optical crystals, where anisotropy is weak. However, in specially designed photonic crystals, the anisotropy may be very strong, thus leading to appreciable increase of the propagation range. A photonic-crystal substrate, being a medium with nonlinear dispersion, also affects the dispersion law of the surface plasmon. All these effects may be used in order to increase the efficiency of modern plasmonic and optoelectronic devices. INTRODUCTION An electromagnetic excitation, propagating along a metal-dielectric interface, is known as a surface plasmon (SP) [1]. It is intrinsically two-dimensional, a surface mode, and, accordingly, it is localized close to the interface. This localization is on the order of the wavelength or smaller, providing potential for near-field scanning optical microscopy (NSOM) [3,4]. The usefulness of plasmonic devices is in essence determined by the propagation range of the surface plasmon, and, to a lesser degree, its penetration depth [3-7]. This decaying propagation along the interface has resulted in the use of SPs as guided carriers in optoelectronic devices [8-11]. The range of plasmonic propagation is limited mostly by Joule losses to the metallic half of the interface (i.e. - j·E). Early work with SPs began in the early 1980s [12], where it was predicted that SPs in thin metal films could travel significantly longer distances than SPs in a semi-infinite metal. Since then, many researchers have attempted to push these propagation lengths further and further at temperatures closer to room temperature. For example, it has been shown that the attenuation of the SP modes can be decreased when a metal strip is placed into the dielectric and the dimensions of the strip are tuned properly [13]. Others have been working to reduce the Joule losses; for example, an original technique uses cladding a metal film between dielectrics with high optical gain [14]. Using these methods, along with others, such as developments of waveguide geometries and manipulations to the properties of the dielectric, has allowed plasmonic devices to actually be created. Devices including plasmonic waveguides, switches, and other various optoelectronic components have proven quite effective in recent years [15-20]. The theoreticians have also been working on better models, such as good numerical simulations for arbitrary geometry plasmonic waveguides [21].
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