Linear and Nonlinear Transmission of Surface Plasmon Polaritons in an Optical Nanowire
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Linear and Nonlinear Transmission of Surface Plasmon Polaritons in an Optical Nanowire N. C. Panoiu and R. M. Osgood, Jr. Department of Applied Physics and Applied Mathematics Columbia University 500 W. 120th Street New York, NY 10027 ABSTRACT Polymer-metal composites offer the possibility of strongly enhanced nonlinear optical properties, which can be used for ultrasmall photonic devices. In this paper, we investigate numerically, by means of the finite-difference time-domain (FDTD) method, the propagation characteristics of surface plasmon polariton (SPP) modes excited in an optical nanowire consisting of a chain of either metallic cylinders or metallic spheres embedded in dielectric shells made of polymers (or other material) with optical Kerr nonlinearity. Our FDTD calculations incorporate both the nonlinear optical response of the dielectrics as well as the frequency dispersion of the metals, which is considered to obey a Drude-like model. It is demonstrated that, in the linear limit, the nanowire supports two SPP modes, a transverse and a longitudinal one, separated by ∆λ = 20 nm. Furthermore, the dependence of the transmission of these SPP modes, on both the pulse peak power and Kerr coefficient of the dielectric shell, is investigated. Nonlinear optical phenomena, such as power-dependent mode frequency, switching, or optical limiting, are observed. INTRODUCTION Until recently, most research work on the optical properties of nanostructured materials has focused on periodic structures consisting of dielectrics, namely photonic crystals. However, recent research studies have shown that it is possible to design metallic photonic crystals with new features: large relative gap width [1,2], unusual transmission properties [3,4], high surface impedance [5], or, arguably the most striking example, structures with negative index of refraction [6-8]. A different class of applications, which is discussed in this paper, is represented by metalbased sub-wavelength-dimension nanodevices used for light guiding. Several approaches to achieve this functionality in passive structures have been proposed and demonstrated. In one case, generally termed "plasmonic" devices, one makes use of the unique optical properties of metallic materials to provide strong optical confinement and eliminate the limitations imposed by strong diffractive effects. For example, cylindrical metallic waveguides with sub-wavelength transverse dimensions [9], plasmon waveguides [10], or optical waveguides consisting of chains of resonantly coupled metallic nanoparticles have been demonstrated [11,12]. The optical properties of these nanoparticle chains can be further improved if their basic building blocks have a more complex geometry, e.g. ellipsoidal particles [12,13], or by combining in the same nanostructure materials with different optical properties. One such example is a metallo-dielectric nanoshell, which consists either of a metallic core surrounded by a dielectric shell [14] or a dielectric core embedded in a metallic shell [15]. An i
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