Alù, Andrea

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2003 - 20092
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  • Publication
    Optical nanoswitch: an engineered plasmonic nanoparticle with extreme parameters and giant anisotropy
    (2009-01-20) Alù, Andrea; Engheta, Nader
    Naturally available optical materials are known to provide a wide variety of electric responses, spanning from positive to negative permittivity values. In contrast, owing to drastically modified conduction properties at the microscopic level, at such high frequencies magnetism and conductivity are very challenging to realize. This implies that extreme (high or low) values of permittivity, although highly desirable for a wide range of optical applications, are difficult to realize in practice. Here, we suggest the design of an engineered resonant nanoparticle composed of two conjoined hemispheres, whose optical response may be changed at will from an ideal electric conductor to an ideal magnetic conductor. Near the nanoparticle internal resonant frequency, we derive a closed-form solution that describes the electromagnetic response of this nanoparticle, showing how its light interaction may become dramatically dependent on the local field polarization, passing through all possible impedance values (from zero to infinity) by a simple mechanical or polarization rotation. Considering realistic frequency dispersion and loss in optical materials, we further show that these concepts may be applied to different geometries, with possibility for future experimental feasibility. We forecast various applications of this geometry as an optical nanoswitch, a novel nanocircuit element and as a building block for novel optical metamaterials.
  • Publication
    Mode Excitation by a Line Source in a Parallel-Plate Waveguide Filled with a Pair of Parallel Double-Negative and Double-Positive Slabs
    (2003-06-22) Alù, Andrea; Engheta, Nader
    In this paper, we investigate theoretically the excitation of modes by a line source, as well as their modal structure and dispersion, in a parallel-plate waveguide that is filled with a pair of parallel slabs; one being a lossless "double-negative (DNG)" material and the other being a lossless conventional "double-positive (DPS)" medium. Previously, we have shown that such "conjugate" pairing of DNG and DPS materials may lead to reduction of size in one-dimensional cavity resonators and waveguides. The analysis presented here describes the proper modes in such a 1-D parallel plate waveguide, and reveals the possibility of no cut-off thickness for this class of parallel-plate waveguides, which implies that a proper TE or TM mode may always be excited in such a waveguide independent of the overall thickness of the waveguide. The excitation of guided modes by a line source and their power-flow peculiarities are discussed, and the analogy to the concept of "open 1-D cavity" in such a waveguide is mentioned. Some of the interesting features and physical insights regarding the power flow in these guided modes will be presented.