Guided Propogation Along Quadrupolar Chains of Plasmonic Nanoparticles

The employment of periodic arrays of plasmonic nanoparticles has been proposed by several groups for enhanced transmission or absorption and for realizing optical nanowaveguides. Generally, due to their small transverse dimensions, such linear arrays have been operated near their dipolar resonance. However, it has been recently shown that nanoscale plasmonic particles may also support higher-order resonances, which provide some advantages in different applications. Here we derive a full-wave analytical closed-form dispersion equation for the guided and leaky modes supported by linear chains of nanoparticles near a quadrupolar resonance. We show that, despite the vanishing bandwidth of the individual quadrupolar resonance in each of the nanoparticles composing the chain, the overall bandwidth of quadrupolar chain guidance is relatively large due to strong coupling, even considering realistic losses and frequency dispersion of optical materials. Applications for low-damping optical nanotransmission lines and leaky-wave nanoantennas are suggested. Disciplines Electrical and Computer Engineering | Engineering Comments Suggested Citation: Alù, A. and Engheta, N. (2009). "Guided propagation along quadrupolar chains of plasmonic nanoparticles." Physical Review B. 79, 235412. © 2009 The American Physical Society http://dx.doi.org/10.1103/PhysRevB.79.235412 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/ese_papers/579 Guided propagation along quadrupolar chains of plasmonic nanoparticles Andrea Alù1,2,* and Nader Engheta2 1Department of Electrical and Computer Engineering, University of Texas at Austin, Austin, Texas 78712, USA 2Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA Received 5 April 2009; published 12 June 2009 The employment of periodic arrays of plasmonic nanoparticles has been proposed by several groups for enhanced transmission or absorption and for realizing optical nanowaveguides. Generally, due to their small transverse dimensions, such linear arrays have been operated near their dipolar resonance. However, it has been recently shown that nanoscale plasmonic particles may also support higher-order resonances, which provide some advantages in different applications. Here we derive a full-wave analytical closed-form dispersion equation for the guided and leaky modes supported by linear chains of nanoparticles near a quadrupolar resonance. We show that, despite the vanishing bandwidth of the individual quadrupolar resonance in each of the nanoparticles composing the chain, the overall bandwidth of quadrupolar chain guidance is relatively large due to strong coupling, even considering realistic losses and frequency dispersion of optical materials. Applications for low-damping optical nanotransmission lines and leaky-wave nanoantennas are suggested. DOI: 10.1103/PhysRevB.79.235412 PACS number s : 78.67.Bf, 42.70.Qs, 42.82.Et, 71.45.Gm