Subwavelength leaky-wave optical nanoantennas: Directive radiation from linear arrays of plasmonic nanoparticles

We analyze here the leaky-wave properties of linear arrays of plasmonic nanoparticles. It is shown that such periodic arrays may support two orthogonal leaky-wave propagation regimes, respectively, with longitudinal and transverse polarization. Using closed-form dispersion relations derived in the complex domain, we analyze their properties in the leaky-wave regime and we derive general conditions under which a nanoparticle array with subwavelength lateral cross section may support a radiating leaky mode with directive properties, conical radiation, frequency scanning and sufficiently long propagation distance, paving the way to potential applications as a leaky-wave optical nanoantenna with subdiffractive properties. Realistic designs and configurations are presented, considering the material dispersion and absorption of optical materials, for which we determine propagation distance, near-field distribution and far-field leaky-wave radiation pattern.