Electromagnetic Superradiation in Cylindrical Geometries

Abstract

Poor isotropic emitters (line sources), of both TM and TE polarization, are found to substantially enhance their radiative power when located internally to cylindrical boundaries involving plasmonic shells or tubular metasurfaces that can be constructed using materials that have been utilized in previous works. Such excitations allow for the analytical treatment of the problem while also providing important physical intuition for the behavior of the setups. The parametric space is extensively searched, in order to extract the optimal structural and textural characteristics of each studied configuration. In most of the optimal designs, the placement of the antenna tailors the interference between multiple in-going and out-going modes to give strong omnidirectional or bipolar patterns, different for each wave polarization. The observed radiation characteristics of each of the selected designs are validated using a commercial electromagnetic solver (COMSOL Multiphysics). The reported superradiating setups carry over the concept of photonic superradiance to classical electromagnetics by utilizing the developed source images in achieving powerful emissive responses for both polarizations concurrently, despite incorporating just a single active element. Not only are these responses on par with, or even greater than the ones reported in previous works but the cylindrical geometries also are less sensitive to nonlocal effects and are easier to fabricate compared to traditional plasmonic antennas. The aforementioned properties make the proposed configurations desirable, since they can be employed as ultra-efficient components in a plethora of optical applications spanning from array design and far-field wireless power transfer to radiative biosensing and polarization-enabled analog signal processing. Moreover, this work can be extended by adding nonlinearities to the cylindrical metasurfaces so as to construct memory elements having suppressed vulnerability to noise.