Analysis of the Effect of Geometrical Characteristics on Frequency Response of Dielectric Resonators

Abstract

Different types of optical devices like nanolenses, sensors, and solar cells require the ability to concentrate and manipulate light at the surface of the device. High index dielectric resonators with low absorption losses have been successful in this field. In contrast to plasmonic nanoparticles, whose scattering resonant is dominated by the electric-type resonances, dielectric nanoparticles can support both electric dipole (ED) and magnetic dipole (MD) resonances simultaneously in the visible and near-infrared spectral ranges. This property offers intriguing applications for novel nanophotonic devices by interplaying between electric and magnetic modes. This paper investigates the electromagnetic properties of different nanoparticles as a function of their materials, shapes, and sizes. This investigation is done based on a multipolar analysis of nanoparticles. To this end, a semi-analytical method is utilized to calculate the polarizability tensors of nanoparticles. Having polarizability tensors of a particle, one can use them as an equivalent of the particle in any electromagnetic problem with plane wave illumination. Unlike Mie theory that has an analytical solution for only specific structures, this method can obtain the polarizability of any arbitrary nanoparticles. It is shown that by engineering the ED and MD of a nanoparticle, different scattering functionality can be achieved. The dipolar responses of nanoparticles are determined by changing their shapes, sizes, and materials. By comparing the frequency responses of two nanoparticles made of gold and silicon, this paper shows that, in contrast to plasmonic nanoparticles, high-index dielectric nanoparticles can support both electric and magnetic resonances in the visible and near-infrared spectral ranges. Moreover, the influence of nanoparticles diameter, height, and shape on their polarizabilities and extinction cross-section (ECS) have been analyzed. In this way, we developed a useful tool to design any desired application.