High-Q Metallic Fano Metamaterials using Subwavelength Slits

Abstract

In this thesis, a high-quality-factor (high-Q) metallic Fano metamaterial, in which subwavelength metallic slits are arranged to form asymmetric unit cells, is demonstrated both experimentally and theoretically. First, the previous works on the optical properties of the subwavelength slits are studied in detail in order to understand the physics behind the Fano resonances existing in this structure. Based on the knowledge, Q of the Fano resonances is deliberately tailored in order to maximize it, which is is measured to be unprecedented at 700 at electronics regime, such as microwave and terahertz. The interplay between an extremely low group velocity from the infinite transverse permittivity of the anisotropic metamaterial and the subradiant damping from a Fano-type slit mode is shown to be responsible for the high-Q value. Moreover, the effect of the unwanted geometric parameters such as structural disorder and surface roughness are experimentally studied for the maximization.<br/> As a next step, the feasibility of this metamaterial for a Cerenkov lasing application is numerically investigated. As the moving electron beam interacts with the waveguide modes of the metallic metamaterial, dipole-like modes are induced at each slit aperture, leading to the formation of the Cerenkov wake, the phase velocity of which is adjusted to match that of the electron beam. The optimum Q for optimum output RF coupling can be obtained by controlling the radiation damping or Rayleigh scattering of the trapped Cerenkov light based on structural asymmetries. The resulting improvement in the Cerenkov lasing efficiency is estimated to be more than two orders of magnitude using a particle-in-cell simulation. The proposed high-Q metallic Fano metamaterial that realizes highly efficient CL without mirrors is a strong candidate for several practical applications, especially in very-high-frequency electronic devices such as terahertz.