Spoof surface plasmon resonant tunneling mode with high quality and Purcell factors

Abstract

A high quality factor and a small modal volume for compact, integrable optical devices have always been in great demand. Although metamaterials may be designed to achieve selected mode confinement at a subwavelength scale, the structures themselves have retained a large size. We address the issue of subwavelength mode confinement in structures of reduced size by utilizing unique properties of spoof surface plasmon polaritons (SSPPs). While SSPP modes are commonly considered in the context of periodic structures, we demonstrate that SSPP formation does not depend crucially on periodicity, and therefore metastructures of minimal length can support a well-formed spoof plasmon state. This general property is explicated through our study of the transmission spectrum of a three-cell waveguide with the spoof plasma frequency of the middle cell (defect cell) different from that of the remaining cells (host). The SSPP state in the defect cell supports resonant tunneling manifested by a narrow transmission resonance inside the band gap of the host structure. Despite the minimal length of the structure, the localized defect SSPP mode is characterized by very high quality $(\ensuremath{\sim}{10}^{5})$ and Purcell $(\ensuremath{\sim}{10}^{3})$ factors. The proposed concept can be a promising alternative for making miniaturized sources, information storage, and sensing devices at low terahertz frequencies.