Single- and dual-plasmonic induced absorption in a subwavelength end-coupled composite-square cavity

A plasmonic end-coupled composite-square cavity (CSC) structure is proposed by adding two horizontal and normal slot cavities into a perfect square cavity (PSC) structure that is regarded as a Fabry-Perot resonator. Owing to the interference effect between the bright and dark modes, which is supported by the PSC and the slot cavities, respectively, a single plasmonic induced absorption (PIA) response with large abnormal dispersion is achieved at the former transmission peak in the CSC structure. The induced absorption window can be tuned to the wavelength of the first or second mode by using the horizontal and normal slot cavities. By changing the refractive index of the insulator inside the horizontal slot cavity, dual PIA responses are also obtained in the CSC structure. The performances of the proposed CSC structure are analyzed and investigated by using the finite-difference time-domain method.