Terahertz plasmon-induced transparency based on asymmetric dual-disk resonators coupled to a semiconductor InSb waveguide and its biosensor application

Abstract

An ultracompact double eight-shaped plasmonic structure for the realization of plasmon-induced transparency (PIT) in the terahertz (THz) region has been studied. The device consists of a semiconductor–insulator–semiconductor bus waveguide coupled to the dual-disk resonators. Indium antimonide is employed to excite SPP in the THz region. The transmission characteristics of the proposed device are simulated numerically by the finite-difference time-domain method. In addition, a theoretical analysis based on the coupled-mode theory for transmission features is presented and compared with the numerical results. Results are in good agreement. Also, the dependence of PIT frequency characteristics on the radius of the outer disk is discussed in detail. In addition, by removing one of the outer disk resonators, double-PIT peaks can be observed in the transmission spectrum, and the physical mechanism of the appeared peaks is investigated. Finally, an application of the proposed structure for distinguishing different states of DNA molecules is discussed. Results show that the maximum sensitivity with 654 GHz/RIU−1 could be obtained for a single PIT structure. The frequency shifts equal to 37 and 99 GHz could be observed for the denatured and the hybridized DNA states, respectively.