Extraordinary transmission through periodic coaxial aperture arrays at terahertz frequencies

Utilizing the finite-difference time-domain (FDTD) method simulation, transmission properties of normally incident plane wave through symmetric and asymmetric cruciform metallic coaxial aperture arrays (CAAs) are investigated. It is found that odd-order resonant peaks can be observed in symmetric CAAs, and both odd- and even-order ones are showed in asymmetric structure. Moreover, the positions of the resonant peaks are not sensitive to the symmetry of coaxial aperture and the polarization of incident light, but strongly depend on the average circumference in a periodic cell. This assumption is further confirmed by examining the CAAs with different circumferences, shapes, as well as periodicities. The underlying origin of multiple resonances is discussed by the simulated fields. These investigations will facilitate the design of desired operating frequencies for various potential applications such as filters and sensors.