Localization of Transverse and Longitudinal Modes in Corrugated Terahertz Waveguides with a Microcavity

Abstract

We propose a type of terahertz (THz) corrugated plate waveguides with a microcavity in the middle. The periodically corrugated walls efficiently attenuate THz radiation passing through the waveguide in the so-called Bragg forbidden bands, whereas the addition of a microcavity to the corrugated waveguide leads to a disruption of periodicity and the appearance of additional transmission peaks in the forbidden bands based on the microcavity resonance. The two transmission peaks are generated in the second Bragg forbidden band, which can be attributed to the creation of transverse and longitudinal cavity mode localizations. Furthermore, by changing the geometrical parameters of the microcavity, the mode transmission peak gradually moves towards the other one and merges into a single peak, which is then separated into the two peaks. The transverse and longitudinal mode localizations are both red shifts, as the cavity size increases, but the transverse one is more sensitive to the changes. The characteristics of the crossed frequency shift are confirmed in the subsequent experiments by the transmitted THz spectra of the fabricated parallel-plate waveguide structure.

Keywords: cavity modes, resonances, periodic corrugations, additional transmission