Terahertz flat-top broadband defect modes generated in periodically undulated waveguides

Abstract

We propose a tunable flat-top broadband defect mode in the terahertz (THz) frequency range by inserting multiple defects into a periodic waveguide with undulated tube walls. When introducing a defect into periodic structures, we can achieve a defect mode with a very sharp transmission peak in the forbidden band due to the local resonance effect. Here, in the proposed multi-defect structure, we find a broadband defect mode with a bandwidth of 38.3 GHz appearing in the transmission spectrum, which is over 21 times that of the traditional defect mode. The simulations reveal that the broadband defect mode is caused by the competition between Bragg scattering and local resonances in multiple defect mode coupling. The bandwidth and center frequency of this broadband defect mode can be manipulated by altering the number and size of defects, which could be applied in various THz systems as functional devices.