Terahertz defect mode coupling in periodic planar waveguides

Abstract

We experimentally and numerically investigate terahertz (THz) defect mode coupling in periodic planar waveguides. The periodicity provides a forbidden band, in which the propagation of THz waves is effectively suppressed. The introduced defects in periodic structures produce two defect modes that lead to two additional transmissions in the forbidden band due to the local resonance. We find that there is a strong coupling effect between the two defect modes. The coupling strength is closely related to the distance between defects. The closer the distance, the stronger the coupling, resulting in the center frequencies of the two transmission peaks being far away from each other. In contrast, an increase in distance between defects weakens the coupling effect, leading to two transmission peaks approaching each other and ultimately overlapping to form a broadband defect mode. Our findings on THz defect mode coupling provide a certain theoretical basis for tunable THz devices such as filters, modulators, and optical switches.