Core-antiresonance-based terahertz cavities and applications [Invited]

This work presents a brief review of our recent research on an antiresonant mechanism named core antiresonant reflection (CARR), which leads to a broadband terahertz (THz) spectrum output with periodic dips at resonant frequencies after its transmission along a hollow-core tubular structure (e.g., a paper tube). The CARR theory relies only on parameters of the tube core (e.g., the inner diameter) rather than the cladding, thus being distinct from existing principles such as the traditional antiresonant reflection inside optical waveguides (ARROWs). We demonstrate that diverse tubular structures, including cylindrical, polyhedral, spiral, meshy, and notched hollow tubes with either transparent or opaque cladding materials, as well as a thick-walled hole, could indeed become CARR-type resonators. Based on this CARR effect, we also perform various applications, such as pressure sensing with paper-folded THz cavities, force/magnetism-driven chiral polarization modulations, and single-pulse measurements of the angular dispersion of THz beams. In future studies, the proposed CARR method promises to support breakthroughs in multiple fields by means of being extended to more kinds of tubular entities for enhancing their interactions with light waves in an antiresonance manner.