In-depth study for confinement of electromagnetic wave in a coupled terahertz nano-slot antenna

We study the electric-field confinement of terahertz waves in an asterisk-shaped nano-slot antenna using finite-element-method-based simulations. The asterisk slot antenna, consisting of a single slot and an X-shaped slot antenna, exhibits near- and far-field characteristics depending on the coupling angle. In a regime of small coupling angles, three-dimensional confinement of terahertz waves is realized in X-shaped and coupled slot antennas. We analyze the coupling-angle-dependent confinement performance in terms of localized field strength and focusing degree, considering the gap size of the slot antennas. These findings provide valuable design insights for studying light-matter interactions in the terahertz frequency regime.