Lattice-induced strong coupling and localized electric field enhancement in complementary diabolo metasurfaces

In this paper, lattice-induced strong coupling and localized electric field enhancement in terahertz (THz) regime are discussed in complementary diabolo metasurface (MS) that composed of a metallic sheet having periodically arranged opening diabolo resonators. By adjusting the lattice period of the MS along x or y axis, hybridization between the lattice mode and eigenmode of the MS leads to strong or ultrastrong coupling. The strong and ultrastrong coupling effect can be used to enhance electric field at two hybridized frequency points. The maximum enhancement are respectively 8855 and 7191 times of the incident field when ultrastrong coupling occurs, which are much larger than 7090 and 6561 times when strong coupling occurs. In addition, the maximum enhancement with ultrastrong coupling effect is 5.4 times comparing with the purely electric resonance of individual complementary diabolo structure. Based on coupled-mode theory (CMT) and coupled oscillator model, the resonant peak positions of two hybridized modes and the transmission spectra of the MS are analyzed. The analyzed results perfectly match with the simulated results, which proves the validity of our perspective. The results suggest that the proposed metamaterials could pave a new way for the electric field enhancement and developments of integrated photonic devices in THz regime.