Observation of normal mode splitting in THz Fabry–Pérot microcavity made of wire grid structures containing cut wire metamaterials

In this study, we realize normal mode splitting in Fabry–Pérot (FP) microcavity structures containing cut wire (CW) metamaterials inside the cavity layer in the terahertz (THz) region. We used a wire grid (WG) structure to mirror the microcavity. To verify this concept, we analyzed the reflection and transmission properties of WG, CW, WG cavity (WGC), and microcavity containing CW (CWWGC) using transmission line theory. Consequently, we discovered that when the resonance frequencies of the CW and WGC matched, normal mode splitting occurred and anti-crossing is observed in the dispersion relation in the CWWGC. The samples are designed by the finite difference time domain method and were fabricated via photolithography. We measured the transmission spectrum of the fabricated samples by THz time domain spectroscopy. Finally, we observed a large splitting of the transmission peak owing to mode coupling between the light mode of the FP microcavity and the electric dipole mode of a single CW in the CWWGC.