Tunable electric split-ring resonator with multi-functional modulation characteristics

This study presents an electrostatically tunable electric split-ring resonator (eSRR) design to investigate its applications in optical modulations and environmental monitors. The eSRR consists of four meta-atoms (MAs) that are centrally symmetric and free to move horizontally and vertically. Each MA is composed of a L-shaped metal structure on silicon nitride (Si₃N₄) layer. By changing the gap between MAs in x-axis (d_x) and y-axis directions (d_y), and height (h) of MAs, the active switching and dynamic modulating behaviors of seven distinct resonance modes are achieved in the eSRR design. The MAs exhibit translational displacement along individual x- and y-axes, as well as x-y planar motion simultaneously. The eSRR demonstrates broadband frequency tuning with 0.41 THz spectral shift via x-axis displacement in TE mode, while y-axis displacement enables dual-band optical switching at 0.54 THz and 0.88 THz in TM mode. Along the vertical direction, the optical properties of the eSRR are systematically investigated by lifting a single MA, two diagonally arranged MAs, and two adjacent MAs. Through changing the h value, eSRR exhibits the switching of single-, dual-, and tri-band resonance characteristics, and reaches the 0.69 resonant intensity in different resonant modes. As the environmental refractive index varies from 1.0 to 2.0, the eSRR demonstrates distinct electromagnetic responses depending on its geometrical parameters. When d_x = 20 μm, d_y = 36 μm, and h = 0 μm, the eSRR shows the maximum sensitivity of 126 GHz/RIU. These results indicate that the proposed eSRR configuration is promising for applications in optical filtering, switching, modulating, biosensing, and environmental monitoring fields.