Weak coupling between bright and dark resonators with electrical tunability and analysis based on temporal coupled-mode theory

We investigate the electrically tunable Electromagnetic induced transparency (EIT)-like effect of active metamaterial structures composed of a wire and a split ring resonator by the simulation, experiment, and temporal coupled-mode theory. It is illustrated that an EIT-like effect appears as a result of weak coupling between bright and dark resonators. Around the EIT-like peak frequency, the superradiant resonance mode of the bright resonator is highly suppressed by the subradiant resonance mode of the dark resonator, and high transmittance as well as large group delay is manifested. By integrating a varactor diode into the EIT structure and altering the bias voltage, the EIT-like effect can be dynamically tuned. As the bias voltage ranges from 0 V to 8 V, the EIT-like peak frequency exhibits a prominent blueshift of 0.22 GHz and the transmittance experiences a modulation with a modulation depth up to 98%. Using the temporal coupled-mode theory, the transmission spectrum of the EIT structure is predicted and the parameters of the resonator system are retrieved.