Graphene-polyimide-integrated metasurface for ultrasensitive modulation of higher-order terahertz fano resonances at the Dirac point

The initial Fermi level of graphene is quite close to the Dirac point. It is ultrasensitive to external stimuli in the modulation of Fano resonance. Thus, the Fermi level directly skips the Dirac point during modulation with strong external excitation. Therefore, the modulation behavior of the Fano resonance is not easy to capture at the Dirac point. Here, we applied a laser pump with micropower densities and a mains with weak voltages to the terahertz metasurface and observed the modulation behavior of higher-order Fano resonance at the Dirac point. Accompanied by Fermi level shifts between the Dirac point, conduction band, and valence band, higher-order Fano resonances exhibited the process of disappearance, appearance, and re-disappearance. Concomitantly, the transmission amplitude underwent an increasing stage and a decreasing stage. More importantly, a 0.05 V change in the bias voltage or a 7.5 mW/cm2 change in the power density enabled a modulation depth of 90%. These findings could be potentially used for designing ultrasensitive terahertz metaphotonic devices.