Tunable Flat-Top Bandpass Filter Based on Coupled Resonators on a Graphene Sheet

We propose a graphene filter with a tunable flat-top bandpass response. Such a filter consists of two cascaded graphene resonators embedded in a graphene waveguide. The evanescence coupling between two cavities is crucial to realize the flat and bandpass transmission. We numerically demonstrate that the flat-top passband can be electrically tuned over a wide wavelength range in the midinfrared spectrum with sharper roll-off, flatter tops, and better out-of-band rejection compared with the single resonator case. The proposed device is very compact compared with its working wavelength. It might facilitate the tunable signal process in the midinfrared region utilizing graphene.