A Graphene-Based Bandwidth-Tunable Mid-Infrared Ultra-Broadband Plasmonic Filter

The closely spaced pair of parallel graphene sheets separated by uniform dielectric gratings is proposed and investigated numerically via the finite-difference time-domain (FDTD) method. This simple structure working as plasmonic Bragg reflectors can produce an original ultra-broadband band-stop filtering effect in the mid-infrared region. The transmission spectrum is tuned dynamically not only via varying the period of the grating but also by a small change in the chemical potential of graphene without re-fabricating new structures. In addition, the bandwidth of the stopband can also be engineered by changing the refractive index of the sandwiched dielectric grating. Simulation results are confirmed by theoretical calculations. As an application, a defect is introduced into the uniform dielectric grating, and the obvious Fabry-Perot-like resonant mode hence forms in the stopband. The proposed device without doubt can be used as highly tunable ultra-broadband band-stop filters and mid-infrared optical modulators. Our studies will play a significant role in the fabrication of ultra-compact versatile integrated circuits.