Bandwidth-tunable optical passband filter based on graphene-silicon waveguide

A bandwidth-tunable optical passband filter based on graphene-silicon waveguide is proposed. The device is designed by utilizing a structure with four triple series-coupled microring resonators. By changing the Fermi level of graphene to lead to the variation of the modal effective index, the transmission spectra of triple series-coupled microring resonators can be coherently combined to provide the adjustable bandwidth as desired. A detailed analysis of the designed device is presented. Numerical simulations show that the effective bandwidth tuning range from 2.70 to 6.30 nm can be obtained when each microring resonator is independently controlled. With the maximum bandwidth tunability, the designed tunable filter has a minimum extinction ratio larger than 92.35 dB.