Tunable slow light based on detuned coupling between graphene nanoribbon and square ring splitting modes

We proposed and numerically investigated a newly slow light structure with graphene doublet detuned coupling effect. The novelty and uniqueness of the proposed structure is that the bandwidth and group index can be enhanced simultaneously by changing the length or chemical potential of the nanoribbon resonator. The maximum group index can attain to 131 at (mu_{c})?=?0.145 eV with the bandwidth of 0.85 THz. By means of the standing wave distribution of square ring splitting modes, the group indices can be enhanced at one window and suppressed at another by adjusting the coupling position of nanoribbon. The proposed structure would have potential prospect in realizing plasmonic filter, optical nonlinearity, optical buffering and storage devices at terahertz frequencies.