Band-stop filter based on tunable Fano resonance and electromagnetically induced transparency in metal-dielectric-metal waveguide coupling systems

Metal-dielectric-metal (MIM) waveguide coupling systems based on surface plasmon polaritons (SPPs) are designed and studied. The finite element method is used to simulate the transmission spectra of structures in the whole simulation process. One waveguide coupling system consists of an inverted T-shaped cavity with defect (ITD) and a waveguide with a metal wall. The filter band appears in the transmission spectrum due to the opposite direction of two Fano resonances. The filter band width and the filtering range can be tuned effectively by changing the structure parameters. In this system, the center frequency and bandwidth of the filter band are 1330 nm and 114 nm, respectively. The insertion loss and reflection loss are −1.41 dB and −16.89 dB, respectively. The optimization is carried out on the basis of the first system in order to improve the filtering performance. Optimized waveguide coupling system contains an ITD and a waveguide with a slot cavity. Electromagnetically induced transparency (EIT) and Fano resonance exist simultaneously, and the filter band is induced in the transmission spectrum. In this system, the center frequency and bandwidth of the filter band are 1412 nm and 120 nm, respectively. The insertion loss and reflection loss are −0.50 dB and −37.32 dB, respectively. EIT and Fano resonance can not only be regulated independently, but also be regulated simultaneously by changing the structural parameters. And the intensity of EIT and the width of the filter band can be manipulated with changes of the structural parameters. The transmission response of SPPs propagating in the structure can be adjusted dynamically. Moreover, these novel SPPs optical waveguide structures have good filtering efficiency and can meet different filtering needs. These results show that the proposed systems are promising for filter, slow light device and photonic device integration applications.