Silicon based tunable Fano resonance with ultrahigh slope rate and extinction ratio

We present a silicon-on-insulator (SOT) based device that exhibits Fano resonance with high extinction slope rate (SR) and extinction ratio (ER). It is constructed by using two cascaded tunable Mach-Zehnder interferometers (MZIs). The first MZI is used to adjust the power splitting ratio of the second MZI. In the second MZI, two add-drop microring resonators (MRRs) are located in each arm of the second MZI, respectively. The MRRs are used to generate a high-Q and low-Q resonance respectively. Due to the interference between these two resonances, a Fano resonance could be implemented. Considering that the optical power splitting ratio and phase difference between the two resonances can be finely adjusted, the ER can be greatly increased. In the experiment, the measured Fano resonance of the fabricated device exhibits simultaneous ER of 41.5 dB and SR of 3388.1 dB/nm. To the best of our knowledge, this is the first time to achieve a Fano resonance with such high ER and SR simultaneously. By adjusting the bias voltage in the fabricated device, a pair of complementary Fano resonance line shapes can be achieved.