On-Chip Double-Fano-Enabled Reconfigurable Optical Notch Filter for Microwave Signal Processing

We propose and demonstrate a fully reconfigurable optical notch filter enabled by on-chip double-Fano resonance. The double-Fano resonance is realized by interfering two independent Fano resonances, of which each one is produced using an add-drop micro-disk resonator and a Mach-Zehnder interferometer. Metal micro-heaters are placed on top of the waveguide to tune each Fano resonance including the resonance wavelength and line shape. When the resonance wavelengths of the two Fano resonances are close to each other and their line shapes have a mirror image, a symmetrical optical notch filter is resulted from the interference of the two asymmetrical Fano resonances. By controlling micro-heaters, the bandwidth, extinction ratio (ER), and center wavelength of the resulted notch filter can be fully tuned. A chip is designed, fabricated, and characterized. The results show that the notch filter has a tunable bandwidth from 46 to 76 pm, a tunable ER from 0 to 30 dB, and a tunable center wavelength from 1544 to 1547 nm, which holds great potential for microwave signal photonic processing.