Twin-Fano resonator with widely tunable slope for ultra-high-resolution wavelength monitor.
A twin-Fano resonator based on a Mach-Zehnder interferometer (MZI) is demonstrated on a silicon-on-insulator platform. A dual-microring resonator replaces one of the couplers of the MZI to achieve twin-Fano resonance, which originates from the interference and coupling of modes in a dual-microring resonator. The slope can be tuned in a wide range from -84.2  dB/nm to 91.0 dB/nm by metal heaters integrated on one arm of the MZI, and the resonant wavelength remains fixed when the slope changes. The "X-type" spectrum is shown by self-alignment, which means manual alignment to form the X-type line is unnecessary after tuning dual-microrings because the X-type line can be produced easily by the difference in two correlated spectra rather than two independent spectra. The measurement shows high wavelength resolution of 1 pm in the region of the slope of 127.4 dB/nm, which can be applied to wavelength monitoring with ultra-high resolution.