A dual-microring resonator replaces one of the couplers of the Mach-Zehnder interferometer (MZI) to achieve a widely tunable twin-fano resonance, which originates from the interference and coupling of mode 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 fixes when slope changes. The “X-type” spectrum is shown by self-alignment, which means manual alignment to form “X-type” line is unnecessary after tuning dual-microrings because the “X-type” line can be produced easily by the difference of two correlated spectrums rather than two independent spectra. Meanwhile, it shows high wavelength resolution of 1 pm with an ideal resolution of 0.4 pm in the region of the slope of 127.4 dB/nm, which can be applied to wavelength monitoring with ultra-high resolution.
Two ultra-compact silicon bandpass filters are proposed and partly experimentally presented. Both of them have wide bandwidth tunability. Based on the first filter (filter-I), the second filter (filter-II) was designed and has large Free Spectrum Range (FSR). Two filters share the same architecture (matrix architecture), consisting two groups of micro-ring resonator-cascade structures (simply called as micro-ring resonator in this letter). Using this matrix architecture, a wide bandwidth tunability from 75 to 300 GHz can be achieved in filter-I. Based on matrix architecture, double micro-ring resonator (MRR) were adopted and Vernier effect was used in design. It is showed both in simulation and experiment that the FSR of filter-II exceeded 35 nm (around 40 nm in simulation), which is much larger than the FSR of single MRR. Filter-II’s tunability of center wavelength in simulation covers most wavelength from 1530 to 1570 nm. The comparison of bandwidth tunability between filter-I and II reveals that adding paths in matrix architecture may be more effective than adopting high-order micro-ring resonators.
An integrated high-resolution ratio-metric wavelength monitor (RMWM) is demonstrated on SOI platform. The device consists of a reconfigurable demultiplexing filter based on cascaded thermally tunable microring resonators (MRRs) and Ge-Si photodetectors integrated with each drop port of the MRRs. The MRRs are supposed to achieve specific resonant wavelength spacing to form the “X-type” spectral response between adjacent channels. The ratio of the two drop power between adjacent channels varies linearly with the wavelength in the “X-type” spectral range, thus the wavelength can be monitored by investigating the drop power ratio between two pre-configured resonant channels. The functional wavelength range and monitor resolution can be adjusted flexibly by thermally tuning the resonant wavelength spacing between adjacent rings, and an ultra-high resolution of 5 pm or higher is achieved while the resonant spacing is tuned to 1.2nm. By tuning the resonant wavelength of the two MRRs synchronously, the monitor can cover the whole 9.6nm free spectral range (FSR) with only two ring channels. The power consumption is as small as 8 mW/nm. We also demonstrate the multi-channel monitor that can measure multi-wavelength-channel simultaneously and cover the whole FSR by presetting the resonant wavelengths of every MRR without any additional power consumption. The improvements to increase the resolution are also discussed.