Bandwidth and center wavelength tunable micro-ring optical filter with Vernier effect by four spectrum combination

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.