Cascaded microring resonators for crosstalk reduction and spectrum cleanup in add-drop filters

The role of cascaded filters for spectrum cleanup and crosstalk reduction in add-drop filters is addressed experimentally for microring resonator cross-grid technology. The fabricated devices consist of glass microring resonators 10 μm in radius vertically integrated above a cross-grid waveguide array. Sharper linewidth rolloff and flattened passband responses are observed. The ratio of 15 to 3 dB bandwidth of a cascaded double filter is reduced by a factor of 3 compared with the single-filter case. Because of the very small dimensions of the resonators, the use of multiple filters to improve the spectral response consumes negligible chip space.