Microring-Resonator Cross-Connect Filters in Silicon Nitride: Rib Waveguide Dimensions Dependence

We report a systematic study of monolithic microring-resonator cross-connect filters with various waveguide widths and heights in silicon-nitride-on-silica substrates. Our experiments reveal that for particular deeply etched rib heights and slab heights, the microring-resonance Q factors rise nearly linearly as a function of the submicrometer waveguide width, while the extinction ratios generally drop nonlinearly. From the measurements, we are able to extract the microring loss and the waveguide-microring coupling coefficient at various waveguide widths and heights by using a Fabry-Perot-like model. The trends of the extracted microring loss and coupling coefficient are in qualitative agreement with the trends of the numerically simulated curved rib waveguide bend loss and straight rib waveguide evanescent field amplitude at the coupling distance