High $Q$ -Factor Microrings Using Slightly Etched Rib Waveguides

The paper reports the design, fabrication and characterization of silicon-on-insulator (SOI) microring resonators using shallow etched rib waveguides. The variation of the $Q$-factor of microring resonators as a function of the ring diameter and coupling gap between the input waveguide and the ring is studied. Such structures are fabricated using e-beam lithography and reactive ion etching steps. Propagation loss of shallow etching rib waveguide has been evaluated to 0.8 dB/cm for wavelengths around 1550 nm. With a ring diameter of 100 $\mu{\rm m}$ and a coupling gap of 450 nm, the measured $Q$ -factor is 35300. These results are matched by 3-D numerical optical modeling.