Modeling and measurement of losses in silicon-on-insulator resonators and bends

We present an analytical model to quantify losses in resonators and bends without uncertain contributions from fiber coupling in/out or waveguide cleavage facets. With resonators in add-drop configuration, intrinsic losses are calculated from the free spectral range, through-port extinction and drop-port bandwidth. We fabricated and characterized silicon-on-insulator resonator for loss analysis. At 1.55 mum, racetrack resonators with a bending radius of 4.5 mum show intrinsic losses as small as 0.14+/-0.014 dB/round-trip. Meanwhile, intrinsic losses increase up to 1.23 dB/round-trip in the racetrack resonator that has a bending radius of 2.25 mum. Losses in a 180 degrees bend are estimated as a half of the intrinsic losses in these racetrack resonators, i.e., 0.07+/-0.007 dB/turn for a bending radius of 4.5 mum and 0.62 dB/turn for a bending radius of 2.25 mum. Loss in a 90 degrees bend with a radius of 4.5 mum is determined to be 0.06+/-0.006 dB/turn at 1.55 mum. The losses in 180 degrees or 90 degrees bends are found to be mainly due to the transition loss between waveguide bends and straight waveguides.