Low-loss ultra-compact photonic bends with enhanced fabrication tolerance for commercial foundry processes.

We present a methodology and experimentally validate it with the design of high-performance integrated photonic waveguide bends in extremely compact footprints (2.3 µm radius). The approach uses what we believe to be a novel contour constraint within a topology optimization framework to improve performance and reduce sensitivity to fabrication variability while ensuring compliance with commercial foundry design rule checks. Performance is demonstrated to rely on whispering gallery mode-like characteristics. Devices fabricated on the GlobalFoundries Fotonix process exhibit a low measured average loss of 0.024 dB across 1526 nm to 1600 nm and robustness to over/under etch with low phase sensitivity of 1.1 degree/nm change in waveguide width.