Compact waveguide bend with digital meta-structures on the silicon-on-insulator platform

Silicon devices have attracted much attention due to their application potential in high-density photonic integrated circuits (PICs). However, it is still challenging to realize light routing within a micro-sized region due to high optical losses introduced by sharp waveguide bends (WBs). Here, we propose and design an ultra-broadband WB with a bending radius of only 2 µm. The design is based on digital meta-structures which are topologically optimized through a genetic algorithm. The designed WB shows an insertion loss of 0.45 dB at the wavelength of 1.55 µm, while the 1 dB-bandwidth reaches 0.3 µm for TE0 mode. With TE0 mode input, modal crosstalk of less than − 20 dB is achieved over a spectral range from 1.5 µm to 1.8 µm. Our study is expected to enable flexible light routing with an ultra-wide bandwidth and compact device footprint, boosting the development of high-density PICs.