Ultra-broadband and ultra-low-loss photonic crystal with band-flatness waveguide 60° bend obtained based on lattice-shifted optimization

This work discusses a novel design for a W1 (one missing row of holes) waveguide 60° bend implemented based on photonic crystal slab in a silicon-on-insulator (SOI) material. The bend has been designed to exhibit broadband and low loss for single-mode operation. The investigated design improvement depends on displacing holes in the bending region, meanwhile adjusting the size of air holes to achieve low dispersion and the transmission spectrum presents flatness over 180 nm bandwidth around 1550 nm. By means of rigorous three-dimensional finite-difference time-domain (3D-FDTD) technique, the 3-dB bandwidth reaches 216 nm and we demonstrate a ultralow-loss output of optimized bend waveguide with an average loss of 0.71±0.19 dB in the broadband range 1462-1643 nm, which covers the entire C-band of optical communication.