Optimal Bezier curve transition for low-loss ultra-compact S-bends

S-bends with a widening of the width at the mid-bend and a Bezier curve transition are proposed and demonstrated for low-loss S-bends. The increased optical confinement and reduced transition loss enable low insertion loss (IL) and compact S-bends with longitudinal offsets as small as 2.5 µm and a wide operating bandwidth (∼100nm) on a 220 nm thick silicon-on-insulator platform. The simulation results show ILs less than (0.22, 0.20, 0.20, 0.20) dB in the wavelength range of (1.5-1.6) µm, while the minimum ILs are (0.13, 0.13, 0.15, 0.16) dB for lateral offsets of (3, 6, 9, 12) µm. The experimental results show that ILs remain less than (0.41, 0.38, 0.36, 0.39) dB for the mid-bend widening Bezier (MWB) S-bends.