Low-phase-error and wavelength-insensitive silica-based 90° optical hybrid

A low-phase-error and wavelength-insensitive silica-based 90° optical hybrid (OH) is designed and fabricated for coherent receivers, which integrates two 3 dB Y-branch splitters, a π /2 phase shifter, and two 2×2 3 dB Mach–Zehnder interferometer (MZI) couplers. Measurements show insertion loss (IL)<6.8dB, excess loss (EL)<0.56dB, uniformity (UNIF)<0.5dB, common-mode rejection ratio (CMRR)>29dB, and phase error <±1.6 ∘ across the C band. These results satisfy the low-loss and tight-phase-tolerance requirements of advanced coherent modulation formats and confirm wavelength-insensitive operation over the entire C band.