Abstract

A 90° optical hybrid (OH) based on a ${{4}} \times {{4}}$ multimode interference (MMI) coupler is characterized and analyzed using the silica-based planar light circuit. The OH is designed to be polarization-insensitive with an extremely low polarization-dependent loss (${\lt}{0.18}\;{\rm{dB}}$) and phase error (${\rm{within}}\;{\rm{\pm 1}.{3}}^\circ)$. The fabricated chip exhibits an excess loss of 3.4 dB and 3.8 dB for TE and TM polarizations at 1550 nm. The measured phase error is ${\rm{within}}\;{\rm{\pm 7}.{2}}^\circ$ over 50 nm in the ${\rm{C}} + {\rm{L}}$ band with a polarization-dependent error ${\rm{within}}\;{\rm{\pm 3}.{5}}^\circ $. The fabrication tolerance of the MMI width and waveguide sidewall angle is analyzed, which can well explain the deviation from the theoretical calculation.

© 2022 Optica Publishing Group

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