Monolithically integrated polarization rotator and splitter with designed power ratio

Abstract

Inverse designs are widely used for creating ultra-compact photonic devices, but suffer from high computation power due to the optimization complexity. General Stoke’s theorem proves that the overall change present at the outer boundary is equal to the integral of the change over the inner intervals, providing the possibility to divide one sophisticated device into several simple building blocks. Thus, we integrate this theorem with the inverse designs as a novel design methodology for optical devices. Compared with conventional inverse designs, the separated regional-optimisations can reduce the computational complexity significantly. The overall computational time is around five times shorter than optimizing the whole device region. To validate the proposed methodology, a monolithically integrated polarization rotator and splitter is designed and fabricated to demonstrate the performance experimentally. The device achieves polarization rotation (TE00 to TE00 and TM00 modes) and power splitting with the designed power ratio. The exhibited average insertion loss is <1 dB and the crosstalk is <−9.5 dB. These findings confirm the advantages of the new design methodology, as well as its feasibility for achieving multiple functions on one monolithic device.