Demonstration of Error-Tolerant Integrated Optical Processors Based on Multi-Plane Light Conversion

An integrated optical unitary processor (OUP) that can perform arbitrary unitary mode conversions is expected to be a key device in diverse applications, including optical communication, deep learning, and quantum computing. While integrated OUPs have been experimentally demonstrated, most of them are sensitive to fabrication errors because of their stringent requirements on the splitting ratio of optical splitters. Here, we experimentally demonstrate that the OUP based on multi-plane light conversion (MPLC) manifests excellent robustness against various deviations in the waveguide geometries and the operation wavelength. By comparing various silicon photonic $4\times 4$ MPLC-based OUPs operated in the intensity-only mode, we show that similar performances are obtained in all cases under large waveguide geometry deviations and wavelength shifts, which would significantly degrade the performance of conventional OUPs.