Multi-wavelength dual-polarization optical unitary processor using integrated multi-plane light converter


 An optical unitary processor (OUP) is a programmable photonic circuit to achieve arbitrary unitary operation for various applications, including optical communication, deep learning technology, and quantum computing. Conventionally, OUPs are implemented by cascading 2×2 reconfigurable interferometers, but this scheme cannot easily be extended to multiple wavelength and polarization channels due to the strict requirement to employ 50:50 beam splitters. Here, we demonstrate that an OUP using multiport directional couplers (DCs) can realize independent unitary conversion of multiple wavelength and polarization channels simultaneously. This OUP is based on the multi-plane light conversion (MPLC) principle, which does not require a specific transformation at each layer, unlike the conventional scheme. Thanks to this unique robustness of the MPLC method and strong wavelength/polarization dependency of multiport DCs, we numerically show that independent unitary transformations can be applied to up to 16 channels (2 polarization × 4 wavelength) using a single device.