Complete vectorial optical mode converter using multi-layer metasurface.

Vectorial optical mode converters that can transform orthogonal sets of multiple input vector beams into other orthogonal sets are attractive for various applications in optics and photonics. While multi-plane light conversion (MPLC) and metasurface technologies have been explored to individually address multiple spatial mode conversion and polarization mode manipulation, there has been no universal methodology to simultaneously convert a set of multiple vectorial modes with spatially non-uniform wavefronts and polarizations. Here, we present a general device framework to achieve complete vectorial mode conversion based on the MPLC concept incorporating multi-layer metasurfaces. The effectiveness of our method is confirmed experimentally by demonstrating 6-mode (3 spatial modes × 2 polarization modes) multiplexer fabricated on a compact chip. Additionally, we apply it to design devices with more advanced functionalities: a mode-division-multiplexed dual-polarization coherent receiver and spatial-mode-multiplexed vectorial holography. The versatility of our protocol makes it a powerful tool for realizing universal optical mode converters.