Phase mask fabrication for multi-plane light conversion using grayscale lithography

Abstract: Direct writing laser (DWL) grayscale lithography is introduced as a novel fabrication technique for multi-plane light conversion (MPLC) phase masks, enabling direct transfer of precise depth profiles onto substrates via reactive ion etching and subsequent reflective coating. An MPLC system employing these masks achieves 92% fidelity in converting a Gaussian (TEM (0,0)) input to a Laguerre-Gaussian (LG(0,0)) mode. The fabricated masks exhibit sub-10 nm vertical resolution, surface roughness below 3 nm, and an R-squared value of 0.976. This method provides a scalable alternative to conventional multi-step lithographic fabrication for advanced photonic systems.