Beam Shaping by Stacked Nonlinear Moiré Metasurfaces.

Moiré phenomena provide a versatile platform for creating tunable lattices with variable symmetries and periodicities, making them a focal topic in recent photonics research. Moiré photonic devices fused with metasurfaces have demonstrated numerous novel functionalities, yet fabricating moiré metasurfaces, particularly in stacked configurations, poses significant challenges. In this paper, we present an innovative nanofabrication approach for stacked nonlinear moiré metasurfaces, using a focused ion beam-assisted nanostructure transfer-welding technique. This approach allows precise control over interlayer twist angles, enabling complex momentum space engineering along with simultaneous frequency conversion and wavefront manipulation. Experimental results reveal intricate far-field second-harmonic radiation patterns, which are effectively tunable by varying the twist angles. This advancement addresses key fabrication challenges in nonlinear photonics, opening new avenues for applications in nonlinear information processing, optical steering, and nonlinear optical switching.