Nanoimprinted Tilt-Free Astigmatic Metasurface for One-Shot Orbital Angular Momentum Beam-Array Readout

Astigmatic conversion of Laguerre-Gaussian (LG) beams into Hermite-Gaussian (HG)-like patterns enables intuitive orbital angular momentum (OAM) readout, but conventional tilted-lens implementations require bulky optics and mechanical tilt alignment. Here, we demonstrate a nanoimprinted tilt-free astigmatic metasurface that performs LG-to-HG-like conversion at normal incidence. A generalized anisotropic quadratic phase is encoded into a cylindrical nanopillar array, with programmable astigmatic axes and a transverse mapping factor. Simulations and experiments show that the converted HG-like patterns reveal the OAM state through the dark-fringe number and orientation, which encode |l| and the sign of l, respectively. The same device further maps sparse LG beam arrays into spatially separated HG-like patterns, enabling one-shot position-mapped spatial-channel and OAM-state readout in a single camera frame. This planar, replication-compatible platform offers a compact route toward OAM mode analysis and structured-light beam-array decoding.