Phase Characterization of Singular Metasurfaces

The controlled generation and accurate characterization of light beams carrying orbital angular momentum (OAM) are essential for emerging applications in optical communication, quantum information, and advanced imaging. Metasurfaces offer a versatile platform for tailoring such structured electromagnetic fields. However, the accurate measurement of wavefronts containing multiple phase singularities remains a significant metrological challenge. In this work, we employ quadriwave lateral shearing interferometry (QLSI) as a quantitative phase imaging technique to retrieve spatially resolved phase maps of OAM beams generated by metasurfaces. We demonstrate that QLSI enables robust reconstruction of perfect and imperfect singular phase profiles, providing a reliable tool for the characterization of complex optical fields. This methodology is applied to evaluate metasurfaces designed using two distinct phase encoding mechanisms: effective refractive index (ERI) modulation and Pancharatnam-Berry (PB) phase. Comparative analysis reveals superior phase accuracy and enhanced fabrication tolerance in PB-based metasurfaces relative to ERI counterparts. These results highlight the potential of QLSI as a diagnostic and validation tool for structured light generation in next-generation photonic devices.