Weak Measurement for Characterizing Effective Jones Matrices of Phase Gradient Metasurfaces

ABSTRACT Pancharatnam‐Berry phase gradients generated by spatially rotated meta atoms are widely used to control optical wavefronts with metasurfaces. Here, we develop a weak measurement method for characterizing the effective Jones matrix parameters of fabricated PB phase gradient metasurfaces. In the specified effective Jones model, the local polarization response is described by the amplitude ratio and phase difference, while the spatial rotation of the meta atoms determines the PB phase gradient. By scanning the imaginary part angle and real part angle, the spin dependent deflection is converted into a two dimensional centroid map. The amplitude ratio, phase difference, and phase gradient produce different spatial features in this map, providing information for their distinction and retrieval. For a fabricated metasurface with a known phase gradient, the amplitude ratio and phase difference are obtained by fitting the measured centroid response with the theoretical model. When all three parameters are unknown, three independently trained machine learning models retrieve the amplitude ratio, phase difference, and phase gradient from the same complete centroid map and its angular coordinates. These results establish two dimensional weak measurement as an optical approach for characterizing the effective parameters of PB phase gradient metasurfaces.