Nonlinear Vectorial Metasurface for Optical Encryption

In the manipulation of the propagation of light, nonlinear optical metasurfaces have enabled a plethora of applications. A key issue in this area is how to arbitrarily control the vectorial polarization profile of nonlinear optical waves. This study demonstrates an ultrathin nonlinear photonic metasurface that can generate a vectorial polarization profile of the second-harmonic-generation beam, and therefore encodes a high-resolution grayscale image. This rich polarization information has significant potential for nonlinear optical image encryption and other security applications, such as anticounterfeiting.