Optical encryption in spatial frequencies of light fields with metasurfaces

Optical encryption has attracted attention recently as information security becomes important in modern society. For most encryption methods based on metasurfaces, however, information is encrypted into the metasurfaces of physical forms, limiting information sharing and compatibility with digital information processing technology. Here, we demonstrate an alternative scheme in which information is encrypted on optical images other than metasurfaces, releasing the constraints mentioned above. This is achieved by modulating the spatial frequencies of optical images with metasurfaces. Specifically, information encryption and decryption based on the intensity or phase of spatial frequency have been demonstrated with the developed microscopic Fourier optics technique. The abundance of spatial frequency also promises a flexible multiplexing platform for increasing information capacity, which has been verified by a 4-bit encryption experiment. These findings could enable high-security and high-capacity optical encryption platforms.