Creating Wavelength-Selective Polarization Digital Numbers

Polarization and wavelength are two important properties of light for understanding optics. Engineered polarization and wavelength profiles have received considerable interest due to their unusual optical features and more degrees of freedom. However, to simultaneously control polarization and wavelengths, conventional methods suffer from big pixel size, complicated fabrication process, and limited levels in phase control. The unprecedented capability of metasurfaces in the light control has shown much promise to tackle these challenges. Polarization digital numbers with ten different wavelengths are proposed and experimentally realized. A geometric metasurface is used to simultaneously realize wavelength multiplexing, phase multiplexing, and polarization rotation, creating wavelength-selective polarization digital numbers. A deep learning approach is used to increase the identification accuracy of the digital numbers. The approach can simultaneously control wavelength and polarization, providing more design flexibility. This work may find applications in many fields such as virtual reality, image steganography, and anti-counterfeiting.