Metasurface-Enabled Cascaded Multispectral Polarization Structures Along the Longitudinal Direction

Generation and manipulation of polarization structures have attracted significant interest due to their unusual optical features and extensive applications. Multispectral information can further increase the information capacity of polarization structures. However, generating multiple cascaded multispectral polarization numbers (letters) at multiple planes arranged along light propagation has not been reported. A geometric metasurface is used to experimentally realize eight cascaded multispectral polarization numbers (letters) at predesigned observation planes along the longitudinal direction. The efficacy of this approach is demonstrated by encoding a single polarization number (letter) with two wavelengths and cascading two polarization numbers with orthogonal polarization rotation angles. Different two-color polarization numbers (letters) are generated by controlling the incident wavelength, while their polarization distributions are modulated by controlling the incident linear polarization. This approach integrates two-dimentional (2D) polarization generation, multiple colors, longitudinal control, and cascading design, providing extra degrees of freedom for customized polarization design and enabling small-volume polarization systems for color display, image steganography, and optical encryption.