Multiple Multicolored\n3D Polarization Knots Arranged\nalong Light Propagation

Polarization and color play essential roles in understanding\noptical\nphenomena and practical applications. Customized three-dimensional\n(3D) light fields, characterized by specific polarization and color\ndistributions, have garnered growing interest owing to their unique\noptical attributes and expanded capacity for information encoding.\nTo align with the ongoing trend of compactness and integration, it\nis desirable to develop lightweight optical elements that can simultaneously\ncontrol polarization and color in 3D space. Although engineering longitudinally\nvariable 3D optical structures with predesigned color and polarization\ninformation can add more degrees of freedom and additional capacity\nfor information encoding, it has not been reported. We propose a metasurface\napproach to generating multiple 3D polarization knots along the light\npropagation direction. Each knot features two colors and an engineered\n3D polarization profile. Different multicolored 3D polarization knots\nare obtained by controlling the observation region along the light\npropagation. Our approach simultaneously combines polarization, color,\nand longitudinal control in 3D environment, offering extra degrees\nof freedom for engineering complex vector beams. The unique properties\nof the developed metadevices, together with the design flexibility\nand compactness of metasurface, pave the way for polarization systems\nwith small volumes applicable to some areas such as complex structured\nbeams and encryption.