Metasurface Generates Time-Varying Orbital Angular Momentum

Researchers from The Hong Kong University of Science and Technology and City University of Hong Kong have developed time-varying orbital angular momentum (OAM) beams using a space-time encoded digital metasurface. By exploiting the flexible programmability of the metasurface, they construct different modes of the time-varying OAM beams having a time-dependent phase profile in each time layer, allowing not only a time-varying topological charge but also a higher-order twist in the envelope wavefront structure of the OAM beam. The proposed time-varying OAM beams have application potential for dynamic particle trapping, time-division multiplexing, information encryption, and beyond.