Fig. 5: Experimental demonstration of information encrytion using designed metasurface.

a The one-to-one mapping between incident states (Stokes parameters and wavelength) and OAM spectrum enabled by the designed metasurface. b The OAM spectra under several distinct incident states, where 0th order (blue) and 2nd order (red) OAM modes are selected to encode information in this example. c By selecting incident states with the two (0th and −2nd orders) appropriate OAM mode intensities, the longitude and latitude coordinate information of Beijing (116.2°E, 39.6°N) are respectively encoded into two sets of incident states (Input states 1, Input states 2). d When obtaining correct keys (metasurface, 0th and −2nd orders), the receiver can encrypt the longitude (116.2° E) and latitude (39.6°N) information of Beijing by analyzing the metasurface-generated OAM mode intensities under the two sets of incident states. The letters “E” and “N” are revealed by the spatial arrangement of −2nd order OAM mode intensities in a square format, and the number “116.2″ and “39.6″ are decoded through binary encoding of 2nd order OAM mode intensities along each line, where a value greater than 0.4 is taken as “1” and a value less than 0.4 is considered as “0”. Here, the highest (leftmost) order is defined as a decimal point.