Single-layer metasurface realizes double image coding and reconstruction

Electromagnetic wave has multiple parameters, including amplitude, phase, polarization, and wavelength. By utilizing multiple parameters of electromagnetic wave simultaneously, the encoding and transmission capacity of information can be effectively improved. Metasurface, a kind of artificial single layer material, provides a possibility to control all parameters of electromagnetic wave using a single device.

   The joint research group of Prof. Yan Zhang from Capital Normal University, Prof. Changzhi Gu from Institute of Physics, CAS, and Prof. Guohai Situ from Shanghai Institute of Optics and Fine Mechanics, CAS introduces a single-layer metasurface, which can successfully encodes double images into this structure by simultaneously modulating the amplitude and polarization of incoming light and independently reconstructs two images at perpendicular polarization directions. 

   Combining with the rotation angle, three kinds of subwavelength rod antennas are utilized to simultaneously manipulate both the amplitude and polarization of electromagnetic wave with a wavelength of 800 nm. Double images were successfully encoded into a single-layer metasurface and two independent images were reconstructed by de-polarization. The rod structures are designed to convert the incoming circularly polarized light into linearly polarization. Since the directions of the metal rods are varied, the directions of the linear polarization are also varied. Three sizes of metal rods are used modulate the intensity of light with relative transmissivity of 0, 1/2, and 1. The images in two orthogonal polarization states can then be synthesized and reconstructed by the above rotation and size parameters, as shown in the figure below. Compared with the phase-polarization modulation, this method is simple and can be easily realized in fabrication. This method is expected to be applied in optical image encryption, information storage, polarization holography, optical communication, and other fields.

Images encoding and reconstruction based on polarization multiplexing

About the Group
Prof. Yan Zhang’s group in Capital Normal University focuses on the research of modulation and measurement of terahertz wave front. The group has a home build terahertz focal imaging system which can measure all parameter of terahertz wave front. Prof. Yan Zhang is the dean of Beijing key lab for matematerials and devices, OSA fellow. He has published more than 230 peer-reviewed papers and coauthored 5 books.

Guo J Y, Wang T, Quan B G, Zhao H, Gu C Z et al. Polarization multiplexing for double images display. Opto-Electron Adv  2, 180029 (2019).