Space-Time Coding Metasurface For Multifunctional Holographic Imaging

Holographic imaging as one of promising image techniques reconstructs object image using the amplitude and phase information scattered from objects. Programmable metasurface composed of digitally coding unit cells can arbitrarily manipulate amplitude and phase of the scattering wave by tailoring operation states of the unit cells, and thus achieves high-resolution imaging reconstruction. However, the conventional metasurface can only achieves a desired holographic image on an imaging plane. This paper presented a time-space coding 2-bit metasurface to overcome this challenge. By rapidly switching PIN diodes loaded in metasurface unit cell according to the customized time sequences, the magnitude and phase of the +/- 1st order harmonic fields can be fully controlled, achieving the hologram imaging at the higher order harmonics. The proof-of-concept measurements are given to demonstrate the versatile holographic imaging functions at the +/- 1st order harmonics including two different holographic images on an imaging plane, holographic imaging and beam scanning, and holographic imaging and orbital angular momentum (OAM) wave generation, which undoubtedly enriches the applications of the programmable metasurfaces in the field of the holographic imaging. A space-time coding metasurface has been presented to achieve near-field holographic reconstruction of two different images on an imaging plane by means of +/- 1st order harmonics, and simultaneous realization of versatile functions including hologram imaging and beam steering or hologram imaging and orbital angular momentum wave generation at different harmonics has been demonstrated. image