Digital coding transmissive metasurface for multi-OAM-beam

Orbital angular momentum (OAM) is a phenomenon of vortex phase distribution in free space, which has attracted enormous attention in theoretical research and practical application of wireless communication systems due to its characteristic of infinitely orthogonal modes. However, traditional methods generating OAM beams are bound to complex structure, large device, multiple layers, complex feed networks, and limited beams in microwave range. Here, a digital coding transmissive metasurfacc (DCTMS) with a single layer substrate and the bi-symmetrical arrow is proposed and designed to generate multi-OAM-beam based on Pancharatnam-Berry (PB) phase principle. The 3-bit phase response can be realized by encoding the geometric phase into rotation angle of unit cell for DCTMS. Additionally, the phase compensation of the metasurfacc is introduced to achieve the beam focusing and the conversion from spherical wave to plane wave. According to the digital convolution theorem, the far-field patterns and near-field distributions of multi-OAM-beam with l = -2 modes are adequately demonstrated by DCTMS prototypes. The OAM efficiency and the purity are calculated to demonstrate the excellent multi-OAM-beam. The simulated and experimental results illustrate their performance of OAM beams. The designed DCTMS has profound application in multi-platform wireless communication systems and the multi-channel imaging systems.