Design of Aperture-Multiplexing Metasurfaces via Back-Propagation Neural Network: Independent Control of Orthogonally-Polarized Waves

In this article, we propose a design method of aperture-multiplexing metasurfaces using back-propagation neural network (BPNN), which can achieve independent wavefront modulation for orthogonally-polarized waves. To this end, we first propose a modified Jerusalem Cross (MJC) structure as the metasurface unit cell, which decouples orthogonal interactions by increasing the effective inductances of each of the two Jerusalem Cross (JC) branches. Due to the reduced orthogonal couplings, the MJC can achieve nearly independent control of orthogonally-polarized waves. Then, via BPNN, a dictionary mapping between reflection phase and structural parameters of MJC is established to facilitate metasurface design using MJCs. It is verified that the fitting degree of dataset exceeds 99.99% and that the prediction error of reflection phase is less than 0.01°. Using this design method, we demonstrated a focusing metasurface that can focus reflected waves for both $x$ - and $y$ -polarized waves simultaneously, with focus lengths of 150 and 300 mm, respectively. The simulated and measured results are well consistent, which prove the feasibility of this method. This work provides an efficient method of designing multiplexing and multifunctional metasurfaces, which may find applications in fields, such as satellite communication and base stations.