Ultra-wideband high-efficiency reflective polarization converter based on a silver metasurface in the near-infrared region

In this paper, a compact multifunctional polarization converter based on a silver metasurface has been designed. For a <i>y</i>-polarized incident light, broadband linear-to-linear polarization conversion with a polarization conversion ratio greater than 0.9 has been achieved. Therefore, dual-band linear-to-circular polarization conversion has been realized. For an incident light with circular polarization, the structure has circular-to-linear and circular-to-circular polarization conversion functions. Moreover, the energy conversion ratio exceeds 0.9 in the broadband wavelength range of 800 to 3000 nm. To elucidate the physical mechanism of polarization conversion, analyses based on the decomposition of polarization of the incident light and the surface current distribution have been presented. Also, the effects of important geometric parameters, polarization, and incident angles on the polarization conversion performance have been investigated. It is shown that the performance of the converter is independent of the incident angle up to 30°. To check the correctness of simulation results, analytical methods of multiple interference theory and equivalent circuit model have been studied. The proposed structure with features such as compactness, multifunctionality, broad bandwidth, low losses, and simple fabrication offers new insights, to our knowledge, for designing integrated optical devices and can be used in various fields such as wireless communication systems, stealth technology, nanoantennas, electromagnetics, and imaging systems.