All-dielectric bifunctional polarization converter with high transmission efficiency in near-infrared region.

In this paper, we demonstrate a polarization control device with different functions for oppositely propagating directions by a two-layer twisted silicon column array separated by a silica layer. The proposed structure can rotate the electric field directions of polarized linear wave backwards by 45º and serve as a linear-to-circular converter for the polarized linear wave forwards . The physical mechanism is discussed by the Jones matrix, and the numerical results show that the maximum transmissions ${ \gt }{0.9}$>0.9 for the two functions of the proposed structure are achieved in the near-infrared region. The high transmission originates from the all-dielectric materials, which is a major advance compared with previously reported bifunctional converters. The proposed simply shaped device with high transmission efficiency has potential applications in optical imaging, sensing, etc.