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 45 degrees 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 > 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. (C) 2020 Optical Society of America
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