Controllable Polarization Rotator with Broadband High Transmission Using All‐Dielectric Metasurfaces

Topology optimization of the azimuth-rotation-independent polarization conversion metasurface for bandwidth enhancement

Metasurfaces offer an unprecedented opportunity for flexible manipulation of electromagnetic wave. The azimuth-rotation-independent (ARI) polarization conversion metasurface (PCM) is an ultrathin device, which could convert an arbitrary linearly-polarized incident wave to its cross-polarized state. However, the bandwidth of an ARI PCM with a high cross-polarized transmission is usually limited. Here, a topology optimization method of multi-feature points based on the differential evolution (DE) algorithm is adopted to enhance the bandwidth of the traditional ARI PCM while maintaining a high transmission and polarization conversion ratio. The simulated results of the optimized structure indicate a 2.08 times bandwidth expansion in the cross-polarization conversion compared with the original structure. In addition, the measured results are consistent with the simulated ones and the ARI characteristic is validated. The proposed method provides a promising route for efficient high-performance metasurface designs.

Graphene-based polarization-sensitive metasurfaces for integrated optics applications

In this study, polarization detection of the incident wave with amplitude and frequency is achieved by proposed graphene-based metasurfaces for integrated optics applications. Metasurfaces consist of elliptical nanodisks of graphene as the meta-atoms. Synthesis of the metasurfaces is based on the analytical approach of the equivalent conductivity method. The elliptical nanodisks play an asymmetric meta-atom role with respect to the polarization of the incident waves. This concept is applied to design polarization selective metasurfaces. Two types of polarization-sensitive metasurfaces are designed. One of them has unique nanodisks that change the absorbance coefficient by varying the polarization of the incident wave in an absorber structure. The second one has three types of elliptical nanodisks with various dimensions and orientations that distinguish the polarization. This metasurface is used in a demultiplexing structure to select a desired wave with a specific frequency.

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.