Nanolithography and Application Research Group, State Key Lab of ASIC and System, School of Information Science and Engineering, Fudan University, Shanghai 200433, P. R. China.
Nanoscale. 2018 Jul 9;10(26):12378-12385. doi: 10.1039/c8nr02088d.
Metasurfaces consisting of a two-dimensional metallic nano-antenna array are capable of transferring a Gaussian beam into an optical vortex with a helical phase front and a phase singularity by manipulating the polarization/phase status of light. This miniaturizes a laboratory scaled optical system into a wafer scale component, opening up a new area for broad applications in optics. However, the low conversion efficiency to generate a vortex beam from circularly polarized light hinders further development. This paper reports our recent success in improving the efficiency over a broad waveband at the visible frequency compared with the existing work. The choice of material, the geometry and the spatial organization of meta-atoms, and the fabrication fidelity are theoretically investigated by the Jones matrix method. The theoretical conversion efficiency over 40% in the visible wavelength range is worked out by systematic calculation using the finite difference time domain (FDTD) method. The fabricated metasurface based on the parameters by theoretical optimization demonstrates a high quality vortex in optical frequencies with a significantly enhanced efficiency of over 20% in a broad waveband.
由二维金属纳米天线阵列组成的超表面能够通过操控光的偏振/相位状态，将高斯光束转换为具有螺旋相位前沿和相位奇点的光学涡旋。这将实验室规模的光学系统小型化到晶圆级组件，为光学领域的广泛应用开辟了新的领域。然而，从圆偏振光产生涡旋光束的低转换效率阻碍了其进一步发展。本文报道了我们在提高可见光波段的效率方面取得的最新成功，与现有工作相比，效率在较宽的波段内得到了提高。通过琼斯矩阵方法对材料选择、亚波长结构的几何形状和空间组织以及制造保真度进行了理论研究。通过有限差分时间域 (FDTD) 方法进行系统计算，得出了在可见波长范围内超过 40%的理论转换效率。基于理论优化参数制作的超表面在光学频率下表现出高质量的涡旋，在较宽的波段内效率显著提高，超过 20%。
