Focused vortex-beam generation using gap-surface plasmon metasurfaces

Fei Ding,Yiting Chen,Sergey I Bozhevolnyi

doi:10.1515/nanoph-2019-0235

Abstract

Abstract In spite of a wide range of applications ranging from particle trapping to optical communication, conventional methods to generate vortex beams suffer from bulky configurations and limited performance. Here, we design, fabricate, and experimentally demonstrate orthogonal linear-polarization conversion and focused vortex-beam generation simultaneously by using gap-surface plasmon metasurfaces that enable high-performance linear-polarization conversion along with the complete phase control over reflected fields, reproducing thereby the combined functionalities of traditional half-wave plates, lenses, and q-plates. The fabricated metasurface sample features the excellent capability of orthogonal linear-polarization conversion and focused vortex-beam generation within the wavelength range of 800–950 nm with an averaged polarization conversion ratio of ~80% and absolute focusing efficiency exceeding 27% under normal illumination with the x-polarized beam. We further show that this approach can be extended to realize a dual-focal metasurface with distinctly engineered intensity profiles by using segmented metasurfaces, where an orthogonal-polarized beam with Gaussian-distributed intensity and a vortex beam with intensity singularity have been experimentally implemented. The proposed multifunctional metasurfaces pave the way for advanced research and applications targeting photonics integration of diversified functionalities.

Highlights

The optical vortex beam with phase singularity was first discovered in the 1990s, which possesses a helical phase front so that the Poynting vector within the beam is twisted with respect to the principal axis of light propagation [1]
The basic gapsurface plasmon (GSP) meta-atom consists of gold (Au) nanoantennas tilted by 45° with respect to the x-axis, a middle silicon dioxide (SiO2) spacer layer, and a bottom continuous Au film, which functions as a nanoscale half-wave plates (HWPs) to, simultaneously and independently, engineer the phase and polarization of the reflected light (Figure 1B) [23]
The cross-polarized scattering is further enhanced by the constructive interference in the multireflection process within the GSP cavity, leading to highly efficient orthogonal linear-polarization conversion [24,25,26]

Summary

Introduction

The optical vortex beam with phase singularity was first discovered in the 1990s, which possesses a helical phase front so that the Poynting vector within the beam is twisted with respect to the principal axis of light propagation [1]. We design, fabricate, and experimentally demonstrate orthogonal linear-polarization conversion and focused vortex-beam generation simultaneously by using gap-surface plasmon metasurfaces that enable high-performance linear-polarization conversion along with the complete phase control over reflected fields, reproducing thereby the combined functionalities of traditional half-wave plates, lenses, and q-plates.

Results

Conclusion