Broadband generation of perfect Poincar\xe9 beams via dielectric spin-multiplexed metasurface

Mingze Liu,Qianwei Zhou,Song Zhang,Cheng Zhang,Amit Agrawal,Lu Chen,Ting Xu,Maowen Song,Yanqing Lu,Si Zhang,Pengcheng Huo,Henri J Lezec,Wenqi Zhu

doi:10.1038/s41467-021-22462-z

Abstract

The term Poincaré beam, which describes the space-variant polarization of a light beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM), plays an important role in various optical applications. Since the radius of a Poincaré beam conventionally depends on the topological charge number, it is difficult to generate a stable and high-quality Poincaré beam by two optical vortices with different topological charge numbers, as the Poincaré beam formed in this way collapses upon propagation. Here, based on an all-dielectric metasurface platform, we experimentally demonstrate broadband generation of a generalized perfect Poincaré beam (PPB), whose radius is independent of the topological charge number. By utilizing a phase-only modulation approach, a single-layer spin-multiplexed metasurface is shown to achieve all the states of PPBs on the hybrid-order Poincaré Sphere for visible light. Furthermore, as a proof-of-concept demonstration, a metasurface encoding multidimensional SAM and OAM states in the parallel channels of elliptical and circular PPBs is implemented for optical information encryption. We envision that this work will provide a compact and efficient platform for generation of PPBs for visible light, and may promote their applications in optical communications, information encryption, optical data storage and quantum information sciences.

Highlights

The term Poincaré beam, which describes the space-variant polarization of a light beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM), plays an important role in various optical applications
Where jPOVR; lmi and jPOVL; lni denote the right-handed circularly polarized (RCP) and left-handed circularly polarized (LCP) perfect optical vortices (POVs) with same ellipticity, and different topological charge numbers of lm and ln, respectively. cosðα2Þ and sinðα2Þ represent the amplitude of RCP and LCP POV and β is the relatively phase difference between them, where α ∈ [0, π] and β ∈ [0, 2π]. jUN i is an arbitrary point on the surface of hybridorder Poincaré Sphere (HyOPS) with spherical coordinates (α, β)
The phase distribution of the perfect Poincaré beam (PPB) is characterized by the topological Pancharatnam charge lp 1⁄4 ðlm þ lnÞ=214,45

Summary

Introduction

The term Poincaré beam, which describes the space-variant polarization of a light beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM), plays an important role in various optical applications. Based on an alldielectric metasurface platform, we experimentally demonstrate broadband generation of a generalized perfect Poincaré beam (PPB), whose radius is independent of the topological charge number. The optical vortices and cylindrical vector vortex beams[10] described by the poles and equator of the HyOPS, respectively, have been demonstrated and applied in a number of applications[11], such as optical trapping, high-resolution microscopy, optical communication, nonlinear optics, and optical encryption[12]. It is difficult to generate a stable and high-quality Poincaré beam by two orthogonally circularly polarized optical vortices with very different topological charge numbers, as the Poincaré beam formed in this way would collapse upon propagation[14]. A silicon metasurface has been designed to generate PPBs45; this design requires simultaneous phase and amplitude modulation and a complicated oblique incidence scheme, which further limit its efficiency and operating bandwidth

Methods

Results

Conclusion