Metasurface Optical Characterization Using Quadriwave Lateral Shearing Interferometry

Abstract

An optical metasurface consists of a dense and usually nonuniform layer of scattering nanostructures behaving as a continuous and extremely thin optical component with predefined phase, transmission and reflection profiles. To date, various sorts of metasurfaces (metallic, dielectric, Huygens-like, Pancharatman-Berry, etc.) have been introduced to design ultrathin lenses, beam deflectors, holograms, or polarizing interfaces. Their actual efficiencies depend on the ability to predict their optical properties and to fabricate nonuniform assemblies of billions of nanoscale structures on macroscopic surfaces. To further help improve the design of metasurfaces, precise and versatile postcharacterization techniques need to be developed. Today, most of the techniques used to characterize metasurfaces rely on light intensity measurements. Here, we demonstrate how quadriwave lateral shearing interferometry (QLSI), a quantitative phase microscopy technique, can achieve full optical characterization of metasurfaces of any kind, as it can probe the local phase imparted by a metasurface with high sensitivity and a spatial resolution that reaches the diffraction limit. As a means to illustrate the versatility of this technique, we present measurements on two types of metasurfaces, namely, Pancharatnam-Berry and effective-refractive-index metasurfaces, and present results on uniform metasurfaces, metalenses, and deflectors.