A Global Phase‐Modulation Mechanism for Flat‐Lens Design

Flat lens also known as metasurface lens is drawing considerable attention nowadays. Thus far, the metasurface lens has been achieved by engineering local phase profile in deep subwavelength scale according to resonant or non-resonant (or both) responses of nanoscatters to light. Such local phase mappings require precise control over each nanoscatter. In addition, there is currently no metasurface lens that exhibits multiple functionalities. Here, a novel working mechanism, named as a global phase-modulation mechanism, for the flat-lens design is demonstrated. To illustrate this concept, a binary amplitude-only hologram is introduced, resulted from an interference between an angular cosine wave and a spherical wave. The resultant flat lens can be made extremely thin (60 nm) and is comprised of spatially shaped apertures. Such a technique allows to globally manipulate the diffractive wave vectors in the reciprocal space. Multiple focusing performances with a single flat lens are demonstrated under different illumination beams including the plane-wave beam, vortex beam, and vector beam. In addition to imaging, the flat lens is able to Fourier transforming a complex self-accelerating Airy beam, which was not considered before. The presented global mechanism facilitates new capabilities and holds for multifunctional flat lens, with potential applications in areas such as imaging and optical information processing.