Axially tailored light field by means of a dielectric metalens

Metasurfaces that enable wave-front manipulation within the subwavelength range exhibit fascinating capabilities and application potentials in ultrathin functional devices. Therein, various metasurfaces to realize delicate transverse and even three-dimensional structured light fields have been proposed for applications such as holographic displays, imaging, optical manipulation, etc. However, a metasurface with the capability of tailoring the axial structure of a light field has not been reported so far. Here, we propose and experimentally demonstrate a dielectric metalens to tailor the axial intensity distribution of a light field, based on the independent control of amplitude and phase. The metalens is designed according to an optimized Fourier spectrum encoding method, which allows construction of an ultrasmall nondiffractive light field with any arbitrary preestablished axial structure. This axial modulation scenario enriches the three-dimensional wave-front modulation functionality of the metasurface, and can be implemented for other waves beyond optics, from acoustic and elastic waves to matter waves.