Near-infrared doublet zoom lens based on Ge2Sb2Te5 metasurface

Although numerous studies showcase the capability of metalenses to serve as crucial elements of miniaturized optical systems, tunable focusing remains an ongoing challenge. Here, we propose a doublet zoom lens based on a Ge2Sb2Te5 (GST) metasurface at a wavelength of 1.55 mu m. Multistep zooming is realized by the joint control of incident circular polarization inversion and GST phase transition. Three tight focal spots, 0.91 lambda, 1.09 lambda and 0.89 lambda, are achieved from the composite lens. The devised highly-integrated doublet lens, with advantages such as as being multi-foci, easily operated and responding quickly, can find applications in fields that require ultracompact zoom imaging and beam focusing.