Advances in optical metalenses

Optical metalenses-two-dimensional arrays of submicrometre scatterers that collectively focus light-have experienced growing research interest in recent years as they can realize conventional optical elements while offering novel functionalities. Their progress is driven by the need for low-cost, high-performance miniaturized optical systems and is supported by advances in nanofabrication and computational tools and techniques. Here we review the main capabilities offered by metalenses, such as their multifunctionality and their ability to efficiently focus light to subwavelength spots. We discuss how these characteristics enable new applications and provide an overview of the current state of the art of optical metasystems. We conclude by discussing the outstanding challenges in the field and highlighting application areas where metalenses could have a substantial impact.