Engineering metalenses for planar optics and acoustics

Metalens, a two-dimensional planar system composed of strategically engineered subwavelength structures, facilitates precise manipulation in the process of both light and sound. Benefiting from the synergy between theoretical exploration and cutting-edge fabrication in the past decade, metalenses have attracted considerable attention owing to their thin structure and large number of degrees of freedom. Herein, we comprehensively review recent developments in optical and acoustic metalenses. Initially, we provide an overview of the fundamental principles and design perspectives of metalenses. Subsequently, we discuss the current challenges affecting planar optical and acoustic technologies. Then, we introduce emerging applications that leverage the capabilities of metalenses. Finally, we summarize this review with a discussion of various perspectives to guide future works.