Progress in metalenses: from single to array

As one of the most promising branches of metasurfaces, metalenses overcome the functional limits of conventional lenses and enable versatile control over light. Their compactness facilitates integration into miniaturized optical systems without significantly increasing the footprint. Recent advances in the field are unfolding along two parallel directions: performance enhancement and functional expansion of single metalenses, and architectural development of multi-metalens systems. In this review, we systematically summarize representative progress in both areas, aiming to clarify major unresolved challenges and highlight the most promising directions for future exploration.