We propose a flat retroreflector that can efficiently reflect the electromagnetic waves back along its incident direction in a wide continuous range of angles. This retroreflector consists of a quadratic metalens and a flat metallic reflector at the focal plane of the former. The quadratic metalens is a dielectric pillar array encoded with a quadratic phase profile and it is embedded in the top side of the substrate. The flat reflector is on the bottom side of the substrate. The designed retroreflector has a diameter of 40 mm, a thickness of 15 mm, and a working frequency of 77 GHz. Through meta-units optimization, a retroreflection efficiency of 38.51% at ± 60° incidence and an average retroreflection efficiency of 46.39% for the incident angles from 0° to 60° can be numerically demonstrated. This flat retroreflector is easy for integration, which is promising for potential applications in the miniature wireless communication systems.

This paper reports a facile and high‐throughput method for the controllable fabrication of polymeric miniature lens arrays. Through filling the miniature holes in an additively manufactured template, the curved lenslets are formed in each hole in s steady state, in which the gravity and surface tension of the liquid resin are balanced. Both shapes and curvatures can be controlled by tuning the gravity force and the boundary condition for the resin in each hole. Taking the circular holes for example, the relationship between the formed curvature and the gravity force is described by both analytical and finite element‐based numerical models. Experimentally, the curvature variation and the effect of various boundary conditions on the lenslet surface shapes are also verified, and further examination on the optical features of the spherical miniature lens arrays including the imaging and focus properties demonstrates the effectiveness of the developed fabrication method.