Collimated flat‐top beam shaper metasurface doublet based on the complex‐amplitude constraint Gerchberg–Saxton algorithm
Dongbai Xue, Xiong Dun, Zeyong Wei, Dongdong Li, Jingyuan Zhu, Zhanyi Zhang, Zhanshan Wang, Xinbin Cheng
Abstract
Abstract Collimated flat‐top beam shapers primarily consisting of freeform lenses have a wide range of applications and pose challenges in terms of processing and integration when the diameter is less than millimeters. Metasurfaces represent a promising solution to planarize optics, can mimic any surface curvature without additional fabrication difficulty, and are suitable for flat‐top optics. The conventional metasurface design approach relies on imparting the required phase using meta‐atoms and encounters challenges in amplitude modulation due to near‐field coupling and varying transmittances among meta‐atoms with different phases, making the design of flat‐top beam shapers difficult. In this paper, we propose a complex‐amplitude constraint Gerchberg–Saxton algorithm for designing a collimated flat‐top beam shaper metasurface doublet, which avoids the influence of strong near‐field coupling on the amplitude distribution and simultaneously considers the amplitude‐phase characteristics of the meta‐atoms. A collimated flat‐top beam with exceptional homogeneity U p of approximately 0.01, a wavefront error less than 0.1 λ , and a transmittance higher than 86 % is experimentally obtained, comparable to commercial products based on freeform lenses. A collimated flat‐top beam shaper metasurface doublet for generating flat‐top beam is introduced, promoting efficient integration with laser systems.