Focal-Length Measurement of Multifocal Metalens by Using Far-Field Imaging

This article used far-field light source to investigate the focal length of the short focal length, multifocal metalens. The feasibility of the scheme was analyzed by using imaging simulation. In addition, the relative error between far-field imaging method and collimated laser measurement was analyzed. The data results show that the relative error is 0.49%, as the point light source located 2000mm away, for ideal test lens with focal length of 10mm. An optical system composed of double lenses was constructed to measure the focal length of a metasurface with four focal points. The experimental results show that the system can determine the focal position within a step of 0.1mm.