Tunable achromatic metalens for generating focused vortex beam in the near-infrared range

Highly precise and controllable focusing of optical vortex beams in the NIR range is essential for applications in biological imaging, nanomanipulation, and other fields. However, achieving tunable vortex beams across a broad spectrum remains a significant challenge. Herein, we propose a varifocal and broadband achromatic metalens capable of effectively correcting chromatic aberration, achieving a maximum focusing efficiency of 40.0% over 1400-1700 nm. Furthermore, through adjustments to the crystalline fraction of Ge2Sb2Te5 (GST), it offers the ability to vary focal lengths from 6.90 to 10.73 mu m. This study may further advance NIR communication and imaging systems.