Numerical study of mid-infrared tunable metalenses based on Ge2Sb2Te5 phase-change material

The mid-infrared (mid-IR) metalens is an advanced but also fundamental element for a variety of dynamic optical applications, e.g. night visualization and spectroscopic sensing. However, the lens quality and tunability is challenging at this strategically important band. Here, we numerically propose a reflective metasurface platform based on Ge2Sb2Te5 (GST) phase-change material to resolve this problem. Our two paradigms, i.e. bifocal and bifunctional metalenses, prove that a diversified range of functions can be modulated in the mid-IR without structural reconfiguration. By converting GST between amorphous and crystalline states, the focus of the bifocal metalens shifts 35.8 mu m (>6 lambda), with maximum focusing efficiency of up to 8%. The continuous modulation of the intensity profile at two focuses is realized by GST phase transition. We have also demonstrated that a one-dimensional focal metalens with focusing efficiency of 28% can be switched into a mid-IR light deflector by converting the GST phase states. The metasurface uses mature optical materials and can be fabricated by standard microfabrication technologies, which makes the tunable mid-IR platform promising for integrated optical systems.

Automated summary

This study proposes a reflective metasurface platform based on phase-change material to address the challenges of lens quality and tunability in the mid-infrared frequency range. By converting the phase of the material, the focal length and intensity profile can be continuously modulated. The platform uses mature optical materials and can be fabricated using standard microfabrication technologies.