paper

Hybrid Si-GST Polarization-Insensitive Dynamically Tunable Bifocal Metalens Operating at 1.55-m Wavelength

arXiv:2511.21138 · doi:10.1364/JOSAB.591582

Abstract

Metasurfaces have become a cornerstone of flat-optics, enabling precise control over light propagation through nanoengineered materials. Dynamic and reconfigurable metalenses are key to next-generation flat-optics platforms, yet their practical realization remains limited by slow response, optical loss, and polarization sensitivity. The integration of chalcogenide phase-change materials with metasurface architectures offers a powerful platform for dynamic optical tunability, owing to materials such as GeSbTe (GST) that can be reversibly switched between amorphous and crystalline states with distinct refractive indices. However, the strong optical absorption of crystalline GST in the visible to near-infrared range has hindered its widespread use in reconfigurable metalenses. In this study, we design an all-dielectric polarization-insensitive metasurface based on hybrid Si-GST nanostructures to realize a dynamically tunable bifocal metalens operating at 1.55 \textmu m. The device achieves a variable focal length from 70 \textmu m to 200 \textmu m, with focusing efficiencies of 30\% in the amorphous state and 20\% in the crystalline state, as validated through finite-difference time-domain (FDTD) simulations. Using COMSOL Multiphysics, we show that flat-top laser excitation enables uniform, reversible phase transitions within tens of nanoseconds, amorphization in ~8 ns and crystallization in ~90 ns, without mechanical motion or electrical bias. For next-generation metasurfaces intended for uses including beam steering, dynamic holography, optical routing, multi-depth imaging, and optical communication, this method shows great promise due to its control and stability.

23 pages, 15 figures

References in corpus (8)