Hybrid Si–GST polarization-insensitive dynamically tunable bifocal metalens operating at a 1.55μm wavelength

@article{J028,
 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 Ge2Sb2Te5 (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 1.55µm. The device achieves a variable focal length from 70 to 200µm, 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.},
 author = {Dipika Rani Nath and Sadid Muneer and Sajid Muhaimin Choudhury},
 citationnos = {1},
 citesurl = {https://scholar.google.com/citations?view_op=view_citation&hl=en&user=Fu8Hkb4AAAAJ&sortby=pubdate&citation_for_view=Fu8Hkb4AAAAJ:l7t_Zn2s7bgC},
 doi = {10.1364/JOSAB.591582},
 issn = {},
 jif = {1.9},
 journal = {J. Opt. Soc. Am. B},
 keywords = {photonics},
 month = {8},
 number = {8},
 pages = {B239--B250},
 publisher = {Optica Publishing Group},
 sjr = {Q2},
 title = {Hybrid Si--GST polarization-insensitive dynamically tunable bifocal metalens operating at a 1.55μm wavelength},
 url = {https://opg.optica.org/josab/abstract.cfm?URI=josab-43-8-B239},
 volume = {43},
 year = {2026}
}