All-Optical Varifocal Switching in a Polarization-Insensitive Si--GST Metalens
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866914171478605824 |
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| author | Nath, Dipika Rani Muneer, Sadid Choudhury, Sajid Muhaimin |
| author_facet | Nath, Dipika Rani Muneer, Sadid Choudhury, Sajid Muhaimin |
| contents | 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 Ge$_2$Sb$_2$Te$_5$ (GST) that can reversibly switch 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 μm. The device achieves a variable focal length from 70 μm to 200 μm, 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 approximately 13~ns and crystallization in approximately 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2511_21138 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | All-Optical Varifocal Switching in a Polarization-Insensitive Si--GST Metalens Nath, Dipika Rani Muneer, Sadid Choudhury, Sajid Muhaimin Optics 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 Ge$_2$Sb$_2$Te$_5$ (GST) that can reversibly switch 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 μm. The device achieves a variable focal length from 70 μm to 200 μm, 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 approximately 13~ns and crystallization in approximately 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. |
| title | All-Optical Varifocal Switching in a Polarization-Insensitive Si--GST Metalens |
| topic | Optics |
| url | https://arxiv.org/abs/2511.21138 |