Research Project: Kızılötesi frekanslarda aktif matelens geliştirilmesi ve fotonik uygulamaları
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Contributors
Funders
ID
TB.00565
Authors
Ramazanoğlu, Serap Aksu
Faculty Member
Publications
Polarization filtering with isomaterial multifocal metalenses at ultraviolet frequencies
(Nature Portfolio, 2025) Ali, Farhan; Yazdaanpanah, Ramin; Ramazanoğlu, Serap Aksu; Yazdaanpanah, Ramin; Ali, Farhan; Korkmaz, Semih; Department of Physics; Graduate School of Sciences and Engineering; Yes; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
The growing demand for complex nanophotonic devices that operate in the ultraviolet (UV) range necessitates the development of innovative compatible optical devices, particularly for use in lithography applications. In this context, we introduce the first non-contrast dielectric flat metalenses that offer tunable multi-focal polarization channeling in the UV region. The metalens we have developed consists of equally spaced Al\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_3$$\end{document} nanoblocks carved on an Al\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_3$$\end{document} substrate. We demonstrate that controlling the arrangement of nanoblocks on the substrate provides a sufficient geometric phase (Pancharatnam-Berry phase) for developing spatially tunable quadruple-focal metalens in the UV region. While illuminating with the linear polarized light, precise manipulation of the phase profile generates multiple tightly confined focal points, where each possesses different controllable circular polarization states. This feature makes the offered approach a suitable strategy for spatially controlled polarization filtering and channeling. Our design also shows high polarization conversion efficiency in the whole UV spectrum. As proof of concept, we show the focusing characteristics of our designed metalens at four chosen wavelengths. This study demonstrates a promising basis for further development of UV nanophotonic devices and potentially opens up new opportunities for future employment of flat optics in a variety of industrial applications in the UV range.
Tackling the focal shift effect for metalenses
(IOP Publishing Ltd, 2024) Ali, Farhan; Ramazanoğlu, Serap Aksu; Yazdaanpanah, Ramin; Department of Physics; Graduate School of Sciences and Engineering; Yes; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
We present a theoretical analysis aimed at comprehending and mitigating the focal shift phenomenon in planar dielectric metalenses. To conduct this analysis, we introduce metalens designs consisting of silicon and germanium nanoblocks on a calcium fluoride substrate, operating in the mid-IR frequency range. The lensing performance of these metalenses is investigated using the finite-difference time-domain method, and they operate at wavelengths of 3 and 4 mu m with a polarization conversion efficiency close to unity. Our findings indicate a strong correlation between the focal shift phenomena on dielectric metalenses and the numerical aperture (NA), revealing that increasing the Fresnel number is not always an effective approach to minimizing the focal shift. In contrast to previous studies, we define a critical NA, independent of the lens size, where the focal shift reaches a minimum, resulting in a symmetric focal intensity distribution and ultimately yielding a better-performing metalens. We demonstrate that for NAs greater than the determined critical value, a positive focal shift is observed on planar metalenses, diverging from the conventional negative shift predicted by existing models. Additionally, we show that by selecting a metalens within a specific NA range and with smaller diameters, high focusing efficiencies can be achieved. The focusing efficiency of the studied metalenses is measured as high as 70%, marking one of the best values reported for the IR range to date. These results serve as a guide for improving the agreement between experimental and designed metalens features, enhancing their practical applications.
