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arXiv · 2610.32494

From Hollow Waveguides to Mie Voids: Low-Index Light Confinement

Dominik Ludescher·Ivan Toftul·Harald Giessen·Yuri Kivshar·Mario Hentschel
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Abstract

The confinement of light within optically thin media challenges the conventional view that optical localization requires high-index dielectric materials and total internal reflection. Over the past decades, a broad range of photonic phenomena has demonstrated that electromagnetic energy can also be guided and localized inside low-index regions or nanoscale void cavities. What first appears to be a curiosity is, in fact, highly relevant: The interaction between light and matter lies at the heart of much in optics and photonics. It enables sensing, nonlinear optical phenomena, and optical manipulation, yet it also inevitably introduces absorption, dissipation, and loss. Pushing localized, enhanced, or guided energy into a lower-index space thus offers entirely new possibilities for light-matter interaction and dispersion control. In this review, we discuss some of these counterintuitive structures, starting with light guidance within optically thin media, such as hollow-core photonic crystal fibers or antiresonant reflecting optical waveguides. We then discuss the optics of bubbles, that is, low-index inclusions in a higher-index surrounding, and ultimately arrive at the so-called Mie void resonators, optical resonators that support localized electromagnetic modes confined within a region of lower refractive index. All these systems demonstrate that there are (resonant) optics beyond simple total internal reflection. Absence can itself become a functional photonic degree of freedom, opening opportunities across sensing, quantum nanophotonics, metasurfaces, and programmable optical matter.

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Dominik Ludescher, Ivan Toftul, Harald Giessen, Yuri Kivshar, Mario Hentschel. 2026-10-23. From Hollow Waveguides to Mie Voids: Low-Index Light Confinement. https://arxiv.org/abs/2610.32494

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