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Fine-tuning of the optical properties of hollow-core light cages using dielectric nanofilms

Jang, Bumjoon; Gargiulo, Julian; Ziegler, Mario; Fatobene Ando, Ron; Hübner, Uwe; Maier, Stefan A.; Schmidt, Markus A.
in: Optics Letters (2020) 169

Here, we show that the optical properties of direct-laser-written on-chip hollow-core waveguides—so-called light cages—can be controlled to a very high degree by dielectric nanofilms. Using low-temperature atomic layer deposition (ALD), alumina nanofilms are concentrically deposited on the high-aspect strands that surround the central air core and confine the light via the anti-resonant effect. In accordance with modal cutoff simulations without any free parameters, a linear spectral shift of the resonances with increasing film thickness is experimentally observed. The phenomenon is explained by a shift in the dispersions of cladding supermodes. As neither cage geometry nor polymer is affected by the film deposition, our results suggest ALD to be an essential tool for fine-tuning the properties of hollow-core light cages and to protect them from aggressive substances, being relevant for, e.g., bioanalytics or quantum technology.

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