J. Eur. Opt. Society-Rapid Publ. 2025, 21, 15 Ó The Author( s), published by EDP Sciences, 2025 https:// doi. org / 10.1051 / jeos / 2025009 Available online at: https:// jeos. edpsciences. org
Journal of the European Optical Society-Rapid Publications
EOSAM 2024 Guest editors: Luca De Stefano and Raffaele Velotta
SHORT COMMUNICATION
Thin layer deposition of TiO 2 and PMMA on optical micro or nano fibers for nonlinear optics
Laurent Divay 1, Etienne Eustache 1, Maha Bouhadida 2, Christian Larat 1, Abderrahim Azzoune 3, Jean-Charles Beugnot 4, and Sylvie Lebrun 2,* 1 Thales Research and Technology, 91767 Palaiseau Cedex, France 2 Université Paris-Saclay, Institut d’ Optique Graduate School, CNRS, Laboratoire Charles Fabry, 91127 Palaiseau, France 3 Ecole Militaire Polytechnique, BP 17, Bordj-El-Bahri, Algiers 16111, Algeria 4 Institut Femto-ST, CNRS, Université Bourgogne, Franche-Comté, 25030 Besançon, France
Received 28 January 2025 / Accepted 21 February 2025
Abstract. Over the last twenty years, silica optical tapered micro or nanofibers( called ONF in the following) have been widely exploited for a large range of potential applications in several areas of research for their original properties of light propagation. The high confinement of the optical mode in the uniform part and the presence of a strong evanescent field near the surface make them devices of choice for nonlinear applications. In this paper we study the coating of ONF with nonlinear materials to expand further the possibilities offered by these devices. Two materials are chosen for the coatings, Titanium Dioxyde( TiO 2) and Polymethyl Metacrylate( PMMA). Two processes have been developed for the coatings. Firstly, Atomic Layer Deposition has enabled to deposit controlled thin layers of TiO 2 of several tens of nm on an ONF having a diameter of 1 lm with very low additional losses( 0.5 dB). Secondly, we have realized a multiple layer deposition process to deposit PMMA layers on ONF. With this technique we were able to reach thicknesses of about 100 nm on ONF diameters as small as 1 lm. The encapsulation of a coated tapered fiber in silicone has been conducted, resulting in minimal additional losses, showing great promises from such a treatment. These initial experimental proofs of concept open the way for further experiments in nonlinear optics using functionalized ONF. Potential applications include the development of Raman converters within the evanescent field of the optical propagating mode, as well as experiments that necessitate precise control of phase matching.
Keywords: Atomic Layer Deposition, Silica micro or nanofiber, Nonlinear optics, Titanium Dioxyde coating, Polymethyl Metacrylate coating.
1 Introduction
Optical tapered micro or nanofibers( designed as ONF in the following) are fabricated by heating and stretching standard fibers until the initial diameter of typically 125 lm becomes comparable or smaller than 1 lm. The uniform micrometer or sub-micrometer part whose length can be of around 10 cm is linked to the unstretched fiber ends by conical sections called the tapers( see Fig. 1). The component can therefore be easily inserted in fibered etworks. Over the last twenty years, silica ONF have been significantly exploited for a large range of potential applications in several areas of research [ 1 ], and particularly in nonlinear optics. Indeed, at such diameters, ONF strongly confine light within the silica, enabling the efficient generation of nonlinear effects,
* Corresponding author: sylvie. lebrun @ institutoptique. fr leading for example to supercontinuum sources [ 2 ]. Propagating mode can also present an intense evanescent tail in interaction with the surrounding medium. This property offers a new degree of freedom for the realization of nonlinear effects by changing the surrounding medium. This option has been experimentally demonstrated for ONF immersed in nonlinear liquids to excite Kerr effect in acetone [ 3 ] and to generate Stimulated Raman Scattering( SRS) in ethanol and toluene [ 4 ].
The purpose of this work is to study the coating of ONF with a nonlinear material to expand even further the possibilities offered by its interaction with the evanescent field. Few studies have been reported on the coating of tapered fibers, with sensing as targeted application. In these works, the technique used was Atomic Layer Deposition( ALD), the smallest diameters were ~ 20 – 25 lm and the total length( comprising the uniform part and the two tapers) was
~ 16 – 17 mm [ 5, 6 ]. However, to our knowledge, no study
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