Internal Ceramic Protective Coating of Hollow-Core Fibers

To optimize the use of hollow-core photonic crystal fibers (HC-PCF), their cores are filled with an atomic gas for an ultra-enhanced interaction with an incident laser beam in applications such as atomic vapor microcells. One challenge in these gas-filled HC-PCFs is to control the physiochemical interactions between the gas medium and the silica inner surface of the fiber core surround. In this work, thus, the processing of ceramic coatings on glass substrates by chemical solution deposition is focused on. Also, the successful implementation of an original coating procedure for a deposition inside hollow-core fibers with complex microstructures is described. It is indeed possible to form a thin, dense, inorganic, and amorphous layer with a low thickness, low roughness, and high transparency. To obtain such a result, several parameters must be controlled, including the concentration of the solution, the technique and the deposition time, as well as the heat treatment undergone by the fiber. In particular, the selected aluminosilicate coatings, which are nonporous and present a 20-30 nm thickness, demonstrate a considerable improvement of the lifetime properties of the fibers filled with rubidium vapor, without modifying its original guiding properties. In this work, the deposition of ceramic coatings at the inner core of hollow-core photonic crystal fibers, the goal being to avoid gas/surface interactions and increase their lifetime, is described. The thin, dense, inorganic, and amorphous films are deposited from sol-gel-based solutions. In addition, their transmission is not different from the original fiber, demonstrating that they can be used as protective coatings in atomic vapor microcells.image (c) 2024 WILEY-VCH GmbH