Experimental investigation on liquid-phase fabrication techniques for multilayer infrared hollow fiber

Infrared hollow fiber with metal and dielectric inner-coatings has found applications in medical and industrial fields. It is a commonly used method to lower the loss by inner-coating multi dielectric layers. In this paper, SiO2 and AgI were selected to fabricate the multilayer mid-infrared hollow fiber. Liquid-phase coating techniques were experimentally discussed in order to control the film thickness. It is shown that concentration and flow speed of the coating solution are key parameters to modify SiO2 film thickness. AgI film was obtained by firstly coating a silver layer and then iodinating the silver layer into AgI. SiO2 and AgI films were deposited orderly on the inner wall of a 0.7-mm bore glass capillary. Both thicknesses for SiO2 and AgI films were well controlled and optimized according to the theoretical calculation. The measured infrared loss spectrum of SiO2/AgI/SiO2/Ag multilayer hollow fiber has a good agreement with the calculated result and shows band gap effect around the wavelength of 5.3 μm.

► Improved liquid-phase coating techniques for smooth silver, SiO2 and AgI films on the inner wall of capillary.
► Optimum film thickness and precise thickness control for low-loss transmission at mid-infrared wavelength.
► Band gap effect at the wavelength of 5.3 μm for the multilayer hollow fiber.