Capillary optical fibers based on SiO 2 –TiO 2 –P 2 O 5 and TiO 2 –P 2 O 5 internal coatings prepared by sol-gel method

This paper presents a novel approach to the preparation of capillary optical fibers using sol-gel method. It employs a novel modification of sol-gel techniques for the application of layers onto the inner walls of silica tubes. This modification was employed for the preparation of multilayer internal coatings of silica tubes which consist of alternating low-index layers of silica and high-index layers containing titania. Novel materials, namely silica-titania-phosphorus pentoxide and titania-phosphorus pentoxide prepared by the sol-gel method, were used in the high-index layers. Morphology and optical properties of single layers of all the materials applied on glass slides are presented as well as the optical properties of multilayer coatings inside silica tubes. The internally coated tubes were drawn into fibers with air and solid cores. Characteristics of the prepared fibers are also shown in the paper. Fibers with optical losses below 0.02 dB/cm have been prepared. Graphical Abstract Sols for the fabrication of SiO 2 -TiO 2 -P 2 O 5 and TiO 2 -P 2 O 5 thin films were prepared. The films were applied inside silica tubes alternating with SiO 2 films by using a novel modified dip-coating technique. Capillary optical fibers with minimum optical losses below 0.02 dB/cm were drawn from the tubes.