The dissertation presents research outcomes in the field of fiber optics, concerning an innovative free-form approach based on the nanostructurization method to modify refractive index distribution in optical fibers. Nanostructuring is based on the design of the refractive index distribution in optical fibers and a patented technological procedure for the fabrication of such fibers, in which the effective properties of a material are shaped by at least. Based on the above method, it is possible to fabricate high-quality all-glass optical fibers with designed, specific properties. Nanostructuring is also competitive with other technologies of optical fibers’ fabrication due to high flexibility in shaping the distribution of refractive index including breaking the circular symmetry in core and cladding parts. It emerges with additional freedom in shaping the optical properties of the effective material of optical fibers, therefore the method can serve to expand the application potential in e.g. telecommunication, laser, measurement and bio-medical sectors. A comprehensive approach to nanostructured optical fibers is a topic of the project TEAM TECH/2016-1/1 "Nanostructurized microoptical components - towards new functionalities and applications". Presented work results were carried out under the TEAM TECH project.
The main objective of the dissertation is focused on broadening the application potential of free-form refractive index modification in optical fibers based on the nanostructurizaton method, mainly in the telecommunication sector. In the work, was provided an analysis of the advantages and disadvantages of commonly used solutions, including technological limitations, which can be eliminated or improved by using the nanostructuring method. Considering the current research state, and the possibilities of methods used so far, four types of free-form optical fibers were proposed. All structures are composed of pure silica glass elements with appropriate doping levels of germanium dioxide and possibly fluorine. In this way, the refractive index of silica glass can be increased (GeO2) or decreased (F), making it possible to modify the optical fiber parameters. By using these types of glass, the positive aspects of low attenuation and thermal matching during processing are simultaneously preserved. All the presented fibers have been optimized and numerically tested. Two of the proposed fibers were fabricated by a modifiled stack-and-draw technology and studied experimentally.