Fabrication of Random Hole Optical Fiber Preforms by Silica Sol-Gel Processing
Ellis, Frederick Paa Kwesi
MetadataShow full item record
Conventional fibers are comprised of a solid glass core and solid glass cladding often protected by a thin polymer sheath. The finely tuned difference in refractive indices, for step index-fibers, is achieved by doping the core with germanium or elements with similar effects. Holey fibers (including photonic crystal fibers) comprise of a pure silica core, and a pure but porous silica cladding of air holes . This provides a huge difference in the refractive indices on the cladding and core without doping. This translates into radiation resistant fibers with very low losses and very robust to high temperatures to mention a few . Several successful attempts have been made for ordered holey optical fibers since the initial publication by Knight et al; random holey optical fibers, which can be just as effective, have yet to be fabricated . Sol-gel processing of silicon alkoxides can be used to fabricate silica monoliths of tailored pore densities and sizes ; this makes the process attractive for random holey fiber preform manufacturing. Similar attempts have been made by Okazaki et al  to make conventional optical fibers. This paper chronicles efforts to make random holey fiber optical preforms from silica sol-gel monoliths, characterized for some structural properties. Silica monoliths can be made by hydrolysis and condensation of TEOS (tetraethylorthosilicate) or TMOS (tetramethylorthosilicate). These can be catalyzed in a single step or two-step process, aged and dried at ambient pressures and temperatures, as well as by supercritical fluid extraction of CO2. Mechanical strengthening techniques as described by Okazaki  have also been employed. The silica gel monoliths are characterized by helium pycnometry and scanning electron microscopy. Various shapes and densities of silica monoliths have been prepared and characterized. Some of these have also drawn into fibers to demonstrate their viability.
- Masters Theses