Fabrication and characterization of calcium aluminate glass fibers

Abstract

Calcium aluminate glasses (CAG) offer excellent chemical durability, high strength, broad spectral transparency, and a refractory nature. This makes them ideal candidates for fiber optic power delivery and sensor systems in the infrared spectrum. CAG also have the potential to form ultra-low loss optical materials. The fabrication of glass optical fibers from CAG was investigated in this study. High quality bulk glasses were obtained from the best industrial sources available. These glasses included silica and baria doped CAG compositions. A preform fabrication method was developed to obtain drawing samples. An optical fiber draw furnace was specially modified to achieve fiber drawing. A novel drawing method was also developed. Solid and hollow CAG waveguides, and CAG core/silica clad waveguides were obtained from drawing preforms. This represents the first successful fiber drawing of this glass system. Teflon coating for optical cladding and strength protection was also investigated. Infrared Spectroscopy was used to assess the attenuation in the drawn fibers. 7 dB/m at 2.7 microns with the baria doped CAG solid waveguide was recorded. This represents the lowest loss documented for fibers fabricated from CAG. Laser power propagation through solid and hollow waveguides was investigated. 24 Watts of CO2 laser power was delivered into a hollow baria doped CAG waveguide. 10.13 J/mm2 of 2.94 microns Erbium YAG laser power was delivered through solid baria doped CAG waveguide. Fiber strength testing was performed on the CAG fibers through four point bend testing. The best strength obtained was 1290 MPa for baria doped CAG. Glass stability was assessed using Differential Thermal Analysis. Fiber surface crystallization products were characterized using Energy Dispersive Analysis, Scanning Electron Microscopy, a specially modified Hot Stage X-Ray, and Guinier Camera X-Ray Analysis. The surface crystallization analysis revealed the formation of Ca3Al2O6 in the silica doped CAG fibers and Ca3Al2O6 and Ba4Al2O7 in the baria doped CAG fibers. Reactive atmosphere processing using propane and NF3 was investigated for reducing the surface crystallization during drawing.%%%%