Drawing of fluoride glass fibers in NF3

Abstract

Due to their low intrinsic optical loss in the infrared wavelength region, optical fibers drawn from heavy-metal fluoride glasses are currently under development for optical signal processing, technological processing and medical engineering apphcations. The susceptibility of these glasses to crystallization induced by hydrolysis, however, reduces the strength of the drawn fibers. A process designed for the fabrication of high-strength fluoride glass fibers is described. The strength of fibers drawn from glasses of the compound systems ZrF4 · BaF2 · LaFs · AIF3 (ZBLA) and ZrF4 · BaF2 · LaF3 · AIF3 · NaF (ZBLAN) was measured by a bending method. Glass surface damage was significantly reduced by adding NF3 to the furnace atmosphere, which increased the strength of ZBLAN fibers by about 40 % and that of ZBLA fibers by even about 75 %. ZBLA fibers drawn in an atmosphere containing fluorine exhibit a mean bending strength in the order of 1400 MPa, which is almost the strength level of smoothly etched fibers. The strength of the fibers that have been etched in a ZrOCl2 solution is shown to be correlated with the light scattering of the preform; it was found to be possible to make fluoride glass fibers with a mean bending strength of at least 1600 MPa.