Minimization of OH absorption and scattering losses in zirconium fluoride glasses

Abstract

The most important criterion in maximizing the IR transparency of fluoride glasses for low-loss optical fiber applications is the elimination of the anionic impurities, mainly OH, which enter the glass during the batching and melting processes.1 By analogy with the OH absorption coefficient in silica glass fiber, it was estimated that 1-ppm OH would give rise to a 5000-dB/km loss at 2.9μm in fluoride glass fibers. In addition, particle inclusions, phase separation, and submicron inhomogeneities or crystallization, which result in high scattering losses, must be totally suppressed. Previously the minimum OH absorption loss reported for a fluoride glass fiber was ~1000 dB/km at 2.9 μm2, and the lowest scattering loss contribution for a fluoride glass rod was estimated to be 65 dB/km at 0.633 μm2 In this paper, substantially lower losses have been achieved using reactive atmosphere processing to remove OH and proper melting, refining, and quenching conditions to eliminate scattering imperfections.