Fluoride glass fibers

Fluoride glass fibers have been first intensively developed for long haut telecommunication applications due to their ultra low theoretical optical loss (0.001 dB/km). After many years of intensive research, unfortunately, this goal has not been reached yet and remains a challenge. In the late nineties, the research activities around fluorides glasses and fibers have slowed down and only a few laboratories continue to have some ongoing activity focusing mainly on short and medium length applications such as fiber lasers, Supercontinuum, spectroscopy and laser power delivery. Glass formation seems to be rather more common in fluoride systems than theoretically expected. Glass and fibers properties could be easily tailored by choosing fluoride glass family and by adjusting the composition. For example, numerical aperture can be linearly adjusted from 0.05 to 0.45 and rare-earth concentration can be adjusted from few hundreds ppm to tens of thousands ppm. Rare-earth concentration is limited to few hundreds of ppm in other glass hosts such as silica and chalcogenide glasses. Standard fluoride glass fibers are made from zirconium fluoride glasses, commonly called ZBLAN. They have been intensively studied and used in many infrared applications. ZBLAN fibers have a transmission window from 0.3 um to 4.3 um. They have low loss and high strength. For application up to 5.5 microns, one can use indium fluoride. Indium fluoride glass fibers have a transmission window from 0.3 to 5.5 microns, much larger than ZBLAN fiber´s window, without any absorption peaks.