Halide Glasses and Chalcogenide Glasses for Ultra Low Loss Fibre Applications — A Comparison

Abstract

Mid infrared transmitting glasses have the potential of becoming the next generation of optical communications fibres. These ultra low loss fibres will need to demonstrate losses of the order of 10⁻² to 10⁻³ dB/km at some particular wavelength between 2.5 and 4.5 μm compared to the present day loss of 0.2 dB/km at 1.55 μm shown by silicate fibres. Candidate glass forming systems are fluoride, fluoride-chloride, chloride, chalcogenide and oxide. The fluoride and fluoride-chloride glasses are leading candidates at the present time largely because major effort has concentrated upon them. The recently reported heavy metal oxide glasses based on bismuth and gallium oxides offer equivalent transmittance range to the fluorides. These oxide glasses are more resistant to devitrification and are likely to be synthesised by the vapour route thus offering a potentially serious challenge to the fluoride glasses for ultra low loss applications if the scatter losses are shown to be acceptably low. The chalcogenide glasses are only likely to be seriously considered for these latter applications if the present drive based on the halide and possibly oxide glasses fails to yield technically acceptable fibres. Thus the chalcogenides are most likely to find use as short length fibres for applications in the far infrared.