Reduction of absorption losses in ZrF4-based IR fibres

By incorporating oxidising gases into the melt atmosphere during the fabrication of ZrF4-based IR fibres, it has been possible to reduce absorption due to Fe2+ to extremely low levels. This was accompanied by an increase in loss from Cu2+, but this absorption tails off rapidly beyond 1.5 ¿m. Overall absorption losses have been reduced to the order of 2 dB/km at 2.5 ¿m, estimated to have arisen from other 3d transition metals and some rare earths.