A large core microstructured fluoride glass optical fibre for mid-infrared single-mode transmission

A microstructured optical fibre based on an alumino-zirco-chloro-fluoride glass has been fabricated in which the light-guiding structure comprises a single ring of air-holes, machined directly into the preform rod using an ultrasonic drill around a large effective solid core. The objective was single-moded transmission of longer mid-infrared wavelengths at high laser power without causing radiation damage to the fibre material. It has been demonstrated that this fibre preserves high laser beam quality and can transmit wavelengths between 2.1 and 4.7 μm, single-moded in an effective core of diameter 79 μm. Optical fibre transmission losses from 1.4 to 10.3 dB m−1 have been measured over this wavelength range. No damage was observed in the fibre at peak pulse power, setting a lower limit of >1 GW cm−2 for the laser damage threshold. Brightness was preserved at wavelengths longer than 4 μm.