1 Perspective and overview.- 1.1 Introduction.- 1.2 Optical fibre fundamentals.- 1.3 Loss mechanisms in optical fibre materials.- 1.3.1 Power losses and units.- 1.3.2 Extrinsic and intrinsic loss mechanisms.- 1.3.3 Intrinsic transparency: mechanisms and models.- 1.4 Long wavelength fibre materials.- 1.4.1 Materials, choices and sources of information.- 1.4.2 Silica-based fibres.- 1.4.3 Crystalline fibre materials.- 1.4.4 Chalcogenide glasses.- 1.4.5 Hollow infrared waveguides.- 1.5 Fluoride glasses and optical fibres.- 1.5.1 Concepts, definitions and materials.- 1.5.2 Fluoride fibre technology: a brief personal history.- 1.6 Applications for infrared optical fibres.- 1.7 Future prospects.- References.- 2 Properties of fluoride glasses.- 2.1 Introduction.- 2.2 Glass-forming systems, structure and crystallization.- 2.2.1 Structural models.- 2.2.2 Crystallization behaviour.- 2.3 Thermal properties.- 2.3.1 Viscosity.- 2.3.2 Thermal expansion behaviour.- 2.3.3 Diffusion.- 2.3.4 Thermal conductivity.- 2.3.5 Heat transfer.- 2.4 Other properties.- 2.4.1 Density.- 2.4.2 Gas solubility.- 2.4.3 Elastic moduli.- 2.4.4 Microhardness.- 2.5 Optical properties.- 2.5.1 Infrared absorption.- 2.5.2 Ultraviolet absorption.- 2.5.3 Intrinsic scattering loss.- 2.5.4 Minimum intrinsic losses.- 2.5.5 Refractive index and dispersion.- 2.5.6 Fluorescence.- References.- 3 Propagation in optical fibres.- 3.1 Introduction.- 3.2 Multimode fibres.- 3.2.1 Propagation in multimode fibres.- 3.2.2 Attenuation.- 3.2.3 Real fibres and fibre links.- 3.3 Monomode fibres.- 3.3.1 Propagation in monomode fibres.- 3.3.2 Optimized fibre design.- 3.3.3 Non-linear effects.- References.- 4 Manufacture of infrared fibres.- 4.1 Materials preparation.- 4.1.1 Introduction.- 4.1.2 Synthetic routes.- 4.1.3 Purification.- 4.2 Melting techniques.- 4.2.1 Melting environments.- 4.2.2 Containment vessels.- 4.2.3 Reactive atmosphere processing.- 4.2.4 Homogenization and fining.- 4.2.5 Crystallization.- 4.3 Fibre fabrication.- 4.3.1 Glass compositions.- 4.3.2 Glass melting.- 4.3.3 Preform fabrication.- 4.3.4 Fibre drawing.- 4.3.5 Other techniques.- 4.3.6 Monomode fibre.- 4.4 Problems.- 4.5 Fibre results.- References.- 5 Intrinsic loss measurements.- 5.1 Introduction.- 5.2 Rayleigh scattering.- 5.3 IR multiphonon edge.- 5.4 Minimum intrinsic loss.- 5.5 Longer wavelength transmitting fibres.- References.- 6 Extrinsic absorption.- 6.1 Introduction.- 6.2 Spectrometer measurements.- 6.2.1 Nomenclature.- 6.2.2 Experimental.- 6.3 Absorption due to water.- 6.3.1 OH- in oxide glasses.- 6.3.2 OH- in fluoride glasses.- 6.3.3 OH- in ZrF4 IR fibres.- 6.4 Absorption due to transition metal ions.- 6.4.1 Introduction.- 6.4.2 Oxidation-reduction equilibrium.- 6.4.3 Ligand field theory.- 6.4.4 Absorption spectra.- 6.4.5 Discussion.- 6.5 Absorption due to rare earth ions.- 6.5.1 Introduction.- 6.5.2 Oxidation states.- 6.5.3 Electronic spectra.- 6.5.4 Absorption spectra.- 6.5.5 Discussion.- 6.6 Other impurities.- 6.6.1 Dissolved gases.- 6.6.2 Molecular ions.- 6.6.3 Reduced species.- 6.6.4 Oxide absorption.- References.- 7 Extrinsic scattering.- 7.1 Introduction.- 7.2 Identification of scattering centres.- 7.2.1 Large crystals.- 7.2.2 Gas bubbles.- 7.2.3 Sub-micron centres.- 7.2.4 Deviations of fibre geometry.- 7.3 Scattering theory.- 7.4 Scattering solutions for limiting cases.- 7.4.1 Small spheres, intermediate index (Rayleigh scattering).- 7.4.2 Small high index spheres.- 7.4.3 Intermediate size spheres with m close to 1 (Rayleigh-Gans).- 7.4.4 Intermediate size sphere with higher refractive index.- 7.4.5 High index (conducting) spheres of small size.- 7.4.6 High index spheres of intermediate size.- 7.4.7 Large spheres with index close to 1.- 7.4.8 Large spheres with high refractive index.- 7.5 Solutions for metallic (absorbing) spheres.- 7.6 Applications to practical examples.- 7.7 Calculations of scattering loss.- 7.8 Scattering loss in fibres.- 7.9 Conclusions.- References.- 8 Measured losses in fibres.- 8.1 Introduction.- 8.2 Available techniques.- 6.2.1 Sources and detectors.- 8.2.2 Total loss.- 8.2.3 Absorption.- 8.2.4 Scattering.- 8.3 Total loss.- 8.4 Absorption.- 8.5 Scattering.- 8.6 Recent results.- 8.7 Predicted minimum loss.- References.- 9 Mechanical properties.- 9.1 Introduction.- 9.2 Fracture and glass parameters.- 9.3 Strength measuring methods.- 9.3.1 What is strength?.- 9.3.2 Tensile measurements.- 9.3.3 Bend measurements.- 9.4 Fibre strengths.- 9.4.1 Mechanical polishing.- 9.4.2 Chemical polishing.- 9.5 Identification of flaws and effect on strength.- 9.6 Ultimate strength and maximum practical strength.- 9.7 Strength and homogeneous crystal growth.- 9.8 Durability.- 9.8.1 Zero stress aging.- 9.8.2 Dynamic fatigue.- 9.8.3 Hermetic coatings.- 9.9 Conclusions.- References.- 10 Applications.- 10.1 Mid-IR communication systems.- 10.1.1 System demonstrations.- 10.2 Active fibres.- 10.2.1 Fibre devices.- 10.2.2 Absorption and fluorescence spectra.- 10.2.3 Fluoride fibre lasers.- 10.2.4 Upconversion.- 10.3 Laser surgery.- 10.4 Infrared fibre sensors.- 10.4.1 IR fibre chemical sensors.- 10.4.2 IR fibre non-chemical sensors.- References.