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Fluoride glass optical fibres are characterized by a large optical window covering the range 0.4–5 μm which permits excitation and fluorescence spectroscopy in a much more extended domain than with silica-based fibres. The local ligand field acting on the rareearth ions affects the radiative lifetime, phonon relaxation, excited state absorption, and emission peak broadening. Finally, the fibre structure provides excellent optical confinement for observing laser emission in the visible and mid-IR regions at very low threshold power, permitting laser diode pumping. Multiphonon processes are also observed leading to the up-conversion of IR into the visible or UV and making possible the development of new laser sources for optical recording laser printing, optical amplification, medical and optical sensor applications.

The physical properties and characteristics of fluoride glasses suitable for the realization of optical fibers and planar waveguides are given. The planar waveguide technology, novel for this type of material, is presented with more details. Active properties of rare-earth-doped fluoride fibers are presented, especially for up-conversion visible fiber lasers, infrared fiber lasers, and fiber lasers and amplifiers for telecommunication.

Glass formation is investigated in systems based on ZnF 2 , SrF 2 , and BaF 2 and containing a low level of trivalent fluorides such as InF 3 or GaF 3 . Physical properties including characteristic temperatures, optical transmission, refractive indices and densities are reported for the most stable compositions. In these low-phonon-energy glasses, the infrared edge is found to be very sensitive to the indium and gallium contents. The fundamental vibrations of the various glasses are investigated by means of Raman spectroscopy and far-infrared absorption spectroscopy.

In this work we have studied the infrared to visible upconversion luminescence of Nd3+-doped fluoroarsenate glasses with different neodymium concentrations (0.1, 0.5, 2, 3, 4, and 5 mol%) under continuous wave and pulsed laser excitation. Green, orange, and red emissions are observed with excitation at 802 and 874 nm within the 4F5/2 and 4F3/2 levels. In addition, a weak blue emission appears under continuous wave (cw) laser excitation which under pulsed laser excitation only occurs for the most concentrated sample at 77 K. The green, orange, and red emissions can be attributed to transitions from the 4G7/2 excited state. The pump power dependencies of these upconverted emissions together with the shape of the upconverted excitation spectra which are similar to the one-photon absorption spectrum and the temporal behavior of the decays, indicate that an ETU process seems to be responsible for the observed visible luminescence, though other possible mechanisms cannot be disregarded.

Fluorine occupies an original and strategic position in modern optics. The F2 excimer lasers are unrivaled sources of deep UV light for semiconductors, microphotolithography and micromachining which has brought on the development of single crystal calcium fluoride optics. Due to the weak polarisability of the fluoride ion, fluoride materials have low refractive index suitable for thin film antireflective coatings specially in IR optics. Transparent magnesium fluoride ceramics, prepared by fine grains hot pressing, are transparent in the mid IR where the transparency windows of the atmosphere are located. They are used as IR domes for missiles guidance. Fluoride glasses when elaborated as optical fibers or channel waveguides and when doped with appropriate lanthanides, are original optical devices for laser operations lying from the mid IR to the UV region where light emission is characterized by up-conversion phenomena. The same devices have also found industrial applications in telecommunications as a new generation of optical amplifiers operating in the ultra-transparency window of the silica fiber.