Optical properties of fluoride glasses

Some of the current status of optical properties of fluoride glasses and fibers are reviewed in this paper. Fluoride glasses possess various desirable optical characteristics, such as a broad transparency range spanning the mid-IR to near-UV, low refractive index and dispersion, low intrinsic Rayleigh scattering, and the potential for ultra-low attenuation in optical fibers. The intrinsic minimum attenuation in fluoride glass fibers is predicted to be as low as 10−3 dB/km at about 3 μm wavelength range. The lowest attenuation measured to date is 0.7 dB/km at 2.6 μm, which is still 2 orders of magnitude higher than the predicted one. The extensive efforts are being made to reduce the extrinsic absorption caused by transition metals and OH ions, and extrinsic scattering caused by imperfections such as microcrystals, phase separation and oxide inclusions.