A PbF2–AlF3 fluoride system has been vitrified in the shape of a ribbon using roller quenching over the composition range 30 to 60 mol% AlF3. The infrared absorption edge of the glass originates from the absorption band of AlF3 in PbF2 around a wavelength of 18 µm. The crystallization temperature is determined by DTA to be 280–350°C, and increases with increasing AlF3 content in the glass. The activation energy of crystallization is found to be about 80 kcal/mol for the PbF2–30 mol% AlF3 glass.

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ABshracr-In order to realize a low-loss fluoride aptical fiber, impurity reduction is indispensable. The methods of recrystalkation, extraction, chemical vapor-phase deposition, distillation, and sublimation were tried to purify the starting materials for a fluoride fiber. These purification methods were evaluated by measuring transmission loss of the fibers prepared by using the purified materials. It was found that recrystallization was useful for reducing impurities in ZrF4 to the level of below 1 ppm. The extraction technique could be also applicable to purificatian of BaF2 and GdF3. It was concluded that the sublimation was the most probable purification in order to prepare fluoride materials with less than 0.1-ppm impurities. As a result, a low-loss fiber with 8.5 dB/km at 2.12 pm was obtained by using the starting materials purified by sublimation. '

Optical spectra for each of the rare earth element doped BaF2-GdF3-ZrF4 glasses were measured. It was found that, in the 2–5 µm wavelength region, Ce, Pr, Nd, Sm, Tb and Dy contribute to the absorption loss and the loss magnitude due to each rare earth element of lppmw is several tens of dB per kilometer at the absorption peaks. It was concluded that the rare earth impurity concentration in fluoride optical fibers should be decreased to less than 0.1 ppbw in order to make the absorption loss 10-3 dB/km in the 3–4 µm wavelength.

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