Abstract: The material of silver halide was ultrapurified by horizontal zone melting purification in reacting
chlorine atmosphere. The chlorine atmosphere was made by decomposed chlorocarbon with low boiling point [CH_nCl_4-n(n=0,1,2)].
The purification parameters were as follows: temperature 450～500℃, speed of zone 0.2～0.8mm/min and the carrier gas Ar 80～160mL/min. Measurement results show that the infrared absorbance
of silver halide will decrease as wavelength increases at 2.5～12.5μm (4000～800cm^-1) after the ultrapurification. The silver halide fiber is
a well transparent medium for transmitting middle infrared at 2.5～16μm (4000～600cm^-1). Forurier transform infrared
spectra (FTIR) show that the transmittance of the fiber is better at 3.3～16μm. The loss is 0.3～0.5dB/m at 10.6μm.

Key words: infrared optical fiber, silver halide, ultrapurification