Abstract: The preparation of high purity raw materials is the foremost section in fabrication of high quality optical fibers. The material of silver halide was ultrapurified by horizontal zone
melting purification in Cl₂ atmosphere. Measurement results show that infrared absorbance will decrease as wavenumber increases at 800～4000cm^-1
after the ultrapurification, and the absorption coefficient of silver halide preform crystal by CO₂ laser calorimeter is less than 5×10^-4cm^-1
at 10.6μm. The absorption coefficient decreases two order of magnitude after ultrapurification. The optical fiber loss is 0.3～0.5 dB/m.

Key words: infrared optical fiber, silver halide, ultrapurification