OPTICAL FIBER PREFORM, METHOD FOR MANUFACTURING THE SAME AND OPTICAL FIBER BY USING THE OPTICAL FIBER PREFORM

摘要

PROBLEM TO BE SOLVED: To provide a large-size optical fiber preform from which an optical fiber with high quality can be produced. SOLUTION: The optical fiber preform 1 is manufactured by forming a glass layer 3 around a center layer 2 to form a porous preform and sintering the porous preform while dehydrating and removing impurities. In the process of manufacturing the glass preform 1, the density of the surface part of the glass layer 3 is controlled to >=0.3 g/cm<3> and <=0.4 g/cm<3> in the process of depositing the glass layer 3. By this method, a gas to remove impurities can easily flow through the glass layer 3 in the succeeding process of removing impurities, and thereby impurities can be easily removed. The concentration of total impurities of aluminum, titanium and vanadium in the surface part of the optical fiber preform can be controlled to >=0.2×10<3> ng/cm<3> and <=16×10<3> ng/cm<3> . Unnecessary crystals are prevented from growing from the impurities as nuclei on the surface of the optical fiber preform 1 and an optical fiber with high quality can be produced.