| 摘要 |
PURPOSE:To obtain optical fiber structure which has a zero dispersion wavelength at a 1.5 micron band and has an extremely low transmission loss by forming a core and clad in such a manner that the refractive index at the boundary therebetween decreases gradually from the core toward the clad. CONSTITUTION:A porous base material consisting of the pure silica prepd. by a VAD method is inserted into a furnace kept at 1,100 deg.C. He and Cl2 are kept kept passed as an atmosphere gas in the furnace to decrease substantially the OH groups in the porous base material. Such porous base material is inserted into a furnace kept at 1,400 deg.C and is thereby shrunk. The material is further inserted into a furnace kept at 1,640 deg.C to form the transparent glass base material. A rod stretched from such base material to 3nm outside diameter is prepd. On the other hand, a quartz glass tube which is similarly synthesized by the VAD method, is added with fluorine, has 0.65% specific refractive index difference as compared to quartz and has the gradually decreasing refractive index is prepd. The rod is inserted into such tube and while the tube is heated from the outside, SiF4, Cl2 and O2 are passed to crush successively the tube. The resulted preform is stretched under heating and SiO2 soot is deposited on the outside circumferential part. Such deposited body is subjected to a treatment for adding fluorine and vitrification to transparent glass in a heating treatment furnace. |
