| 摘要 |
PURPOSE:To prepare optical fibers having uniform core diameter in the long direction, improved characteristics and a retained plane of polarization, by heating a quartz tube having a glass film for forming a clad and core in the interior thereof, and collapsing the interior while reducing the pressure of the interior. CONSTITUTION:A low-melting glass film 2 of 200mum thickness having a lower refractive index than quartz glass is formed on the inner wall of a quartz glass tube 1, and a glass film 3 of 30mum thickness, doped with fluorine, and having a lower refractive index than the glass film 2 is further formed on the inner surface thereof. Oxygen or an inert gas is passed through the resultant quartz tube 5 while heating the quartz tube 5 to diffuse the fluorine through the inner surface of the glass film 3. The glass film 3 is partially modified to form a core member. The pressure in the interior of the quartz tube 5 is then reduced by a vacuum apparatus 7 to fuse the interior of the quartz tube 5. Thus, the aimed base material for optical fibers having a retained plane of polarization in which the glass film 2 is formed into an ellipse under the reduced pressure. |
