| 摘要 |
<p>A method for controlling the refractive index achieved using a fluorine dopant gas, wherein CF4 is employed as the dopant gas, and the soot preform (12) is doped using the CF4 for a time and temperature sufficient to result in a decrease in fluorine dopant nearest the surface which is in contact with the CF4 gas. Preform (12) is mounted on handle (11) which is fused to handle (14) and the assembly (20) is heated in a furnace muffle (15). The CF4 flows through furnace muffle (15), as indicated by arrows (17), and preferably contains a diluent gas such as helium. An optional centerflow gas (16) may be flowed through the centerline hole (18) in several embodiments, which consists of helium. The end of the porous preform (12) may optionally include a capillary tube (19) to prevent the muffle gases (17) from entering the preform.</p> |
