| 摘要 |
PURPOSE:To efficiently manufacture preforms for spinning optical fibers by successively forming gelled layers of plural kinds of metallic alkoxide solns. having different compositions on the inner wall of each of silica tubes. CONSTITUTION:By rotating a stand 8 provided with a screw thread 11a, a vessel 13 filled with a metallic alkoxide soln. 14 is vertically moved to charge the soln. 14 into high purity silica tubes 4 through a pipe 15 and a horizontal pipe 2 and to discharge the soln., thereby sticking thin layers of the metallic alkoxide soln. on the inner walls of the tubes 4. Air is introduced into a container 1 at high temp. and humidity from an inlet 6 and fed into the tubes 4 through porous plugs 4a to hydrolyze the metallic alkoxide layers. By the hydrolysis the layers gel and are hardened. Hardened layers are then formed successively on each of said hardened layers with plural kinds of metallic alkoxide solns. having different compositions prepared by adding additives 16a-16c to the metallic alkoxide soln. 14. Thus, preforms for spinning optical fibers whose refractive index changes gradually from the inside toward the outside are manufactured efficiently. |
