| 摘要 |
1500530 Production of optical fibres WESTERN ELECTRIC CO Inc 19 Feb 1975 [22 Feb 1974] 7092/75 Heading C1M In the production of a preform for making a core/cladding glass fibre optical transmission line, wherein the cladding has an index of refraction of a value less than that of the core, a moving stream of a vapour mixture including at least one compound glass-forming precursor together with an oxidizing medium for forming the glass of the core is fed into a glass tube forming the cladding or outer coating therefor, while heating the tube to react the mixture and produce a glassy deposit on the inner surface of the tube, the heating being by a moving hot zone by movement of a heat source relative to the exterior of the tube and the temperature of the hot zone, the vapour mixture composition and the rate of introduction of the vapour mixture being such that at least a part of the reaction takes place within the vapour mixture at a position spaced from the inner walls of the tube to produce a suspension of oxidic reaction product particulate material which comes to rest on the inner surface of the tube as it travels downstream and is fused to form a glassy deposit from a position within the hot zone. The coated tube may be drawn under the influence of the moving heating zone or otherwise conventionally. The glass tube may be vertically positioned, but as shown (Fig. 1), the tube 2 is held in a glass lathe 1 in a horizontal position and rotated, 5a. The tube 2 is heated by heating means 3 mounted for horizontal movement 5b on a support 4 moved by a threaded feed member 6, movement towards the exit 18 of the tube being relatively slow with rapid return movement. The required vapour mixture is introduced into tube 2 by inlet tube 7 fed from any or all of sources 9, 10, 11 and 13; as shown, oxygen is bubbled through liquid reactant material 16, 17 in flasks 14, 15 with additional oxygen through source 9. The preferred glass-forming precursor is a silicon compound and undoped silica or silica doped with B 2 O 3 (to lower the refractive index) is normally used for an initial layer on a pure silica tube followed by silica with dopants such as GeO 2 to increase the refractive index. Hydrides may be used, but should be diluted by inert material such as a carrier gas of N 2 or He. Chlorides are preferred, the inert gas being in small amounts only as a carrier. Examples are given, using Si- Cl 4 + BCl 3 + O 2 initially abruptly or gradually changing to SiCl 4 + GeCl 4 + O 2 or SiH 4 + BH 4 + O 2 changing abruptly or gradually to SiH 4 + GeH 4 + O 2 , with specified volumes and temperatures used. |
