| 摘要 |
1498907 Optical fibres NIPPON TELEGRAPH & TELEPHONE PUBLIC CORP 17 April 1975 [24 April 1974 30 April 1974] 15927/75 Heading C1M A method of manufacturing optical fibres comprises (a) forming a glass core rod 48 by heating rotatable and movable refractory mandrel 44 at 1600-1800‹ C. by irradiation with CO 2 laser beam 42; ejecting a gaseous mixture 47 of oxygen, the vapour of an oxidizable silicon compound and the vapour of a compound oxidizable to form a dopant oxide for SiO 2 , towards heated mandrel 44, so as to deposit SiO 2 and the dopant oxide thereon; and fusing the deposited oxides; (b) forming a glass cladding layer 55 on said core rod 48 by heating the rod surface at 1600-1800‹ C. by irradiation with CO 2 laser beam 51; ejecting a gaseous mixture 54 comprising oxygen and the vapour of an oxidizable silicon compound towards the surface of core rod 48, so as to deposit SiO 2 thereon; and fusing the deposited oxide; and (c) heating the core/cladding assembly to above the cladding softening temperature, and drawing down the assembly to an optical fibre. The operations of forming the core and providing a cladding therefor may be carried out separately (Figs. I and 2, not shown). Alternatively, as shown in Fig. 3, the core rod 48 is formed on rotating mandrel 44, the mandrel 44 raised at a rate equal to the growth rate of core rod 48, and the cladding 55 applied simultaneously. In a further embodiment (Fig. 4, not shown), the mixture 54 also comprises a vapour of a compound oxidizable to form a dopant oxide for SiO 2 , the concentration of this vapour being gradually reduced so that the composition of cladding 55 changes outwardly until the outer layer is 100% SiO 2 . The silicon compound may be SiCl 4 , and the dopant compound may be aluminium trichloride, triisobutyl aluminium, germanium tetrachloride, titanium tetrachloride, gallium chloride, phosphonyl trichloride or trimethyl gallium. In a preferred embodiment, the core consists of 96 mole per cent SiO 2 and 4 mole per cent Al 2 O 3 and has a refractive index of 1À466, the cladding being 100% SiO 2 (refractive index 1À458). The mandrel 44 may be of fused SiO 2 , and is preferably disposed in an evacuable vessel of fused SiO 2 , which vessel is electrically pre-heated to about 1000‹ C. The mandrel is further heated by the laser beams to 1600-1800‹ C. |
