Optical fibres having a large numerical aperture.

摘要

An optical fibre of germanium-free multi-component glasses having a core glass which has the molecular composition: SiO2: 57.5-65%; (ZrO2+1/2 Y2O3): 0-5%; (MgO + CaO + SrO + BaO + ZnO): 12.5-27.5 on the understanding that MgO: 0-5%, CaO: 0-10%, SrO: 0-7.5%, BaO: 0-15% ZnO: 0-20%, in which, if no BaO is present, the ZnO content is 12,5-20% and, if no ZnO is present, the BaO content is 5-15%, (Li2O + Na2O + K2O) 10-25% having a K2O content which is preferably smaller than half of the total alkali metal oxide content and the cladding glass consists of a silicate glass or a borosilicate glass having a refractive index which is at least 2% lower than the refractive index of the core glass and the viscosity of which at the processing temperature is 0.5 to twice the viscosity of the core glass expressed in Pa.s.