Patent ID: 6073465
Filing Date: 2000-06-13
Classification: C03B,G02B,H01S

Abstract:
A method of making a double-clad optical fibre comprising a substantially single mode core, with an index of refraction n.sub.1, an inner multimode cladding surrounding said core, with an index of refraction n.sub.2, and an outer cladding surrounding said inner multimode cladding, with an index n.sub.3 where n.sub.3 <n.sub.2 <n.sub.1, the position of said core relative to the cross sectional plane of the inner cladding varies continuously along the length of the fibre so that multimode radiation which is launched into said inner multimode cladding is efficiently coupled into said core, comprising the steps of:a) providing a fibre preform of determined length having a core doped with an active lasant material and a multimode inner cladding surrounding said core;b) forming a series of opposing offset V-grooves along the length of said preform;c) drawing said preform into a fibre in which said fibre core is substantially single mode and said fibre inner cladding is substantially multimode and the ratio of areas of said fibre inner cladding to said fibre core is 12:1 to 400:1; andd) forming an outer coating on the drawn fibre.