Patent ID: 6882788

Claim:
An optical fibre mainly consisting of silica glass, which fibre comprises: i) an inner core having a first refractive index n1 and a first diameter a; ii) an outer core surrounding the outer circumference of the inner core and having a second refractive index n2 and a second diameter b; and iii) a cladding surrounding the outer circumference of the outer core, which cladding has a third refractive index n3, wherein n1>n2>n3, characterized in that the optical fibre has a zero dispersion wavelength of less than 1500 nm, and in that it meets the following requirements: 0.2 <a/b< 0.55 0.05 <D 2/ D 1<0.3 wherein: D2=((n2−n0)/n2)*100% D1=((n1−n0)/n1)*100% n0=refractive index value undoped silica glass n1=refractive index value doped inner core n2=refractive index value doped outer core, wherein the refractive index n1 is substantially constant in an area surrounding the central axis of symmetry having diameter a′, wherein this maximum refractive index n1 decreases towards the outer core to a value n2 in an area having diameter a, wherein n1>n2 and a′<a<b.