Patent ID: 7734136

Claim:
Single mode optical fibre, comprising a first central region having a radius r 1 , a maximum refractive index value n 1 and at least one second ring surrounding said first central region, which second ring has a radius r 2 and a minimum refractive index value n 2 , wherein n 2 <n 1 , characterized in that the refractive index value is substantially constant in the second ring and decreases in radial direction over a distance r 1 from n 1 to n 2 from the central axis of symmetry in the first central region, with the decrease, which is substantially linear, taking place in accordance with the following equation: slope = ( D ⁢ ⁢ 1 - D ⁢ ⁢ 2 ) / ( r ⁢ ⁢ 1 ) , ⁢ where 0.11 < slope < 0.22 , ⁢ D i = n i 2 - n C ⁢ ⁢ 1 2 2 · n i 2 · 100 ⁢ % ⁢ and ⁢ n i > n C ⁢ ⁢ 1 , wherein D i =refractive index contrast for position i, n i =refractive index of position i, and n Cl =refractive index of an outer fibre cladding.