Single mode optical fiber with particular graded index as well as optical communication system

Single mode optical fibre comprising a first central region having a radius r1, a maximum refractive index value n1 and at least one second ring surrounding said first central region, which second ring has a radius r2 and a minimum refractive index value n2, wherein n2<n1, characterized in that the refractive index value n1 is substantially constant in the first central region having radius r1, and in the second ring having radius r2 the refractive index value decreases in radial direction from n1 to n2 over a distance r1−r2, with the decrease, which is substantially linear, taking place in accordance with the following equation:

• slope=(D1−D2)/(r2−r1), where
• 0.11<slope<0.22, and
• D
• i
• =
• n
• i
• 2
• -
• n
• Cl
• 2
• 2
• ·
• n
• i
• 2
• ·
• 100
• ⁢
• %
• ⁢
• ⁢
• and
• ⁢
• ⁢
• n
• i
• >
• n
• Cl
• ,
• Di=refractive index contrast for position i,
• ni=refractive index of position i,
• nC1=refractive index of an outer fibre cladding,
• wherein a dispersion slope ranges from 0.07 to 0.095 ps/km2 at 1550 nm.