Patent ID: 8588569

Claim:
A single mode optical fiber comprising: a graded index central core region having outer radius r 1 , having a refractive index Δ 1 , a maximum refractive index Δ 1max and having an alpha profile, alpha core , of 0.5≦alpha core ≦4; a cladding region comprising (i) a first inner cladding region having an outer radius r 2 ≦10 microns and refractive index Δ 2 and 0.65≦r 1 /r 2 ≦1; (ii) and a second inner cladding region having an outer radius r 3 >10 microns and comprising a refractive index Δ 3 and a minimum refractive index Δ 3min , wherein said second cladding region has a refractive index delta that becomes more negative with increasing radius, wherein said second cladding region has an alpha profile, alpha t , of 0.5≦alpha t ≦5; (iii) an outer cladding region surrounding the inner cladding region and comprising refractive index Δ 4 , wherein Δ 1max >Δ 2 >Δ 3min , and Δ 3min <Δ 4 ; and wherein 0.5≦(r 3a −r 2 )/(r 3 −r 2 )≦1, where r 3a is a distance from fiber centerline where Δ 3 first reaches the value Δ 3min .