Large effective area high sbs threshold optical fiber

An optical fiber comprising:

• a core having a refractive index profile and a centerline;
• and
• a cladding layer surrounding and directly adjacent the core.
• wherein the core comprises:
• a first portion extending from the centerline to a radius of 1 μm, the first portion comprising a relative refractive index profile, ΔCORE1(r), having a maximum relative refractive index Δ1MAX less than 0.7% and occurring at a radius rΔMAX, wherein Δ1MAX is the maximum relative refractive index ΔMAX for the entire core, wherein ΔΔCORE1(r) is greater than 0.3% and less than 0.6% for all radii between rΔMAX and r=1 μm;
• a second portion surrounding and directly adjacent to the first portion, the second portion comprising a relative refractive index profile ΔCORE2(r) having a minimum relative refractive index Δ2MIN<0.3%, and extending from a radius of 1 μm to a radius of 2.5 μm, wherein ΔCORE2(r) is between 0. 15% and 0.5%, wherein (Δ1MAX−Δ2MIN)>0.25%;
• a third portion surrounding and directly adjacent to the second portion, the third portion comprising a relative refractive index ΔCORE3(r) extending from a radius of 2.5 μm to a radius of 4.5 μm, wherein ΔCORE3(r) is between 0% and about 0.6% and has a maximum relative refractive index Δ3MAX, wherein ΔCORE3 (r=4μm)>0.2%, wherein Δ2MIN<Δ3MAX<Δ1MAX, and wherein (Δ3MAX−Δ2MIN)>0.10%;
• and
• a fourth portion surrounding and directly adjacent to the third portion, the fourth portion having a relative refractive index ΔCORE4(r) extending to a radius of between 4.5 and 12 μm;
• wherein the cladding surrounds and is directly adjacent to the fourth portion, and wherein the core ends and the cladding begins at rCORE>4.5 μm.