Single mode optical fiber with chlorine doped core and low bend loss

An optical fiber comprising:

• a. a chlorine doped silica core comprising a core alpha α≥10, a core radius r1 and maximum refractive index delta Δ1max % and Cl concentration≥0.9 wt %;
• b. a cladding surrounding the core, the cladding comprising:
• a. an inner cladding region immediately surrounding the core and comprising first and second cladding regions with respective outer radii r2a and r2 where r2a<r2, the second cladding region comprising a refractive index delta Δ2 with a minimum refractive index delta Δ2min at radius r2a and maximum refractive index delta Δ2max at radius r2 such that Δ2min<Δ2max<Δ1max, and comprising an index slope TS=(Δ2max−Δ2min)/(r2−r1)>0;
• b. an outer cladding region surrounding the first inner cladding region and comprising an outer radius rmax and refractive index delta Δ5, such that Δ2min<Δ5<Δ2max
• c. wherein the optical fiber comprises a mode field diameter MFD at 1310 nm of larger than 9 microns, a cable cutoff wavelength of ≤1260 nm, zero dispersion wavelength λ0, where 1300 nm≤λ0≤1324 nm and bend loss at 1550 nm for a 20 mm mandrel of less than 0.5 dB/turn;
• and
• d. said optical fiber having a core radius r1 such that 3.5 microns≤r1≤5.5 microns and 0.1%≤Δ1max≤0.4%;
• and wherein the inner cladding region comprises an outer radius r2 such that 5 microns≤r2≤20 microns and −0.35%≤Δ2min<0%.