Optical fiber with increased bend performance

1. A single mode optical fiber comprising:

a core region having an outer radius r 1 and a maximum relative refractive index Δ 1max ; and

a cladding region surrounding the core region, the cladding region comprising a depressed-index cladding region, a first outer cladding region surrounding the depressed-index cladding region, and a second outer cladding region surrounding the first outer cladding region,

the first outer cladding region having a relative refractive index Δ 4 that is lower than a relative refractive index Δ 5 of the second outer cladding region,

wherein the single mode optical fiber has a bend loss at 1550 nm for a 15 mm diameter mandrel of less than about 0.75 dB/turn, has a bend loss at 1550 nm for a 20 mm diameter mandrel of less than about 0.20 dB/turn, and a bend loss at 1550 nm for a 30 mm diameter mandrel of less than about 0.005 dB/turn, and

wherein the single mode optical fiber has a mode field diameter of 9.0 microns or greater at 1310 nm wavelength and a cable cutoff of less than about 1260 nm.

2. The single mode optical fiber of claim 1 , wherein the mode field diameter is about 9.1 microns or greater.

3. The single mode optical fiber of claim 2 , wherein the mode field diameter is about 9.2 microns or greater.

4. The single mode optical fiber of claim 1 , wherein the mode field diameter is less than about 9.6 microns.

5. The single mode optical fiber of claim 1 , wherein a minimum relative refractive index Δ 3 of the depressed-index cladding region is between about −0.20% and about −0.60%.

6. The single mode optical fiber of claim 1 , wherein the relative refractive index Δ 4 of the first outer cladding region is between about −0.01% and about −0.15%.

7. The single mode optical fiber of claim 1 , wherein the optical fiber cable has zero dispersion wavelength between about 1300 nm and about 1324 nm.

8. The single mode optical fiber of claim 1 , wherein the bend loss at 1550 nm for a 15 mm diameter mandrel is less than about 0.50 dB/turn.

9. The single mode optical fiber of claim 1 , wherein the bend loss at 1550 nm for a 20 mm diameter mandrel is less than about 0.15 dB/turn.

10. The single mode optical fiber of claim 1 , wherein the bend loss at 1550 nm for a 30 mm diameter mandrel is less than about 0.0035 dB/turn.

11. The single mode optical fiber of claim 1 , wherein the first outer cladding region is directly adjacent to the depressed-index cladding region.

12. The single mode optical fiber of claim 1 , where the depressed-index cladding region has a volume V 3 in a range of about 30% Δ-micron 2 to about 70% Δ-micron 2 .

13. The single mode optical fiber of claim 1 , where the first outer cladding region has a volume V 4 in a range of about 3% Δ-micron 2 to about 25% Δ-micron 2 .

14. A method of making a single mode optical fiber, the method comprising:

providing an overclad assembly that forms a central channel;

fire polishing the overclad assembly to form a fire polished layer;

inserting a consolidated core assembly, having a core region and a depressed-index cladding region, into the central channel to form a core-cladding assembly such that a gap is disposed between the consolidated core assembly and the overclad assembly; and

heating the core-cladding assembly while exposing the core-cladding assembly to either (i) an up-dopant to increase the relative refractive index of a portion of the core-cladding assembly that is radially outside of the fire polished layer, or (ii) a down-dopant to decrease the relative refractive index of a portion of the core-cladding assembly that is radially inside of the fire polished layer.

15. The method of claim 14 , wherein the fire polished layer has a thickness between about 50 microns and about 2,000 microns.

16. The method of claim 14 , wherein the fire polished layer (i) prevents diffusion of the up-dopant to portions of the core-cladding assembly that are radially inside of the fire polished layer, and (ii) prevents diffusion of the down-dopant to portions of the core-cladding assembly that are radially outside of the fire polished layer.

17. The method of claim 14 , wherein heating the core-cladding assembly while exposing the core-cladding assembly to either the up-dopant or the down-dopant forms a first outer cladding region, which surrounds the depressed-index cladding region, and a second outer cladding region, which surrounds the first outer cladding region, the first outer cladding region having a relative refractive index Δ 4 that is lower than a relative refractive index Δ 5 of the second outer cladding region.

18. The method of claim 14 , further comprising:

after heating the core-cladding assembly, drawing the single mode optical fiber,

wherein the single mode optical fiber has a bend loss at 1550 nm for a 15 mm diameter mandrel of less than about 0.75 dB/turn, has a bend loss at 1550 nm for a 20 mm diameter mandrel of less than about 0.20 dB/turn, and a bend loss at 1550 nm for a 30 mm diameter mandrel of less than about 0.005 dB/turn, and

wherein the single mode optical fiber has a mode field diameter of about 9.0 microns or greater at 1310 nm wavelength and a cable cutoff of less than about 1260 nm.

19. The method of claim 14 , wherein the single mode optical fiber has a cladding region comprising the depressed-index cladding region, a first outer cladding region surrounding the depressed-index cladding region, and a second outer cladding region surrounding the first outer cladding region.

20. The method of claim 14 , wherein the first outer cladding region has a relative refractive index Δ 4 that is less than about 0.15% lower than a relative refractive index Δ 5 of the second outer cladding region.