Optical fiber containing an alkali metal oxide and methods and apparatus for manufacturing same
Disclosed is an optical fiber having a core with an alkali metal oxide dopant in an peak amount greater than about 0.002 wt. % and less than about 0.1 wt. %. The alkali metal oxide concentration varies with a radius of the optical fiber. By appropriately selecting the concentration of alkali metal oxide dopant in the core and the cladding, a low loss optical fiber may be obtained. Also disclosed are several methods of making the optical fiber including the steps of forming an alkali metal oxide-doped rod, and adding additional glass to form a draw perform. Preferably, the draw preform has a final outer dimension (d2), wherein an outer dimension (d1) of the rod is less than or equal to 0.06 times the final outer dimension (d2). In a preferred embodiment, the alkali metal oxide-doped rod is inserted into the centerline hole of a preform to form an assembly.
1. An optical fiber comprising:
a silica-based core comprising fluorine, and K 2 O in a peak concentration between 20 and 1000 ppm; and
a silica-based cladding surrounding and directly adjacent the core;
wherein the attenuation at 1550 nm is less than 0.185 dB/km.
2. The optical fiber of claim 1 wherein the attenuation at 1550 nm is less than 0.18 dB/km.
3. The optical fiber of claim 1 wherein the attenuation at 1550 nm is less than 0.17 dB/km.
4. The optical fiber of claim 1 wherein the attenuation at 1550 nm is less than or equal to 0.167 dB/km.
5. The optical fiber according to claim 1 wherein the concentration of K 2 O in the core decreases with a radius of the optical fiber.
6. The optical fiber according to claim 1 wherein the peak concentration of K 2 O in the core is greater than about 20 ppm and less than about 700 ppm.
7. The optical fiber according to claim 1 wherein the concentration of K 2 O at a radius equal to a mode field radius of the optical fiber is at least about 1 ppm.
8. The optical fiber according to claim 1 wherein the core comprises GeO 2 .
9. The optical fiber according to claim 1 wherein the core comprises a plurality of segments.
10. The optical fiber according to claim 1 wherein the cladding comprises F.
11. The optical fiber according to claim 1 wherein the peak amount of K 2 O in the core is greater than about 20 ppm and less than about 500 ppm.
12. The optical fiber according to claim 1 further comprising an exterior hermetic coating.
13. The optical fiber according to claim 1 wherein the core has a graded refractive index profile and the optical fiber is a multimode fiber.
14. The optical according to claim 1 wherein the dispersion at 1550 nm is between 1 and 6 ps/nm-km.
15. The optical according to claim 1 wherein the dispersion at 1550 nm is between 6 and 15 ps/nm-km.
16. An optical fiber comprising:
a silica-based core comprising fluorine and K 2 O in a peak concentration between 20 and 1000 ppm; and
a silica-based cladding surrounding and directly adjacent the core;
wherein the core has a refractive index profile with a peak relative refractive index, Δ mAx , greater than 0.2%, relative to the cladding.
17. The optical fiber of claim 16 wherein the optical fiber has an attenuation at 1550 nm of less than 0.185 dB/km.
18. The optical fiber of claim 16 wherein the attenuation at 1550 nm is less than 0.18 dB/km.
19. The optical fiber of claim 16 wherein the attenuation at 1550 nm is less than or equal to 0.17 dB/km.
20. The optical fiber of claim 16 wherein the attenuation at 1550 nm is less than or equal to 0.167 dB/km.
21. The optical fiber of claim 16 wherein the fiber is a multimode fiber and the core comprises at least 70 wt % SiO 2 .
22. The optical fiber of claim 16 wherein the core comprises at least 80 wt % SiO 2 .
23. The optical fiber of claim 13 wherein the core comprises at least 90 wt % SiO 2 .
24. The optical fiber of claim 16 wherein the core further comprises chlorine in a peak concentration of less than 3000 ppm.
25. The optical fiber of claim 16 wherein the peak concentration of the K 2 O is less than 700 ppm.
26. The optical fiber of claim 16 wherein the average concentration of the K 2 O is less than 350 ppm.
27. The optical fiber of claim 16 wherein the peak concentration of the K 2 O is less than 500 ppm.
28. The optical fiber of claim 16 wherein the peak concentration of the K 2 O is between 20 and 500 ppm.
29. The optical fiber of claim 16 wherein the peak concentration of the K 2 O is between 30 and 150 ppm.
30. The optical fiber of claim 27 wherein the core further comprises chlorine in a peak concentration less than 3000 ppm.
31. The optical fiber of claim 27 wherein the core has a maximum concentration of fluorine of less than 0.2 wt %.
32. The optical fiber of claim 16 wherein the peak concentration of the K 2 O is between 200 and 500 ppm.
33. The optical fiber of claim 16 wherein the average concentration of the K 2 O is between 100 and 300 ppm.
34. The optical fiber of claim 32 wherein the core has a concentration of fluorine of greater than 0.02 wt %.
35. The optical fiber of claim 32 wherein the core has a concentration of fluorine of greater than 0.15 wt %.
36. The optical fiber of claim 32 wherein the core has a maximum concentration of fluorine of between 0.5 and 1.5 wt %.
37. The optical fiber of claim 32 wherein the core contains no germania.
38. The optical fiber of claim 32 wherein the core further comprises chlorine in a peak concentration less than 500 ppm.