Low loss optical fiber and method for making same
A method of forming an alkali metal oxide-doped optical fiber by diffusing an alkali metal into a surface of a glass article is disclosed. The silica glass article may be in the form of a tube or a rod, or a collection of tubes or rods. The silica glass article containing the alkali metal, and impurities that may have been unintentionally diffused into the glass article, is etched to a depth sufficient to remove the impurities. The silica glass article may be further processed to form a complete optical fiber preform. The preform, when drawn into an optical fiber, exhibits a low attenuation.
1. An optical fiber wherein the core is comprised of SiO 2 and an alkali metal oxide of the form X 2 O where X is selected from the group consisting of K, Na, Li, Cs and Rb and 0.035≦X 2 O≦6 mole percent, wherein said core is further comprised of less than about 100 ppm chlorine and less than about 100 ppb − OH, and wherein an optical attenuation of the optical fiber at a wavelength of 1550 nm is less than 0.18 dB/km.
2. The optical fiber of claim 1 wherein said core is comprised of less than about 50 ppm Cl.
3. The optical fiber of claim 1 wherein said core of said optical fiber is comprised of less than about 20 ppb − OH.
4. An optical fiber, comprising:
SiO 2 and an alkali metal oxide in the form of X 2 O where X is selected from a group consisting of K, Na, Li, Cs and Rb, and GeO 2 ; and
wherein an optical attenuation at 1550 nm is less than 0.18 dB/km.
5. The optical fiber according to claim 4 wherein the alkali metal oxide and the GeO 2 are present in a core of the optical fiber.
6. The optical fiber according to claim 5 wherein a chlorine content in the core is less than 500 ppm.
7. The optical fiber according to claim 6 wherein a chlorine content in the core is less than 100 ppm.
8. The optical fiber according to claim 7 wherein a chlorine content in the core is less than 50 ppm.
9. The optical fiber according to claim 6 wherein a water content in the core is less than 100 ppb.
10. The optical fiber according to claim 9 wherein the water content in the core is less than 20 ppb.
11. An optical fiber, comprising:
a core comprising SiO 2 and an alkali metal oxide in the form of X 2 O and GeO 2 , where X is selected from a group consisting of K, Na, Li, Cs and Rb; and
wherein an optical attenuation at 1550 nm of the optical fiber is less than about 0.18 dB/km.