Optical fiber
An optical fiber includes a core portion made of silica-based glass; and a cladding portion made of silica-based glass having lower maximum refractive index than the core portion, the cladding portion surrounding an outer periphery of the core portion. The core portion is doped with an alkali metal element and chlorine. An average concentration of chlorine is higher than 800 atomic ppm on a cross-section perpendicular to a longitudinal direction of the core portion. A region doped with the alkali metal element is larger than a region doped with chlorine at 800 atomic ppm or higher.
1 . An optical fiber comprising:
a core portion made of silica-based glass; and
a cladding portion made of silica-based glass having a maximum refractive index lower than the core portion, the cladding portion surrounding an outer periphery of the core portion, wherein the core portion is doped with an alkali metal element and chlorine,
an average concentration of the chlorine is higher than 900 atomic ppm and lower than 3000 atomic ppm on a cross-section of the core portion perpendicular to a longitudinal direction, and a region of the core portion doped with the alkali metal element is larger than a region of the core portion having a chlorine concentration of 800 atomic ppm or higher,
a ratio of a diameter of a substantially circular region doped with the alkali metal element to a diameter of a substantially circular region of the core portion having a chlorine concentration of 800 atomic ppm or higher is greater than 1.0,
the substantially circular region doped with the alkali metal element and the substantially circular region of the core portion having a chlorine concentration of 800 atomic ppm or higher are centered at a center of the core portion, and
an average concentration of the alkali metal element is equal to or higher than 10 atomic ppm and equal to or lower than 100 atomic ppm.
2 . The optical fiber according to claim 1 , wherein a region in the cladding portion adjacent to the core portion is doped with a refractive-index reducing dopant that reduces a refractive index of the silica-based glass.
3 . The optical fiber according to claim 2 , wherein the refractive-index reducing dopant is any one of fluorine and fluorine compound.
4 . The optical fiber according to claim 1 , wherein the alkali metal element is potassium.
5 . The optical fiber according to claim 1 , wherein the average concentration of the chlorine is 1000 atomic ppm or higher.
6 . The optical fiber according to claim 1 , wherein the average concentration of the alkali metal element is equal to or lower than 60 atomic ppm.
7 . The optical fiber according to claim 1 , wherein at least one of peaks of concentration of the alkali metal element is positioned at a position different from a peak of concentration of the chlorine.
8 . The optical fiber according to claim 7 , wherein the peak of the chlorine is positioned at a center of the core portion or at a vicinity of the center.
9 . The optical fiber according to claim 1 , wherein the optical fiber has a step-index type refractive index profile.
10 . The optical fiber according to claim 1 , wherein the optical fiber has a W-shaped refractive index profile.
11 . The optical fiber according to claim 1 , wherein the optical fiber has a trench type refractive index profile.
12 . The optical fiber according to claim 1 , wherein a transmission loss at a wavelength of 1550 nm is equal to or lower than 0.185 dB/m.
13 . The optical fiber according to claim 1 , wherein light of a wavelength of 1550 nm is propagated in single mode, and an effective core cross-sectional area at a wavelength of 1550 nm is equal to or smaller than 160 μm 2 .
14 . The optical fiber according to claim 2 , wherein the average concentration of the chlorine is 1000 atomic ppm or higher.
15 . The optical fiber according to claim 3 , wherein the average concentration of the chlorine is 1000 atomic ppm or higher.
16 . The optical fiber according to claim 4 , wherein the average concentration of the chlorine is 1000 atomic ppm or higher.
17 . The optical fiber according to claim 1 , wherein:
the substantially circular region in which the alkali metal element is present at a concentration of 0.1 atomic ppm or higher has a first diameter, and
the substantially circular region having a chlorine concentration of 800 atomic ppm or higher has a second diameter, and a ratio of the first diameter to the second diameter is equal to or greater than 1.2.