Optical fiber
An optical fiber includes: a core portion; a side core layer surrounding a circumference of the core portion; and a cladding portion surrounding a circumference of the side core layer. Relations, Δ1>ΔClad>Δ2 and 0>Δ2, hold, where Δ1 denotes an average maximum relative refractive-index difference of the core portion with respect to an average refractive index of the cladding portion, Δ2 denotes a relative refractive-index difference of an average refractive index of the side core layer with respect to the average relative refractive index of the cladding portion, and ΔClad denotes a relative refractive-index difference of the average refractive index of the cladding portion with respect to pure quartz glass, Δ1 is 0.24% or more and 0.30% or less, Δ2 is −0.27% or more and −0.08% or less, (Δ1−Δ2) is 0.36% or more and 0.57% or less.
1 . An optical fiber comprising:
a core portion;
a side core layer surrounding a circumference of the core portion; and
a cladding portion surrounding a circumference of the side core layer, wherein
relations, Δ1>ΔClad>Δ2 and 0>Δ2, hold, where Δ1 denotes an average maximum relative refractive-index difference of the core portion with respect to an average refractive index of the cladding portion, Δ2 denotes a relative refractive-index difference of an average refractive index of the side core layer with respect to the average relative refractive index of the cladding portion, and ΔClad denotes a relative refractive-index difference of the average refractive index of the cladding portion with respect to pure quartz glass,
Δ1 is 0.24% or more and 0.30% or less,
Δ2 is −0.27% or more and −0.08% or less,
(Δ1−Δ2) is 0.36% or more and 0.57% or less,
b/a is 2 or larger where a core diameter of the core portion is 2a and an outer diameter of the side core layer is 2b,
the optical fiber has an effective core area of 107 μm 2 and larger and 130 μm 2 or smaller, at a wavelength of 1550 nm,
b/a is 4 or smaller, and
the cable cutoff wavelength is 1460 nm or shorter.
2 . The optical fiber according to claim 1 , wherein
the optical fiber has a bending loss of 1 dB/m or smaller at the wavelength of 1550 nm upon bending of the optical fiber at a diameter of 30 mm.
3 . The optical fiber according to claim 2 , wherein the bending loss is 0.5 dB/m or smaller.
4 . The optical fiber according to claim 2 , wherein the cable cutoff wavelength is 1386 nm or longer.
5 . The optical fiber according to claim 1 , wherein ΔClad is less than 0%.
6 . The optical fiber according to claim 1 , wherein the core portion includes a dopant that increases a refractive index of a material that the core portion is made of.
7 . The optical fiber according to claim 1 , wherein (Δ1+ΔClad) is 0.03% or more and 0.18% or less.