Optical fiber

1. An optical fiber comprising:

a core;

a depressed layer surrounding the core; and

a cladding surrounding the depressed layer,

wherein a refractive index profile of the core is an α-th power distribution having an index α of 1.0 or more and 2.9 or less,

wherein a relative refractive index difference Δ − of the depressed layer with respect to the cladding has an absolute value |Δ − | that is 0.05% or more and 0.15% or less,

wherein a ratio r1/r2 of a radius r1 of the core to an outer radius r2 of the depressed layer is 0.35 or more and 0.60 or less,

wherein a cable cutoff wavelength λcc of 22 m is less than 1.26 μm,

wherein a mode field diameter at a wavelength of 1.31 μm is larger than 8.6 μm and smaller than 9.5 μm and

wherein the index α is obtained by calculating the α-th power distribution that minimizes a square error of an actual refractive index profile n′(r) of the optical fiber in a range of 0 ≤r≤r0,

where r is a distance from a central axis of the optical fiber, and r0 is a radius of the optical fiber for obtaining a minimum value of a first order differential dn′(r)/dr of n′(r).

2. The optical fiber according to claim 1 ,

wherein the ratio r1/r2 is 0.40 or more and 0.60 or less.

3. The optical fiber according to claim 1 ,

wherein a loss increase at a wavelength of 1.55 μm is less than 0.03 dB when the optical fiber is wound 10 times around a cylindrical mandrel with a radius of 15 mm,

wherein a loss increase at a wavelength of 1.625 μm is less than 0.1 dB when the optical fiber is wound 10 times around a cylindrical mandrel with a radius of 15 mm,

wherein a loss increase at a wavelength of 1.55 μm is less than 0.1 dB when the optical fiber is wound once around a cylindrical mandrel with a radius of 10 mm, and

wherein a loss increase at a wavelength of 1.625 μm is less than 0.2 dB when the optical fiber is wound once around a cylindrical mandrel with a radius of 10 mm.

4. The optical fiber according to claim 1 ,

wherein any one condition is satisfied from the group consisting of:

a value of a zero dispersion wavelength ZDW is 1.305 μm or more and 1.319 μm or less;

a value of a zero dispersion slope is 0.092 ps/km/nm 2 or less; and

a value of chromatic dispersion at a wavelength of 1.55 μm is 18.00 ps/km/nm or less.

5. The optical fiber according to claim 1 ,

wherein the index α is 1.0 or more and 2.2 or less, and the absolute value |Δ − | is 0.08% or more and 0.15% or less.

6. The optical fiber according to claim 5 ,

wherein a loss increase at a wavelength of 1.55 μm is less than 0.03 dB when the optical fiber is wound 10 times around a cylindrical mandrel with a radius of 15 mm,

wherein a loss increase at a wavelength of 1.625 μm is less than 0.1 dB when the optical fiber is wound 10 times around a cylindrical mandrel with a radius of 15 mm,

wherein a loss increase at a wavelength of 1.55 μm is less than 0.1 dB when the optical fiber is wound once around a cylindrical mandrel with a radius of 10 mm,

wherein the loss increase at a wavelength of 1.625 μm is less than 0.2 dB when the optical fiber is wound once around a cylindrical mandrel with a radius of 10 mm,

wherein the loss increase at a wavelength of 1.55 μm is less than 0.5 dB when the optical fiber is wound once around a cylindrical mandrel with a radius of 7.5 mm, and

wherein the loss increase at a wavelength of 1.625 μm is less than 1.0 dB when the optical fiber is wound once around a cylindrical mandrel with a radius of 7.5 mm.

7. The optical fiber according to claim 1 ,

wherein the ratio r1/r2 is 0.40 or more and 0.55 or less.

8. The optical fiber according to claim 1 ,

wherein the mode field diameter at a wavelength of 1.31 μm is 8.8 μm or more and 9.2 μm or less.