I/We Claim:
[Claim 1]
An optical fiber comprising:
5 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 a-th power distribution
having an index a of 1.0 or more and 2.9 or less,
10 wherein a relative refractive index difference A- of the depressed layer with
respect to the cladding is set such that an absolute value IA"I is 0.05% or more and 0.15% or less,
wherein a ratio rl/r2 of a radius rl of the core to an outer radius r2 of the
depressed layer is set to 0.35 or more and 0.60 or less,
15 wherein a cable cutoff wavelength Xcc of 22 m is less than 1.26 jam, and
wherein a mode field diameter at a wavelength of 1.31 jam is larger than 8.6 jam and smaller than 9.5 jam.
[Claim 2]
20 The optical fiber according to claim 1,
wherein the ratio rl/r2 is set to 0.40 or more and 0.60 or less.
[Claim 3]
The optical fiber according to claim 1 or 2,

wherein a loss increase at a wavelength of 1.55 jam when the optical fiber is wound 10 times around a cylindrical mandrel with a radius of 15 mm is less than 0.03 dB,
wherein a loss increase at a wavelength of 1.625 jam when the optical fiber is 5 wound 10 times around a cylindrical mandrel with a radius of 15 mm is less than 0.1 dB,
wherein a loss increase at a wavelength of 1.55 jam when the optical fiber is wound once around a cylindrical mandrel with a radius of 10 mm is less than 0.1 dB, and
wherein a loss increase at a wavelength of 1.625 jam when the optical fiber is wound once around a cylindrical mandrel with a radius of 10 mm is less than 0.2 dB. 10
[Claim 4]
The optical fiber according to any one of claims 1 to 3,
wherein any one of conditions in which a value of a zero dispersion wavelength ZDW is 1.305 to 1.319 jam, a value of a zero dispersion slope is 0.092 ps/km/nm2 or less, 15 or a value of chromatic dispersion at a wavelength of 1.55 jam is 18.00 ps/km/nm or less is satisfied.
[Claim 5]
The optical fiber according to any one of claims 1 to 4,
20 wherein the index a is set to 1.0 or more and 2.2 or less, and the relative
refractive index difference A- is set such that the absolute value IA"I is 0.08% or more and 0.15% or less.
[Claim 6]

The optical fiber according to claim 5,
wherein a loss increase at a wavelength of 1.55 jam when the optical fiber is
wound 10 times around a cylindrical mandrel with a radius of 15 mm is less than 0.03
dB,
5 wherein a loss increase at a wavelength of 1.625 jam when the optical fiber is
wound 10 times around a cylindrical mandrel with a radius of 15 mm is less than 0.1 dB,
wherein a loss increase at a wavelength of 1.55 jam when the optical fiber is wound once around a cylindrical mandrel with a radius of 10 mm is less than 0.1 dB,
wherein the loss increase at a wavelength of 1.625 jam when the optical fiber is 10 wound once around a cylindrical mandrel with a radius of 10 mm is less than 0.2 dB,
wherein the loss increase at a wavelength of 1.55 jam when the optical fiber is wound once around a cylindrical mandrel with a radius of 7.5 mm is less than 0.5 dB, and
wherein the loss increase at a wavelength of 1.625 jam when the optical fiber is 15 wound once around a cylindrical mandrel with a radius of 7.5 mm is less than 1.0 dB.
[Claim 7]
The optical fiber according to any one of claims 1 to 6, wherein the ratio rl/r2 is set to 0.40 or more and 0.55 or less. 20
[Claim 8]
The optical fiber according to any one of claims 1 to 7,

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