Patent ID: 8903213

Claim:
An optical fiber comprising a center core a center of which extends along a predetermined axis, a side core provided on an outer peripheral surface of the center core, and a cladding provided on an outer peripheral surface of the side core, wherein in an index profile defined by relative index differences with respect to a refractive index of the cladding, of respective portions along a reference line perpendicular to the predetermined axis, a region corresponding to the center core has a peak part including a position where the relative index difference is maximum, and a tail part, the tail part including a part in which the relative index difference decreases continuously from the peak part toward the cladding, and a ring part in which the relative index difference has a shape projecting along a direction that the relative index difference increases, wherein when a is a radius along the reference line from the center of the center core to an outside of the ring part and c is a radius along the reference line from the center of the center core to a position where the relative index difference is maximum in the side core, the index profile has a shape in which c/a is in the range of 2.25 to 2.50, so as to realize a first dispersion value in the range of 2.0 to 5.5 ps/nm/km at the wavelength of 1530 nm, a second dispersion value in the range of 4.5 to 6.0 ps/nm/km at the wavelength of 1565 nm, a third dispersion value in the range of 8.5 to 11.2 ps/nm/km at the wavelength of 1625 nm, a cable cutoff wavelength in the range of not more than 1.45 μm, a bending loss in the diameter of 20 mm in the range of not more than 20 dB/m at the wavelength of 1550 nm, and an effective area in the range of 64 to 75 μm 2 at the wavelength of 1550 nm.