Optical fiber and optical communication system including same

A silica-based optical fiber having a transmission loss of 0.19 dB/km or less at a wavelength of 1550 nm, an effective area Aeff of 110 μm2 or more at the wavelength of 1550 nm, and a fiber cutoff wavelength λC of 1.3 μm or more but 1.53 μm or less as a medium for transmitting light with a wavelength of 1625 nm or less, the optical fiber comprising:

• a core comprised of pure silica, the core having a refractive index n1 and a diameter 2a;
• an inner cladding, provided at an outer periphery of the core, having a refractive index n2 and a diameter 2b;
• and
• an outer cladding, provided at an outer periphery of the inner cladding, having a refractive index n3,
• wherein the refractive index n3 is smaller than the refractive index n1 but greater than the refractive index n2;
• wherein the relative refractive index difference Δ31 (=100×(n2−n3)/n3) of the inner cladding with respect to the outer cladding is −0.12% or more but −0.06% or less, and
• wherein the ratio Ra(=2b/2a) of the diameter of the inner cladding to the diameter of the core is 2.5 or more but 3.5 or less.

An optical communication system, comprising:

• a plurality of first optical fibers disposed at two or more locations in a repeater span of 80 km or more;
• a plurality of second optical fibers connected to the first optical fibers at four or more locations in the repeater span including both ends thereof, each of the second optical fibers having an effective area Aeff of 85 μm2 or less at a wavelength of 1550 nm, the second optical fibers including those disposed at both ends of the repeater span and at one location in the repeater span,
• wherein each of the first optical fibers has a transmission loss of 0.19 dB/km or less at the wavelength of 1550 nm, an effective area Aeff of 110 μm2 or more but 150 μm2 or less at the wavelength of 1550 nm, and a fiber cutoff wavelength λC of 1.3 μm or more but 1.45 μm or less, and
• wherein propagating light is Raman-amplified in each of the first optical fibers.