Optical cable and optical transmission system

An optical cable comprising:

• an optical fiber;
• and
• a sheath covering the optical fiber,
• said optical fiber comprising a core having a refractive index n1, a first cladding surrounding the core and having a refractive index n2 smaller than the refractive index n1, a second cladding surrounding the first cladding and having a refractive index n3 smaller than the refractive index n2, and a third cladding surrounding the second cladding and having a refractive index n4 greater than the refractive index n3,
• wherein, with respect to the refractive index n4 of the third cladding, the relative refractive index difference of the core is in the range of 0.3% to 0.38%, the relative refractive index difference of the first cladding is in the range of −0.3% to 0.2%, and the relative refractive index difference of the second cladding is greater than −1.8%,
• wherein the inner radius r2 of the second cladding and the outer radius r3 of the second cladding satisfy the expression,
• 0.4r2+10.5<r3<0.2r2+16,
• and the inner radius r2 of the second cladding is equal to or greater than 8 μm, and
• wherein the bending loss at a wavelength of 1550 nm and at a radius of curvature of 7.5 mm is smaller than 0.1 dB/turn, and the bending loss at a wavelength of 1625 nm and at a radius of curvature of 4 mm is greater than 0.1 dB/turn, and
• wherein a loss increase is smaller than 0.1 dB/km at a wavelength of 1550 nm and at a temperature of −30° C.