Patent ID: 8081856

Claim:
An optical fiber comprising a core having a refractive index n 1 , a first cladding surrounding the core and having a refractive index n 2 smaller than the refractive index n 1 , a second cladding surrounding the first cladding and having a refractive index n 3 smaller than the refractive index n 2 , and a third cladding surrounding the second cladding and having a refractive index n 4 greater than the refractive index n 3 , wherein, with respect to the refractive index n 4 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 larger than −1.8%, wherein the inner radius r 2 of the second cladding and the outer radius r 3 of the second cladding satisfy the expression, 0.4 r 2 +10.5 <r 3 <0.2 r 2 +16 and the inner radius r 2 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.