Patent ID: 7440663

Claim:
A single-mode optical fiber comprising: a central core which has a radius r 1 and a refractive index n 1 ; an inner cladding which is provided around an outer circumference of the central core and has a radius r 2 and a refractive index n 2 ; a trench portion which is provided around an outer circumference of the inner cladding and has a radius r 3 and a refractive index n3; and an outer cladding which is provided around an outer circumference of the trench portion and has a radius r 4 and a refractive index n 4 , wherein: n 1 >n 4 ≧n 2 >n 3 , a cut-off wavelength is not greater than 1260 nm, a zero-dispersion wavelength is between 1300 nm and 1324 nm, a zero-dispersion slope is not greater than 0.093 ps/nm 2 /km, a mode field diameter at a wavelength of 1310 nm is between 5.5 μm and 7.9 μm, a bending loss produced if the fiber is wound around a 10-mm radius for 10 turns is not greater than 0.5 dB at a wavelength of 1550 nm, 1.5 <r 2 /r 1 <3.0, and 0.5<( r 3 −r 2 )/ r 1 <3.0.