Patent ID: 7742671

Claim:
A silica-based optical fiber comprising: a core including three or more layers, each of the three or more layers being doped with at least one of germanium and fluorine, the three or more layers include at least: a center core layer, an inner core layer formed on an outer circumference of the center core layer, and an outer core layer formed on an outer circumference of the inner core layer, wherein a total relative refractive index difference in the core layers is 0.3% to 0.4%, and when a relative refractive index difference of a center core layer caused by the germanium is Δ1-GeO 2 , a relative refractive index difference of the center core layer caused by the fluorine is Δ1-F, a relative refractive index difference of an inner core layer caused by the germanium is Δ2-GeO 2 , a relative refractive index difference of the inner core layer caused by the fluorine is Δ2-F, a relative refractive index difference of an outer core layer caused by the germanium is Δ3-GeO 2 , a relative refractive index difference of the outer core layer caused by the fluorine is Δ3-F, and a core diameter of the outer core layer is 2 c, Δ 1-GeO 2 is 0.45% to 1.1%, Δ1-F is −0.7% to −0.1%, (Δ1-GeO 2 )−(Δ2-GeO 2 ) is larger than 0%, (Δ1-F)−(Δ2-F) is smaller than 0%, (Δ2-GeO 2 )−(Δ3-GeO 2 ) is larger than 0.1%, (Δ2-F)−(Δ3-F) is smaller than −0.1%, and 2 c is 7.5 μm to 10.0 μm.