Patent ID: 7680390

Claim:
A polymer clad optical fiber comprising: an outer core provided on an outer circumference of an inner core formed from quartz glass, the outer core being formed from fluorine-doped glass having a refractive index lower than that the refractive index of the inner core; and a polymer cladding provided on an outer circumference of the outer core and formed from a polymer, wherein if the diameter of the inner core is taken as a 1 , and the diameter of the outer core is taken as a 2 , and a cross-sectional area of the inner core is taken as (πa 1 2 )/4, and a cross-sectional area of the outer core is taken as (πa 2 2 )/4, then a parameter X defined as X(=a 2 2 /a 1 2 ) is within a range of 1.8≦X≦2.2, and wherein if a relative refractive index difference between the inner core and the outer core is taken as Δ 1 , if a relative refractive index difference between the outer core and the cladding is taken as Δ 2 , if a relative refractive index difference between the outer core and the polymer cladding at a high temperature is taken as Δ 2 max, if a relative refractive index difference between the outer core and the polymer cladding at a low temperature is taken as Δ 2 min, and if a parameter Y is defined as Y=Δ 1 /Δ 2 , Ymax=Δ 2 max/Δ 2 at a high temperature, and Ymin=Δ 2 min/Δ 1 at a low temperature, then a relationship is established in which, when the parameter X is within a range of 1.8≦X≦2.0, the Ymin is 0.25≦Ymin≦0.84X−0.68, and the Ymax is 0.25≦Ymax≦0.84X−0.68, and, when X is within a range of 2.0≦X≦2.2, the Ymin is 0.48X−0.71≦Ymin≦−2/9X+13/9, and the Ymax is 0.48X−0.71≦Ymax≦−2/9X+13/9.