Patent ID: 6999667

Claim:
A dispersion-controlled optical fiber comprising: a center core having a refractive index N 1 for forming a passageway for transmitting optical signals; a cladding having a refractive index N 0 for enclosing said center core; an upper core surrounding said center core and having a refractive index distribution increased starting from a refractive index N 2 at its outer circumference to the refractive index N 1 at its internal circumference; and, a minutely depressed refractive index region having a reflective index N 3 and interposed between said upper core and cladding, wherein the refractive index N 3 is lower than the refractive index N 0 , wherein the internal radius a and external radius b of said upper core, and the internal radius c of said cladding meet with the relationships: 0.06≦a/b≦0.8 and 0.02≦a/c≦0.9.