Optical fiber and optical device using the same

摘要

An optical fiber 10 is one in which at a mean zero dispersion wavelength » 0 in an overall length, an absolute value of the fourth order dispersion ² 4 of propagation constant ² with respect to frequency É is not more than 5 × 10 -56 s 4 /m and a fluctuation of the zero dispersion wavelength along the longitudinal direction is not more than ±0.6 nm in the overall length. The optical fiber 10 comprises at least a center core part 11 having a maximum refractive index N 1 and an outside diameter 2a, a depressed part 12 having a minimum refractive index N 2 and an outside diameter 2b, and a cladding part 13 having a maximum refractive index N 3 . The refractive indices of the respective parts satisfy the relation of "N 1 > N 3 > N 2 ." With respect to the refractive index of the cladding part, a relative index difference of the center core part is defined as ” + and a relative index difference of the depressed part as ” - ; then a difference "” + -” - " is not less than 2.2%, and a ratio Ra (= 2a/2b) of the outside diameters of the center core part and the depressed part is in the range of 0.2 to 0.7.