Patent ID: 7925132

Claim:
A nonlinear optical fiber comprising: a core including a center core region, a core layer that is formed around the center core region and that has a refractive index lower than a refractive index of the center core region, and at least one buffer core layer that is formed between the center core region and the core layer and that has a refractive index lower than a minimum refractive index of the center core region and higher than the refractive index of the core layer; and a cladding that is formed around the core layer and that has a refractive index lower than the refractive index of the center core region and higher than the refractive index of the core layer, wherein an effective core area at a wavelength of 1550 nanometers is equal to or smaller than 18 μm 2 , a ratio of an outer diameter of the buffer core layer to a diameter of the center core region is equal to or larger than 1.2 and equal to or smaller than 2.0, and a relative refractive index difference between the buffer core layer and the cladding is equal to or larger than 0.1% and equal to or smaller than 0.6%.