Patent ID: 7126748

Claim:
An optical fiber comprising: a first core region of an α-shaped profile at a center; a second core region surrounding the first core region in which refractive index is lower than the first core region; and a cladding surrounding the second core region in which refractive index is lower than the first core region and higher than the second core region, wherein a relative refractive index difference of the first core region with a cladding region Δ 1 is not less than 2.4% and not more than 2.8%, a Raman gain efficiency with a pump power at 1450 nanometers of equal to or more than 4 m/W, and a ratio of a nonlinear parameter γ at a wavelength of 1550 nanometers to the Raman gain efficiency with a pump power of 1450 nanometers of equal to or less than 3.