Patent ID: 8233761

Claim:
An optical fiber comprising: a core region having a first refractive index; and a cladding region having a second refractive index lower than the first refractive index, the cladding region surrounding the core region, wherein the cladding region includes only four holes formed in a four-fold rotational symmetry around the core region with respect to a center axis and in a longitudinal direction, such that a zero-dispersion wavelength is 900 nm to 1150 nm and a cutoff wavelength is equal to or shorter than 950 nm, a relative refractive index difference of the core region with respect to the cladding region is 0.3% to 1.5%, a diameter of the core region is equal to or larger than 3 μm and equal to or smaller than 7 μm, a diameter of each of the holes is larger than 1 μm and equal to or smaller than 8 μm, and a shortest distance D between the core region and each of the holes defined by D={L−(A+B)}/2 is equal to or larger than 0 μm and equal to or smaller than 1.2 μm, where A is a diameter of the core region in micrometers, B is a diameter of each of the holes in micrometers, and L is a distance between centers of the core region and the holes in micrometers.