Patent ID: 8567217

Claim:
An optical fiber preform comprising: a center glass rod having a radius of r a expressed in millimeters, and including a core portion and a first portion of a cladding; and an outer layer, which is a second portion of the cladding, surrounding the center glass rod and having an outer radius of r b expressed in millimeters measured from a center axis of the center glass rod, wherein the radiuses r a and r b satisfy the following inequalities: 0.002<( r a /r b )/ c< 0.01, where “c” expressed in ppm is a maximum value of hydroxyl group concentration in the vicinity of a boundary between the center glass rod and the outer layer; and wherein a hydroxyl group concentration in the outer layer decreases with distance from the boundary between the center glass rod and the outer layer, and does not increase between the boundary between the center glass rod and the outer layer and the outer radius of the outer layer.