Patent ID: 7813386

Claim:
An optical fiber for an optical fiber laser comprising: a rare earth element doped core doped with a rare earth element, the rare earth element doped core being divided into a plurality of core regions along a longitudinal direction of the optical fiber, dopant concentrations of the rare earth element in each of the core regions being different from adjacent core regions; and a cladding formed at an outer periphery of the rare earth element doped core, the cladding having a first end and a second end, wherein an exciting light is inputted into both ends of the cladding to excite the rare earth element, respectively, thereby outputting a laser exciting light, wherein dopant concentrations of the plurality of core regions are line symmetrical with respect to a center part along the longitudinal direction of the optical fiber and are increased gradually from the first and the second ends of the cladding to the center part along the longitudinal direction of the optical fiber, wherein dopant concentrations of at least two of the plurality of core regions are equal, and wherein lengths of the at least two of the plurality of core regions are equal.