Patent ID: 8456737

Claim:
An amplification optical fiber, which has a core and a clad covering the core, wherein the core propagates light with a predetermined wavelength in at least an LP01 mode, an LP02 mode, and an LP03 mode, when the LP01 mode, the LP02 mode, and the LP03 mode are standardized by power, in at least a part of a region where the intensity of the LP01 mode is larger than at least one of the intensities of the LP02 mode and the LP03 mode, an active element inducing and emitting the light with a predetermined wavelength is added to the core at a higher concentration than a central portion of the core, and at least one of the following formulae (1) and (2) is satisfied: ∫ 0 b n ( r )×{ I 01 ( r )− I 02 ( r )} rdr> 0 (1) ∫ 0 b n ( r )×{ I 01 ( r )− I 03 ( r )} rdr> 0 (2) (where r represents a distance from the center in the radial direction of the core, I 01 (r) represents intensity in the distance r from the center in the radial direction of the core in the LP01 mode, I 02 (r) represents intensity in the distance r from the center in the radial direction of the core in the LP02 mode, I 03 (r) represents intensity in the distance r from the center in the radial direction of the core in the LP03 mode, n(r) represents an additive concentration of the active element in the distance r from the center in the radial direction of the core, and b represents a radius of the core).