Patent ID: 8755111

Claim:
An amplification optical fiber, comprising: a core and a clad which covers the core, wherein the core propagates light having a predetermined wavelength in at least an LP 01 mode, an LP 02 mode, and an LP 03 mode, in the core, when the LP 01 mode, the LP 02 mode, and the LP 03 mode are standardized by a power, in at least a part of a region where an intensity of at least one of the LP 02 mode and the LP 03 mode is stronger than an intensity of the LP 01 mode, an active element which stimulates and emits the light having the predetermined wavelength is added with a higher concentration than that in at least a part of a region where the intensity of the LP 01 mode is stronger than the intensities of the LP 02 mode and the LP 03 mode, and at least one of the following Formulae (1) and (2) is satisfied ∫ 0 b n ( r )×{ I 02 ( r )− I 01 ( r )} rdr>O (1) ∫ 0 b n ( r )×{ I 03 ( r )− I 01 ( r )} rdr>O (2) (In this case, r is a distance from the center in the radial direction of the core, I 01 (r) is an intensity of the LP 01 mode in the distance r from the center in the radial direction of the core, I 02 (r) is an intensity of the LP 02 mode in the distance r from the center in the radial direction of the core, and I 03 (r) is an intensity of the LP 03 mode in the distance r from the center in the radial direction of the core, n(r) is a concentration of an added active element in the distance r from the center in the radial direction of the core, and b is a radius of the core.)