Patent ID: 8116607

Claim:
A rare-earth doped optical fiber comprising a core and one or more clad layers surrounding the core, wherein the core comprises a rare earth dopant, and a relationship of Equation (1) is satisfied: 0 < ∫ r 0 r c ⁢ D ⁡ ( r ) · P p 2 ⁡ ( r ) · P s 2 ⁡ ( r ) ⁢ r ⁢ ⁢ ⅆ r ∫ r 0 r c ⁢ D ⁡ ( r ) · P p 2 ⁡ ( r ) ⁢ r ⁢ ⁢ ⅆ r ≤ 0.35 ( 1 ) where P p (r) represents an electric field distribution in an exciting wavelength, P s (r) represents an electric field distribution in wavelengths of spontaneous emission and/or stimulated emission carried in the core, D(r) (mass %) represents a rare-earth dopant distribution, r o represents a core center, and r c represents a core radius.