Patent ID: 8306073

Claim:
A fiber laser device comprising: a pumping light source configured to output pumping light having a wavelength λ; and a rare earth-doped fiber to which the pumping light is input and which has a core doped with a rare earth element that absorbs the pumping light, wherein when an intensity change rate of the pumping light output from the pumping light source with respect to a temperature is denoted by ΔP dB/° C., a wavelength change rate of the pumping light output from the pumping light source with respect to the temperature is denoted by Δλp nm/° C., a pumping light absorption change rate of the pumping light in the rare earth-doped fiber per unit wavelength change at the wavelength of λ nm when the wavelength of the pumping light changes is denoted by A′ (λ) dB/nm, and a pumping light absorption change amount of the rare earth-doped fiber per unit temperature change at the wavelength of λ nm when the temperature of the rare earth-doped fiber changes is denoted by ΔA (λ) dB/° C., the wavelength λ of the pumping light is such a wavelength λ that ΔP, Δλp×A′ (λ) and ΔA (λ) compensate with each other.