Patent ID: 8571074

Claim:
A fiber laser device comprising: a pumping light source configured to output pumping light; a rare earth-doped fiber to which the pumping light is input; and a first FBG formed on one side of the rare earth-doped fiber and a second FBG formed on the other side of the rare earth-doped fiber that are configured to reflect light amplified in the rare earth-doped fiber, wherein the second FBG has a reflectance lower than that of the first FBG, a reflection wavelength band in that of the first FBG, and a center wavelength on short wavelength side of a center wavelength of the first FBG, wherein the entire reflection wavelength band of the second FBG is on short wavelength side of the center wavelength of the first FBG and within the reflection wavelength band of the first FBG on the short wavelength side of the center wavelength of the first FBG such that the first FBG exerts a property of a normal dispersion with respect to an input light reflected from the second FBG to prevent a modulation instability.