Patent ID: 8565273

Claim:
An optical fiber laser comprising: a master oscillator which is a laser oscillator producing a seed beam; and a power amplifier which is an optical amplifier connected to a subsequent stage of the master oscillator and amplifying the seed beam emitted from the master oscillator and outputting a laser beam, wherein the master oscillator comprises: an excitation light source; a WDM coupler that is connected to the excitation light source for combining an excitation light from the excitation light source with a laser beam; an optical fiber connected to the WDM coupler; an output coupler connected to the optical fiber; and an isolator, wherein the WDM coupler, the optical fiber, the output coupler, and the isolator are connected in this order in a ring, wherein the optical fiber has a loss wavelength characteristic in that a photonic bandgap region is narrower than a gain wavelength band in a graph with an axis of abscissa representing a wavelength and an axis of ordinate representing a loss amount, and wherein the optical fiber comprises: a region; a core portion made of a solid material doped with a rare-earth element, provided in the region, and having a higher refractive index than the region; a first cladding provided around the region; and a periodic structure portion in which a multitude of high refractive index portions with a refractive index higher than that of the first cladding are arranged in a periodic structure portion being provided in a vicinity of the region in the first cladding.