Fiber laser light source

A fiber laser light source comprising:

• a fiber containing a laser active material;
• a pump laser light source which emits pump light into the fiber;
• and
• a laser resonator including a pair of fiber gratings optically connected to the fiber in a state that the fiber containing the laser active material is interposed between the paired fiber gratings, wherein
• the laser resonator is configured to emit light of a single polarization by a polarization maintaining fiber,
• the fiber laser light source has a wavelength characteristic that a reflection center wavelength of a laser-exit side fiber grating, out of the paired fiber gratings, lies in a wavelength range, where a reflectance of a fiber grating, out of the paired fiber gratings, closer to the pump laser light source is not smaller than 80% but not larger than 98%
• a wavelength band of the fiber grating closer to the pump laser light source is 1 nm or more,
• a wavelength band of the laser-exit side fiber grating is 0.05 nm or less, and
• the laser resonator emits self oscillated pulse laser light by shifting a reflection center wavelength of the laser-exit side fiber grating depending on a change in a refractive index of the laser-exit side fiber grating in response to incidence of light into the laser-exit side fiber grating.