Patent ID: 7489713

Claim:
A tunable fiber laser light source comprising: an optical fiber loop which serves as an optical path of laser oscillation; a gain medium which is connected to said optical fiber loop and has a gain with respect to an oscillating wavelength; a light branch incident section which divides a plurality of light from said optical fiber loop and returns light to said optical fiber loop through the same optical path as the divided light; a tunable optical filter which receives the plurality of divided light divided by said light branch incident section, selects each same wavelength continuously changed, and supplies light of the selected wavelength said light branch incident section through the same optical path; and an optical coupler which is connected to said optical fiber loop and takes out a part of light passing through said optical fiber loop, wherein said tunable optical filter includes: an optical beam deflector which periodically changes a reflecting angle of an optical beam, obtained from said light branch incident section, within a certain range; and a diffraction grating which receives light deflected by said optical beam deflector and reflects light of selected wavelength changing according to an incident angle in the same direction as the incident angle; and wherein said light branch incident section is a spatial circulator element, and said spatial circulator element comprises: a doubly refracting crystal; a ¼ wavelength plate which is formed at a central portion of a first surface of said doubly refracting crystal; a reflection plate which is stacked on said ¼ wavelength plate; a Faraday rotator which rotates polarization through 45-degrees in opposite directions to each other with respect to light from said first surface to said second surface and light from said second surface to said first surface; and a ½ wavelength plate which, when light transmits therethrough, rotates polarization through 45-degrees in the same direction as either of the directions of rotation by said Faraday rotator; wherein one of said Faraday rotator and said ½ wavelength plate is stacked on a second surface opposing said first surface of said doubly refracting crystal and the other of said Faraday rotator and said ½ wavelength plate is stacked on said one of said Faraday rotator and said ½ wavelength plate which is stacked on the second surface.