| 摘要 |
A loop is formed with an optical fiber by providing a gain medium having a gain with respect to an oscillation wavelength. Light retrieved by the optical circulator 13 from the optical fiber loop is enlarged and projected to a mirror 23 . A diffraction grating 25 is provided with respect to the light reflected in the mirror. The diffraction grating 25 has a Littrow arrangemnt wherein the light is reflected in a same direction as incident light. A selected wavelength is changed in accordance with an incident angle with respect to the diffraction grating 25 . Therefore, when the mirror 23 is rotated so as to change the selected wavelength, the oscillation wavelength can be changed at high speed.
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