| 摘要 |
A light amplifier includes an optical fiber doped with a rare-earth ion, a light source emitting an exciting light and thereby exciting the optical fiber, and an optical system which applies a given light component to the optical fiber in a first direction opposite to a second direction in which a signal light is propagated through the optical fiber when a light exceeding a threshold level is propagated through the optical fiber, so that a gain of the optical fiber can be reduced.
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