| 摘要 |
The present invention relates to an optical amplifier with a structure for more effectively suppressing the over/undershoot in transient responses in high-speed AGC. This optical amplifier is an optical device for amplifying signal light inputted therein, and comprises a rare-earth-element-doped optical fiber, an optical coupler, a light-receiving section, a pumping light source, and a control section. In particular, as a typical structure of the optical amplifier, the rare-earth-element-doped optical fiber has a cutoff wavelength lambdac set longer than the pumping light wavelength lambdap but shorter than the signal light wavelength lambdas, and mainly allows a pumping light component in a fundamental mode to propagate therethrough. The pumping light and signal light are made incident on the first rare-earth-element-doped optical fiber such that only the pumping light component in the fundamental mode and a signal light component in the fundamental mode propagate through the first rare-earth-element-doped optical fiber in a state where the first rare-earth-element-doped optical fiber extends straight.
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