Optical amplifier

摘要

An optical amplifier includes a first optical path, second optical path, semiconductor optical amplifier, and multi-mode interference 3-dB coupler. The first optical path guides oscillation light. The second optical path guides signal light. The semiconductor optical amplifier causes oscillation on the first optical path. The multi-mode interference 3-dB coupler crosses the first and second optical paths in the gain medium of the semiconductor optical amplifier.