Semiconductor optical amplifier

An optical amplifier comprising:

• an n-type semiconductor layer;
• a p-type semiconductor layer;
• an active layer provided between the n-type semiconductor layer and the p-type semiconductor layer, the active layer transmitting an optical signal;
• and
• a current-injection part that injects current into the active layer via the n-type semiconductor layer and the p-type semiconductor layer,
• the active layer includes a first active layer and a second active layer, the second active layer inputting the optical signal output from the first active layer, the first active layer and the second active layer are butt-jointed, and
• a differential gain factor of the first active layer is greater than a differential gain factor of the second active layer at a given carrier density.

An optical module comprising:

• a semiconductor optical amplifier;
• an input part that inputs an optical signal to a first active layer of the semiconductor optical amplifier;
• and
• an output part that outputs the optical signal from a second active layer of the semiconductor optical amplifier, the semiconductor optical amplifier including:
• an n-type semiconductor layer;
• a p-type semiconductor layer;
• an active layer provided between the n-type semiconductor layer and the p-type semiconductor layer, the active layer transmitting the optical signal;
• and
• a current-injection part that injects current into the active layer via
• the n-type semiconductor layer and the p-type semiconductor layer, the active layer includes the first active layer including AlGaInAs, and the second active layer including GaInAsP, the second active layer provided closer to an output side of the optical signal than the first active layer, and the first
• active layer and the second active layer are butt-jointed.

An optical communication system comprising:

• a first optical signal transmission line;
• an optical repeater that amplifies an optical signal transmitted through the first optical signal transmission line;
• and
• a second optical signal transmission line through which the optical signal that is amplified by the optical repeater is transmitted,
• the optical repeater includes an optical module, the optical module including:
• a semiconductor optical amplifier;
• an input part that inputs the optical signal to a first active layer of the semiconductor optical amplifier;
• and
• an output part that outputs the optical signal from a second active layer of the semiconductor optical amplifier,
• the semiconductor optical amplifier including:
• an n-type semiconductor layer;
• a p-type semiconductor layer;
• an active layer provided between the n-type semiconductor layer and the p-type semiconductor layer, the active layer transmitting the optical signal;
• and
• a current-injection part that injects current into the active layer via the n-type semiconductor layer and the p-type semiconductor layer,
• the active layer includes the first active layer including AlGaInAs, the second active layer including GaInAsP, the second active layer provided closer to an output side than the first active layer, and the first active layer and the second active layer are butt-jointed.