Multistage tunable gain optical amplifier

A multi-stage tunable gain optical amplifier for amplifying an optical signal, the multi-stage tunable gain optical amplifier comprising a first, a second and a third optical amplifier stage coupled in series, wherein:

• the first optical amplifier stage has better noise performance than the second optical amplifier stage;
• the third optical amplifier stage has a higher power output than the second optical amplifier stage;
• and
• the second optical amplifier stage includes a tunable-gain lasing semiconductor optical amplifier (SOA) stage comprising:
• a semiconductor gain medium having an amplifying path for amplifying an optical signal propagating along the amplifying path,
• a laser cavity including the semiconductor gain medium, wherein pumping the laser cavity above a lasing threshold substantially clamps a gain of the semiconductor gain medium to a constant value, and an overall gain of the tunable-gain lasing SOA stage is tunable.

A tunable gain lasing semiconductor optical amplifier (SOA) device for amplifying an optical signal, the device comprising:

• an input for receiving the optical signal;
• an output for transmitting an amplified version of the optical signal;
• a semiconductor gain medium having an amplifying path coupled between the input and the output for amplifying the optical signal propagating along the amplifying path;
• a laser cavity including the semiconductor gain medium;
• a pump input coupled to the semiconductor gain medium for receiving a pump to pump the semiconductor gain medium above a lasing threshold for the laser cavity, whereby a gain of the semiconductor gain medium is clamped to a gain value which is substantially independent of an amplitude of the optical signal propagating along the amplifying path;
• wherein each point along the amplifying path is characterized by a design parameter which varies along the amplifying path;
• and
• wherein the gain is tunable at some point along the amplifying path.

In a multi-stage tunable gain optical amplifier comprising an optical amplifier stage coupled in series to a tunable-gain lasing SOA stage, a method for amplifying an optical signal comprising:

• receiving an optical signal;
• amplifying the optical signal as the optical signal propagates through the optical amplifier stage and through the tunable-gain lasing SOA stage;
• and
• adjusting a gain of the tunable-gain lasing SOA stage.