A multi-stage tunable gain optical amplifier device amplifies an optical signal
by a gain amount which can be adjusted in one of the stages of the amplifier. The
multi-stage amplifier includes at least two optical amplifier stages coupled in
series, one of which is a tunable gain amplifier stage. The optical amplifier stages
are characterized by a design parameter which varies from stage to stage. In a
preferred embodiment, the design parameter includes a noise figure and a saturable
power, with both parameters increasing as the optical signal propagates from stage
to stage. As a result, the multi-stage tunable gain optical amplifier can achieve
better noise performance and higher output power than a single stage optical amplifier
with a constant noise figure and saturable power.
