Lecture 8: Laser amplifiers

Amplifier noise
The ASE of a laser amplifier is directly proportional to the optical
bandwidth of the amplifier.
To increase the signal-to-noise ratio (SNR) at the amplifier output, the
total noise power can be reduced to a minimum by placing at the output
end of an amplifier an optical filter that has a narrow bandwidth matching
the bandwidth of the optical signal.
Because of the spontaneous emission noise, the SNR of an optical signal
always degrades after the optical signal passes through an amplifier.
The degradation of the SNR of the optical signal passing through an
amplifier is measured by the optical noise figure of the amplifier defined
as
F o
SNR in
SNR out
where SNRin and SNRout represent the values of the optical SNR at the
input and output ends of the amplifier.
109