Comparison of noise characteristics of Fabry-Perot-type and travelling-wave-type semiconductor laser amplifiers

We report results of comparative noise measurements on AlGaAs semiconductor laser amplifiers of the Fabry-Perot and travelling-wave types. We show that, for the same net gain, the electrical baseband signal/noise ratio of a photodetector placed at the amplifier output (after an optical filter) is higher for a travelling-wave-type amplifier, especially at high-gain values where the Fabry-Perot amplifier is operated at oscillation threshold. For a net gain of 20.5 dB, the signal/noise ratio of the travelling-wave-type amplifier is 4¿5 dB better.