Heterodyne gain and noise measurement of a 1.5 µm resonant semiconductor laser amplifier

The noise and gain characteristics of a 1.5μm resonant semiconductor laser amplifier have been measured. A heterodyne detection scheme was used to measure the gain and noise properties relevant to coherent communication applications. Measurements were made with the amplifier operating in unsaturated, saturated, and injection-locked regimes. Unsaturated internal gain as high as 29 dB was measured with the amplifier operating close to threshold. Measured signal-to-noise ratios agree well with calculated results and are 9 dB below the input quantum shot noise limit. A degradation in the amplifier performance is observed when operated above or at threshold. Gain saturation for high input powers also degrades the noise characteristics of the amplifier.