Non-white photodetection noise at the output of an optical amplifier: Theory and experiment

Based on the statistical properties of amplified spontaneous emission, the photodetection noise spectrum at the output of an optical amplifier is calculated. The results revealed that the signal-spontaneous emission beat noise spectrum is a transposition of the spontaneous-emission spectrum to the low-frequency domain, and the spontaneous emission-spontaneous emission beat noise spectrum is the auto-correlation function of the spontaneous-emission spectrum. These theoretical results are verified experimentally on an erbium-doped fiber amplifier, filtered by a Mach-Zehnder interferometer.