Noise measurements on distributed-feedback optical amplifiers used as tunable active filters

Resonant, single-mode optical amplifiers that show promise for use as fast, tunable filters in multiwavelength communication networks are discussed. According to recent theoretical predictions, the photocurrent signal-to-noise ratio at the output of such a filter should exhibit a simple dependence on both the mean amplified-signal power and the mean amplified-spontaneous-emission power. This prediction is confirmed via direct measurement of the photocurrent signal-to-noise ratio at the output of a 1.5- mu m distributed-feedback amplifier biased slightly below its lasing threshold.<>