Reduction of signal-spontaneous noise in optical amplifiers

The beat between an amplified optical signal and the amplified spontaneous emission (ASE) noise is typically the primary limitation to the performance of optical fiber amplifiers. A filtering technique which might reduce this beat noise by 3dB creates a paradox since the noise figure's quantum limit of 3dB could then be reduced to 0dB implying noiseless amplification, which is impossible. The conjecture that this paradox might be resolved by different attenuations of the quantum and semiclassical descriptions of signal-spontaneous noise has been experimentally rejected . Herein, we present a variation of that experiment and telecommunication' applications of this filtering technique are discussed.