Noise in Dual-Pumped Fiber-Optical Parametric Amplifiers: Theory and Experiments

The noise figure of a dual-pumped parametric amplifier with co-polarized pumps is quantified, for the first time to our knowledge. It is shown that the noise figure is increased by the noise on the pump sources, in agreement with theory, and that it gives a uniform noise-figure degradation due to a uniform gain spectrum. The magnitude of the noise-figure degradation increases with increasing input-signal power. Various aspects of the noise figure are studied, such as the effects of three idlers generated by the four-sideband interaction, and Raman-induced losses and excess noise caused by the population of thermal phonons. It is shown that the use of unequal pump powers only affect the low-power noise figure to a minimal degree. Also, the gain dependence of the noise figure is studied, as are the wavelength and signal-power dependences of the noise figure. It is shown that at high gain the noise figure saturates, even when pump noise is an issue. Also, unequal pump powers with a fixed gain have a minor impact on the noise performance of the amplifier. Theory and experiments agree well with each other.