Modelling of noise suppression in gain-saturated fiber optical parametric amplifiers

Noise properties of both one-pump (1-P) and two-pump (2-P) fiber optical parametric amplifiers (FOPAs) are theoretically investigated and particularly the unique feature of FOPAs for the noise suppression in the gain-saturated regime is modeled. For the 1-P FOPAs, the simulation results are compared with the available experimental data and a very good agreement is obtained. Also, for the 2-P FOPA where no experimental work has been reported regarding their noise properties in the saturation regime, the noise behavior of the amplified signal is simulated for the first time. It is shown that for a specific power in the deep saturation regime, the signal noise is suppressed; and with further increase of the signal power when the gain saturation reaches its new cycle, a periodic behavior of noise suppression is observed originating from the phase-matching condition. The existence of a negative feedback mechanism which is responsible to the suppression of the excess noise in the first cycle of the gain saturation is confirmed both for 1-P and 2-P FOPAs. Generally, it is shown that the noise suppression can be observed for several specific powers at which the slope of the output signal power versus the input one is zero. The results of this paper may have some applications in signal processing, e.g., cleaning noisy signals.