A fiber optical parametric amplifier (OPA) has a unique saturation property such that, with increase in signal input, the signal output power increases, reaches a peak level, then decreases. Around the output peak condition,a negative feedback mechanism works to suppress intensity fluctuations in the signal output. This paper experimentally studies noise characteristics of such a gain-saturated fiber OPA. Two kinds of incident signals are injected into a fiber OPA. One is intentionally fluctuated light with large excess noise and the other is excess-noise-free (or shot-noise-limited) light. It is demonstrated that the noise suppression has an effect both on the excess noise and on beat noise due to amplified spontaneous emission generated inside the amplifier.
Kyo Inoue and Takaaki Mukai, "Experimental Study on Noise Characteristics of a Gain-Saturated Fiber Optical Parametric Amplifier," J. Lightwave Technol. 20, 969- (2002)