This paper describes the theoretical and experimental investigation of the transfer of low-frequency intensity modulation (IM) from pump to signal in fiber optical parametric amplifiers (OPAs). It is first established that low-frequency IM of the pump remains unchanged over the length of the amplifier in spite of the presence of parametric gain. The pump-power dependence of the OPA gain is then used to calculate the instantaneous effect of pump IM on the signal and idler output powers. These calculations are performed for both one- and two-pump OPAs. The main predictions are that 1) the ratio rho of the signal intensity modulation depth to that of the pump varies across the OPA gain spectrum and 2) for a 20-dB gain, rho can exceed 10 at some wavelengths, which indicates that this effect can be detrimental. Experiments have been performed to verify these predictions. Using sinusoidal IM of the pump, the resulting amplified signal IM was measured, and the experimental results were found to be in good agreement with the theoretical predictions.
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