Crosstalk in double-pumped fiber optic parametric amplifiers for wavelength division multiplexing systems

We study experimentally inter-channel crosstalk in double-pumped fiber optic parametric amplifiers constructed with conventional dispersion shifted fibers (DSFs) having different lengths (LA = 13.8, LB = 6.8, LC = 4.3, and LD = 0.8 km). For long fibers (LA and LB), eye diagram measurements in a 5-channel (100 GHz spacing) system show that in order to have negligible crosstalk, the output signal power per channel, Ps, should be limited to Ps < 0 dBm. By decreasing the fiber length (to LC) it is possible to increase the output signal power and/or the number of signals while keeping the crosstalk on negligible levels. This trend was further confirmed by using a very short DSF (LD = 0.8 km).Finally, we experimentally demonstrate that a general trend in 2P-FOPAs is that spurious FWM increases with the number of signal channels up to a given number of channels when a saturation regime is reached. This saturation of the generation of spurious tones occurs when the bandwidth occupied by the signals exceeds ∼4–5 nm.