Analysis of optical phase-conjugate characteristics of picosecondfour-wave mixing signals in semiconductor optical amplifiers

摘要

We have analyzed for the first time the optical phase-conjugatencharacteristics of picosecond four-wave mixing (FWM) signals innsemiconductor optical amplifiers (SOAs) using the finite-difference beamnpropagation method (FD-BPM). We show that the optical phase-conjugatencharacteristics of the FWM signals are strongly dependent on input pumpnpulsewidths. As a typical example, we have demonstrated that SOAs act asnan ideal phase-conjugator, within the confines of reversing the chirp ofnoptical pulses, for a 10-ps input pump pulse and a ~2.2-ps linearlynchirped input probe pulse. When the pulsewidth of pump pulse becomesnshort, the minimum compressed pulsewidth is obtained by using a fibernshorter in length than the input fiber, but having the same groupnvelocity dispersion as the input fiber. For a much shorter pump pulsensuch as 1 ps, the short FWM signal can be obtained via the gatingncharacteristics of the FWM. However, only a part of the phaseninformation is copied to the FWM signal due to such gatingncharacteristics. The phase information is also degraded due to the fastnnonlinear effect in the SOA. Thus, the pulsewidth is not compressed bynpropagation through a dispersive medium