Investigation of four-wave mixing in flared-waveguide quantum-dot semiconductor optical amplifiers

Four-wave mixing (FWM) optical parametric amplification using uniform-width and flared-waveguide quantum dot semiconductor optical amplifiers (FW-QDSOAs) as a nonlinear interaction medium has been investigated in this report. The analysis has been performed based on numerical simulation of a set of rate equations along with the modified nonlinear Schrödinger equation (NSE). All results have been obtained in unsaturated and saturated modes for different types of waveguides (uniform-width, exponentially flared, and linearly flared). The frequency spectra of the input and output pulses have been reported and discussed. For a comprehensive and detailed comparison, both input and output pulses (i.e., pump and probe pulses) and the produced FWM pulse have been investigated in the time domain. The FWM pulse energy and the changes in the FWM pulse peak versus the device length are studied as well. Also, the peak position deviation of the FWM pulses and the pulse energy versus the input pulse energy (i.e., pump pulse) are obtained. It has been shown that the FW-QDSOAs generate a FWM pulse with higher energy and the minimum peak shift in saturated mode compared with the uniform-width amplifier. Also, in this mode, the output pump and probe pulses have the maximum peak power, maximum symmetry, and lowest distortion. The obtained results demonstrate well that in saturated mode the performance of the FW-QDSOAs is much better than the uniform-width amplifier due to a broader active region that provides a higher carrier number. Results obtained in this study agree well with previously published results for conventional flared amplifiers.