Frequency conversion in travelling wave semiconductor laser amplifiers with bulk and quantum well structures

A microscopic model of four-wave mixing in semiconductor materials is applied to the analysis of bulk and multiple quantum well travelling wave amplifiers. The nonlinear optical response includes, in the framework of the density matrix formalism, the main four-wave mixing processes for frequency detuning of the input optical fields up to the THz region. A typical pump and probe configuration is considered, where a strong pump at angular frequency omega(pump) with a weaker probe omega(probe) is injected at the input; at the output a new signal appears with omega(signal) = 2 omega(probe) - omega(probe). Particular emphasis is given to the comparison and the optimisation of frequency conversion in bulk and quantum well amplifiers. In optimised devices, the numerical results show good conversion performances in the two kinds of structures, even if quantum well amplifiers give higher conversion gains.