Quantum dot semiconductor optical amplifiers for wavelength conversion using cross-gain modulation

Wavelength conversion using cross-gain modulation in quantum dot semiconductor optical amplifiers is investigated. Small signal measurements reveal that with increasing bias the cross-gain modulation converts from low efficiency, limited to 10 GHz bandwidth to a very efficient one with bandwidths well exceeding 40 GHz. Two different saturation mechanisms are responsible for this pronounced influence of the bias current: a) total carrier depletion which leads to a slow broadband cross gain saturation and b) spectral hole burning which causes spectrally narrowband high speed XGM. With increasing current the saturation by depleting the carrier reservoir, which feeds the quantum dots, is minimized and therefore spectral hole burning becomes more dominant. Large signal wavelength conversion experiments using 50 ps pulses indicate that efficient high speed cross gain modulation is feasible for pump and probe signal detuning up to 10 nm. With increasing detuning larger pulse broadening and a decreasing efficiency is observed, consistent with the small signal results.