Two-photon-absorption-assisted Tera Hertz optical gain modulation in quantum-dot optical amplifiers

Ultrafast carrier dynamics is examined in a quantum-dot (QD) semiconductor optical amplifier with a rate equation model which includes two-photon absorption (TPA) and gain bleaching during the propagation of 120 fs optical pulses at the wavelength near telecommunication wavebands. The TPA-generated carriers in the bulk region of the waveguide relax to the QDs via the wetting layer, which occurs synchronously in time and space with QD carrier depletion. This leads to efficient enhancement of the rate of carrier capture into the QDs, reducing the pattern effects for ultra high-speed optical signal processing.