We report direct observations of Rabi oscillations and self-induced transparency in a quantum dot optical amplifier operating at room temperature. The experiments make use of pulses whose durations are shorter than the coherence time which are characterized using Cross-Frequency-Resolved Optical Gating. A numerical model which solves the Maxwell and Schrödinger equations and accounts for the inhomogeneously broadened nature of the quantum dot gain medium confirms the experimental results. The model is also used to explain the relationship between the observability of Rabi oscillations, the pulse duration and the homogeneous and inhomogeneous spectral widths of the semiconductor.

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InP diode lasers with InAs quantum dot (QD) like active regions emitting at 1.55 μm have been fabricated. The QDs were grown in an As2 mode, which reduces the degree of elongation of the nanospecies yielding nearly circular shapes. Lasers with four to six dot layers show low absorption αi<10 cm−1 and high modal gain Γg0 of 10 cm−1 per QD layer (QDL) and above. The high gain values are compatible with an inhomogeneous linewidth that is much narrower than in quantum dash material, which is the common nanoscale gain material in the InP system.

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We report on a characterization of fundamental gain dynamics in recently developed InAs/InP quantum-dot semiconductor optical amplifiers. Multi-wavelength pump-probe measurements were used to determine gain recovery rates, following a powerful optical pump pulse, at various wavelengths for different bias levels and pump excitation powers. The recovery was dominated by coupling between the electronic states in the quantum-dots and the high energy carrier reservoir via capture and escape mechanisms. These processes determine also the wavelength dependencies of gain saturation depth and the asymptotic gain recovery level. Unlike quantum-dash amplifiers, these quantum-dots exhibit no instantaneous gain response, confirming their quasi zero-dimensional nature.