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IEEE Journal of Quantum Electronics

On the noise properties of linear and nonlinear quantum-dot semiconductor optical amplifiers: the impact of inhomogeneously broadened gain and fast carrier dynamics

A. Bilenca, G. Eisenstein

Published Jun 1, 2004• 63 citations

Abstract

We present a detailed analytical model describing the noise properties of quantum-dot (QD) optical amplifiers operating in the linear and saturated regimes. We describe the dependence of the optical noise on the main physical parameters characterizing the QD gain medium as well as on operating conditions. The optical noise at the amplifier output shows a broad-band spectrum with an incoherent spectral hole due to the gain inhomogeneity. A coherent spectral dip stemming from noise-signal nonlinear interactions is superimposed on that broad-band spectrum. The broad-band incoherent component is also calculated using an approximate model which makes use of an equivalent inhomogeneous population inversion factor. The validity of the approximation is examined in detail. We also calculate the electrical relative intensity noise and observe a spectral hole corresponding to the spectral shape of the optical noise. The most important characteristics of the optical and electrical noise spectra are determined by the degree of inhomogeneous broadening and by the fast carrier dynamics of QD amplifiers. The fast dynamics causes a very wide noise spectral hole which has important potential consequences for detection of fast data and for all optical signal processing.

DOI: 10.1109/jqe.2004.828260

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The gain and phase recovery dynamics of quantum-dot (QD) semiconductor optical amplifiers are calculated, including all the optical transitions involved in successive carrier recovery processes. The carrier recovery dynamics of inhomogeneously broadened QDs is simulated by solving 1088 coupled rate equations. The respective contributions of QD states and quantum-well carrier reservoirs to the gain and phase changes are identified both temporally and spectrally. We show that the slow phase recovery component of the QD ground state is induced by the slow carrier dynamics of the carrier reservoir due to a slowly varying line shape function of the refractive index change.

We present a theoretical model for the description of carrier and light dynamics in a quantum dot semiconductor optical amplifier that includes the inhomogeneous broadening of the quantum dots (QDs) via a spatially resolved statistical approach. The model is based on Maxwell-Bloch equations and takes into account the scattering of charge carriers between 2-D wetting layer states and bound quantum dot states, the amplification, and the wave-guiding of the light fields in the optical cavity. Simulations allow the analysis of the occupation probability of the quantum dot levels at steady state and during optical excitation by a femtosecond pulse. The influence of homogeneously and inhomogeneously broadened quantum dot media on spatial and spectral hole burning is revealed and discussed. It is shown that spatially varying dot properties lead to the reshaping of the optical pulse in the active medium.