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Acta Physica Polonica A

Sub-Nanosecond Phase Recovery in Quantum-Dot Semiconductor Optical Amplifiers

Kambiz Abedi, H. Taleb

Published Feb 1, 2013• 0 citations

Abstract

In this paper, optimal design of a pumping scheme for achieving the best gain and phase response in quntum--dot semiconductor optical ampliers is investigated.For the rst time, the dynamic response of the quntum-dot semiconductor optical amplier is evaluated under three dierent pumping schemes, known as optical pumping, electrical pumping, and electro-optical pumping.Simulation results show that the shortest gain recovery time in quntum-dot semiconductor optical ampliers can be achieved under the electrical pumping scheme.However, under the optical pumping and electro-optical pumping schemes, the quntum-dot semiconductor optical amplier represents a shorter phase recovery compared to the electrical pumping scheme.We found that a sub-nanosecond phase recovery in the quntum-dot semiconductor optical amplier can be achieved under the OP and electro--optical pumping schemes, which can never be achieved under the electrical pumping, because of the slow carrier dynamics of the carrier reservoir.Also, it was found that the gain recovery process in an optically pumped quntum-dot semiconductor optical amplier can be signicantly accelerated at cryogenic temperatures.This result demonstrates the superiorities of the optical pumping scheme over the electrical pumping and electro-optical pumping schemes at low temperatures, where both the gain and phase recovery times of an optically pumped quantum-dot semiconductor optical amplier are drastically decreased.

DOI: 10.12693/aphyspola.123.407

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The effect of additional optical pumping injection into the ground-state ensemble on the ultrafast gain and the phase recovery dynamics of electrically-driven quantum-dot semiconductor optical amplifiers is numerically investigated by solving 1088 coupled rate equations. The ultrafast gain and the phase recovery responses are calculated with respect to the additional optical pumping power. Increasing the additional optical pumping power can significantly accelerate the ultrafast phase recovery, which cannot be done by increasing the injection current density.

We numerically investigate the effect of the wetting-layer (WL) density of states on the gain and phase recovery dynamics of quantum-dot semiconductor optical amplifiers in both electrical and optical pumping schemes by solving 1088 coupled rate equations. The temporal variations of the ultrafast gain and phase recovery responses at the ground state (GS) are calculated as a function of the WL density of states. The ultrafast gain recovery responses do not significantly depend on the WL density of states in the electrical pumping scheme and the three optical pumping schemes such as the optical pumping to the WL, the optical pumping to the excited state ensemble, and the optical pumping to the GS ensemble. The ultrafast phase recovery responses are also not significantly affected by the WL density of states except the optical pumping to the WL, where the phase recovery component caused by the WL becomes slowed down as the WL density of states increases.

We numerically investigate the influence of the optical pumping wavelength on the ultrafast gain and phase recovery acceleration of quantum-dot (QD) semiconductor optical amplifiers (SOAs) by solving 1088 coupled rate equations. The temporal variations of the gain and phase recovery response at the ground state (GS) of QDs are calculated at various signal wavelengths when the optical pumping wavelengths at the excited state (ES) of QDs are varied. The phase recovery response is fastest when the wavelength of the signal and pumping beams corresponds to the respective emission wavelength of the GS and the ES in the same size of QDs. The absorption efficiency of the optical pumping beam at the ES is determined by the Lorentzian line shape function of the homogeneous broadening.

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.

In this study, design of optical pumping (OP) scheme for quantum‐dot semiconductor optical amplifiers (QD‐SOAs) is investigated. To evaluate the static and dynamic responses of the QD‐SOA under OP, a non‐linear state‐space model is derived in which the effects of the homogeneous and inhomogeneous broadening of the gain medium and the spectral dependence of the input signals are taken into account. Using this model, the effects of the wavelength and power of the pump signal and the homogeneous and inhomogeneous linewidths are studied in detail. Simulation results demonstrate that optimal operation of the QD‐SOA under the OP scheme is realised if the detuning between the pump wavelength and the input signal wavelength is constant (around 100 nm for our investigated device). The authors found that OP scheme can be employed for non‐linear signal processing applications, where the superiorities of the OP against the electrical pumping appear for small values of the homogeneous and inhomogeneous linewidths.

We numerically investigate the influence of the pump-probe wavelength on the gain and phase recovery dynamics of quantum-dot (QD) semiconductor optical amplifiers (SOAs). The temporal variations of the gain and phase recovery response are calculated at various pump-probe wavelengths, covering the emission wavelength of both the QD ground and excited states. The gain recovery becomes faster at the longer pump-probe wavelength due to the enlarged carrier escape time. The initial phase change turns from a negative to a positive value as the pump-probe wavelength becomes smaller, which is determined by the spectral position of the pump-probe wavelength in reference to the Gaussian-shaped inhomogeneous broadening. The calculated results agree with the previous experimental results measured by other experimental groups.