17 research outputs found
Strong amplitude-phase coupling in submonolayer quantum dots
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 109, 201102 (2016) and may be found at https://doi.org/10.1063/1.4967833.Submonolayer quantum dots promise to combine the beneficial features of zero- and two-dimensional carrier confinement. To explore their potential with respect to all-optical signal processing, we investigate the amplitude-phase coupling (α-parameter) in semiconductor optical amplifiers based on InAs/GaAs submonolayer quantum dots in ultrafast pump-probe experiments. Lateral coupling provides an efficient carrier reservoir and gives rise to a large α-parameter. Combined with a high modal gain and an ultrafast gain recovery, this makes the submonolayer quantum dots an attractive gain medium for nonlinear optical signal processing
Feedback and injection locking instabilities in quantum-dot lasers: a microscopically based bifurcation analysis
We employ a nonequilibrium energy balance and carrier rate equation model based on microscopic semiconductor theory to describe the quantum-dot (QD) laser dynamics under optical injection and time-delayed feedback. The model goes beyond typical phenomenological approximations of rate equations, such as the α-factor, yet allows for a thorough numerical bifurcation analysis, which would not be possible with the computationally demanding microscopic equations. We find that with QD lasers, independent amplitude and phase dynamics may lead to less complicated scenarios under optical perturbations than predicted by conventional models using the α-factor to describe the carrier-induced refractive index change. For instance, in the short external cavity feedback regime, higher critical feedback strength is actually required to induce instabilities. Generally, the α-factor should only be used when the carrier distribution can follow the QD laser dynamics adiabatically.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement
Many-body and nonequilibrium effects on relaxation oscillations in a quantum-dot microcavity laser
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 97, 111102 (2010) and may be found at https://doi.org/10.1063/1.3488004.We investigate many-body and nonequilibrium effects on the dynamical behavior of a quantum-dot laser diode. Simulations, based on the Maxwell-semiconductor-Bloch equations, show strong dependence of the turn-on delay on initial cavity detuning, because of a dynamical shift in the quantum-dot distribution caused by band gap renormalization. Gain switch behavior is found to be insensitive to inhomogeneous broadening, because the balancing between many-body and free-carrier effects inhibits a cavity resonance walk-off. Both the relaxation oscillation damping and frequency are found to increase with decreasing inhomogeneous broadening widths. However, in contrast to bulk and quantum-well lasers, oscillation damping increases less than the frequency.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement
Influencing modulation properties of quantum-dot semiconductor lasers by carrier lifetime engineering
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 101, 131107 (2012) and may be found at https://doi.org/10.1063/1.4754588.The relaxation oscillation (RO) parameters and modulation properties of quantum-dot lasers are investigated depending on effective charge carrier scattering lifetimes of the confined quantum-dot states. We find three dynamical regimes of the laser, characterized by the level of synchronization between carrier dynamics in quantum-dots and quantum-well. For scattering rates similar to the RO frequency, a strong damping is found. On either side of this regime, simulations show low RO damping and improved dynamical response. Depending on the regime, the modulation response differs from conventional analytical predictions. Our results suggest the possibility of tailoring quantum-dot laser dynamical behavior via bandstructure engineering.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement
Self-induced ultrafast electron-hole plasma temperature oscillations in nanowire lasers
Nanowire lasers can be monolithically and site-selectively integrated onto
silicon photonic circuits. To assess their full potential for ultrafast
opto-electronic devices, a detailed understanding of their lasing dynamics is
crucial. However, the roles played by their resonator geometry and the
microscopic processes that mediate energy exchange between the photonic,
electronic, and phononic subsystems are largely unexplored. Here, we study the
dynamics of GaAs-AlGaAs core-shell nanowire lasers at cryogenic temperatures
using a combined experimental and theoretical approach. Our results indicate
that these NW lasers exhibit sustained intensity oscillations with frequencies
ranging from 160 GHz to 260 GHz. As the underlying physical mechanism, we
identified self-induced electron-hole plasma temperature oscillations resulting
from a dynamic competition between photoinduced carrier heating and cooling via
phonon scattering. These dynamics are intimately linked to the strong
interaction between the lasing mode and the gain material, which arises from
the wavelength-scale dimensions of these lasers. We anticipate that our results
could lead to new approaches for ultrafast intensity and phase modulation of
chip-integrated nanoscale semiconductor lasers.Comment: Revised manuscrip
Dynamics of a stochastic excitable system with slowly adapting feedback
We study an excitable active rotator with slowly adapting nonlinear feedback
and noise. Depending on the adaptation and the noise level, this system may
display noise-induced spiking, noise-perturbed oscillations, or stochastic
busting. We show how the system exhibits transitions between these dynamical
regimes, as well as how one can enhance or suppress the coherence resonance, or
effectively control the features of the stochastic bursting. The setup can be
considered as a paradigmatic model for a neuron with a slow recovery variable
or, more generally, as an excitable system under the influence of a nonlinear
control mechanism. We employ a multiple timescale approach that combines the
classical adiabatic elimination with averaging of rapid oscillations and
stochastic averaging of noise-induced fluctuations by a corresponding
stationary Fokker-Planck equation. This allows us to perform a numerical
bifurcation analysis of a reduced slow system and to determine the parameter
regions associated with different types of dynamics. In particular, we
demonstrate the existence of a region of bistability, where the noise-induced
switching between a stationary and an oscillatory regime gives rise to
stochastic bursting
Self-induced ultrafast electron-hole-plasma temperature oscillations in nanowire lasers
Nanowire lasers can be monolithically and site-selectively integrated onto silicon photonic circuits. To assess their full potential for ultrafast optoelectronic devices, a detailed understanding of their lasing dynamics is crucial. However, the roles played by their resonator geometry and the microscopic processes that mediate energy exchange between the photonic, electronic, and phononic subsystems are largely unexplored. Here, we study the dynamics of GaAs-AlGaAs core-shell nanowire lasers at cryogenic tem- peratures using a combined experimental and theoretical approach. Our results indicate that these NW lasers exhibit sustained intensity oscillations with frequencies ranging from 160 GHz to 260 GHz. As the underlying physical mechanism, we have identified self-induced electron-hole plasma temperature oscilla- tions resulting from a dynamic competition between photoinduced carrier heating and cooling via phonon scattering. These dynamics are intimately linked to the strong interaction between the lasing mode and the gain material, which arises from the wavelength-scale dimensions of these lasers. We anticipate that our results could lead to optimised approaches for ultrafast intensity and phase modulation of chip-integrated semiconductor lasers at the nanoscale
Broadband semiconductor light sources operating at 1060 nm based on InAs:Sb/GaAs submonolayer quantum dots
In this paper, we investigate the potential of submonolayer-grown InAs:Sb/GaAs quantum dots as active medium for opto-electronic devices emitting in the 1060 nm spectral range. Grown as multiple sheets of InAs in a GaAs matrix, submonolayer quantum dots yield light-emitting devices with large material gain and fast recovery dynamics. Alloying these structures with antimony enhances the carrier localization and red shifts the emission, whereas dramatically broadening the optical bandwidth. In a combined experimental and numerical study, we trace this effect to an Sb-induced bimodal distribution of localized and delocalized exciton states. While the former do not participate in the lasing process, they give rise to a bandwidth broadening at superluminescence operation and optical amplification. Above threshold laser properties like gain and slope efficiency are mainly determined by the delocalized fraction of carriers