Kerr nonlinearity enhancement by double tunnelling from quantum dot nanostructure

A model of the dynamical equations of the density matrix describes double tunnelling between double quantum dot (QD) system states, this is to study Kerr nonlinearity in QD structure. Inhomogeneity in the QD system is included which is not included in earlier studies of Kerr nonlinearity in QDs. Possibilities of subluminal and superluminal light propagation and switching between them are examined. Double tunnelling is shown to obtain giant Kerr dispersion compared with single tunnelling. High conduction- and low valence-band tunnelling components are required to obtain high Kerr dispersion. Working with one tunnel component reduced Kerr dispersion and switching between subluminal and superluminal can be obtained and the EIT window can be removed. Keywords: Quantum dot, Tunnelling, Kerr dispersio

Optical gain of CdxZn1−xTe quantum dot structures

Abstract Gain spectra of CdxZn1−xTe/AlGaN undoped and doped quantum dot (QD) structures are studied under the inhomogeneous broadening assumption at four Cd mole fractions (x=0.25,0.5,0.75,0.95). For the Cd0.25Zn0.75Te QD structure, two peaks appear due to the excited state (ES) and ground state (GS) transitions. The gain for the doped structures doubles the undoped ones. The gain increases while the wavelength is reduced with increasing Cd content due to the broader band discontinuity between the QD states. The discontinuity of the bands for each structure (mole fraction) is calculated, which is one of the merits of this work. While the structure Cd0.25Zn0.75Te offers the peak wavelengths 470 and 630 nm, other mole fractions offer the wavelengths between them. These visible bands are essential in different applications. The effect of QD size effect is also examined. The wavelength is extended by 20 nm for each 1 nm QD height increment

Four-wave mixing in quantum dot SOAs: Theory of carrier heating

Carrier heating (CH) theory in a four-wave mixing quantum dot structure has been investigated. The impact of wetting layer (WL) carrier density, CH time constant, effective intraband relaxation time have been examined. The derived heat capacity for QD structure have (T-1) dependence. It is shown here that both WL carrier density and QD excited state (ES) occupation controls the overall nonlinear contributions. Then inclusion of WL and ES in the CH induces a new equilibrium reached at a faster recovery time. The proposed model yields results in a line with experiments at high carrier density reflecting the efficiency of our model. Keywords: Quantum dot, Carrier heating, Four-wave mixing, Excited stat

Giant gain from spontaneously generated coherence in Y-type double quantum dot structure

A theoretical model was presented for linear susceptibility using density matrix theory for Y-configuration of double quantum dots (QDs) system including spontaneously generated coherence (SGC). Two SGC components are included for this system: V, and Λ subsystems. It is shown that at high V-component, the system have a giga gain. At low Λ-system component; it is possible to controls the light speed between superluminal and subluminal using one parameter by increasing SGC component of the V-system. This have applications in quantum information storage and spatially-varying temporal clock. Keywords: Quantum dot, Spontaneously generated coherence, Linear susceptibilit

Complex dynamics in quantum dot light emitting diodes

We report both experimentally and theoretical investigation the appearance of Mixed Mode Oscillations (MMOs) and chaotic spiking in a Quantum Dot Light Emitting Diode (QDLED). In the theoretical treatment the proposed model reproduces Homoclinic Chaos (HC) and MMOs. The dynamics is completely determined by the variation of the injecting bias current in the wetting layer of the QDLED. The influence of the injecting current on the transition between Mixed Mode Oscillations and chaotic behavior has been also investigated. It was found that the theoretical model verifies the experimental findings