We have introduced a Y-configuration model from the double-quantum-dot (QD) system to study third-order Kerr nonlinearity based on the density-matrix method. Inhomogeneity in QDs has been included in the calculations of the real (Kerr) and imaginary (absorption) parts of the density matrix, which has not been covered in the earlier Kerr calculations. Our system exhibits high controllability with a single parameter. Giant Kerr dispersion, propagation without distortion, wide electromagnetic-induced transparency, and switching between subluminal to superluminal propagation are obtained by tuning its fields. Controlling and cycling fields can also control the system in addition to the pump field.

This work proposes the double quantum dot (DQD)-metal nanoparticle (MNP) hybrid system for a high energy absorption rate. The structure is modeled using density matrix equations that consider the interaction between excitons and surface plasmons. The wetting layer (WL)-DQD transitions are considered, and the orthogonalized plane wave (OPW) between these transitions is considered. The DQD energy states and momentum calculations with OPW are the figure of merit recognizing this DQD-MNP work. The results show that at the high pump and probe application, the total absorption rate $$({Q}_{tot})$$( Q tot ) of the DQD-MNP hybrid system is increased by reducing the distance between DQD-MNP. The high $${Q}_{tot}$$Q tot obtained may relate to two reasons: first, the WL washes out modes other than the condensated main mode. Second, the high flexibility of manipulating DQD states compared to QD states results in more optical properties for DQD. The $${Q}_{DQD}$$Q DQD is increased at a small MNP radius on the contrary to the $${Q}_{MNP}$$Q MNP which is increased at a wider MNP radius. Under high tunneling, a broader blue shift in the $${Q}_{tot}$$Q tot due to the destructive interference between fields is seen and the synchronization between $${Q}_{MNP}$$Q MNP and $${Q}_{DQD}$$Q DQD is destroyed. $${Q}_{tot}$$Q tot for the DQD-MNP is increased by six orders while $${Q}_{DQD}$$Q DQD is by eight orders compared to the single QD-MNP hybrid system. The high absorption rate of the DQD-MNP hybrid system comes from the transition possibilities and flexibility of choosing the transitions in the DQD system, which strengthens the transitions and increases the linear and nonlinear optical properties. This will make the DQD-MNP hybrid systems preferable to QD-MNP systems.

An ${\mathrm{InSb}}_{1-x}{\mathrm{Bi}}_x$ quantum dot (QD) photodetector was studied in this work. First, the quantum efficiency (QE) was modeled for this structure where the relations of electron and hole densities and their contribution to current density are derived. The absorption of $p$-, $n$- and depletion regions were calculated before specifying their contribution to QE. It is shown that adding Bi to Sb-based QD structures increases their absorption and QE. High Bi content extended the cutoff detection wavelength of these detectors.

Quantum entropy in a ladder-plus-Y double quantum dot system was calculated. The controlling parameters that are examined are four coherent optical fields, three tunneling components, and incoherent optical pumping. This work differs from others by the inclusion of a wetting layer (WL) and the calculation of momenta for each transition. The results showed that the entropy depends on the difference between the carrier occupations in the states of these two quantum dots (QDs). It is also shown that the probe optical field reduces the entropy, while the pumping field increases it. Turning off the main tunneling component removes the entropy, while high WL–QD momentum increases the entropy. Taking the same value of momentum for all transitions (the case of other works) underestimates the entropy.

The theory of four-wave mixing (FWM) in quantum dot (QD) semiconductor optical amplifiers (SOAs) has been discussed by the combination of the QD rate equations system and the pulse propagation in QD SOAs. This study has covered two types of QD structures: the two-level QD structure, where the ground state (GS) and wetting layer have been considered; and the three-level QD structure, where the excited state (ES) has been taken into account. The relations for differential gain were also discussed. FWM efficiency and its components, comprising spectral hole burning, carrier heating and carrier density pulsation (CDP), are calculated. The results show that inclusion of ES is essential. At a high carrier density and for a long term frequency, the FWM was found to be detuning independently while it is symmetric for short pulses. Neglecting CH makes the FWM in QD SOAs symmetric and detuning independent, which are desired characteristics for optical communication applications. The results corroborate available experimental observations. The effective capture time of QD is the main parameter and can be ascribed to the differences between the two- and three-level models.