Incoherent Pumping Field Research Articles

Proposal for a compact design for real-time optical bistability switching via a semiconductor cavity containing quantum wells.

A compact design for semiconductor cavities including coupled AlGaN/AlGaAs quantum wells is proposed for all-optical switching of the bistability process. First, physical and geometrical parameters are optimized to engineer the conducting electrons' energy levels in the quantum wells. Then, finite element simulations based on Schrödinger equations are executed to estimate the states of the charge carriers for AlGaN/AlGaAs as the active region. Next, the optical coupling and pumping fields are applied to the active region to both initiate the bistability and facilitate its real-time control. The Maxwell-Bloch approach based on rotating-wave approximation is employed to analyze the optimal conditions for controlling the behavior of optical bistability (OB). It is found that the threshold of OB can be optimized to have low values by tuning the intensity of coupling fields and the rate of an incoherent pumping field. This provides a fast real-time switching facility to control output intensity of the systems. The proposed scheme could have potential applications in optical memories, in which it is paramount to have active control over the readout of the system's quantum states. Thanks to the high nonlinear response of semiconductors, the featured device would be a prospective candidate for on-chip ultrasubluminal wave propagation studies and narrowband real-time switching and filtering applications.

Pulse propagation through a dielectric slab doped with a triple quantum dot nanostructure

The propagation of an electromagnetic pulse through a dielectric slab doped with a triple quantum dot (QD) nanostructure has been discussed in the presence of electron tunneling. We include the effect of an incoherent pump field in the transmission and reflection of a pulse in a triple QD. It is shown that the reflected and transmitted pulses can be switched from subluminal to superluminal light propagation by changing either the rate of the incoherent pump field or the inter-dot tunneling between QD1, QD2 and QD3 in a slab. Furthermore, it is demonstrated that the inter-dot tunnel coupling can significantly affect the behavior of optical bistability (OB) and optical multi-stability (OM) in a dielectric slab. The obtained results can be used for the development of new types of nanoelectronic devices for realizing the switching process.

Controlling the electromagnetically induced grating via spontaneously generated coherence

A new arrangement of an electromagnetically induced grating in a three-level Ladder-type atomic system with indirect incoherent pumping field is proposed. It is found that the diffraction intensity can efficiently be controlled by the spontaneously generated coherence (SGC). In addition, the diffraction intensity spectrum can dramatically be tuned by manipulating the coupling field intensity, resonance conditions, the rate of an indirect incoherent pumping field, and interaction length.

Adjusting the left-handedness in a cold 87Rb atomic system via multiple parameter modulation

We demonstrate adjusting the left-handedness in a cold 87Rb atomic system by its number density, the strong coupling field and two incoherent pumping fields. The results show that a higher density of 87Rb atoms and a stronger coupling field can influence the left-handedness more, while increasing the two incoherent pumping fields enhances the negative magnetic response but depresses the negative electric response. The left-handedness adjusted by multiple parameter in a cold 87Rb atomic system provides the flexibility and feasibility for the coming experiments.

Impact of the incoherent pump fields on the optical bistability of a dielectric slab doped with semiconductor quantum wells

The behavior of the optical bistability (OB) and optical multi-stability (OM) is investigated in an optical system which consists of a dielectric slab doped with a three-level asymmetric semiconductor quantum well system. It is found that the optical bistability can be converted to optical multi-stability (or vice versa) by adjusting different physical parameters such as the strength of Fano interference and the rate of incoherent pump field. Moreover, we find that the OB converts to OM by increasing the slab thickness. This optical system may provide some new possibilities for test the switching process.

Propagation of a laser pulse and electro-optic switch in a GaAs/AlGaAs quadruple-coupled quantum dot molecule nanostructure

Based on a GaAs/AlGaAs quadruple-coupled quantum dot heterostructure, an optical switch for controlling superluminal and subluminal light propagation is suggested. The transient and steady state behaviour of the absorption and dispersion of a probe pulse laser field through a quadruple quantum dot molecule are studied. We show that the group velocity of a light pulse can be controlled from superluminal to subluminal, or vice versa, by controlling the tunnelling rates between the quantum dots. The required switching time is calculated and we find it to be about 8 ps. We also investigated a method for the all-optical switching of probe field absorption from a large amount to nearly zero just by applying an incoherent pumping field. We estimated the required switching time for this case to be between 3 and 14 ps.

Incoherent control of Goos–Hänchen shifts in a four-level InGaN/GaN quantum dot nanostructure

In this paper, we propose a new configuration for manipulating Goos–Hänchen (GH) shifts in reflected and transmitted probe beams in a fixed geometrical scheme with a confined four-level InGaN/GaN quantum dot nanostructure. Here, the four-level quantum dot nanostructure is driven by a weak probe light, a coherent coupling field, and two broadband polarized fields that serve as the incoherent pumping fields. We theoretically show that by modulation of the external coupling field, incoherent pumping rates, and detuning of the probe light, the GH shifts in the reflected and transmitted probe light can be controlled. Our results show that enhanced GH shifts of reflected and transmitted probe beams can be obtained by simultaneous use of incoherent pumping rates and detuning of the probe light. Moreover, we find that the GH shifts in both reflected and transmitted probe beams can be negative or positive at certain angles of the incident probe field. Thus, these results may provide some new possibilities for technological applications in all-optical systems based on nanostructure devices.

Influence of Fano interference and incoherent processes on optical bistability in a four-level quantum dot nanostructure

Role of Fano interference and incoherent pumping field on optical bistability in a four-level designed InGaN/GaN quantum dot nanostructure embedded in a unidirectional ring cavity are analyzed. It is found that intensity threshold of optical bistability can be manipulated by Fano interference. It is shown that incoherent pumping fields make the threshold of optical bistability behave differently by Fano interference. Moreover, in the presence of Fano interference the medium becomes phase-dependent. Therefore, the relative phase of applied fields can affect the behaviors of optical bistability and intensity threshold can be controlled easily.

Slow and fast light propagation in a triple quantum well nanostructure

In this paper, we investigate the absorption and dispersion properties of a weak probe field in a triple quantum well nanostructure by using the incoherent pumping fields. A deep 7.1 nm-thick GaAs well is coupled, on one side, to two shallow 6.8 nm-thick Al0.2Ga0.8As wells by a 2.5 nm-thick Al0.4Ga0.6As barrier. The two shallow wells are separated by a 2.0 nm-thick Al0.4Ga0.8As barrier. Both sides of quantum well contact with 36 nm Al0.4Ga0.6As. Therefore, this type of triple quantum well nanostructure can be used as a suitable medium for studying the effect of spontaneously generated coherence (SGC) and interference between incoherent pumping fields on absorption and dispersion properties of weak probe light. We find that the interferences from spontaneous emission and incoherent pumping processes can change the slope of dispersion and group velocity of the probe light from slow to fast or vice versa. Moreover, it is demonstrated that the group velocity of the light pulse can be controlled with the rates of incoherent pumping fields.

Controlling the Goos–Hänchen Shift via Incoherent Pumping Field and Electron Tunneling in the Triple Coupled InGaAs/GaAs Quantum Dots

We study the controlling of the Goos-Hänchen (GH) shifts in reflected and transmitted light beams in the triple coupled InGaAs/GaAs quantum dot (QD) nanostructures with electron tunneling and incoherent pumping field. It is shown that the lateral shift can become either large negative or large positive, which can be controlled by the electron tunneling and the rate of incoherent pump field in different incident angles. It is also demonstrated that the properties of the GH shifts are strongly dependent on the probe absorption beam of the intracavity medium due to the switching from superluminal light propagation to subluminal behavior or vice versa. Our suggested system can be considered as a new theoretical method for developing a new nano-optoelectronic sensor.

Controllable optical bistability and multistability in a graphene structure under external magnetic field

We investigate the behavior of optical bistability (OB) and optical multistability (OM) based on quantum coherence in a Landau-quantized graphene structure. Such a tunable four-level system is driven coherently by two coherent fields and an incoherent pumping field inside the unidirectional ring cavity. The influence of system parameters on the threshold of the onset of OB and OM is studied. It is found that one can efficiently control the OB/OM threshold intensity and the hysteresis loop by using the system parameters. The results obtained may be used in real experiments for the development of new types of nanoelectronic devices for realizing an all-optical switching process.

Controlling the optical bistability in a quantum-well nanostructure via indirect incoherent pump field

We investigate the optical bistability (OB) behavior in an asymmetric two-coupled quantum well structure inside a unidirectional ring cavity. By controlling the assisting coherent driven field and frequency detuning of the driven laser field, the threshold of OB can be controlled, and even OB converted to optical multistability (OM) by adjust driven pump field detuning. In addition, when we apply an incoherent indirect pump field, we find that the appearance and disappearance of OB and its threshold can easily be controlled by incoherent indirect pump rate.

Quantum theory of the emission spectrum from quantum dots coupled to structured photonic reservoirs and acoustic phonons

Electron-phonon coupling in semiconductor quantum dots plays a significant role in determining the optical properties of excited excitons, especially the spectral nature of emitted photons. This paper presents a comprehensive theory and analysis of emission spectra from artificial atoms or quantum dots coupled to structured photon reservoirs and acoustic phonons, when excited with incoherent pump fields. As specific examples of structured reservoirs, we chose a Lorentzian cavity and a coupled cavity waveguide, which are of current experimental interest. For the case of optical cavities, we directly compare and contrast the spectra from three distinct theoretical approaches to treat electron-phonon coupling, including a Markovian polaron master equation, a non-Markovian phonon correlation expansion technique and a semiclassical linear susceptibility approach, and we point out the limitations of these models. For the cavity-QED polaron master equation, we give closed form analytical solutions to the phonon-assisted scattering rates in the weak excitation approximation, fully accounting for temperature, cavity-exciton detuning and cavity dot coupling. We show explicitly why the semiclassical linear susceptibility approach fails to correctly account for phonon-mediated cavity feeding. For weakly coupled cavities, we calculate the optical spectra using a more general reservoir approach and explain its differences from the above approaches in the low Q limit of a Lorentzian cavity. We subsequently use this general reservoir to calculate the emission spectra from quantum dots coupled to slow-light photonic crystal waveguides, which demonstrate a number of striking photon-phonon coupling effects. Our quantum theory can be applied to a wide range of photonic structures including photonic molecules and coupled-cavity waveguide systems.

Investigate the entanglement of a quintuple quantum dot molecule via entropy

The time evaluation of quantum entropy in the quintuple-coupled quantum dots based on a GaAs/AlGaAs heterostructure is theoretically investigated. The quantum entanglement of quantum dot molecules (QDMs) and their spontaneous emission fields is then discussed via quantum entropy. The effects of the tunneling effect, i.e. , an incoherent pumping field and voltage controllable detuning on entanglement between QDMs and their spontaneous emission fields is then discussed. We found that in the presence of the tunneling effect and an incoherent pumping field the entanglement between the QDMs and their spontaneous emission fields is increased, while in the presence of voltage controllable detuning the entanglement reduced. Finally, we investigated the switching time from a disentangled state to an entangled state. The results may provide some new possibilities for technological applications in optoelectronics, solid-state quantum information science, quantum computing, teleportation, encryption, and compression codec.

The gain amplification via spontaneously generated coherence with incoherent pump field: A comparison of optical properties between open and closed four level systems

We studied the steady state and transient evolution of probe absorption and population in an open four level N-type atomic system and compared its transient and steady state properties with the corresponding closed system. The effects of incoherent pump field, spontaneously generated coherence, probe detuning and cavity parameters (i.e. the atomic exit rate from cavity and atomic injection rates) on transient and steady state response of probe field and lasing with and without inversion are investigated. It is realized that in an open N-type system, regardless of incoherent pump field applied or not, due to existence of cavity parameter, by adjusting the values of other parameters, we can always obtain lasing without inversion, while there is no gain in closed system without incoherent pump field. Also results are shown that, the probe gain can be greatly amplified with SGC at the presence of incoherent pump field and absence of population inversion. We found that in the same condition the open system is favorable scheme for lasing without inversion.

Bistable behaviors of weak probe light via coherent and incoherent fields

In this paper, the bistable behaviors of weak probe light in a unidirectional ring cavity with a four-level atomic system are discussed. We find that in the presence of spontaneously generated coherence (SGC), the medium is completely phase dependent and the intensity threshold of optical bistability can be controlled. The effect of an incoherent pumping field on optical bistability in the presence and absence of SGC is also analyzed. Moreover, the group index behavior of weak probe light is investigated. We show that the intensity threshold of optical bistability can be controlled by light propagation switching from slow to fast by different parameters of the atomic medium.

Large Kerr coefficient via quantum interference induced by incoherent pump field and spontaneous emission

Nonlinear response of a four-level atomic system with two closely lying intermediate levels to the incoherent pump field is investigated. It is shown that without coherent laser control field and just by quantum interference of incoherent pumping field and spontaneous emission, a giant Kerr nonlinearity can be achieved. It is also demonstrated that the enhanced Kerr nonlinearity is located in the reduced absorption region. In addition, the effect of direct and indirect incoherent pump rates on Kerr nonlinearity is then discussed.

Influence of incoherent pumping field on spatial evolution of gain without inversion in a four-level quantum dot nanostructure

We investigated the propagation effect on gain without inversion (GWI) phenomena in an open four level quantum dot nanostructure in the presence and absence of incoherent pumping field. The simulation results show that, the ratio of the injection rates and strength of incoherent pumping field has remarkable effect on spatial evolution of GWI and output. We can obtain the optimal GWI and output by choosing appropriate values of parameters. The theoretical results show that, in the open system the value of gain (output) in the absence of incoherent pumping field is much larger than that in the presence of incoherent pumping field.

Manipulation of tunneling induced transparency windows and optical switching features in fivefold quantum dot molecules

Transient and steady-state behavior of the probe absorption in a multiple quantum dot (QD) molecule composed of five quantum dots molecules (with a center dot and four satellite dots) is explored with application in all-optical switching. We find that the absorption spectra of the light pulse can be efficiently modified via the effect of inter-dot tunnel couplings of QDs and incoherent pumping field. Results show that depending on the values of system parameters, at least one and at most four tunneling induced transparency (TIT) windows can be established in the multiple QD medium. We then investigate the dynamical behavior of the probe absorption-amplification as well as the optical switching in pulsed regime. By adjusting the incoherent pumping rate, the required switching time for changing the gain to the absorption or vice versa is then estimated approximately to be 20.7 nanosecond (ns), that is an appropriate time for such a QDM-based switch.

Electrical and optical control of entanglement entropy in a coupled triple quantum dot system

We investigated theoretically the entanglement creation through tunneling rate and fields in a four-level triple quantum dot molecule based on InAs/GaAs/AlGaAs heterostructure in both steady state and transient state. We demonstrate that the entanglement entropy among the QDM and its spontaneous emission fields can be controlled by coherent and incoherent pumping field and tunnel-coupled electronics levels. The results may provide some new possibilities for technological applications in solid-state quantum information science, quantum computing, teleportation, encryption, compression codec, and optoelectronics.