Phase-dependent optical bistability and multistability in a semiconductor quantum well system

We theoretically investigate the hybrid absorptive-dispersive optical bistability and multistability in a four-level inverted-Y quantum well system inside a unidirectional ring cavity. We find that the coupling field, the pumping field as well as the cycling field can affect the optical bistability and multistability dramatically, which can be used to manipulate efficiently the threshold intensity and the hysteresis loop. The effects of the relative phase and the electronic cooperation parameter on the OB and OM are also studied. Our study is much more practical than its atomic counterpart due to its flexible design and the wide adjustable parameters. Thus, it may provide some new possibilities for technological applications in optoelectronics and solid-state quantum information science.     

非对称耦合量子阱的吸收非线性增强

基于V 形三能级模型运用密度矩阵方程推导了非对称耦合量子阱三阶光学非线性极化率. 具体分析了三阶吸收非线性效率（三阶光学非线性极化率与线性吸收系数之比）随阱间电子相干振荡频率的变化规律. 理论结果表明：三阶吸收非线性效率对阱间电子相干振荡频率相当敏感，当阱间电子相干振荡频率增大时三阶吸收非线性效率显著增强，而当阱间电子相干振荡频率为零时，这种非线性效率类似于单量子阱情况. 与单量子阱相比，对于已设计好的非对称耦合量子阱结构其突出特征表现在，其非线性吸收与色散特性可经由沿材料生长方向偏压进行控制. 据此，我们预期利用这种非对称耦合量子阱结构能设计成光通信中的光限幅器和可控克尔光开关.     

Influences of control coherence and decay coherence on optical bistability in a semiconductor quantum well

We discuss the influences of two different types of mechanisms of quantum coherence on optical bistability in a semiconductor quantum well structure.In the first mechanism,only quantum coherence induced by the resonant coupling of a strong control laser is considered.In the second mechanism,the decay coherence is taken into account under the condition where the control field is weak.In two different cases,optical bistability can be obtained through choosing appropriate physical parameters.Our studies show quantum coherence makes the optical nonlinear effect of the system become stronger,which takes an important role in the process of generating optical bistability.A semiconductor quantum well with flexibility and easy integration in design could potentially be exploited in real solid-state devices.     

Switching times in absorptive optical bistability

We give analytic expressions for the up-switching and the down-switching times of an optical bistable device in the limit of large C. In the case of up-switching the jump time is proportional to the atomic relaxation time. In the case of down-switching, the jump time is proportional to the cavity relaxation time. No assumption on the relative magnitude of the cavity and the atomic relaxation times is introduced.     

Transverse effects in absorptive optical bistability

Absorptive bistability loops are computed for a laser beam with a gaussian input spatial profile incident on a unidirectional ring cavity containing a saturable nonlinear medium. Sharp radially dependent switching with wide bistable loops is predicted for large Fresnel numbers. Intermediate Fresnel numbers result in whole beam switching with significant narrowing of the associated bistable loops. At low Fresnel numbers, bistability can disappear. Radially integrated hysteresis loops differ quantitatively from plane-wave predictions.     

Quasibound states in semiconductor quantum well structures

We present a study on quasibound states in multiple quantum well structures using a finite element model (FEM). The FEM is implemented for solving the effective mass Schrödinger equation in arbitrary layered semiconductor nanostructures with an arbitrary applied potential. The model also includes nonparabolicity effects by using an energy dependent effective mass, where the resulting nonlinear eigenvalue problem was solved using an iterative approach. We focus on quasibound/continuum states above the barrier potential and show that such states can be determined using cyclic boundary conditions. This new method enables the determination of both bound and quasibound states simultaneously, making it more efficient than other methods where different boundary conditions have to be used in extracting the relevant states. Furthermore, the new method lifted the problem of quasibound state divergence commonly seen with many other methods of calculation. Hence enabling accurate determination of dipole matrix elements involving both bound and quasibound states. Such calculations are vital in the design of intersubband optoelectronic devices and reveal the interesting properties of quasibound states above the potential barriers.     

A survey of band-gap renormalization in quantum well structures

The band-gap renormalization at finite temperatures in quantum wells is calculated from the dynamical self energy. Sublevel formfactors and non-diagonal screening are taken into account. In order to compare with these calculations, the chemical potential and the carrier density in the active layer of a quantum-well laser diode are determined experimentally based on a novel non-spectroscopic method.     

Photorefractive saturable absorptive and dispersive optical bistability

It is shown that photorefractive wave-mixing gives saturable gain, saturable absorption and Kerr-like nonlinear phase retardation. An analogy between photorefractive two-beam coupling and two-level atom system is then drawn. We investigate optical bistability in a ring cavity, utilizing these phenomena, and compare our results with classical absorptive and dispersive optical bistability.     

Shallow impurity centers in semiconductor quantum well structures

Interest in the study of the behavior of shallow impurity centers in superlattices and quantum well structures is fairly recent. This paper reviews briefly both the theoretical and experimental work done in this field in the last few years. Several recent calculations of the energy levels of hydrogenic impurity states in quantum well structures, such as Ga_1?xAl_xAsGaAsGa_1?xAl_xAs, are reviewed. The behavior of these levels as a function of the quantum well size is discussed. Recent experimental data concerning the variations of the binding energies of shallow donors and acceptors as a function of the GaAs quantum well size are reviewed. A comparison between these experimental measurements and the results of recent calculations is presented.     

Optical bistability in a triple semiconductor quantum well structure with tunnelling-induced interference

We study the behavior of optical bistability (OB) in a triple semiconductor quantum well structure with tunnelling-induced interference, where the system is driven coherently by the probe laser inside the unidirectional ring cavity. The results show that we are able to control efficiently the bistable threshold intensity and the hysteresis loop by tuning the parameters of the system such as laser frequency and tunnelling-induced frequency splitting. This investigation can be used for the development of new types of nanoelectronic devices for realizing switching process.     

Observation of absorptive optical bistability in a fabry-perot cavity containing multiple atomic beams

Using an arrangement of highly collimated sodium atomic beams in a Fabry-Perot cavity absorptive optical bistability has been observed. The response of the optically bistable system was investigated on a time scale of the order of 100 times the characteristic time of the cavity. Even so a non steady state behaviour of the system was observed. Good qualitative agreement with the two-level atom mean field radiation theory has been obtained.     

ZnSe／ZnS多量子阱激子光学双稳性

用MOCVD在CaF_2衬底上生长的ZnSe/ZnS多量子阱材料,在77K下用N_2激光泵浦染料获得的宽带光脉冲进行了非线性光学测量,首次观察到ZnSe/ZnS多量子阱的激子光学双稳性,据分析这是由激子的能带增宽效应引起的增强吸收光学双稳性.     

Ultraslow optical solitons in tunnel-coupled double semiconductor quantum well

This paper investigates the nonlinear evolution of the pulse probe field in an asymmetric coupled-quantum well driven coherently by a pulse probe field and two controlled fields. This study shows that, by choosing appropriate physical parameters, self-modulation can precisely balance group velocity dispersion in the investigated system, leading to the formation of ultraslow optical solitons of the probe field. The proposed scheme may lead to the development of the controlled technique of optical buffers and optical delay lines.     

Transient electron population and optical properties in a semiconductor quantum well

We investigate the transient behaviors of the dispersion and the absorption in a three-level GaAs/AlGaAs semiconductor quantum well system. It is found that the Fano interference and the energy splitting affect the transient behaviors dramatically, which can be used to manipulate efficiently the gain-absorption coefficient and group velocity of the probe field. The dependence of transient electron population on the Fano interference and the energy splitting is also discussed.     

Extended temperature range of absorptive optical bistability in semiconductors

Optical bistability based on the temperature dependence of the absorption coefficient in a semiconductor is considered. It is theoretically demonstrated that the upper bound of the thermostat temperatures at which the bistability is possible can be raised by a factor of three as against its conventional value reported in the literature. This can be achieved in the case of the Auger recombination of free electrons in semiconductors.     

Coherent resonance line broadening effects in absorptive optical bistability

The effect of resonant exchange of quanta between coherently driven atoms on absorptive bistability is examined. Expressions for the variation of the effect with density are presented.