Optical bistability and multistability in a defect slab doped by GaAs/AlGaAs multiple quantum wells

We proposed a new model for controlling the optical bistability(OB) and optical multistability(OM) in a defect slab doped with four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15-nm Al_(0.3)Ga_(0.7)As barriers. The effects of biexciton energy renormalization, exciton spin relaxation, and thickness of the slab on the OB and OM properties of the defect slab were theoretically investigated. We found that the transition from OB to OM or vice versa is possible by adjusting the controllable parameters in a lab. Moreover, the transmission, reflection, and absorption properties of the weak probe light through the slab were also discussed in detail.     

级联型四能级原子相干介质中的光学双稳态和多稳态

主要研究了在一单向环形腔内的级联型四能级原子被三个光场驱动的光学双稳态和多稳态行为. 三个单模光场通过三个光子跃迁路径与原子系统耦合. 在这种情况下,中间两能级间所加的耦合场Ω_B变得非常重要. 研究显示耦合场Ω_B的增加会使光学双稳态的阈值减小,同时也会导致光学多稳态的产生.对上面两能级间所加的耦合场的作用也进行了讨论,同时还讨论了探测场失谐和合作参数对光学双稳态及多稳态的影响. 关键词： 原子相干 光学双稳态和多稳态 四能级原子     

Optical bistability and multistability via quantum interference in an Er-doped optical fiber

The optical bistability and multistability in an Er³⁺-doped ZrF₄-BaF₂-LaF₃-AlF₃-NaF optical fiber inside a ring cavity are investigated. The underlying mechanism shows some new characteristics that other schemes do not have. Thus, it may provide some new possibilities for technological applications in optoelectronics and quantum information science.     

Optical bistability and multistability in a four-level quantum system in the presence of plasmonic nanostructure

In this paper, the effect of plasmonic nanostructure on behavior of optical bistability and multistability in a four-level quantum system embedded in a unidirectional ring cavity has been studied. It is found that the distance between plasmonic nanostructures and a four-level quantum system is varied from 4.4 nm to 14.4 nm and has an essential role for controlling the threshold of optical bistability and multistability. Moreover, obtained results show that the group velocity of pulse propagation through the medium is strongly depended on the distance between the plasmonic nanostructure and the four-level quantum system.     

Controllable optical bistability and multistability in asymmetric double quantum wells via spontaneously generated coherence

We investigate the nonlinear optical phenomena of the optical bistability and multistability via spontaneously generated coherence in an asymmetric double quantum well structure coupled by a weak probe field and a controlling field. It is shown that the threshold and hysteresis cycle of the optical bistability can be conveniently controlled only by adjusting the intensity of the SGC or the controlling field. Moreover, switching between optical bistability and multistability can be achieved. These studies may have practical significance for the preparation of optical bistable switching device.     

Controllable optical bistability and multistability in a rare-earth-ion-doped optical fiber

We investigated the optical bistability and multistability in an Er³⁺-doped ZrF₄–BaF₂–LaF₃–AlF₃–NaF optical fiber inside an optical ring cavity. It is found that the optical bistability and multistability can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optoelectronics and optical-fiber communication.     

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.     

非旋波耦合条件下微波控制的光学双稳与多稳

研究了在非旋波耦合条件下微波场建立的原子相干对光学双稳与多稳的控制.通过改变微波场的初始相位,可以有效地控制双稳与多稳的存在与否、迟滞环宽度和阈值强度的高低.旋波和非旋波耦合在物理上可视为双色激发,耦合的能级分裂成无穷多个子能级,原来的裸态跃迁变成无穷多个不同频率的跃迁.这些跃迁的相干叠加决定了介质的非线性吸收与色散,相干叠加的结果取决于微波场的相位. 关键词： 原子相干 非旋波耦合 光学双稳与多稳 相位控制     

光学空间相干度双稳态

本文首次提出一种由相干度非线性调制得到的新型光学双稳态——空间双稳态及其作用无耦合和有交叉耦合情况下,经γ/υ和υ/ν变换反馈可得到多种形式的双稳态,且给出了几种情况下的稳态特性方程、参数选择区域以及翻转条件等.     

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 In Ga N/Ga N 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.     

Optical bistability and multistability via multi-Raman-channel interference

We investigate the optical bistability and multistability behaviors in a closed three-level A-type atomic system. By adding a sideband on either hand of the transitions which are originally coupled by a coherent control field and a coherent probe field to disturb the two-photon resonance, bistability occurs due to two-channel interference. Increasing the sideband Rabi frequency leads to the switching from bistability to tristability. When the sideband simultaneously couples with both hands, we can easily obtain quadrastability.     

Incoherent control of optical bistability in an InGaN/GaN quantum dot nanostructure

The manipulation of bistable curve in the infrared (IR) region has been investigated theoretically in a unidirectional ring cavity doped by a four-level InGaN/GaN quantum dot nanostructure. The four-level quantum dot nanostructure is designed numerically by using the Schrödinger and Poisson equations. By controlling the size of the quantum dot and external voltage, one can design a four-level quantum dot with appropriate energy levels which can be suitable for interaction with IR signals. It is realized that the incoherent pumping fields play an essential role in controlling the intensity threshold of optical bistability. Decoherence effects such as the dephasing rate and electron density of the quantum dot are also analyzed at the threshold of optical bistability. Our proposed model due to its important application in all-optical systems may be favorable for real experimental evolution in infrared regions.     

n型主动拉曼增益原子介质中的光学双稳态

研究了主动拉曼增益原子介质在单向环形腔中的光学双稳态．该系统是一个相干共振的n型四能级原子系统,可在室温下实现,有能级失谐量、原子数密度、抽运场、控制场等较多的可调参数,且有无增益的透明窗口．完全通过解析方法定量给出实现光学双稳态的条件,以及可调参数的取值范围,并进一步给出实现光学多稳态的条件,为实验上实现光学双稳态与多稳态提供了理论依据．     

颗粒复合介质在高温下的光学双稳特性

利用Maxwell-Garnett近似，结合谱表示方法，理论研究了金属/绝缘颗粒复合介质的光学双稳特性随环境温度的依赖关系.数值结果表明，体系的光学双稳区域随环境温度的升高而逐渐变窄，甚至消失.还进一步研究了复合体系的折射系数和消光系数随温度的变化关系. 关键词： 颗粒复合介质 光学双稳     

梯度颗粒复合介质的光学双稳

重点研究了组分的梯度构形对带壳球形颗粒复合介质的光学双稳特性的影响.其中球形颗粒是由非线性核和介电函数具有梯度分布的线性壳组成.对于壳层介电函数具有幂指数分布的情况,通过求解麦克斯韦方程,得到各区域的势能分布函数,从而求得核内电场的数学表达式.数值研究发现,该复合介质的光学双稳阈值和区域与壳层的厚度及壳层的介电幂指数有关,随着壳层厚度增大或幂指数增大,双稳阈值将变宽.此外,还研究了正入射情况下复合材料体系的反射系数随外电场的变化情况, 发现其关系曲线是一条回线. 关键词： 梯度颗粒 复合介质 光学双稳     

All-Optical Switching between Optical Bistability and Multistability via Exciton Spin Relaxation

All-optical coherent control of optical bistability(OB) and optical multistability(OM) in the 4.8 nm Zn Se single-quantum well based on excitons and biexciton transitions is investigated. By applying a pair of phase-locked laser pulses all-optical coherent control can be obtained. Theoretical analysis with density matrix and Maxwell equations then yield the optical bistability and optical multistability. It is shown that by controlling the coherent and incoherent processes, the intensity threshold of OB and OM can be modified. Also, it is found that the switching between OB and OM or vice versa can be occurred for some controllable parameters.     

Enhanced Kerr nonlinearity in a quantized four-level graphene nanostructure

In this paper, a new model is proposed for manipulating the Kerr nonlinearity of right-hand circular probe light in a monolayer of graphene nanostructure. By using the density matrix equations and quantum optical approach, the third-order susceptibility of probe light is explored numerically. It is realized that the enhanced Kerr nonlinearity with zero linear absorption can be provided by selecting the appropriate quantities of controllable parameters, such as Rabi frequency and elliptical parameter of elliptical polarized coupling field. Our results may be useful applications in future all-optical system devices in nanostructures.     

Fluctuations,stochastic resonance and noise-protected heterodyning in bistable optical systems

Summary Statistical distributions, power spectra and susceptibilities of an all-optical bistable system subject to noise are considered. In the presence of an additional small periodic signal, a stochastic-resonance phenomenon for additive noise is found to occur, and has been investigated theoretically and experimentally. A new form of optical heterodyning related to stochastic resonance, in which two high-frequency signals (an input signal and a reference one) are applied to an all-optical bistable system, is reported. A noise-induced enhancement of the heterodyne signal has been investigated theoretically, by means of analogue electronic simulation and in experiments in which a optical system was driven by two modulated laser beams at different wavelengths. Paper presented at the International Workshop “Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing and Related Phenomena?, Elba, 5–10 June 1994.     

Effect of Quantum Interference from Incoherent Pumping Field and Spontaneous Emission on Controlling the Optical Bistability and Multi-Stability

Optical bistability (OB) and optical multi-stability (OM) of a four-level Λ-type atomic system with two fold lower levels inside a unidirectional ring cavity is investigated. The effect of quantum interference arising from spontaneous emission and incoherent pumping on OB and OM is discussed. It is found that the threshold of OB and OM can be controlled by quantum interference mechanisms. In addition intensity of coupling field and the rate of an incoherent pumping field on behavior of OB and OM are then discussed.