Controlling the optical bistability via quantum interference in a four-level N-type atomic system

We investigate the optical bistability (OB) and optical multi-stability (OM) in a four-level N-type atomic system. The effect of spontaneously generated coherence (SGC) on OB and OM is then discussed. It is found that SGC makes the medium phase dependent, so the optical bistability and multi-stability threshold can be controlled via relative phase between applied fields. We realize that the frequency detuning of probe and coupling fields with the corresponding atomic transition plays an important role in creation OB and OM. Moreover, the effect of laser coupling fields and an incoherent pumping field on reduction of OB and OM threshold is then discussed.     

Electromagnetically induced grating in a four-level tripod-type atomic system

An electromagnetically induced grating in a four-level tripod-type atomic system is studied theoretically. By virtue of a weak standing-wave signal field, the phase modulation effectively diffracts a weak probe field into the first-order direction. By changing the weak signal field, the diffraction of the weak probe field can be modulated in real time, and a first-order diffraction efficiency of more than 32% can be obtained with proper parameters. Such a system has a potential application in an all-optical switch controlled by a weak optical signal.     

Optical bistability using quantum coherence in a microwave-driven four-level atomic system

The behavior of the optical bistability (OB) is investigated in an optical system which consists of a four-level atomic system with a microwave drive field and an optical cavity. It is found that the optical bistability can be accomplished by adjusting different physical parameters in both steady and transient process. Due to the existence of the microwave drive field, the optical bistability can be also obtained even under weak coherent coupling field condition. Since the intensity and phase of microwave drive field can be conveniently modulated, this optical system provides a new experimental method to test the optical bistability theory.     

Double dark resonances and the dispersion properties in a four-level inverted-Y atomic system

The electromagnetically induced transparency (EIT) and its dispersion properties in a four-level inverted-Y atomic system are investigated. The absorption spectrum of a weak probe field shows two EIT windows (dark resonances) whose location, width, and depth can be controlled by manipulating the parameters of the coupling fields; the corresponding dispersion properties are also measured by using a Mach-Zehnder interferometer. The experimental measurements agree well with the theoretical calculations. This kind of system can find important applications in two-channel quantum communication and information storage.     

A study of optical properties of a four-level atomic system via vacuum-induced coherence effects

This paper studies the effects of vacuum-induced coherence(VIC) in a four-level atomic system.The effects of VIC lead to the coherent hole burnings exhibited in the system at some certain points of the Rabi frequency.This is also the reason for the enhancement of the coherent population trapping.In addition,optical bistability occurs in the evolution curves of absorption versus the phase of Rabi frequencies.     

利用腔内四能级原子相干效应实现全光学信号存储

在光学腔与四能级原子组成的非线性光学双稳系统中,利用调谐于不同能级附近的控制信号光脉冲可以使光学腔模产生“正”或“负”的非线性相移,从而实现了光学双稳迟滞曲线的受控移动及双稳“高态”与“低态”之间的可控跃变.基于上述效应,完成了光学信号的全光存储与腔输出状态的低功率控制开关.这一结果为全光及量子信息处理提供了新的可供利用的物理机制.     

利用腔内四能级原子相干效应实现全光学信号存储

在光学腔与四能级原子组成的非线性光学双稳系统中，利用调谐于不同能级附近的控制信号光脉冲可以使光学腔模产生“IT”或“负”的非线性相移，从而实现了光学双稳迟滞曲线的受控移动及双稳“高态”与“低态”之间的可控跃变，基于上述效应，完成了光学信号的全光存储与腔输出状态的低功率控制开关．这一结果为全光及量子信息处理提供了新的可供利用的物理机制．     

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.     

All-optical switching with a biexcitonic double lambda system

A double lambda four-level system could be implemented with biexcitonic transitions on GaAs quantum well. We observed that the phase dependent biexcitonic transition could be explained by interference between one-photon and three-photon transition in a double lambda four-level system. An ultralow-light switch pulse could control 80% of biexcitonic absorption, which demonstrated all-optical switching with biexcitonic double lambda system.     

基于量子干涉效应的四能级原子系统中的vacuum-induced coherence效应

多能级系统中的vacuum-induced coherence(VIC)效应是一种重要的量子干涉效应，研究了VIC效应导致的系统电磁感应透明现象，并且改变了系统的吸收、增益和色散等性质，分析了在发生VIC效应时系统能级粒子数分布规律.另外，考虑复数拉比频率的相位变化时系统可呈现出光学双稳态效应.     

All-optical polarization switching based on Bragg-spaced quantum dots layers

One kind of Bragg-spaced all-optical switching has been proposed in this paper, and the quantum dots ensembles are used in it as active layers. By one-dimensional photonic crystal theory and transmission matrix method, we have studied the reflectivity stop band and switching effect based on the ac Stark effect. The reflectivity stop band of this switch can be suppressed or recovered, and the circular dichroism and birefringence are induced by a circle-polarized control light, which result in a significant polarization switching effect. This switching structure shows great advantages of lower requirement of pump light intensity, larger contrast ratio than that of Bragg-spaced quantum wells with the same period, especially this switching can be used at room temperature theoretically. So we predict that there are prodigious prospects for its using in high speed optical communications as all-optical switching.     

All-optical switching between quantum dot nanoarrays

An all-optical switching device is proposed, based on a sandwich structure comprising two-dimensional square-lattice nanoarrays of donor and acceptor quantum dots. The system operates on Förster energy transfer between the dark states of the individual nanoparticles, normally precluded by selection rules. On application of an off-resonant laser beam, a nonlinear mechanism activates transfer between spatially correlated quantum dots across an optically passive spacer layer, signifying an active switching action with parallel processing capability. In this report, electrodynamic theory is employed to analyse the system and to evaluate its energy transfer fidelity. The results of model calculations are presented in graphical form.     

Dynamical switching and memory via incoherent pump assisted optical bistability

We analyze the dynamical behavior of all-optical switching and memory based on tunable optical bistability in a three-level Λ-type atomic system driven by a probe field circulating in an optical ring cavity, a coherent coupling field and an incoherent pump field outside cavity. Owing to the incoherent pump process, the absorption and Kerr nonlinearity near the atomic resonance change dramatically as a result of varied population distribution and atomic coherence, and then the switch-up and switch-down thresholds, as well as the width (or area) of bistable curve, can be manipulated effectively. By tuning the intensity of either coherent coupling field or incoherent pump field, we can make the system output flip between the lower and upper branches of different bistable hysteresis loops while the cavity input keeps to a constant value. Accordingly, all-optical switching and memory can be implemented via dynamical control of the bistable behavior under the assistance of incoherent pump. The proposed scheme can find potential applications in all-optical communication and computation.     

四能级原子系统中的电磁诱导吸收

以三个电偶极跃迁(中间跃迁作为探测跃迁、两边分别是耦合跃迁和控制跃迁)构成N型四能级系统为例，研究介质对探测光的吸收.揭示了在N型四能级系统中，既可产生电磁诱导吸收又可产生电磁诱导透明.这不仅取决于非相干转移率的大小，而且还取决于耦合场、控制场的强度和第四个简并能级的衰减速率大小. 关键词： 电磁诱导吸收 电磁诱导透明 原子相干的自发转移 能级的衰减速率     

One- and two-photon absorption-amplification response in a four-level atomic system with vacuum-induced coherence

This paper theoretically studies the effects of the vacuum-induced coherence on one- and two-photon absorption in a four-level atomic medium. It finds that the one- and two-photon absorption and amplification properties are quite sensitive to the vacuum-induced coherence. It is also shown that the one- and two-photon absorption spectra can be dramatically affected by modulating the relative phase of the applied fields. With the proper choice of the relative phase, the amplification without inversion for the probe field can be realized.     

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     

Study on dense multi-fiber backplane for a large-scale switching system

Dense multi-fiber backplane has great prospect in large-scale multi-rack connection system and optical Routers next generation as connecting equipment. The operation principle of multi-fiber backplane is presented in this paper. In order to conquer the difficulties in producing and upgrading the backplane with dense multi-fibers, starting from the traditional crossbar structure in switching backplane, an original method for optimizing the configuration of fiber circuit on backplane is adopted, and applied to the preparation of backplanes. An experimental setup and flow of producing are also proposed to predigest the process of producing. The advantage of this proposed method in maintaining and upgrading the backplane is proved through the achievement of two sample backplanes with 8(×8) × 8(×8) and 12(×8) × 8(×12) configuration and their testing results.     

All-optical switching in an antiwaveguiding structure

We consider a multichannel optical switch based on a combination of a nonlinear antiwaveguide and several parallel waveguides. The switching is controlled by a perpendicular laser beam focused on the surface of the device. We perform numerical simulations and consider in detail the 1 N switching in such a structure.     

Enhancement of Kerr nonlinearity via spontaneously generated coherence in a four-level N-type atomic system

A theoretical investigation is carried out into the effect of spontaneously generated coherence (SGC) on Kerr nonlinearity of a four-level N-type system. It’s found that the Kerr nonlinearity can be obviously enhanced with SGC present. We attribute the enhancement of Kerr nonlinearity mainly to the generation of extra coherences induced by the superposition of the two SGC channels, and when the superposition is controlled by the interference between two SGC channels properly, the maximal Kerr nonlinearity does not only enter the electromagnetically induced transparency window as the spontaneous generated coherences intensify, but also gets enhanced about 10 times with very large SGC coefficients than that with no SGC effect.     

Coherence switching in a four-level system: quantum switching

Dark resonance switching among three-laser interactions in a four-level system is observed by using an enhanced nondegenerate four-wave mixing technique. This coherence switching mechanism is based on simultaneous suppression and enhancement of two-photon absorption and has a novel application to high-speed optical switches.