Noticeable positive Doppler effect on optical bistability in an N-type active Raman gain atomic system

We theoretically investigate the Doppler effect on optical bistability in an N-type active Raman gain atomic system inside an optical ring cavity.It is shown that the Doppler effect can greatly enhance the dispersion and thus create the bistable behaviour or greatly increase the bistable region,which has been known as the positive Doppler effect on optical bistability.In addition,we find that a positive Doppler effect can change optical bistability from the hybrid dispersion-gain type to a dispersive type.     

Optical bistability by two laser beams in photorefractive crystals

For a nonlinear medium, a given incident laser beam may produce different transmitted light waves. This phenomenon (the so-called optical bistability) corresponds to multiple solutions of the boundary value problems of the nonlinear Helmholtz equation. Optical bistability can be useful in the design of optical switches. Devices that display this behavior could potentially play a major role in the development of optical communication systems and computing. In this article we present experimental results concerning the optical bistability in photorefractive BaTiO₃:Fe crystal. Two laser beams were used to interact with the photorefractive crystal which resulted in the bistability of the intensity of transmitted wave. This was achieved without the application of any optical resonator. High contrast optical bistability is found experimentally in the pump-ratio dependence of the output intensity.     

非线性包层多量子阱波导的TE波

给出用以分析非线性包层多量子阱波导ＴＥ模光学非线性与双稳性的理论公式与计算方法。指出用均方根等效折射率法解本征方程是有效的简化方法。用本文方法分析了模折射率对波导总功率的依赖关系,芯区功率与总功率之间的双稳性以及模场分布与模折射率的关系。讨论了波导参数对光学非线性、双稳性及模场的分布的影响。     

介电体超晶格的研究

介电体超晶格是一种新型的有序微结构材料.它具有通常均质材料所不具有的独特优异性能,展现出重要的应用前景.文章介绍了南京大学研究组关于介电体超晶格研究所取得的进展,如将多个光参量过程集成于一块介电体超晶格之中获得了多波长激光同时输出,研制成超晶格全固态三基色激光器原型,在介电体超晶格中将拉曼散射强度增强到104-105倍,用超晶格研制的器件填补了体波超声器件从几百MHz到几千MHz的空白频段,发现了微波与超晶格振动的强烈耦合以及极化激元(polariton)的激发与传播等.     

ZnSe－ZnTe多量子阱室温下的反射型皮秒激子光双稳

本文首次研究了ＺｎＳｅ－ＺｎＴｅ多量子阱在室温下的反射型皮秒激子光双稳，实验结果表明，ＺｎＳｅ－ＺｎＴｅ多量子阱在室温下的反射型皮秒光双稳的阈值光强和对比度分别为１．１ＭＷ／ｃｍ２和６：１．根据测量得到的ＺｎＳｅ－ＺｎＴｅ多量子阱在室温下的激子吸收光谱及激子的非线性吸收理论，归结ＺｎＳｅ－ＺｎＴｅ多量子阱室温下的皮秒光双稳的主要非线性机理为ＺｎＳｅ－ＺｎＴｅ多量子阱的激子饱和吸收引起的折射率变化．     

ZnSe-ZnTe多量子阱室温下的反射型皮秒激子光双稳

本文首次研究了ZnSe-ZnTe多量子阱在室温下的反射型皮秒激子光双稳,实验结果表明,ZnSe-ZnTe多量子阱在室温下的反射型皮秒光双稳的阈值光强和对比度分别为1.1MW/cm²和6:1.根据测量得到的ZnSe-ZnTe多量子阱在室温下的激子吸收光谱及激子的非线性吸收理论,归结ZnSe-ZnTe多量子阱室温下的皮秒光双稳的主要非线性机理为ZnSe-ZnTe多量子阱的激子饱和吸收引起的折射率变化.     

Thin CdS platelets — a model case for the study and optimization of thermally induced absorptive and dispersive optical bistability

Thermally induced optical bistability of thin CdS platelets is shown to be a highly suitable model case for the study of interactions between absorptive and dispersive switching mechanisms. Beyond previous studies concerning this type of bistability, systematic investigations were necessary to obtain a set of optimization criteria concerning a desired hysteresis feature. Despite the fact that thermally induced bistability of CdS may exhibit too long switching times for application in optoelectronics, it is a valuable system for the investigation of general features of bistable processes in a very detailed manner and for the development of reliable quantitative models. The appearance of different forms of thermally induced optical bistability in CdS is discussed in dependence of switching power, temperature, shallow-impurity concentration, and of system as well as of sample configuration.     

Bistability in cell signaling: How to make continuous processes discontinuous,and reversible processes irreversible

Xenopus oocyte maturation is an example of an all-or-none, irreversible cell fate induction process. In response to a submaximal concentration of the steroid hormone progesterone, a given oocyte may either mature or not mature, but it can exist in intermediate states only transiently. Moreover, once an oocyte has matured, it will remain arrested in the mature state even after the progesterone is removed. It has been hypothesized that the all-or-none character of oocyte maturation, and some aspects of the irreversibility of maturation, arise out of the bistability of the signal transduction system that triggers maturation. The bistability, in turn, is hypothesized to arise from the way the signal transducers are organized into a signaling circuit that includes positive feedback (which makes it so that the system cannot rest in intermediate states) and ultrasensitivity (which filters small stimuli out of the feedback loop, allowing the system to have a stable off-state). Here we review two simple graphical methods that are commonly used to analyze bistable systems, discuss the experimental evidence for bistability in oocyte maturation, and suggest that bistability may be a common means of producing all-or-none responses and a type of biochemical memory. (c) 2001 American Institute of Physics.     

All-optical bistability due to charge transfer in a type II heterostructure

We report bistability of low temperature photoluminescence in a n-i-n type II GaAs/AlGaAs/AlAs heterostructure. The luminescence intensity ratio between the two states reaches 50, and no external bias is needed. The bistability range lies between 40 and 280 W/cm². The two states are thought to correspond to different charge accumulations in the structure. The redistribution of charges is due to competition between slow type II and fast type I recombination in the center of the structure.     

Multiple wavelength electroluminescence and laser generation in p-i-n resonant tunneling heterostructures

We report a design and electroluminescence (EL) investigation of a p-i-n resonant tunneling device based on an Al_0.4Ga_0.6As/GaAs graded-index waveguide heterostructure. The intrinsic region of the structure consists of a quantum well (QW) surrounded by multiple barrier energy filters providing simultaneous resonant occupation of electron and heavy-hole second excited subbands in the QW. Several peaks are observed in the EL spectra, confirming occupation of the excited subbands. The EL efficiency displays a resonant behavior accompanied by an S-shaped negative differential resistance region in the voltage–current characteristic. Current bistability is demonstrated, leading to bistability in the EL and laser generation spectra.     

Optical bistability based on surface plasmon coupled between a noble metal film and a metal grating involving Kerr materials

A phenomenon about optical bistability is successfully investigated in a layered structure consisting of a silver film with Kerr medium and a silver grating sandwiched between semi-infinite linear dielectrics.This type of structure can lead to the optical bistability phenomena occurring in reflection and transmission.There exists an optimal thickness of the metal grating that can cut off the effect of the near-field enhancement and may have the lowest effect on conversion from surface plasmon to light.This structure can realize the functions of the beam splitter and the polarization splitter and will be essential for future classical and quantum information processing.     

Multiple Effective Two-photon Correlated-emission Optical Bistability with Injected Squeezed Vacuum

ＭｕｌｔｉｐｌｅＥｆｅｃｔｉｖｅＴｗｏ┐ｐｈｏｔｏｎＣｏｒｅｌａｔｅｄ┐ｅｍｉｓｉｏｎＯｐｔｉｃａｌＢｉｓｔａｂｉｌｉｔｙｗｉｔｈＩｎｊｅｃｔｅｄＳｑｕｅｚｅｄＶａｃｕｕｍＨＵＡＮＧＨｏｎｇｂｉｎａ），ｂ）ＸＩＮＧＬｉｎｇｌｉｎｇｃ）ＳＯＮＧＪｉｌ...     

Flip-flop between soft-spring and hard-spring bistabilities in the approximated Toda oscillator analysis

We study theoretically the effect of truncating the nonlinear restoring force (exp(F)-1=?_n=1^￥Fⁿ/n!\exp (\Phi)-1={\sum}_{n=1}^{\infty}\Phi^{n}/n!) in the bistability pattern of the periodically driven, damped one-degree-of-freedom Toda oscillator that originally exhibits soft-spring bistability with counterclockwise hysteresis cycle. We observe that if the truncation is made third order, the harmonic bistability changes to hard-spring type with a clockwise hysteresis cycle. In contrast, for the fourth-order truncation, the bistability again becomes soft-spring type, overriding the effect of third-order nonlinearity. Furthermore, each higher odd-order truncation attempts to introduce hard-spring nature while each even-order truncation turns to soft-spring type of bistability. Overall, the hard-spring effect of every odd-order nonlinear term is weaker in comparison to the soft-spring effect of the next even-order nonlinear term. As a consequence, higher-order approximations ultimately converge to the soft-spring nature. Similar approximate analysis of Toda lattice has in recent past revealed remarkably similar flip-flop pattern between stochasticity (chaotic behaviour) and regularity (integrability).     

室温CdxZn1—xTe／ZnTe多量子阱光学双稳态的研究

研制了室温ＣｄｘＺｎ１－ｘＴｅ／ＺＮＴｅ多量子阱法布里－珀罗腔光双稳器件，并在该器件上观察到皮秒一级的室温激子光双稳。研究结果表明，ＣｄＺｎ１－ｘＴｅ／ＺｎＴｅ多量子阱光双稳器件的光双稳值和对比度分别为３６３ｋＷ／ｃｍ＾２和４：１。根据ＣｆｘＺｎ１－ｘＴｅ／ＺｎＴｅ多量子阱的吸收谱和激子非线性理论，归结了ＣｄｘＺｎ１－ｘＴｅ／ＺｎＴｅ多量子阱光双稳的主要非线性机理为激子的饱和和吸收。     

Vertical and direct integration of heterojunction phototransistors and laser diodes

An optoelectronic integrated device based on the concept of vertical and direct integration is described. Four types of integrated devices composed of multiple heterojunction phototransistors and laser diodes are developed and the devices successfully achieve thirteen functions: optical switching, amplification, thresholding, bistability, light-controlled optical bistability, light-controlled optical thresholding, tristability, set and reset functions in tristable states, set and reset functions in tetrastable states, and bistable and tristable flip-flop functions.     

Logical and relational operations of optical bistable devices operating without external bias

We report successful optical realization of both logical and relational functionality using a multiple quantum well optical bistable device operating without external bias and a simple experimental setup. For the nonbiased optical bistability, we employed extremely shallow quantum wells and asymmetric Fabry-Perot cavity structure in self electro-optic effect device. The change between logical and relational mode was simply realized by controlling the intensity of the optical bias beam into devices following the basic operation principle of the optical bistability.     

Two optical bistability domains in composites of metal nanoparticles with nonlinear dielectric core

It is shown that the local field in metal spherical particles with a dielectric core in an external varying electric field has two maxima at two different frequencies. The second maximum becomes more important with an increment in the metal fraction. Due to the nonlinear dielectric function of the core, the composite of these inclusions may have two optically induced bistability domains at different frequencies. At rather high metal fraction, two bistability domains merge and form one entire bistability domain. The parameters of these domains are studied numerically. The paper focuses on the second bistability domain, which has not been discussed in the literature so far. This domain exists in a comparatively narrow frequency range and its onset fields are lower than those of the first bistability domain. The lowest bistability onset fields are obtained in the entire domain. This peculiarity of the optical induced bistability in the metal composite with small dielectric cores can be attractive for possible applications.     

Subband-level renormalization and absorptive optical bistability in semiconductor multiple quantum well structures

A microscopic theory of many-body effects in the lowest subbands of semiconductor multiple quantum well structures is presented. The renormalized subband levels are calculated for a broad temperature range and optical bistability due to induced absorption is predicted.     

Holstein–Primakoff (H-P) Approach to Determine the Optical Response of Hybrid Optomechanical System Containing Multiple Quantum Dots

A theoretical model is presented to study the hybrid optomechanical system comprising an ensemble of N number of quantum dots (QDs). Utilizing the Holstein–Primakoff (H-P) transformation formalism, the calculations become easily scalable. The bistability in this hybrid optomechanical system is studied in the presence of third order nonlinear χ⁽³⁾ medium using the H-P transformation method and to verify the results, numerical method has also been utilized. It is also demonstrated that the system's parameters may be tuned to alter the bistability phenomenon and absorption spectrum's response, which exhibits both positive and negative absorption (emission). This alternative approach (H-P transform) is demonstrated to solve analytically the system containing multiple QDs in an elegant manner.     

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.