Flip-flop operation in opto-thermal bistable devices with localized absorption

We consider nonlinear interferometric devices based on opto-thermal bistability with localized absorption and show how the introduction of composite structures within the interferometer makes feasible its setting and resetting between stable outputs by applying positive light pulses on different parts of the bistable device. Experimental demonstration of all-optical flip-flop operation is reported for two interferometric configurations, one of them being extremely simple and well suited for parallel processing.     

All-optical computation — A parallel integrator based upon a single gate full adder

The achievement of low power all-optical bistability in small semiconductor devices at the end of the 1970's led to an upsurge in interest in all-optical information processing and optical computing. Based on the proven characteristics of existing bistable systems designs are put forward in this paper for a parallel optical integrator, using a single bistable element for full-adder operation. Optical storage or beam delay computational loops, and time-series to space-parallel conversion designs are presented.     

有源半导体双稳放大器稳定性分析

本文从半经典理论出发,对有源双稳放大器进行了稳定性分析,其结果表明:有源双稳器件远较无源器件易产生正沿不稳定性。在此基础上,我们讨论了有源E-P型双稳开关器件的实用开关速度的极限,实验中我们采用两个InGaAsP/InP双异质结单纵模激光器观察到了全光型开关现象。     

Saturating refractive non-linearities and optical bistability: implications for excitonic switching

We examine the operation of a refractive Fabry-Perot bistable device and consider the importance of saturation of the non-linear refraction using a simple model. A condition is formally derived which determines whether a particular material with a limited refractive index change may be used to make an all-optical bistable switch. This is evaluated for the GaAs/AlGaAs quantum-well system by comparison with four-wave mixing measurements of the non-linear refraction associated with the exciton feature.     

Transients in all-optical bistability using transverse optical pumping: Observation of critical slowing down

We report on the transient response of an all-optical bistable device to step-inputs of light. The nonlinear mechanism used for bistable switching relies on transverse optical pumping within the Zeeman sublevels of the sodium ground state. Our measurements demonstrate the crucial role of critical slowing down for switching time. We also find that time-dependent diffusion processes can strongly affect the dynamics of this bistable device. Numerical calculations are shown to yield results in satisfactory agreement with experimental data.     

A New Architecture for Optical Data Processing Devices by the Application of Bistability in Luminescence

Recently, we have discovered that—besides the all-optical photo-thermal bistability in transmission—the excitation of thin CdS films with the 514.5 nm line of an argon laser causes all-optical bistability in the luminescent radiation. The emitted radiation of the CdS layers lies far enough in the infrared region of the spectrum so that all-optical bistability in luminescence can be observed through GaAs wafers, i.e. an all-optical bistable loop remains in the direction of the propagation of the incident laser beam even though GaAs is strongly absorptive at the excitation wavelength. On the basis of this penetrating feature of all-optical bistability, we present a new concept for an architecture of future optical data processing devices.     

Switching of liquid-crystal devices between reflective and transmissive modes using long-pitch cholesteric liquid crystals

We propose liquid-crystal (LC) devices capable of switching between reflective and transmissive modes using the scattering and transparent states of long-pitch cholesteric LCs (CLCs). Two different device configurations can be realized by changing the location of a CLC layer. Low-power operation without the parallax problem can be achieved using the bistable switching of CLCs. We believe that the proposed devices are potential candidates for highly efficient transflective displays.     

基于SOA的环形腔激光器在全光信号处理中的应用

半导体光放大器（SOA）因其具有良好的光光互作用特性,包括交叉增益调制、交叉相位调制、交叉偏振调制以及四波混频等,在全光信号处理技术中已经获得了广泛的应用。利用SOA与光纤反馈可构成环形腔激光器S_FRL。在S—FRL中将SOA的光一光互作用特性与反馈条件相结合,可以改变孓FRI．的起振、抑制、选频等多种状态,从而构成不同功能的全光信号处理器件。在分析S—FRL激光振荡原理的基础上,提出了双环耦合的S-FRL,并以此为基础构成一种双环耦合的双稳态触发器,进而构成一种同步脉冲展宽器;还提出了一种级联的S-FRL,由此构成一种基于负逻辑的全光判决器。     

The metal-insulator (tunnel)-silicon-thyristor thresholding transducer in optical systems

We consider in this paper the system properties of the optical metal-insulator (tunnel)-silicon-thyristor (MIST) device when operating as a threshold transducer. Measured values of switching speed, noise performance and sensitivity for devices operated in the monostable mode are reported. Improvements in these parameter values are also predicted for operation in the bistable mode. For our non-optimized experimental devices, operation at 2 Mbit s^–1 with a–36 dBm receiver sensitivity is shown to be possible, thereby illustrating the suitability of the MIST in its present form for data bus applications. Areas for further improvement and development are outlined.     

Temperature switch based on optical bistability

We have demonstrated a temperature switch based on an optically bistable device integrated with an optical fibre. The principle demonstrated here might lead to the development of new types of all-optical temperature sensors.     

Optical bistability and signal processing in a microstructured fiber ring resonator

We explore theoretically the effects of bistability in a microstructured fiber-based ring resonator. Numerical simulations indicate that bistable behavior of the fiber cavity can be observed with a short length of fiber. Feasibility of all-optical processing using this type of cavity is also investigated. In particular, we show that a ring cavity including a microstructured fiber should allow one to perform flip-flop and time-division demultiplexing functions. The analysis presented here will be useful for future design of bistable microstructured fiber device.     

Optical bistability in a three-level semiconductor quantum-well system

Optical bistable behavior in a unidirectional ring cavity (or a Fabry–Pérot cavity) containing a semiconductor quantum well, described as a three-level ladder-type system with similar transition energies, has been studied. The system interacts with a strong driving field which is in two-photon resonance with the intersubband transition and thus simultaneously drives all three levels into phase-locked quantum coherence. The threshold for switching to upper branch of the bistable curve is found to be reduced due to the presence of quantum interference. Such system can be used for making efficient and fast all-optical switching devices. PACS 78.67.De; 42.50.Hz; 78.20.Bh     

Optically bistable nonlinear interference filters for use with near-infrared laser diodes

ZnSe nonlinear interference filters, configured as optothermal bistable etalons with absorbed transmission (BEAT) devices, have been operated as all-optical switches using 830 nm diode laser illumination and fibre-optic coupling. Stable switching at powers down to 3 mW have been demonstrated for spot diameters of 10 μm. An observed increase in switch power when using large numerical-aperture illumination is analysed in terms of a reduction in effective cavity finesse.     

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.     

All-optical flip-flop based on an active Mach-Zehnder interferometer with a feedback loop

A novel architecture for an all-optical flip-flop is validated experimentally. The architecture comprises a single semiconductor optical amplifier-based Mach-Zehnder interferometer with an external feedback loop. The experimental results show optical bistable operation for a latching device with an on-off contrast ratio of 11 dB that employs set and reset pulses of less than 250 pJ, although the energy of these pulses could be greatly reduced by optical integration of the whole device.     

Characteristics of all-optical 3R regenerators using cascaded second-order nonlinear effect in quasi-phase matched lithium niobate devices

We numerically show that quasi-phase matched (QPM) lithium niobate (LN) devices employing the cascaded second-order nonlinear effect of second harmonic generation (SHG) and difference frequency mixing (DFM) have all-optical decision gate characteristics. The decision gate function is realized by a parabolic transmittance for a low-power region and a limiting characteristic for a high-power region. The limiter function is attributed to the large group-velocity mismatch between the fundamental and second harmonic pulses. This operation principle differs from those of other all-optical 2R (reamplification and reshaping) or 3R (2R and retiming) regenerators that have been proposed in the past. Furthermore, we show that an initial time offset between the signal and clock pulses can improve the output signal power or the switching efficiency of the device. Based on the numerical results, we propose a method for designing all-optical 3R regenerators using the cascade of SHG and DFM in the QPM-LN devices. Following the design method, all-optical 3R operation at the bit rate of 200 Gbps can be achieved using a 1-cm-long waveguide device.     

A Complex Approach to Noninvasive Estimation of Microcirculatory Tissue Impairments in Feet of Patients with Diabetes Mellitus using Spectroscopy

We investigate conditions for the occurrence of a bistable response from a thin layer of an ensemble of two-level inhomogeneously broadened emitters upon their interaction with resonant radiation. A Lorentz correction to the local field that acts on emitters is taken into account. Bistability phase diagrams in the parameter space (inhomogeneous broadening, detuning away from resonance, and local field) are calculated, and the occurrence of optical hysteresis of the system is demonstrated. In addition to this, we study the switching time from the lower stable branch of the bistable characteristics to the upper one and vice versa against the intensity of the driving field, which determines the operation speed of a bistable device. The possibility of using a thin layer of resonant emitters as a multichannel all-optical switch is discussed.     

Modeling of optical devices for the design of multistage interconnection network systems

Guidelines of the modeling of an all-optical architecture is presented. This basic architecture is universal and flexible. It can be used as the switching building block for a number of interconnection networks. The power analysis of an all optical buffering architecture [1] that can be interfaced with such an element is discussed. The modeling analysis is given in terms of the switch model, the multistage model and the power analysis of the optical buffer. The architecture uses bistable optical devices such as Fabry-Perot etalons, SEED and S-SEED. A number of important issues remain to be addressed, such as the use of different nonlinear optical devices, synchronization, and simulation.     

Electrical bistability of tris-(8-hydroxyquinoline) aluminum (Alq3)/ZnSe organic-inorganic bistable device

We present that the electrical bistability in organic-inorganic bistable devices based on tris-(8-hydroxyquinoline) aluminum (Alq₃) and zinc selenide (ZnSe) with the tri-layer structure of Alq₃/aluminum (Al)/ZnSe. The current-voltage characteristics of the bistable device exhibit two electrical states as low (OFF state) and high (ON state) conductivity with ON/OFF ratio about four orders of magnitude. The conduction mechanisms in both ON and OFF states were analyzed by theoretical model. In the OFF state, the conduction mechanisms can be explained by thermionic emission model, which the ON state can be described by ohmic conduction model. The retention times of both states are more than 8000 s, and the device can reproduce continuous write-read-erase-read switching cycles. Moreover, for the organic-inorganic bistable device was kept at one year in ambient condition without encapsulation. The device still exhibited the electrical bistable behavior. Consequently, the ZnSe layer may be led to improve the lifetime property of the bistable device which acted as a self-encapsulating layer.     

Nanoelectronic devices from self-organized molecular switches

The development of molecular electronic switching devices for memory and computing applications presents one of the most exciting contemporary challenges in nanoscience and nanotechnology. One basis for such a device is a two-terminal molecular-switch tunnel junction that can be electrically switched between high- and low-conductance states. Towards this end, the concepts of self-assembly and molecular recognition have been pursued actively for synthesizing two families of redox-controllable mechanically interlocked molecules – bistable catenanes and bistable rotaxanes – as potential candidates for solid-state molecular-switch tunnel junctions. This article reviews logically the development and understanding of Langmuir, Langmuir–Blodgett and self-assembled monolayers of amphiphilic bistable and functionalized bistable rotaxanes and their catenanes counterparts. Our increased understanding of the superstructures of these monolayers has guided our recent efforts to incorporate these self-organized molecular switches into devices. The methodologies that are being employed are in their early stages of development. Certain characteristics of the molecules, monolayers, electrodes and devices are emerging that serve as lessons to be consider in responding to the ample opportunities for further research and process development in the field of nanoelectronics. PACS 81.07.-b; 81.07.Nb; 85.65.+h