All optical SR and D flip-flop employing XGM effect in semiconductor optical amplifiers

This paper presents a simple and novel scheme for all-optical SR and D flip-flop employing cross gain modulation (XGM) effect in two wideband semiconductor optical amplifiers. The proposed flip-flop has a fast response, with less than 20 ps transition times for both rising and falling edges. The FF speed-limit is mainly determined by the SOA recovery time and the intra-FF coupling length. The simulation results exhibit a contrast ratio of 13 dB between two states with an AM of less than 2.5 dB.The distinctive simplicity of the flip-flop implies reduced footprint and low power consumption which makes it ideal for photonic integration.     

All-optical flip-flop based on vertical cavity semiconductor optical amplifiers

We report the operation of an all-optical set-reset (SR) flip-flop based on vertical cavity semiconductor optical amplifiers (VCSOAs). This flip-flop is cascadable, has low optical switching power (~10 microW), and has the potential to be integrated on a small footprint (~100 microm(2)). The flip-flop is composed of two cross-coupled electrically pumped VCSOA inverters and uses the principles of cross-gain modulation, polarization gain anisotropy, and highly nonlinear gain characteristics to achieve flip-flop functionality. We believe that, when integrated on chip, this type of all-optical flip-flop opens new prospects for implementing all-optical fast memories and timing regeneration circuits.     

Optical flip-flop and astable nultivibrator functions by vertical and direct integration of heterojunction phototransistors and laser diodes

A optoelectronic integrated device in which six heterojunction phototransistors and two laser diodes are vertically and directly integrated is developed to achieve new functions important for optical signal processing and optical computing. It is demonstrated that the device has a bistable flip-flop function, in which the output portion is switched alternately by the corresponding optical input. The function is extended to a tristable flip-flop, which is especially important for multistable logic, by using multiple HPTS and their internal optical and/or electrical couplings. Moreover, an astable multivibrator function or a self-oscillating function, is successfully demonstrated by applying the interconnecting technique to the bistable flip-flop function.     

An ultra-fast all-optical RS flip-flop based on nonlinear photonic crystal structures

In this paper, an all-optical RS flip-flop was proposed using nonlinear Kerr effect in photonic crystals. The proposed structure is composed of a core section and two optical switches. The core section consists of two cross-connected resonant cavities whose resonant mode are at wavelengths 1586 and 1620 nm. The cavities were designed such that the resonance of one cavity prevents the signal coupling through the other one. For designing the switch sections, a bias port was used to keep data when there is no input for the flip-flop. Therefore, when both input ports are inactive, the previous state of the flip-flop will be kept. Total footprint and maximum frequency of the proposed structure are obtained 361 μm² and 320 GHz, respectively.     

Dynamic memory arrays and chaos in a spatial-light-modulator ring circuit

An optical ring circuit with two spatial light modulators is capable of supporting a variety of nonlinear spatio-temporal dynamics, including an array of bistable spots with novel Trigger-type flip-flop operation.     

Effect of spin flip-flop on electron-spin-echo decay due to instantaneous diffusion

The effect of electron spin flip-flop on two- and 2 + 1-pulse electron-spin-echo decay due to instantaneous diffusion was studied on hydrogen atoms in y-irradiated quartz. The observed decay was slower than the theoretical decay including no spin flip-flop, and the discrepancy increased with the concentration of the hydrogen atoms. A comparison of the theoretical and the experimental decay rates revealed that the main factor diminishing the effect of instantaneous diffusion is not the direct flip-flop between on-resonant spins, but the fluctuation of the local magnetic fields for on-resonant spins due to the flip-flop of adjacent spin pairs.     

All-optical set-reset flip-flop based on the passive microring-resonator bistability

In this paper, we propose a design for an all-optical R-S flip-flop with separate set and reset inputs, which is based on the optical bistability due to Kerr and two-photon absorption (TPA) effects in the microring resonators. Based on the steady state analysis of the light propagation in nonlinear microrings, variations of hysteresis parameters versus the system variables, such as transmission coefficient, nonlinear refractive index and detuning angle, are analyzed. The switching temporal behavior of the proposed flip-flop is obtained by the microring transient analysis. It is shown that the contrast ratio parameter and the switching power of the proposed all-optical flip-flop can be controlled by system parameters.     

Multi-state optical flip-flop memory based on ring lasers coupled through the same gain medium

We investigate a system consisting of multiple ring lasers coupled by a single gain medium. All the ring lasers share a common feedback arm. The output power of an individual laser shows periodic oscillations as a function of time. The periodicity of the oscillation is determined by the ratio of the roundtrip times of the feedback arm and the ring cavity. In the case that two of such ring lasers are coupled, either their oscillation periodicities are synchronized, or the system is bi-stable. In the latter operation regime, the system can act as an optical flip-flop memory whose state be switched by injection of external light. The concept can be extended to multi-state operations; an eight-state optical flip-flop memory is experimentally demonstrated.     

LiNbO3交叉型波导光触发器

利用在集成光路中串联的两个LiNbO_3交叉型光波导调制器,代替KDP晶体普克尔效应调制器,构成两个混合双稳态器件,制成光学T触发器(flip-flop),并给出实验结果.     

Atomically resolved local variation of the barrier height of the flip-flop motion of single buckled dimers of Si(100)

The dynamics of the flip-flop motion of single buckled dimers of Si(100) was elucidated by locating the tip of a scanning tunneling microscope over a single flip-flopping dimer and measuring the tunneling current (time trace). Based on a statistical analysis of the time trace, we succeeded in estimating the activation energy and the energy splitting between the two stable configurations of buckling. Strong dependence of the dynamics of the flip-flop motion on the local environment was found: Activation energy differs significantly (directly measured 32 meV, estimated approximately 110 meV) for dimers in different domains.     

Poissonian asymptotics of a randomly perturbed dynamical system: Flip-flop of the stochastic disk dynamo

A dynamical system with two stable equilibrium points will show a flip-flop motion between the neighborhoods of the two points when it is perturbed by small random noises. A typical example is the stochastic disk dynamo model where the two equilibrium points correspond to the two polarities of the earth's magnetic field. We prove what has been suggested by a computer simulation, that the counting process of the flips or the reversals of the earth's field converges to a standard Poisson process if the time is suitably scaled.     

Fluorescence Lifetime Tuning—A Novel Approach to Study Flip-Flop Kinetics in Supported Phospholipid Bilayers

In the present work we introduce a straightforward fluorescent assay that can be applied in studies of the transbilayer movement (flip-flop) of fluorescent lipid analogues across supported phospholipid bilayers (SPBs). The assay is based on the distance dependent fluorescence quenching by light absorbing surfaces. Applied to SPBs this effect leads to strong differences in fluorescence lifetimes when the dye moves from the outer lipid leaflet to the leaflet in contact with the support. Herein, we present the basic principles of this novel approach, and comment on its advantages over the commonly used methods for investigating flip-flop dynamics across lipid bilayers. We test the assay on the fluorescent lipid analog Atto633-DOPE and the 3-hydroxyflavone F2N12S probe in SPBs composed of DOPC/ DOPS lipids. Moreover, we compare and discuss the flip-flop rates of the probes with respect to their lateral diffusion coefficients.     

Remote optical control of an optical flip-flop

We experimentally demonstrate control of a holding-beam-enabled optical flip-flop by means of optical signals that act in a remote fashion. These optical-control signals vary the holding-beam power by means of cross-gain modulation within a remotely located semiconductor optical amplifier (SOA). The power-modulated holding beam then travels through a resonant-type SOA, where flip-flop action occurs as the holding-beam power falls above and below the switching thresholds of the bistable hysteresis. Control is demonstrated using submilliwatt pulses whose wavelengths are not restricted to the vicinity of the holding beam. Benefits of remote control include the potential for controlling multiple flip-flops with a single pair of optical signals and for realizing all-optical control of any holding-beam-enabled flip-flop.     

Control of cavity solitons and dynamical states in a monolithic vertical cavity laser with saturable absorber

We present recent experimental results on the control and dynamics of cavity solitons in a monolithic, vertical cavity surface emitting laser with saturable absorber. On one hand, the fast and independent manipulation of two laser cavity solitons is achieved and a flip-flop operation is demonstrated with a single control-beam. On the other hand, a pulsing localized structure is presented and we demonstrate the control of a pulsing multispot structure that we can switch-on and off. These results are promising in view of the obtainment of a pulsed and monolithic cavity soliton laser.     

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.     

A new alternative approach of all optical frequency encoded clocked S-R flip-flop exploiting the non-linear character of semiconductor optical amplifiers

In all optical networking and computing system, the role of all-optical flip-flops is very much essential. For signal synchronization with a reference clock and for storage of digital bits the flip-flop has no alternative. In this communication the authors propose a method of developing an all optical frequency encoded clocked R-S flip-flop using the non-linear character of semiconductor optical amplifiers. Frequency is the basic character of light and several encoding/decoding problems in computations and communications can be solved using the frequency encoding principle of optical data. The proposed system is all-optical and therefore it can extend a super fast speed of operation (far above THz limit).     

Dynamic model of ortho-para conversion of water molecules

A quantum model of mutual conversion of spin isomers of the water molecule, involving a proton of a neighboring water molecule, is proposed. Molecules interact due to magnetic dipole-dipole forces which give rise to flip-flop processes. An additional adsorption energy different in magnitude and sign for singlets and triplets arises from a fast exchange of spin states within an acceptor molecule. A slower flip-flop process controls the simultaneous evolution of all three protons, which results in the transition between singlet and triplet states. Based on the developed model, experimental data on ortho-para-water are discussed.     

Nanostructured silicon geometries for directly bonded hybrid III–V-silicon active devices

We discuss geometries with nanostructured cladding for active InP/silicon structures made by hetero-epitaxial bonding, which means that InP is directly bonded to silicon from a silicon-on-insulator without any intermediate layer. Such a cladding features low-index confinement and adds thermal sinking channels to those practised on the InP side. The first approach is a one-dimensional effective medium viewpoint, easily showing why grooves parallel to the waveguide are better. Then, two dimensional nanostructures are examined and found to perform better, given etching constraints. A more sophisticated geometry balancing thermal and optical confinement merits is then introduced thanks to a flip-flop algorithm.     

Toward Efficient Design of Flip-flops in Quantum-Dot Cellular Automata with Power Dissipation Analysis

Quantum-dot cellular automata (QCA) is one of the emergent nano-technologies and a potential substitute for transistor based technologies. In this research, an efficient QCA based T, SR and JK flip-flops have been proposed. The proposed gates are implemented with multiplexer, three-input Majority gate and XOR gate. The circuit layouts are designed and verified using QCADesigner version 2.0.3. The simulation result reviles the excellence of the proposed design. The proposed T flip-flop archives 35% improvement in terms cell count. Similarly, the reported RS and JK flip-flop requires 43% and 50% less area respectively in comparison to the previous best single layer design. In addition, QCAPro tool has been used to estimate the power dissipation of all considered designs at different tunneling energy level.