Bistable Type Research Articles

Structural dependence of optical bistability of In 0.52Al 0.48As/InP type II MQW diodes grown by gas source molecular beam epitaxy

The structural dependence of optical bistability was studied for the In 0.52Al 0.48As/InP type II multiple quantum well diodes grown by gas source molecular beam epitaxy. Two types of optical bistability were observed. One of them shows a sudden increase of light output with increasing injection current, while the other shows a sudden decrease of light output with increasing injection current. The former is considered to be induced by holes tunneling in the valence band, while the latter is considered to be induced by the resonant tunneling effect of electrons in the conduction band.

From bistability to oscillations in a model for the isocitrate dehydrogenase reaction

Considered is a bienzymatic system consisting of isocitrate dehydrogenase (IDH, EC 1.1.1.42), which transforms NADP + into NADPH, and of diaphorase (DIA, EC 1.8.1.4), which catalyzes the reverse reaction. Experimental evidence as well as a theoretical model show the possibility of a coexistence between two stable steady states in this reaction system. The phenomenon originates from the regulatory properties of IDH. We extend the analysis of a theoretical model proposed for the IDH–DIA bienzymatic system and investigate the occurrence of different modes of bistability, with or without hysteresis, i.e. in the presence of two or only one limit point bounding the domain of multiple steady states. The analysis indicates that the two types of bistability may sometimes be observed sequentially as a given control parameter is progressively increased. We further obtain conditions in which sustained oscillations develop in the model. These results establish the isocitrate dehydrogenase reaction coupled to diaphorase as a suitable candidate for further experimental and theoretical studies of bistability and oscillations in biochemical systems.

Atomic cooperation and nonlinear dynamics in a mesoscopic maser

We consider a mesoscopic maser, in which a beam of excited two-level Rydberg atoms interacts with a single radiation mode during propagation through a resonant cavity. The number of atoms in the cavity ranges from a few tens to a few hundreds. Steady-state and nonlinear dynamics are investigated both with and without a coherent driving field. At steady state, atomic cooperation can induce multistability and temporal instabilities. A novel type of bistability is predicted for the amplitude of the coherently driven cavity field as a function of atomic density. The system dynamics exhibits a variety of regimes, including chaos. We have explored them by varying the experimentally accessible parameters: atomic density, cavity linewidth and driving field amplitude.

Solitary wave propagation and bistability in the normal dispersion region of highly nonlinear optical fibres and waveguides

Properties of bright solitary wave solutions of the cubic-quintic nonlinear Schrödinger equation are considered in the normal dispersion region of optical fibres and waveguides with third- and fifth-order nonlinearities. The case of an optical fibre is concretely considered but other possible waveguide geometries are also discussed. For comparison, the properties of the black solitary wave existing in the same parameter range are also considered. All soliton parameters are presented in a unified way as functions of the normalised pulse energy. The possibility for bistable behaviour of the solitary waves is examined and a new type of solitary wave bistability (bright—dark) is introduced. The role of the geometry of the waveguide and the appropriate materials for experimental observation of such waves are also discussed.

Stability of Travelling Multiple-Front (Multiple-Back) Wave Solutions of the FitzHugh--Nagumo Equations

Consideration is devoted to travelling multiple-front (back) wave solutions of the FitzHugh--Nagumo equations of bistable type. In particular, stability of the 1-front (back) wave is proven. In the proof, the eigenvalue problem for the 1-front wave bifurcating from coexisting simple front and back waves is regarded as a bifurcation problem for projectivized eigenvalue equations, rather than treated as a linear eigenvalue problem for each fixed wave.

Observation of bistability in GaAs quantum-well vertical-cavity surface-emitting lasers

Two different types of bistability in proton-implanted GaAs quantum-well (QW) vertical-cavity surface-emitting lasers (VCSELs) have been observed. The first type of bistability has a small hysteresis width (/spl sim/50 /spl mu/A) in the light versus current and voltage versus current characteristics. Light-induced large negative differential resistance, random fluctuations, and self-pulsations are observed at the switching point. The emission patterns show that the bistability occurs at a spatially localized area under the output facet that covers only a small fraction of the N1S-/spl mu/m-diameter aperture. The bistability stems from spatially localized saturable absorption. The second type of bistability has a large hysteresis width (/spl sim/1 /spl mu/A) in the L-1 characteristics and is observed well above the threshold current. In this case, no observable bistable loop exists in the voltage versus current characteristics, and the bistability is associated with transverse mode-hopping.

A quasi-optimal error estimate for a discrete singularly perturbed approximation to the prescribed curvature problem

Solutions of the so-called prescribed curvature problem min A ⊆ Ω P Ω (A) - ∫ A g(x), g being the curvature field, are approximated via a singularly perturbed elliptic PDE of bistable type. For nondegenerate relative minimizers A ⊂⊂ Ω we prove an O(∈ 2 |log∈| 2 ) error estimate (where ∈ stands for the perturbation parameter), and show that this estimate is quasi-optimal. The proof is based on the construction of accurate barriers suggested by formal asymptotics. This analysis is next extended to a finite element discretization of the PDE to prove the same error estimate for discrete minima.

Optically controlled S- and N-shaped negative differential resistances by resonant-tunnelling triangular-barrier optoelectronic switch (R-TOPS)

We report novel optoelectronic functions in a resonant-tunnelling triangular-barrier optoelectronic switch (R-TOPS). We successfully observed optically controlled S- and N-shaped negative differential resistances (NDRs) simultaneously in a single device. Different types of optoelectronic bistabilities originating from S- and N-shaped NDRs were obtained by changing the input light power. We also obtained the differential gain characteristics and latch characteristics from S-shaped NDR by changing the bias voltages. These characteristics with their different behaviours make it possible to realize novel optoelectronic switching.

Dynamic transmission properties of a nonlinear fiber ring resonator

We present a method for calculating the dynamic input–output characteristics of a nonlinear fiber ring resonator caused by a change in input intensity. It is based on an original method developed by Bischofberger and Shen [Phys. Rev. A 19, 1169 (1979)] to study a transient nonlinear Fabry–Perot resonator. We treat a double-coupler fiber ring resonator, in which two types of optical bistability (transmission bistability and reflection bistability) are available and present the illustrative numerical results for a few cavity parameters. This analysis will be useful for a future experimental verification of optical bistability in fiber ring resonators and for the design of fiber bistable devices.

Different types of optoelectronic bistabilitiesinresonant-tunnelling triangular-barrieroptoelectronic switch (R-TOPS)

Novel optoelectronic bistabilities in a resonant-tunnelling triangular-barrier optoelectronic switch (R-TOPS) are reported. Optically controlled S-shaped and N-shaped NDRs were observed simultaneously in a single device. Different types of optoelectronic bistabilities originated from S-shaped and N-shaped NDRs were obtained by changing the input light power.

Two-photon optical bistability in polar molecules: vibrational coupling effects

Single-beam two-photon optical bistability in a two-level system where the levels have unequal electric dipole moments is analyzed theoretically. By means of unitary transformations the system is transformed into a two-level nonpolar system with a field-dependent effective transition dipole moment. Two-photon optical bistability is found to be favored as the difference between the dipole moments grows. When the excited electronic system is coupled to a vibrational normal mode of the nuclei, the susceptibility becomes three-valued and consequently a different type of optical bistability appears, which can coexists with the previous one.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pitchfork bifurcation polarization bistability in laser diodes with external cavities

A new pitchfork bifurcation polarization bistability in laser diodes with a two-armed polarization-selective external cavity is examined theoretically and experimentally. The rate-equation analysis taking into account gain saturation has been carried out using the model for a laser diode whose laser thresholds of the TE and the TM modes can be changed independently through the changing of their photon lifetimes. It is shown from the analysis that pitchfork bifurcation polarization bistability appears when the laser thresholds for both modes are very close to each other and the switching between two stable states is obtained by means of a photon lifetime changing or a coherent or incoherent light injection. In the experiment, a 1.3-/spl mu/m InGaAsP laser diodes with a T-shaped polarization-selective external cavity mas used. A new type of polarization bistability was observed when one arm was blocked and then recoupled. The two stable states mere also switched by means of an optical injection. All-optical flip-flop operation has been successfully demonstrated by using both TE and TM trigger inputs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Possibility of intrinsic optical (far-IR) bistability in an asymmetric double quantum well

A new type of optical bistability in a double quantum well is predicted. This is a pure intrinsic bistability which is not accompanied by any dc current in an external circuit and requires no source of electric energy. The effect is based on counterfield electron transfer and is driven and controlled by far-IR radiation resonant to an intersubband transition. Bistable switching and hysteresis can be monitored either electrically or optically. Theory shows the effect to be readily observable.

Stability of some structures in a cholesteric liquid crystal layer for tilted anchoring

Abstract An analysis of the permitted structures for a cholesteric liquid crystal based on the continuum theory as a function of the anchoring conditions and the thickness of the liquid crystal layer is presented. A new type of bistability is found. The stability domains of various structure types are given.

Travelling fronts in cylinders

This work is concerned with travelling front solutions of semilinear parabolic equations in an infinite cylindrical domain Σ = R × ω where ω ⊂ Rn−1 is a bounded domain. We write for x in Σ, x = (x1, y), with y ∊ ω. The problems we consider are of the following type {Δu−(c+α(y))∂1u+f(u)=0inΣ∂u∂ν=0on∂∑u(−∞,.)=0,u(+∞,.)=1where the unknowns are the parameter c ∊ R and the function u. The function α∈C0(ω¯) and the nonlinear term f: [0, 1] → R are given. (More general coefficients than c + α (y), β (y, c) are also treated.)We obtain a fairly general resolution of this problem. The results depend on the type of nonlinearity considered. When f is of the bistable type, or of the “ignition temperature” type in combustion, we show the existence and uniqueness of c and of the profile u. In the case that f > 0 in (0, 1), we show the existence of c* ∊ R such that a solution exists if and only if c ≧ c*. These results extend to higher dimensions various classical results. In particular they extend the result of Kolmogorov, Petrovsky and Piskounov.

Phonon effects on optical bistability in a two-photon resonant absorber

Single beam two-photon optical bistability in a Fabry-Perot cavity is analyzed taking into account phonon effects. The Maxwell-Bloch equations of the system are further coupled by a term that is dependent on the electron-phonon interaction. It is shown that such an interaction can lead to a new type of optical bistability which competes with the ordinary absorptive one.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Kerr-lens-mediated dynamics of two nonlinearly coupled mode-locked laser oscillators

The dynamics of two nonlinearly coupled femtosecond oscillators are investigated for the case where two distinct nonlinear mechanisms are balanced to determine the temporal relationship and properties of the pulses in the two oscillators. In the time domain the shared bleaching of a common absorber creates an attractive mechanism for the pulses, while interactive Kerr lens deflections create a repulsive mechanism. The interplay of these two mechanisms causes a variety of dynamical behaviors, including pulse synchronization, pulse duration switching, and a latching type of amplitude bistability.

Increasing absorption optical bistability in highly concentrated dye solutions

We report the results of experimental observation of increasing absorption optical bistability in highly concentrated aqueous solutions of toluidine blue dye. The thermal shift of the monomer-dimer equilibrium towards higher monomer concentration is identified as the nonlinear optical mechanism that ensures also the positive local feedback. A simple model that gives the criteria for the occurence of this type of optical bistability and which enables selections of effective dyes is presented.

Dynamics of an optical ring circuit having photorefractive gain and loss and history-dependent feedback

An optical ring circuit is considered in which gain, loss, and feedback are provided by refractive-index gratings in photorefractive crystals. The photorefractive feedback coupling element, which replaces an ordinary mirror, is assumed to be much slower than either the gain or the loss. As a result, the state of the photorefractive mirror depends on past states of the circuit; that is, the photorefractive mirror has a memory. The system’s behavior is then determined by the relative speeds of the gain and the loss. When their speeds are roughly equal, the system exhibits both ordinary bistability and history-dependent bistability, whose character changes as the system evolves. Graphic techniques aid in the understanding of the nature of both types of bistability. When the gain is significantly faster than the loss, the system exhibits one of three varieties of self-pulsing: pure self-pulsing, interrupted self-pulsing, or delayed self-pulsing.

Dynamics of circularly polarized eigenstates in lasers with nonweak atomic coupling

It is shown theoretically and experimentally that the two circularly polarized eigenstates of a laser oscillating on a nonweak atomic coupling transition exhibit two types of vectorial bistability. A rotation and an inhibition mechanism are isolated, depending on the eigenfrequency difference of the two eigenstates. For both mechanisms, the evolution of the hysteresis loop with this frequency difference shows good agreement with a phenomenological Landau's potential model.