Excitonic Optical Bistability Research Articles

Bistability in the transmission ofCu2O: Optical hysteresis in the high-resolution limit

Excitonic optical bistability in ${\mathrm{Cu}}_{2}\mathrm{O}$ is studied in a high-resolution transmission experiment. The bistability arises from non-linear photothermal interplay between the sharp yellow 1S orthoexciton resonance and a single mode photon source. All optical switching is demonstrated, where changes in the excitation energy of $200\phantom{\rule{0.3em}{0ex}}\mathrm{neV}$ act as discriminator between states of high and low transmission. The dynamics of the bistability as well as the transmission hysteresis are monitored. The spectral width of the hysteresis loop can be tuned from $8\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{eV}$ down to $80\phantom{\rule{0.3em}{0ex}}\mathrm{neV}$, by adjusting the excitation power. The experimental findings are in agreement with model calculations.

Picosecond optical bistability in ZnSeCdZnSe multiple quantum wells with a Fabry-Pérot cavity

Excitonic optical bistability with picosecond switching time in ZnSeCdZnSe multiple quantum wells (MQWs) with a Fabry-Pérot (FP) cavity is investigated at room temperature. The result indicates that the threshold and switching time for the optical bistability in ZnSeCdZnSe MQWs with a FP cavity are about 210 kW/cm2 and 50 ps, respectively. On the basis of the excitonic nonlinear theories, excitonic absorption spectra in the ZnSeCdZnSe MQWs under different excitation intensities obtained here, we attribute the major nonlinear mechanism for the optical bistability in ZnSeCdZnSe MQWs with a FP cavity to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.

Dispersive optical bistability in ZnCdSe-ZnSe/GaAs strained-layer superlattices on reflection at room temperature

The excitonic optical bistability with nanosecond switching time in ZnCdSe-ZnSe/GaAs strained-layer superlattices has been studied on reflection at room temperature. On the basis of the shape of the measured hysteresis loops, photoluminescence and absorption spectra, the origin of the optical bistability is attributed to the effect of excitonic saturating absorption.

Excitonic Optical Nonlinearity and Optical Bistability in ZnSe–CdZnSe MQWs at Room Temperature

Excitonic optical bistability with picosecond switching time in ZnSe-CdZnSe multiple quantum wells (MQWs) optical bistable device is investigated at room temperature for the first time. The result indicates that the threshold and contrast ratio for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device are about 210 kW/cm2 and 2 : 1, respectively. On the basis of the excitonic nonlinear theories, excitonic absorption and excitonic emission under different excitation intensities in the ZnSe-CdZnSe MQWs obtained here, we attribute the major nonlinear mechanism for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.

Excitonic optical bistability of ZnSe—ZnS/GaAs MQWs on reflection at room temperature

We present the first observation of room-temperature nanosecond excitonic optical bistability on reflection in ZnSe—ZnS/GaAs multiple quantum wells, in which the switching intensity and contrast ratio for the optical bistability are about 0.6 MW/cm2 and 7 : 1. The research results indicate that the nonlinear mechanism for the optical bistability is due to the excitonic saturating absorption effect.

Growth and optical bistability of Zn 0.78Cd 0.22Se-ZnSe multiple quantum wells by metalorganic chemical vapor deposition

Room temperature (RT) excitonic optical bistability has been investigated in multiple quantum wells (MQWs) of (Zn, Cd) Se-ZnSe at blue-green wavelengths. The (Zn, Cd) Se-ZnSe MQWs with 50 periods were grown by atmospheric pressure MOCVD technique. Photoluminescence (PL) and transmission spectra of Zn 0.78Cd 0.22Se-ZnSe MQWs at RT were measured. Optical bistability (OB) of the MQWs at RT was obtained by an incident beam of 515 nm wavelength. The origin of the OB obtained here was attributed to the excitonic absorption.

Excitonic bistabilities, instabilities and chaos in laser-pumped semiconductors

The Hurwitz criteria are used for a stability analysis of the steady state excitonic optical bistability curves in a semiconductor pumped by an external laser resonant with the exciton level. Besides the middle branch of the bistability curves which is unstable in the sense of the linear stability theory, we have found other domains of instability in the upper and lower branches of the steady state curves. Numerical results show that a possible route to chaos in the photon-exciton system is period-doubling self-oscillation process. The influence of the presence of free carriers that coexist with the excitons is also discussed.

An analytic study of the switching process in excitonic optical bistability in semiconductors

The authors study analytically the switching process in excitonic optical bistability in a semiconductor near the hysteresis limit points in the case of fully developed hysteresis. They consider four different time-dependent input pulse shapes that induce switching: a single rectangular pulse, a single triangular pulse, a sequence of rectangular pulses and a sequence of triangular pulses. The dependence of the switching time on the characteristics of these inputs is analysed.

Excitonic optical bistability in n-type-doped semiconductors

A resonant monochromatic pump laser generates coherent excitons in an n-type-doped semiconductor. Both exciton–exciton and exciton–donor interactions come into play. The former interaction can give rise to the appearance of optical bistability, which is heavily influenced by the latter one. When optical bistability occurs at a fixed laser frequency both its holding intensity and hysteresis-loop size are shown to decrease with increasing donor concentration. Two possibilities are suggested for experimentally determinng one of the two parameters of the system, the exciton–donor coupling constant or the donor concentration if the other is known.

Transient dynamics in excitonic optical bistability in polymers.

Transient behavior in the optical bistability mediated by phonon-mode and virtual-exciton coupling is studied for an electron-phonon-coupling system, such as polydiacetylene toluene sulfonate. Numerical calculations are used to analyze the evolution between bistable states, and switching behavior and Rabi oscillations are found.

Phonon-mediated excitonic optical bistability in polymers.

For a polymer inside an optical cavity, optical multistability mediated by phonon modes and virtual exciton coupling is investigated. The cavity field, excitons, and phonon modes are treated as damped oscillators, and the equations of motion for the dynamical variables are obtained by applying Dekker's theory for dissipative systems. Steady-state results are obtained numerically for polydiacetylene [bis(p-toluene sulfonate)] with the input field frequency on or off resonance with the cavity field. The variation of the cavity-field intensity follows a reversed hysteresis loop on resonance, while it may follow either a normal or a reversed hysteresis loop off resonance depending on the course of change of the driving-field intensity at the unstable turning point. The variation is inverted when the detuning changes its sign. It is also found that the virtual excitons, phonon modes, and feedback of the cavity are all indispensable to such tristability.

Effects of mirror reflectivity in excitonic optical bistability

The intensity-dependent nonlinearity of the dielectric function resulting from two-photon generation of excitonic molecules has been used to predict optical bistability in CuCl. The prediction is shown numerically to be highly affected by the mirror reflectivity in the Fabry–Perot cavity. In general, the reflectivity makes optical bistability possible at less stringent conditions.

Quantum theory of excitonic optical bistability

We present a fully-quantum-mechanical theory of the intracavity interaction of coherent light with semiconductors. Interaction is assumed to occur via excitons. Using a master-equation approach we include such effects as exciton-lattice and exciton-exciton interactions. In the two cases of high and low exciton densities, steady-state analysis reveals bistability and hysteresis in the system. Bistability of a dispersive and absorptive nature in both exciton number and output intensity, dependent on input intensity is found. The bistability displayed in the high-density case agrees qualitatively with the experimental curves obtained by Gibbs et al. for GaAs. As yet the low-density bistability has not been experimentally observed.