Optical bistability was observed in a multiquantum well microcavity, with a 500 W/cm2 intensity threshold and a 10:1 contrast. The device design enhances the cavity finese (here up to 250), by increasing the number of layers in the Bragg mirror stacks, and simultaneously reducing the active layer thickness (here 3λ/2, i.e. 360 nm).
Monolithic bistable microcavities with a GaAs/Al0.3Ga0.7As multiple quantum well active layer and AlAs/Al0.1Ga0.9As Bragg reflectors have been fabricated by metalorganic vapor phase epitaxy. The design of the whole structure is such that a good cavity finesse and a high contrast in the reflective mode are simultaneously obtained. This results in a bistability power threshold of less than 3 mW at 838 nm and a contrast ratio as high as 30:1. A new method is proposed, which allows to measure the nonlinear refractive index in a quasi-continuous regime, and in the operating conditions for bistability. The nonlinear index is shown to saturate at higher power, which evidences the need of a good cavity finesse for such bistable devices. Memory effect is then demonstrated: the sample can stay in either of its two stable states for more than 1 ms without spontaneously switching, and for input pulses as short as 60 ns. Finally we describe two-beam experiments with a new experimental configuration, also in reflection, which allows to mix the two input beams and extract the output beam with an ideal 100% efficiency.
We report on a novel monolithic all-optical bistable device operating at 980 nm, based on the dispersive optical nonlinearity of strained InGaAs/GaAs quantum wells located at the antinodes of the microcavity optical field. This design maximizes the interaction with the intracavity field and allowed to use only twelve quantum wells of 10 nm thickness. The first observation of all-optical bistability with strained InGaAs/GaAs quantum wells is reported, with a contrast ratio of 7:1 and a threshold intensity of 1 kW/cm2. The operating wavelength offers key advantages such as the substrate transparency and compatibility with vertical cavity surface emitting lasers.
Epitaxial methods allow the fabrication of nonlinear interferomethc structures which include the mirrors and the GaAs Multiple Quantum Wells (MQW) nonlinear medium in a single crystal. This results in very compact nonlinear microcavities with typically 5im overall thickness. Optical bistability is observed in these structures at mW optical power. We review our latest experimental results on these structures including the observation of high contrast switching in the reflection mode the direct measurement of dispersive optical nonlinearities in MQWs evidencing their saturation behavior at high intensities. Finally we report external-beam switching experiments which allow to assess the potential of these structures as all-optical gates.
We report an experimental study of the optical bistability in a semiconductor microcavity (MC), consisting of a wedged λ GaAs spacer containing a single 8.5 nm In 0.04 Ga 0.96 As quantum well (QW). Increasing the excitation power, a transition between the normal coupling and the weak coupling regime of the MC modes is observed. At intermediate excitation power the reflectivity spectrum shows the simultaneous presence of three resonances, with a third peak spectrally lying between the two normal modes. Monitoring the reflected signal for different laser energy as a function of the excitation power, we found that optical bistability is observed only at the energy of the third peak. The experimental findings do not agree with transfer matrix calculations based on exciton bleaching, suggesting that more complex nonlinear mechanisms are relevant in the observed bistable behaviour.
The band edge nonlinear absorption in ZnTe/CdZnTe multiple quantum wells (MQWs) is studied at room temperature. It is found that the exciton absorption peak tends to saturate, broaden and the absorption edge shift to lower energy side with increasing of pump intensities. The optical bistability in ZnTe/CdZnTe MQWs optical bistable device is investigated on transmission at room temperature. The research result indicates that the threshold and contrast ratio for the optical bistability in ZnTe/CdZnTe MQWs optical bistable device are about 292.5 kW/cm2 and 3:1, respectively.