We discuss the optical bistability and multistability properties of incident light on a unidirectional ring cavity consisting of a hybrid semiconductor quantum dot-metal nanoparticle system driven by coupling and incoherent pumping fields. We consider the quantum dot system as a three-level V-type configuration which is placed near the metallic nanoparticle. We realize that the threshold of optical bistability and optical multistability can be controlled by tuning the center-to-center distance between quantum dots and metallic nanoparticles. Moreover, the effect of incoherent pumping field on optical bistability and optical multistability has been discussed for different distances between quantum dots and metallic nanoparticles.

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In this paper, long wavelength superluminal and subluminal properties of pulse propagation in a defect slab medium doped with four-level GaAs/AlGaAs multiple quantum wells (MQWs) with 15 periods of 17.5 nm GaAs wells and 15 nm [Formula: see text] barriers is theoretically discussed. It is shown that exciton spin relaxation (ESR) between excitonic states in MQWs can be used for controlling the superluminal and subluminal light transmissions and reflections at different wavelengths. We also show that reflection and transmission coefficients depend on the thickness of the slab for the resonance and nonresonance conditions. Moreover, we found that the ESR for nonresonance condition lead to superluminal light transmission and subluminal light reflection.