Theory of all-optical switching based on the Kerr nonlinearity in metallic nanohybrids

Abstract

We have developed a theory for the Kerr nonlinearity in nanohybrids made of an ensemble of metallic nanoshells and low concentration of quantum emitters. A metallic nanoshell is made of a metallic core sphere and dielectric shell. We consider that quantum emitters are four-level quantum systems. When a probe laser light falls in the metallic nanoshells, the surface plasmon polariton electric field is produced at the interface between the metal sphere and dielectric shell. This electric field along with the probe field induces dipoles in metallic nanoshells. These dipoles interact with each other via the dipole-dipole interaction. The Kerr nonlinearity has been calculated by using the quantum density matrix method in the presence of the dipole-dipole interaction (coupling). We found that in the weak-coupling limit there is an enhancement in the Kerr nonlinearity. On the other hand, in the strong-coupling limit, the peaks in the Kerr coefficient split from two peaks to four peaks when the frequency of the dipole electric field is in the resonance with the exciton frequency. The splitting in the spectrum is due to the presence of the dressed sates created in the system. We showed that heights and locations of peaks are very sensitive to the strength of the dipole-dipole interaction. Physics of the enhancement can be used fabricate Kerr nanosensors. On the other hand, physics of the splitting from two peaks (ON) to four peaks (OFF) can be used to fabricate Kerr nanoswitches.