Competition between electronic Kerr and free carrier effects in an ultimate-fast optically switched semiconductor microcavity

TL;DR

This study investigates ultrafast optical switching in a GaAs-AlAs microcavity, revealing the competition between electronic Kerr and free carrier effects at different pump energies, and develops a model to predict this behavior.

Contribution

It introduces a new analytic model that accounts for probe intensity effects and demonstrates how to distinguish Kerr from free carrier effects in cavity resonance shifts.

Findings

Kerr effect dominates at low pump energies within 300 fs

Free carrier effects reduce resonance shift at high pump energies

Model accurately predicts the competition between effects

Abstract

We have performed ultrafast pump-probe experiments on a GaAs-AlAs microcavity with a resonance near 1300 nm in the "original" telecom band. We concentrate on ultimate-fast optical switching of the cavity resonance that is measured as a function of pump-pulse energy. We observe that at low pump-pulse energies the switching of the cavity resonance is governed by the instantaneous electronic Kerr effect and is achieved within 300 fs. At high pump-pulse energies the index change induced by free carriers generated in the GaAs start to compete with the electronic Kerr effect and reduce the resonance frequency shift. We have developed an analytic model which predicts this competition in agreement with the experimental data. Our model includes a new term in the intensity-dependent refractive index that considers the effect of the probe pulse intensity, which is resonantly enhanced by the cavity. We calculate the effect of the resonantly enhanced probe light on the refractive index change induced by the electronic Kerr effect for cavities with different quality factors. By exploiting the linear regime where only the electronic Kerr effect is observed, we manage to retrieve the nondegenerate third order nonlinear susceptibility for GaAs from the cavity resonance shift as a function of pump-pulse energy.