Identification of competing ultrafast all-optical switching mechanisms in Si woodpile photonic crystals

TL;DR

This paper systematically investigates ultrafast all-optical switching mechanisms in silicon photonic crystals, identifying the electronic Kerr effect and two-photon absorption as key processes, and introduces a figure of merit for nondegenerate switching.

Contribution

It unambiguously identifies the electronic Kerr effect as a dispersive switching mechanism and introduces a nondegenerate figure of merit for optical switching in photonic crystals.

Findings

Dispersive and absorptive features observed at coincidence in pump-probe spectra.

Kerr effect identified as the dispersive switching mechanism.

Nondegenerate figure of merit (NFOM) proposed for evaluating switching quality.

Abstract

We present a systematic study of ultrafast all-optical switching of Si photonic band gap woodpile crystals using broadband tunable nondegenerate pump-probe spectroscopy. At pump-probe coincidence, we investigate the behavior the differential reflectivity at the blue edge of the stopband for a wide range of pump- and probe frequencies. Both dispersive and absorptive features are observed from the probe spectra at coincidence. As the pump frequency is tuned through half the electronic bandgap of Si, the magnitude of both these features increases. For the first time we unambiguously identify this dispersive effect with the electronic Kerr effect in photonic crystals, and attribute the the absorptive features to nondegenerate two photon absorption. The dispersive and absorptive nonlinear coefficients are extracted, and are found to agree well with literature. Finally, we propose a nondegenerate figure of merit (NFOM), which defines the quality of switching for all nondegenerate optical switching processes.