Ultrafast optical switching of three-dimensional Si inverse opal photonic band gap crystals

TL;DR

This paper demonstrates ultrafast optical switching in 3D silicon inverse opal photonic crystals using free-carrier excitation, achieving large spectral shifts and potential GHz switching rates for advanced photonic applications.

Contribution

It introduces a novel ultrafast switching method for 3D photonic band gap crystals via two-photon excitation of free carriers in silicon inverse opals.

Findings

Achieved up to 1.5% spectral shift in photonic band gap features.

Observed a 21 ps decay time indicating GHz switching potential.

Demonstrated large refractive index change of 2.0%.

Abstract

We present ultrafast optical switching experiments on 3D photonic band gap crystals. Switching the Si inverse opal is achieved by optically exciting free carriers by a two-photon process. We probe reflectivity in the frequency range of second order Bragg diffraction where the photonic band gap is predicted. We find good experimental switching conditions for free-carrier plasma frequencies between 0.3 and 0.7 times the optical frequency: we thus observe a large frequency shift of up to D omega/omega= 1.5% of all spectral features including the peak that corresponds to the photonic band gap. We deduce a corresponding large refractive index change of Dn'_Si/n'_Si= 2.0% and an induced absorption length that is longer than the sample thickness. We observe a fast decay time of 21 ps, which implies that switching could potentially be repeated at GHz rates. Such a high switching rate is relevant to future switching and modulation applications.