Ultrafast nonlinear response of AlGaAs two-dimensional photonic crystal waveguides

We have used femtosecond pump-probe spectroscopy to study the ultrafast nonlinear response of AlGaAs two-dimensional photonic crystal waveguides in the near-infrared spectral region. The modulation of the reflectivity spectra due to the refractive index change produced by photogenerated carriers was measured. We observed an instantaneous pump-induced shift in the wavelength of a photonic resonance at 882 nm with a fast decay time of ≈8 ps. The magnitude of the reflectivity change was very large at wavelengths close to the photonic resonance, with a maximum value of $\mathrm{\Delta R/R}$ >30% at 877 nm. These results confirm the excellent potential of photonic crystal waveguides in ultrafast nonlinear switching applications.