Mechanism of ultrafast modulation of the refraction index in photoexcited In_xGa_(1-x)As/AlAs_ySb_(1-y) quantum well waveguides

摘要

Ultrafast index change induced by intersubband excitation in In_nGa_(1-x)As/AlAs_ySb_(1-y) quantum well waveguides was evaluated by measuring the phase shift Δφ in a wide spectral range of 1.2-1.7 μm based on a spectral analysis. We obtained a large enhancement in Δφ by tuning the probe photon energy to interband absorption edge. The measured induced absorption ΔA also increased with reduction in the wavelength. The spectra of Δφ and ΔA were well explained by the interband dispersion model under intersubband excitation while the intersubband plasma dispersion previously reported has a negligible contribution.