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The authors report a direct measurement of the absorption dynamics in an InAs p-i-n ridge waveguide quantum dot modulator. The carrier escape mechanisms are investigated via subpicosecond pump-probe measurements at room temperature, under reverse bias conditions. The optical pulses employed are degenerate in wavelength with the quantum dot ground state transition at 1.28μm. The absorption change recovers with characteristic times ranging from 62ps (0V)to∼700fs (−10V), showing a decrease of nearly two orders of magnitude. The authors show that at low applied fields, this recovery is attributed to thermionic emission while for higher applied fields, tunneling becomes the dominant mechanism.

We have explored the dependence of electron spin relaxation in undoped GaAs/AlGaAs quantum wells on well width (confinement energy) at 300 K. For wide wells, the relaxation rate tends to the intrinsic bulk value due to the D’yakonov–Perel (DP) mechanism with momentum scattering by phonons. In narrower wells, there is a strong dependence of relaxation rate on well width, as expected for the DP mechanism, but also considerable variation between samples from different sources, which we attribute to differences in sample interface morphology.

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Direct measurement of the group index of photonic crystal waveguides via Fourier transform spectral interferometry

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