Femtosecond dynamics of active semiconductor waveguides: microscopic analysis and experimental investigations

Abstract

We present theoretical and experimental results of nonlinear amplification and propagation of short optical pulses in Fabry–Perot semiconductor lasers. The theoretical description is based on spatially resolved Maxwell–Bloch–Langevin equations that take into account the spatially varying light-field dynamics including counterpropagation, diffraction, self-focusing, and the microscopic carrier dynamics including carrier heating and carrier relaxation. Femtosecond pump–probe measurements using upconversion and femtosecond-resolved pump–probe measurements and frequency-resolved optical gating on a Fabry–Perot laser allow a combined analysis of the transmitted pulses in real time and the spectral domain. The experimental results are compared with the microscopically calculated gain and index distributions, pulse shapes, and optical spectra. In order to assess the full potential of semiconductor lasers and amplifiers, a quantitative measurement and understanding of amplitude and phase dynamics is required. The computer simulations of the ultrashort dynamics of semiconductor waveguides with optical injection of light pulses provide insight into the dynamic spectral gain and index changes responsible for frequency drifts and self-phase modulation, visualization of propagation effects, and a time- and frequency-resolved analysis of the amplified light pulses.