Ultrafast pulse propagation in direct gap semiconductor quantum well waveguide structures

Abstract

Using the Luttinger formulations, we have analysed the propagation characteristics of an ultrashort (femtosecond) coherent radiation pulse in the transverse plane of a direct gap semiconductor quantum well waveguide structure (QWWS). The semiconductor QWWS is considered to possess degenerate valence subbands near the centre of the Brillouin zone. The photoinduced resonant transitions below the band edge to both 1s and 2s excitonic states from the light hole (lh) and heavy hole (hh) subbands have been considered. The cross-over between the lh and hh bands occurs in the case of the transverse plane where the light holes are found to play a more dominant role than the heavy holes. Efforts have been directed towards analysing the transient pulse propagation characteristics such as pulse break-up and optical nutation. We have also studied the transverse electric mode propagation in the QWWS assuming the same to behave as a three-layer asymmetric optical planar waveguide. Numerical analysis made for GaAs/AlGaAs QWWS illuminated by a 150 fs Ti : sapphire laser shows good qualitative agreement of the present results with those available in literature.