Anomalous carrier-induced dispersion in quantum-dot active media

The complex optical susceptibility in a quantum-dot active medium is investigated theoretically. It is found that the Coulomb coupling of the localized discrete states in a quantum dot to extended continuum states in the surrounding quantum well region strongly influence optical properties under high excitation conditions. As a result, the behavior of the carrier-induced refractive index change (formula presented) differs significantly from that expected from the often used atomlike description, where the interaction between a quantum dot and the surrounding region involves only the transfer of electrons and holes. Furthermore, there is the possibility of increasing (formula presented) with increasing carrier density under conditions where laser gain is present, which is a distinct departure from bulk and quantum well behavior. Therefore, quantum-dot lasers may not show beam filamentation tendency, which has been a long-standing problem in semiconductor lasers. © 2002 The American Physical Society.