THEORY OF INTERBAND COHERENCE AND INVERSIONLESS BISTABILITY IN SEMICONDUCTOR LASERS

摘要

Coherent transitions of charge carriers between the conduction and valence bands of a semiconductor medium are essential for the operation of a semiconductor laser.In this paper,we study how such interband coherence can be set up by an injection current and a coherent pump-field.In the absence of the pump-field,the injection current is the only source to establish the interband coherence in a semiconductor laser system.A laser threshold is obtained,which shows that a strongly coupled high-Q microcavity has a low threshold value.However,when an external pump-field serving as another mechanism to create the interband coherence is applied,the threshold value of the injection current can be lowered and it vanishes for sufficiently strong field.Besides,if the pump-field exceeds a threshold value,it is even possible to achieve a bistability in the inversionless region.Some fundamental macroscopic properties,including polarization,absorption and dispersion for the semicoductor system,are also obtained analytically.