QUANTUM SIZE EFFECT ON LONGITUDINAL SPATIAL HOLE BURNING IN MQW LAMBDA-4-SHIFTED DFB LASERS

This paper describes a new method for reducing the effect of longitudinal spatial hole burning on the spectral properties of lambda/4-shifted DFB lasers. The method is based on the quantum size effect in the MQW structure, and it is demonstrated experimentally and theoretically for the first time. First, the effects of the longitudinal spatial hole burning on the spectral behavior are theoretically shown to be determined by the linewidth enhancement factor (alpha-parameter), not by the differential index or the optical confinement in the active layer. The reduction of the alpha-parameter is found to be very effective in suppressing the spectral instability and broadening induced by the longitudinal spatial hole burning. Finally, the theory is confirmed by qualitative and quantitative experimental measurements.