Quantum size effect on longitudinal spatial hole burning in MQW lambda /4-shifted DFB lasers

A method for reducing the effect of longitudinal spatial hole burning on the spectral properties of lambda /4-shifted distributed feedback (DFB) lasers is presented. The method is based on the quantum size effect in the multiquantum well (MQW) structure, and is demonstrated experimentally and theoretically. First the effects of the longitudinal spatial hole burning on the spectral behavior are shown to be determined by the linewidth enhancement factor, not by the differential index or the optical confinement in the active layer. The reduction of the linewidth enhancement factor is found to be effective in suppressing the spectral instability and broadening induced by the longitudinal spatial hole burning. The theory is confirmed by qualitative and quantitative experimental measurements.< >