The amplitude-phase coupling factor α (linewidth enhancement factor) is compared for typical semiconductor quantum-well and bulk double heterostructure lasers. As a direct consequence of the reduction of the differential gain, there is no reduction of α in single-quantum-well lasers compared to bulk lasers. The number of quantum wells strongly affects the amplitude-phase coupling in quantum-well lasers. It is shown that the interband transition induced amplitude-phase coupling dominates that induced by the plasma effect of carriers in typical quantum-well lasers. By considering the spontaneous emission factor in the spectral linewidth, the authors show that there is an optimal number of quantum wells for achieving the narrowest spectral linewidth.
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