Concept of linewidth enhancement factor in semiconductor lasers: its usefulness and limitations

The usefulness and the limitations of the concept of the linewidth enhancement factor alpha in semiconductor lasers are examined by considering the laser dynamics without the rate-equation approximation. The rate equations with a constant value of alpha can be used for semiconductor lasers operating continuously or modulated directly such that the carrier density does not change significantly during each modulation cycle. A new set of generalized Bloch equations should be used whenever subpicosecond optical pulses are involved.<>