Spectral stability analysis of weakly coupled external-cavity semiconductor lasers

The spectral stability of weakly coupled external-cavity semiconductor lasers is studied theoretically. The carrier density modulation induced at the frequency of the external-cavity mode spacing fexplays an important role in the spectral instability. Therefore, the laser under optical feedback reveals different spectral behaviors, depending on the relation between the frequency of the external-cavity mode spacing and the relaxation resonance frequency fRof the carrier density. For a better spectral stability, fexmust be larger than fR.