The linewidth enhancement factor (α-factor) of semiconductor quantum dot laser
has been widely investigated and measured in recent years. The pubilished methods of
measuring the α-factor are focus on the α-factor only, ignoring other intrinsic parameters
of semiconductor lasers. These intrinsic parameters of lasers are much dependent on
determine the characteristics of the laser nonlinear dynamic. Therefore, we apply the
four-wave mixing analysis on quantum dot lasers both numerically and experimentally.
Through the four-wave mixing analysis, we can not only obtain the α-factor but also
other intrinsic parameters.
By analyzing the four-wave mixing state of quantum dot lasers, we derive and obtain
the relation between optical spectra of the regenerated signal versus detuning and power
spectra of four-wave mixing state versus dteuning, respectively. Fitting the experimental
result with those derived from the relations, the α-factor and intrinsic parameters can be
obtained.
From the experimental result, it is found that the appearance of the optical spectra
of quantum dot lasers is different from that of quantum well lasers . Through numerical
analyzing, the difference is found resulting from the larger value of the differential gain
and carrier decay rate. The α-factor extracted from the fitting result is also compared to
that obtained by injection locking technique, which show similar values. Therefore, using the four-wave mixing analysis to measure the linewidth enhancement factor of quantum dot lasers is shown to be reliable.

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