Measurement of linewidth enhancement factor of different semiconductor lasers in operating conditions

We apply the self-mixing method for the measurement of the linewidth enhancement factor of several types of semiconductor lasers. The α-factor value above threshold is determined by analysing the small perturbations that occur to the laser when it is subjected to moderate optical feedback, relying on the well-known Lang-Kobayashi equations. The method is applied to Fabry-Perot, VCSEL, External Cavity Laser (ECL), DFB, Quantum Cascade Laser. It is found that for some lasers the α-factor varies with the emitted power, and these variations can be correlated with variations in the laser linewidth.