Dependence of the Linewidth Enhancement Factor on the Temperature Induced Detuning of a Distributed Feedback Grating in a Quantum Cascade Laser

The linewidth enhancement factor (or alpha parameter) describes the coupling of amplitude and phase in a semiconductor laser. In quantum cascade lasers, the self-mixing effect necessary for single mode operation, is usually realized by using a distributed feedback grating. Such a grating is optimized to work for a special wavelength at a fixed temperature. If the temperature of the laser device differs from the optimum temperature the grating was designed for, there is a detuning of the grating wavelength from the gain peak. We investigate the effect of this detuning on the value of the linewidth enhancement factor.