Frequency noise in mid-infrared quantum cascade lasers

Full text: Quantum Cascade Lasers (QCLs) are semiconductor lasers whose emission wavelength can be tailored in order to reach the absorption bands of a wide variety of molecules in the mid-IR. In this work we present recent results of frequency-noise measurements in distributed feedback QCLs at 4.6 μm. We report a very different dependence of the frequency noise as a function of temperature between buried-heterostructure and ridge-waveguide lasers. A strong correlation between internal electrical fluctuations and fluctuations of the laser optical frequency is shown. Finally, the mechanisms of noise generation as well as the importance of the laser thermal resistance are discussed. (author)