Measurement of the linewidth enhancement factor of quantum cascade lasers by the self-mixing technique

Abstract

We present measurements of the linewidth enhancement factor of a distributed feedback quantum cascade laser (DFB-QCL) using the so-called self-mixing technique. The linewidth enhancement factor is investigated by analyzing optical feedback induced changes of the emission properties of the laser. We will demonstrate that our self-mixing setup works well with QCLs in the mid infrared wavelength regime, and that it is possible to use the obtained signal to extract the linewidth enhancement factor. We present a setup that records the self-mixing signal with the voltage signal across the laser device using the laser as a detector itself. In this contribution we will show the advantages of this measurement technique. First measurements of the linewidth enhancement factor yield values that rise from 0.24 to 2.6 with an increase of the injection current of the QCL. We will discuss the influence of the injection current on the linewidth enhancement factor.