Properties of self-mixing interference in terahertz distributed feedback quantum cascade lasers

Abstract

The properties of self-mixing interference in terahertz distributed feedback quantum cascade lasers (THz DFB-QCLs) were studied by coupled wave theory and the multimode rate equation method. Under weak self-mixing optical feedback, the response behaviors of the DFB-QCLs are similar to those of Fabry–Pérot lasers and can be described by the Lang–Kobayashi equations with a modified feedback parameter. The amplitudes of the self-mixing power and frequency signals decrease with the increasing DFB coupling factor. Under strong feedback, new side modes arise, which broaden the laser linewidth. The number of side modes decreases with the increasing DFB coupling factor. The simulation also demonstrates that the maximum power mode of a THz DFB-QCL under strong self-mixing feedback is the minimum linewidth mode. These results support the development of self-mixing interferometers based on DFB-QCLs.