Widely tunable quantum cascade lasers with coupled cavities for gas detection

The authors report the fabrication of widely tunable monolithic quantum cascade lasers (QCLs) with coupled Fabry–Pérot (FP) cavities on indium phosphide. Quasicontinuous tuning of the single mode emission over a total spectral range of 242 nm was realized at two regions between 8.394 and $8.785μm$⁠. An absorption experiment with ammonia shows principle feasibility of gas detection with multisegment QCL devices. Good agreement of the experimentally observed tuning behavior with the one expected from calculated FP mode-combs indicates that the change in the refractive index is mainly due to thermal heating as a result of current injection.