Tuning a distributed feedback laser with a coupled microcavity

We show that a distributed-feedback terahertz quantum cascade laser can be tuned with a coupled microcavity by anti-crossing of the respective eigenfrequencies. In this proof-of-concept experiment, a tuning range of 20 GHz is obtained, in good agreement with a simple finite element model, which shows that the tuning is determined by the coupling strength between the resonators. The concept could be applied to any laser cavity, but becomes progressively more attractive the lower the emission frequency.