Ultra-widely tunable quantum cascade laser based on scalable external cavity with multiple chips

Tunable lasers in mid-wave infrared band (3–5 μm) are needed in many areas, such as gas sensing, terahertz-wave generation via difference frequency mixing, space communications and so on. In this paper, a specially designed external cavity is introduced into conventional Littrow configuration. In this new configuration, double quantum cascade laser (QCL) chips with adjacent gain spectrums are integrated into one compact volume by beam combination so as to realize ultra-widely tunable range. In the experiment, tunable range from 3779 nm to 4831 nm (including a transition region of 199 nm without output) was obtained, while linear tuning operation was achieved through nearly the entire tunable range. This proposed scheme, which is also compatible with other kinds of semiconductor lasers, is scalable for even wider tunable range by introducing more laser chips.