High performance monolithic, broadly tunable mid-infrared quantum cascade lasers

Mid-infrared lasers, emitting in the spectral region of 3–12 μm that contains strong characteristic vibrational transitions of many important molecules, are highly desirable for spectroscopy sensing applications. High-efficiency quantum cascade lasers have been demonstrated with up to watt-level output power in the mid-infrared region. However, the wide wavelength tuning that is critical for spectroscopy applications still largely relies on incorporating external gratings, which have stability issues. Here, we demonstrate a monolithic, broadly tunable quantum cascade laser source emitting between 6.1 and 9.2 μm through an on-chip integration of a sampled grating distributed feedback tunable laser array and a beam combiner. High peak power up to 65 mW has been obtained through a balanced high-gain active region design, efficient waveguide layout, and the development of a broadband antireflection coating. Nearly fundamental transverse-mode operation is achieved for all emission wavelengths with a pointing stability better than 1.6 mrad (0.1°). The demonstrated laser source opens new opportunities for mid-infrared spectroscopy.