Offset-free mid-infrared frequency comb based on a mode-locked semiconductor laser

waveguide followed by amplification in an Er gain fiber. DFG between the 1030 and 1560 nm pulse trains results in a coherent and offset-free MWIR frequency comb, verified with optical heterodyne beat note measurements. Active stabilization of the VECSEL repetition rate provides a fully stabilized high repetition rate frequency comb in the MWIR, uniquely suited for applications in molecular spectroscopy.