Coherent control of QCL frequency combs for miniaturized dual-comb spectroscopy (Conference Presentation)

Quantum cascade laser (QCL) frequency combs are electrically pumped and have a small footprint which makes them an ideal candidate for an all-solid-state MIR spectrometer integrated at the chip-level. However, optical feedback is fatal for frequency comb generation in QCLs by destroying intermodal coherence, which limits the versatility and possible degree of integration of QCL frequency combs. In this work, we show how QCL frequency combs can be stabilized. Thereby, the frequency comb state becomes more robust against drift and noise, as well as virtually insensitive against static and dynamic optical feedback. The stability of the comb states are experimentally checked by shifted wave interference Fourier transform spectroscopy (SWIFTS), as well as by the multi-heterodyne signal using a second comb. An optimized RF compatible QWIP and phase retrieval algorithm enable the robust measurement of intermodal coherence and phase of the comb state from single shot SWIFTS interferograms in FTIR rapid-scan. The presented results pave the way to miniaturized and potentially single chip MIR spectrometers. To demonstrate that dual-comb spectrometers can be realized on a small footprint, we demonstrate a first prototype.