Coherent injection locking of quantum cascade laser frequency combs

Quantum cascade laser (QCL) frequency combs are a promising candidate for chemical sensing and biomedical diagnostics(1-4). They are electrically pumped and compact, making them an ideal platform for on-chip integration(5). Until now, optical feedback is fatal for frequency comb generation in QCLs(6). This property limits the potential for integration. Here, we demonstrate coherent electrical injection locking of the repetition frequency to a stabilized radio-frequency oscillator. We prove that the injection-locked QCL spectrum can be phase-locked, resulting in the generation of a frequency comb. We show that injection locking is not only a versatile tool for all-electrical frequency stabilization, but also miti-gates the fatal effect of optical feedback. A prototype self-detected dual-comb set-up consisting only of an injection-locked dual-comb chip, a lens and a mirror demonstrates the enormous potential for on-chip dual-comb spectroscopy. These results pave the way to miniaturized and all-solid-state mid-infrared spectrometers.