Battery-operated mid-infrared diode laser frequency combs

Mid-wave infrared (MIR, 3--5 $\mu$m) optical frequency combs (OFC) are of critical importance for spectroscopy of fundamental molecular absorption features in space and terrestrial applications. Although in this band OFCs can be obtained via supercontinuum or difference frequency generation using optical pumping schemes, unprecedented source miniaturization and monolithic design are unique to electrically-pumped semiconductor laser structures. To date, high-brightness OFC generation in this region has been demonstrated in quantum- and interband cascade lasers (QCL/ICL), yet with sub-optimal spectral properties. Here, we show the first MIR quantum well diode laser (QWDL) OFC, whose excellent spectral uniformity, narrow optical linewidths, and milliwatt optical power are obtained at a fraction of a watt of power consumption. The continuously tunable source offers ~1 THz of optical span centered at 3.04 $\mu$m, and a repetition rate of 10 GHz. As a proof-of-principle, we show a directly-battery-operated MIR dual-comb source with almost 0.5 THz of optical coverage accessible in the electrical domain in microseconds. These results indicate the high suitability of QWDL OFCs for future chip-based real-time sensing systems in the mid-infrared.