On-chip dual quantum walk comb in the mid-infrared

Dual-comb spectroscopy in the mid-infrared provides an unparalleled combination of wide optical bandwidth and high resolution with fast acquisition times. In addition, the absence of moving mechanical parts makes it especially suitable for portable sensors, offering the availability of compact and controllable dual-comb sources. In this work, we demonstrate a quantum walk comb source with an optical bandwidth of 78 cm ^-1 near 1330 cm ^-1 wavenumber (440 nm and 7.5 μm wavelength, respectively), and use it to report a dual quantum walk comb demonstration over a bandwidth of 34 cm ^-1 (192 nm). Analysis of the dual-comb signal demonstrates that in the quantum walk comb, the repetition frequency is fully locked to the external RF source, whose power also determines the comb bandwidth, allowing a high control of the power-per-line distribution. In addition, a multi-heterodyne signal is collected from the RF feed of the device, providing a dual-comb reference signal and avoiding the need to split the optical beam and use a second photodetector. The proof-of-concept spectroscopy of a plastic film reported shows the great potential of quantum walk combs for the realization of high-performance and cost-effective spectroscopy systems consisting of only a dual-comb source, an interaction cell and a photodetector, thus having a major impact on a plethora of sensing applications.