ONE-MIX proposes to develop single-source dual-comb lasers for applications in the short-wave infrared (SWIR) and mid-infrared (mid-IR) spectral region potentially enabling many new applications in science and industry, such as environment, safety, pharma, and health. We leverage our know-how in near-infrared MIXSELs (Modelocked Integrated eXternal-cavity Surface Emitting Lasers) with III-V GaSb (gallium-antimonide) semiconductor epitaxy operated out of the FIRST lab at ETH Zurich. The MIXSEL is an optically pumped surface emitting semiconductor laser that has the gain and the saturable absorber integrated into one semiconductor chip which forms one end mirror of a linear straight laser cavity. We use polarization duplexing to obtain two optical frequency combs with an adjustable pulse repetition rate difference for dual-comb applications allowing for fast, accurate, and sensitive measurements.
Dual-comb applications are currently limited by the cost, complexity, and size of conventional optical comb systems, typically based on two modelocked lasers with four active stabilization loops. The single-source dual-comb MIXSEL, however, substantially reduces the complexity of existing systems to a single compact free-running laser with no requirement for an additional stabilization loop for most applications. In comparison to other competing new approaches such as quantum cascade lasers or micro resonator combs, the free-running dual-comb MIXSEL provides substantially more power per comb line with low linewidth and noise, and is ideally suited for a 1 to 5 GHz comb spacing, which is optimal for many molecular spectroscopy and lidar applications and previously demonstrated in the near-infrared regime [1-3].
There is a convenient spectral window between 2.0 and 2.6 µm which is free of strong water absorption lines, allowing for spectroscopic monitoring of atmospheric trace gases, remote sensing, laser ranging, and free-space communication. Initially we will focus our MIXSEL comb development for a center wavelength around 2 µm. The first proof-of-principle spectroscopy demonstration will focus on carbon dioxide CO2 which been recognized as the main anthropogenic contributor to climate change. Moreover, mid-IR sources of femtosecond pulses with high average power are especially useful to drive nonlinear processes, e.g. long-wave infrared supercontinuum generation, difference frequency generation, and optical parametric amplification. This for example enables efficient frequency conversion to the important molecular fingerprint spectral region.
[1] S. M. Link, D. J. H. C. Maas, D. Waldburger, U. Keller, “Dual-comb spectroscopy of water-vapor with a free-running semiconductor disk laser” Science, vol. 356, pp. 1164-1168, 2017
[2] J. Nürnberg, C. G. E. Alfieri, Z. Chen, D. Waldurger, N. Picque, U. Keller, “An unstabilized femtosecond semiconductor laser for dual-comb spectroscopy of acetylene” Optics Express, vol. 27, No. 3, pp. 3190-3199, 2019
[3] J. Nürnberg, B. Willenberg, C. R. Phillips, U. Keller, “Dual-comb ranging with frequency combs from single cavity free-running laser oscillators” Optics Express, vol. 29, No. 16, pp. 24910-24918, 2021
