Versatile silicon-waveguide supercontinuum for coherent mid-infrared spectroscopy
Nima Nader, Daniel Maser, Flavio Caldas da Cruz, Abijith S. Kowligy, Henry R. Timmers, Jeffrey T. Chiles, Connor D. Fredrick, Daron A. Westly, Richard P. Mirin, Jeffrey M. Shainline, Scott A. Diddams
Infrared spectroscopy is a powerful tool for basic and applied science. The rich spectral fingerprints of compounds in the 3 um - 20 um region provide a means to uniquely identify the molecular structure for applications that include fundamental spectroscopy, tmospheric chemistry, trace and hazardous gas detection, and biological microscopy. Driven by such applications, the development of low-noise coherent laser sources with broad tunable coverage is a topic of great interest. Laser frequency combs possess a unique combination of precisely defined spectral lines and broad bandwidth that can fill the infrared gap and enable the above-mentioned applications. Here, we leverage robust fabrication and geometrical dispersion engineering of silicon nanophotonic waveguides for coherent frequency comb generation in the mid-infrared 3 um - 6.4 um. Precise waveguide fabrication provides user-defined spectra targeted at specific mid-infrared bands, as well as broad coverage exceeding 60 THz. The noise properties of this chip-based frequency comb source are evaluated, and we use the output to perform dual-comb spectroscopy of carbonyl sulfide around 5 um.