Highly efficient 4 micron light generation through fs-fiber laser driven supercontinuum in Si$_3$N$_4$ waveguides

Directly accessing the middle infrared, the molecular functional group spectral region, via supercontinuum generation processes based on turn-key fiber lasers offers the undeniable advantage of simplicity and robustness. Recently, the assessment of the coherence of the mid-IR dispersive wave in silicon nitride waveguides, pumped at telecom wavelength, established an important first step towards mid-IR frequency comb generation based on such compact systems. Yet, the spectral reach and efficiency still fall short for practical implementation. Here, we experimentally demonstrate for the first time to our knowledge, that fs-fiber laser driven systems based on large-cross section silicon nitride waveguides can reach, with powers sufficient to drive dual-comb spectroscopy, the important greenhouse gases spectral region near 4 micron, typically accessed through different frequency generation or more complex approaches. We show, from a 2 micron femtosecond fiber laser, up to 30% power conversion and milliwatt-level output powers, proving that such sources are suitable candidate for compact, chip-integrated spectroscopic and sensing applications.