Mid infrared gas spectroscopy using efficient fiber laser driven photonic chip-based supercontinuum

TLDR

Supercontinuum generation from turnkey fiber lasers enables simple, robust access to the mid‑IR molecular functional group region, but coherence studies of Si3N4 waveguides pumped at telecom wavelengths show that spectral reach and efficiency remain insufficient for practical use. We use a 2 µm fs‑fiber laser pumped large‑cross‑section Si3N4 waveguide to generate a 3–4 µm supercontinuum and demonstrate absorption spectroscopy of C₂H₂. The 2 µm fs‑fiber laser pumped Si3N4 waveguide achieves up to 35 % power conversion and milliwatt‑level output in the 3–4 µm range, making it a suitable candidate for compact, chip‑integrated spectroscopic and sensing applications.

Abstract

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 (Si3N4) 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 that large cross-section Si3N4 waveguides pumped with 2 μm fs-fiber laser can reach the important spectroscopic spectral region in the 3-4 μm range, with up to 35% power conversion and milliwatt-level output powers. As a proof of principle, we use this source for detection of C2H2 by absorption spectroscopy. Such result makes these sources suitable candidate for compact, chip-integrated spectroscopic and sensing applications.