Photonic Integrated Tunable and Narrow-Linewidth Lasers Spanning the 2–3 μm Wavelength Range for Spectroscopic Sensing

Semiconductor lasers in the 2–3 μm spectral region are highly attractive for spectroscopic sensing because many industrial gases and biomolecules exhibit strong absorption bands in this range. However, the limited gain bandwidth of conventional semiconductor lasers restricts their wavelength tunability, making broadband or multispecies detection with a single source challenging. Here, we report a photonic integrated, wavelength-tunable, and ultra-narrow linewidth hybrid laser platform spanning the 2–3 μm band, enabled by the integration of centimeter-scale low-loss silicon nitride (Si 3 N 4 ) photonic circuits with GaSb-based gain chips. Using a post grating distributed Bragg reflector (DBR) configuration, intrinsic linewidths at the kilohertz level are achieved, together with on-chip output power up to 28 mW at 2.6 μm. Four gain chips integrated on a single Si 3 N 4 feedback circuit provide single-mode emission from 1.96 to 2.91 μm, representing the longest-wavelength hybrid external-cavity lasers realized with Si 3 N 4 feedback. To validate the suitability of this platform for mid-infrared sensing, tunable diode laser absorption spectroscopy of CO 2 and CH 4 is performed, clearly resolving their characteristic absorption features with picometer wavelength resolution. These results establish a scalable hybrid integration approach for high-power, narrow linewidth, and broadband mid-infrared laser sources, paving the way toward compact and integrated spectroscopic sensing systems.