Tuneable mid-infrared sources for spectroscopy through difference frequency generation in Lithium Niobate ridge waveguides

Over the past two decades, significant advancements have been made in the miniaturization of mid-infrared (MIR) spectroscopy sources. However, achieving a fully integrated solution presenting high optical power and wide tuneability within the so-called atmospheric window (2.5 – 5 μm) remains an open challenge. This thesis explores the development of a broadband, frequencytuneable MIR source exploiting the effect of difference frequency genera tion (DFG) in a Periodically Poled Lithium Niobate (PPLN) ridge waveguide. By employing pump- and signal-tuned lasers operating near 1 μm and 1.55 μm, respectively, this work successfully achieves comprehensive spectral coverage in the ≈ 3-3.5 μm range. The innovative use of a PPLN waveguide with a larger cross-section compared to traditional Thin-Film Lithium Niobate (TFLN) waveguides reduces propagation and coupling losses while supporting a higher damage threshold. As a result, the designed system generates mW-level output power in the MIR spectrum, bridging a crucial technological gap and enhancing the potential for MIR applications.