A broadband grating-coupled silicon nitride waveguide for the mid-IR: characterization and sensitive measurements using an external cavity quantum cascade laser

We present the design and fabrication of a single-mode slab waveguide structure for mid-infrared spectroscopy optimized for broadband coupling. The sensor uses grating couplers for robust off-axis coupling and a silicon nitride guiding layer for mechanical robustness. An external cavity quantum cascade laser-based transmission method is introduced for characterizing the structure’s broadband coupling behavior. Light from an external cavity quantum cascade laser with a spectral range of 0.5 μm around 6 μm was coupled into the waveguide without the need for moving parts. First spectra taken with this sensor are presented.