Hybrid integrated germanium-on-zinc selenide waveguides for enhanced longwave infrared sensing

Integrated longwave infrared (LWIR) photonics hold promise for enhancing on-chip molecular sensing due to the strong light-matter interaction in the LWIR spectrum, which is orders of magnitude more intense than in the near-infrared. However, conventional photonic materials suffer from high optical losses in this range. Specifically, silicon and III-V materials exhibit absorption losses due to multiphonon processes, which limit their applicability for LWIR systems. To address this issue, our work introduces a hybrid germanium-on-zinc selenide (GOZ) platform. This platform leverages the lower multiphonon absorption onset frequencies of germanium and the suitable cladding properties of zinc selenide to reduce optical losses. By employing a direct wafer bonding technique, our study achieves a waveguide system that is transparent from 2 μm to 14 μm, with measured optical losses as low as 1 cm−1 at 7.8 μm, indicating a significant improvement over traditional materials. Our findings demonstrate that the GOZ platform effectively reduces the intrinsic optical losses typical of epitaxiallygrown materials in LWIR devices, thereby paving the way for advancements in quantum and nonlinear photonic applications.