▎ 摘　　要

Mid-infrared photonic integrated circuits (PICs) are important for sensing and optical communications, but their operational wavelengths are usually limited below 4 mu m. Here, the authors report the realization of photothermoelectric graphene photodetectors incorporated in a chalcogenide glass-on-CaF2 PIC operating at 5.2 mu m, showing promising results for gas sensing applications. The development of compact and fieldable mid-infrared (mid-IR) spectroscopy devices represents a critical challenge for distributed sensing with applications from gas leak detection to environmental monitoring. Recent work has focused on mid-IR photonic integrated circuit (PIC) sensing platforms and waveguide-integrated mid-IR light sources and detectors based on semiconductors such as PbTe, black phosphorus and tellurene. However, material bandgaps and reliance on SiO2 substrates limit operation to wavelengths lambda less than or similar to 4 mu m. Here we overcome these challenges with a chalcogenide glass-on-CaF2 PIC architecture incorporating split-gate photothermoelectric graphene photodetectors. Our design extends operation to lambda = 5.2 mu m with a Johnson noise-limited noise-equivalent power of 1.1 nW/Hz(1/2), no fall-off in photoresponse up to f = 1 MHz, and a predicted 3-dB bandwidth of f(3dB) > 1 GHz. This mid-IR PIC platform readily extends to longer wavelengths and opens the door to applications from distributed gas sensing and portable dual comb spectroscopy to weather-resilient free space optical communications.