Waveguide-integrated mid-infrared photodetection using graphene on a scalable chalcogenide glass platform.

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 SiO substrates limit operation to wavelengths λ ≲ 4 μm. Here we overcome these challenges with a chalcogenide glass-on-CaF PIC architecture incorporating split-gate photothermoelectric graphene photodetectors. Our design extends operation to λ = 5.2 μm with a Johnson noise-limited noise-equivalent power of 1.1 nW/Hz, no fall-off in photoresponse up to f = 1 MHz, and a predicted 3-dB bandwidth of f > 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.