Monolithic on-chip mid-IR methane gas sensor with waveguide-integrated detector

We demonstrate a monolithic waveguide sensor integrated with a detector on-chip for mid-infrared absorption spectroscopic sensing. The optical sensing element comprises a chalcogenide glass spiral waveguide, and the detector is a PbTe photoconductor integrated directly with the chalcogenide waveguide. The limit of detection of the sensor for methane gas was experimentally assessed to be 1% by volume. Further optimization of the fabrication process and normalization of the laser power fluctuations should result in a maximum sensitivity of 330 ppmv.