Towards Integrated Plasmonic Gas-Sensors in the MWIR

Integrated environmental sensing for personal health care monitoring is a topic of increasing interest. Optical measurement approaches could provide intrinsic selectivity and the sensitivity, required for the development of integrated gas sensors. In an ongoing project, we work towards a Si-photonics non-dispersive infrared gas sensor and are investigating the possibility of the incorporation of IR-active plasmonic materials, which could allow to increase sensitivities and reduce size of such sensors. We will first present the overall idea of combining pillar photonic crystal waveguides with plasmonic elements to provide maximal interaction with gaseous analytes, which was proposed, recently. Then, we describe the characterization of the very first test structures, which were fabricated. Reflectivity measurements on grating structures allow the detailed characterization of the plasmon resonances, which can also be related to theoretical estimations and FEM simulations. The simulation results predicted narrow line widths of only a few wavenumbers for Ag coated gratings, which were, indeed, observed in reflectance measurements with a quantum cascade laser at 4.26 µm. We hope that approaches incorporating plasmonic structures will significantly extend the range of possibilities in the field of integrated infrared sensors.