Liquid sensing on the chip-scale: towards complex mid-IR photonic integrated circuits (PICs)

Abstract

Mid-infrared liquid sensing on the chip-scale is a newly emerging field of research, especially with respect to fully monolithic integrated devices. They enable addressing applications scenarios in chemical reaction monitoring and real-time sensing, which were so far prevented by the existing much more bulky technology (e.g. FTIR-based systems). In this work we present a quantum cascade laser (QCL), QC detector (QCD) and novel type of midinfrared plasmonic waveguide that are integrated into one substrate and which we use in real-time protein sensing and residual water in solvent measurements. Furthermore, we present how this rather simple linear geometry can be further improved by implementing other (more spectrally broadband) materials such as Germanium and integrating surface-passivation and -functionalization for improving sensing capabilities. In the last part we will demonstrate two pathways for introducing plasmonic mode-guiding along the chip-surface, which is the key to realizing much more complex geometries including integrating more active and passive elements into one PIC.