Micro-mirror aided mid-infrared plasmonic beam combiner monolithically integrated with quantum cascade lasers and detectors

The development of novel mid-infrared (MIR) devices and systems is crucial for addressing applications in biomedical analysis, chemical reaction-monitoring, or high-bitrate free-space telecommunication. Combining multiple functional elements on one chip into complex miniaturized photonic integrated circuits (PICs), is the next step in these developments, yet limited by existing material and technology constraints. In this work, we introduce a new concept for realizing fully monolithic MIR-PICs based on low-loss on-chip plasmonic guiding and beam combining. The core of our study demonstrates a monolithic beam combiner by integration of active quantum cascade (QC) devices at ∼8 µm (laser and detector) with tailored passive waveguides based on weakly-coupled Ge/Au plasmonics and on-chip micro-mirror optics. The on-chip gold-coated micro-mirrors enhance the directional control and beam combining capabilities of the plasmon waveguides while minimizing energy dissipation typically associated with tight plasmon confinement. We discuss the MIR-PIC beam combiner design, micro-fabrication, and characterization and compare it to the routing concept of simple plasmonic Ge/Au y-couplers exploiting strong-confinement.