From high-performance detectors to surface emitting rings : integrating miniaturized spectroscopic technologies on a chip

Abstract

This thesis presents advancements in mid-infrared optoelectronic devices with both in-plane and out-of-plane light emitting properties. Quantum cascade lasers (QCL) have grown to a more and more established source of coherent mid-infrared (MIR) radiation since their first implementation in the mid-1990s. As a further development, the interband cascade laser (ICL) blends the principles of traditional interband diode lasers with the periodic structure of QCLs, exploiting intersubband transitions. ICLs leverage the extended upper laser level lifetime from diode lasers and the voltage-efficient multiple active region design of QCLs. Their inherent low power consumption, often utilizing only a few periods in the active region, renders them particularly appealing for compact and portable applications across the midinfrared spectrum. This encompasses areas such as trace gas sensing, process monitoring, and medical diagnosis. Building upon previous research, this work introduces the next generation of vertical emitting ring-ICLs capable of low-dissipative continuous wave emission at room temperature, achieved through innovative mounting techniques and effective cooling strategies. Through the integration of second-order distributed feedback gratings and advanced fabrication techniques, the emitted light can be tailored for specific applications, demonstrating the versatility and practicality of these devices. The usability of these ring-laser devices is further demonstrated through noise measurements, unveiling their exceptional performance especially in areas where low noise behavior is crucial. Additionally, this thesis explores a novel approach to on-chip guiding of MIR radiation. Utilizing bi-functional quantum cascade material as a laser and a photodetector on the same chip, the focus is directed towards minimizing losses in Germanium-based plasmonic waveguides for on-chip beam combining. This concept enables the compact and cost-effective integration of previously table-top-sized optical systems onto areas smaller than a fingertip, with the added benefit of eliminating the need for manual alignment of optical components. Through simulation studies and experimental validation, novel solutions are proposed to mitigate losses and enhance device performance through the integration of Au-covered micro-mirror structures to efficiently redirect surface plasmon polaritons, facilitating low-loss on-chip routing over extended waveguide lengths. The research presented here contributes to the advancement of MIR optoelectronic technology and the on-chip integration of optical systems, offering insights into device design, fabrication techniques, and practical applications. The demonstrated capabilities of the developed devices pave the way for future innovations various fields ranging from telecommunications to environmental monitoring and healthcare.