Mid-infrared optical sensors integrating plasmonic waveguides and quantum cascade optoelectronics are an emerging field of research leading to promising results in chemical sensing, environmental monitoring, and biomedical diagnosis. In this work, we investigate TiO2 as waveguiding material for mid-infrared surface plasmon polariton waveguides and show its potential for integrated sensors. Simulations reveal suitable TiO2 dimensions and diffraction grating couplers for ~4.3 µm light. Following these theoretical considerations, we fabricated such devices monolithically integrated with quantum cascade detectors (QCDs) and present their characterization. We further discuss their application in innovative biosensing experiments including glucose detection.
Semiconductor-loaded plasmonic (SLSPP)-waveguides are a very efficient link for optoelectronic devices, facilitating miniaturized photonic integrated circuits. However, for long-wave infrared applications (8-12 µm), the material selection is challenging as most commonly used mid-IR materials absorb in this region. Therefore, we selected and investigated the properties of germanium in a hybrid semiconductor-metal-configuration to overcome these limitations. The experimental characterization of Si(substrate)-Au-Ge fabricated SLSPP-waveguides show very good agreement with FEM-simulations. Moreover, the realized devices offer low losses between 8.8 and 22 dB/mm (single device) and even within 8.8-15 dB/mm (multiple devices), respectively, for the entire investigated octave-spanning 5.6 – 11.2 µm range.
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