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.
Interband Cascade Lasers are becoming more and more attractive sources for sensing applications due to their direct mid-IR emission and low power consumption. In many demanding applications of precision spectroscopy and imaging, the laser frequency and intensity noise represent the ultimate limiting factor for the final sensitivity. Here, we first characterize the response of a DFB ICL to a frequency modulation and measure its tuning coefficients. A frequency noise analysis of the ICL is then provided, through experimental investigation of the frequency noise power spectral density, with a particular attention to the technical noise contribution. A possible scheme for frequency stabilization and linewidth narrowing is presented through frequency locking to a high-Q factor microresonator.
In many precision sensing applications, the final detection sensitivity is tightly related to the intensity noise of the laser source, which might represent the ultimate limit to the sensor performance. In this framework, we present here the intensity noise characterization of three different mid-infrared semiconductor devices (two quantum cascade lasers and one interband cascade laser). A fast homemade balanced detection system is used to measure the intensity noise of the emitted radiation over a broad Fourier-frequency range, facilitating the observation of shot-noise-limited radiation under specific measurement conditions and detection efficiency. This study allows for a direct performance comparison of the most widespread laser sources in mid-infrared sensing systems.
The mid-IR band recently attracted great interest for future wireless communication due to its low attenuation and high tolerance against atmospheric perturbations. Recent advances in monolithic integration of same-wavelength quantum cascade lasers (QCLs) and detectors (QCDs) paved the way for a new generation of functional photonic integrated circuits. In this context, integrating novel mid-IR plasmonic waveguides has been highly suitable for realizing efficient chip-scale optical links between different active components. Here we report on developing a mid-IR on-chip heterodyne receiver. This includes the first demonstration of plasmonic waveguides for on-chip beam-guiding in the long-wave infrared and novel high-performance QCLs and QCDs.
We present the first realization of substrate-emitting double-ring Interband Cascade Lasers (ICLs) in Continuous-Wave (CW) mode. The devices are realized in the GaSb material system and emit at around 2.77 µm wavelength. Through the implementation of second-order distributed feedback gratings, single-mode and simultaneous vertical emission through the GaSb substrate are realized. By implementing a concentric double-ring arrangement (diameters of approximately 700µm and 900 µm), two-wavelengths emission on the same optical axis can be achieved, which is desirable for spectroscopic applications. For improved thermal management, the devices are mounted epitaxial side down on custom-made AuSn/AlN heatsinks, enabling individual laser operation.
We present a novel InGaAs/InAlAs/InP quantum cascade detector (QCD) operating in the long wave infrared (LWIR) range, crucial for the exploitation of new free-space optical telecommunication channels at wavelengths between 8-12 µm. The comparison of differently sized detector ridges, processed on substrates with a 15-period as well as a single-period design, allows a characterization of the spectral photocurrent and a comparison of their performance in terms of sensitivity, spectral responsivity, detector noise etc. The goal is to distinguish design guidelines for the best candidate to establish a monolithic-integrated heterodyne detection system, able to secure high-speed and low-noise free-space data transmission.
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