QCL Sources
Within M3NIR, ALPES develops QCLs tailored for integration on a Ge-on-SOI PIC platform developed by IMEC. Ge-on-SOI is widely transparent in the mid-infrared (2-8.5 µm band), the high refractive index allows for dense integration, and efficient heaters can be realized on the platform. The aim is to combine the Ge-on-SOI waveguides with QCL gain chips to make high quality tunable lasers for the mid-infrared with a high yield. Moreover, multiple wavelength bands can be targeted, required for practical applications.
This integration demands close collaboration between ALPES and IMEC. Numerical simulations have defined the required mode structures in QCLs and Ge waveguides on PICs, optimizing the coupling efficiency and guiding the integration strategy. ALPES has provided first sets of DFB-QC and FP-QC chips to IMEC. The next steps involve processing and characterizing dedicated QC chips for flip-chip integration, targeting specific wavelengths for the different M3NIR use cases.
Ge-on-SOI PIC platform
Two different integration approaches were defined, thereby maximizing the availability of QC chips on short-term for hybrid integration experiments, and at the same time defining a more scalable flip-chip integration approach for which customized QC chips are being processed. Several DFB-QCLs have been integrated on sub-mounts for hybrid integration, allowing for high alignment accuracy when coupling to multiple QCLs to Ge-on-SOI waveguides. First assemblies have been characterized, and steps for further improvement have been defined. A detailed thermal model was also developed by ARGO to optimize the cooling and temperature modulation of QCLs. For the Ge-on-SOI PIC platform, initial design efforts by VLC focused on the beam combiner, Distributed Bragg Reflector, and Vernier Rings, to be continued in the next few months.
Passive Ge-on-Si PICs
VLC also undertook the optical design for the passive Ge-on-Si PIC platform for liquid analyzer use case, focusing on creating essential building blocks such as single-mode Ge waveguides, grating couplers, and multimode interference couplers. IMEC handled fabrication on a 2 μm thick Ge-on-Si platform, with the first version of the PIC already fabricated. Ongoing efforts aim to refine the process, achieving fine resolution for grating couplers, while providing smooth waveguide sidewalls.
Self-Mixing Detection
NKUA studied the self-mixing (SM) method to enable detector-less gas sensing by measuring terminal voltage variations caused by optical feedback. The goal is to integrate SM into the breath analysis use case, enhancing energy efficiency by eliminating the need for cooled mid-IR detectors. Efforts are concentrated on improving SM sensitivity, with current setups providing gas concentration sensitivity in the order of 100s ppm at 1 sec integration time. A QCL numerical model is also under development to simulate various SM scenarios, with ongoing validation efforts.
Microfluidics
CHIPSH developed a microfluidics chip for aligning fluidic channels to Ge waveguide structures on the PIC. This will enable a flexible assembly method to evaluate different liquid interaction lengths, while providing leakage during liquid sample insertion. Current chips are produced by milling, while future designs will be based on injection moulding, once designs have been frozen. Testing of different microfluidic designs is currently ongoing.
Electronics
EUL developed the first version of the electronics for M3NIR, for both the TEC (thermo-electric cooler) driver and laser drivers. The electronics offer a serious reduction in size and power consumption, as required for the use case of air quality monitoring on a drone platform from ALTUS.
Data Acquisition
CYRIC initiated discussions on M3NIR platform requirements, dashboard visualizations, and machine learning models. Data upload protocols were defined, and the M3NIR cloud platform was developed for data retrieval, storage, and visualization. A dashboard demo was shared early in the project, and further development of visualization tools and machine learning models is ongoing.
Use Case 1: Environmental sensing
A drone-mounted ICAPS-based sensor (Interferometric Cavity-Assisted Photothermal Spectroscopy, ICAPS) is being developed through collaboration among TUW, ALPES, EUL, CYRIC, and ALTUS. The sensor utilizes an optical cavity for sensitive gas detection via photothermal spectroscopy. ALPES provided DFB-QCLs as excitation sources, with EUL developing the necessary electronics. The set-up is being constructed on an optical table by TUW, and following successful testing the procedures for mounting the sensor module on a drone platform from ALTUS will be initiated.
Use Case 2: Liquids analysis
The development of a miniaturized platform for ionic species detection in water involves collaboration among TUW, IMEC, VLC, CHIPSH, ALPES, and BADGER. The platform uses mid-IR dispersion spectroscopy with Ge waveguides in MZI structures. VLC designed waveguide components, being manufacturing by IMEC. Testing and benchmarking of the sensor are planned at TUW, after integration with the microfluidics from CHIPSH. Next steps will be to test the system on real life samples by BADGER, which could include river water as well as wastewater effluent and potentially wastewater influent.
Use Case 3: Exhaled breath analysis
The M3NIR exhaled breath analyser is designed to detect Helicobacter pylori infection by identifying the presence of 13CO2 in exhaled breath following the administration of urea labeled with 13C which is metabolized by H. pylori. The sensor, developed by UULM, ALPES, IMEC, NKUA, EUL, and CYRIC, integrates mid-IR absorption with self-mixing detection, offering a potentially low cost and miniaturized solution. UULM designed the substrate-integrated hollow waveguides (iHWG) for optimal interaction with the target analytes, and IMEC is integrating the necessary components on the Ge waveguide PIC platform. Once the different building blocks are available, the sensor module will be validated by UULM.
