A graphene-based infrared emitter
Researchers say the device, which is integrated with silicon photonic waveguides, represents a significant step towards efficient, miniaturised and reliable PIC-based gas sensors
Researchers at AMO GmbH, RWTH Aachen University, KTH Royal Institute of Technology, Senseair AB, and the University of Bundeswehr have reported successfully developing a waveguide-integrated incandescent thermal mid-infrared emitter using graphene as the active material. According to the scientists, this approach significantly enhances the efficiency, compactness, and reliability of gas sensor systems, paving the way for widespread application across various industries.
Gas leak detection, industrial process control, environmental monitoring, and medical diagnostics all require robust, real-time air quality monitoring solutions, driving the demand for distributed, networked, and compact gas sensors. Traditional gas sensing methods, including catalytic beads and semiconducting metal oxide sensors, suffer from performance degradation, the need for frequent calibration, and limited sensor lifetimes, due to their reliance on chemical reactions.
Absorption spectroscopy offers a promising alternative by utilising the fundamental absorption lines of several gases in the mid infrared (mid-IR) region, including greenhouse gases. This method provides high specificity, minimal drift, and long-term stability without chemically altering the sensor. The ability to “fingerprint” gases through characteristic absorption wavelengths, such as carbon dioxide, at 4.2 μm, makes it an ideal technology for precise gas detection.
PICs represent a significant advancement in miniaturising spectroscopy equipment to chip size, resulting in highly compact and cost-efficient optical gas sensor systems. However, the integration of light sources and detectors directly on the wafer level remains a challenge. Overcoming this hurdle could further reduce sensor size and cost, enhance mechanical stability, and improve performance.
The researchers say that graphene has emerged as an excellent candidate for mid-IR emitters, due to its ability to reach the necessary temperatures for thermal emission and its favourable emissivity. They add that its monolayer structure allows for ideal near-field coupling without significantly distorting the waveguided mode, making it perfect for integration with silicon photonic waveguides.
In the new study, reported in the journal ACS Photonics, Nour Negm and colleagues report integrating graphene emitters directly on top of silicon photonic waveguides, enabling direct coupling into the waveguide mode. According to the team, this setup successfully detected emissions in the spectral range of 3-5 μm, demonstrating the potential of graphene-based emitters for air quality monitoring.
The scientists say this result marks a significant step forward in developing efficient, compact, and reliable gas sensor systems. The work has been performed within the EU projects Ulisses and Aeolus, which aim at developing enhanced capabilities for real-time air quality monitoring in diverse applications in urban areas.
