Mid-infrared optical sensors for portable devices

In less than a decade, chemical sensing has become a key application for these devices because of the growing potential of spectroscopy, materials processing, and chemical and biomolecular sensing, as well as security and industrial applications. Measurement in this spectral range provides highly selective, sensitive and unequivocal identification of chemicals. 

The coin-size, on-chip, IoT-ready sensors prototyped by Leti combine high performance and low power consumption and enable such consumer uses as air-quality monitoring in homes and vehicles, and wearable health and well-being applications. Industrial uses include real-time air-quality monitoring and a range of worker-safety applications.

Mid-IR optical sensors available on the market today are typically bulky, shoebox-size or bigger, and cost more than €10,000. Meanwhile, current miniaturised and inexpensive sensors cannot meet consumer requirements for accuracy, selectivity and sensitivity. While size and price are not the most critical concerns for industrial applications, bulky and costly optical sensors represent a major barrier for consumer applications, which require wearability and integration in a range of portable devices. 

CEA-Leti presented its R&D results on February 5th at SPIE Photonics West 2019 in a paper titled ‘Miniaturisation of Mid-IR Sensors on Si: Challenges and Perspectives’.

“Mid-IR silicon photonics has enabled creation of a novel class of integrated components, allowing the integration at chip level of the main building blocks required for chemical sensing,” said Sergio Nicoletti, Lead Author of the paper. “Key steps in this development extend the wavelength range available from a single source, handling and routing of the beams using photonic-integrated circuits, and the investigation of novel detection schemes that allow fully integrated on-chip sensing.”

CEA-Leti’s breakthrough combined three existing technologies necessary to produce on-chip optical chemical sensors: 

• Integrating a mid-IR laser on silicon.
• Developing photonic integrated circuits (PICs) in the mid-IR wavelength range.
• Miniaturising a photoacoustic detector on silicon chips.

“While other R&D efforts have had similar results, our project’s key achievement is the use of tools and processes typical of the IC and MEMS industries,” Nicoletti added. “Our focus on the choice of the architectures and processes, and the specific linkage of the series of steps also were critical to developing this optical chemical sensor, which CEA-Leti is now realising as demo prototypes.”