Pathway to versatile, point of care, and wearable photonics in the mid-infrared and fingerprint region based on quantum-cascade lasers and analytical and computational advances [Invited]

This paper aims to propose and discuss a pathway to versatile, portable, and wearable photonics devices in the mid-infrared region. We address the benefits and challenges of mid-infrared spectroscopy in the fingerprint region and the development of low-cost mass production devices for real-world applications in the near future. Firstly, the paper briefly introduces the mid-infrared and fingerprint region and discusses the importance of the detection of mid-infrared biomarkers for point-of-care medical applications, stressing the importance of multi-wavelength probing systems. We also discuss the challenge of long-wavelength signals through the matter and the benefits of photo-acoustic detection. The pathway we envisage is twofold: the first is to improve and predict deviation from the standard Bouguer–Beer–Lambert approximation for light propagation in tissue and matter. This approach requires calibrated and wavelength-specific sources. Secondly, to address these requirements, the paper presents the potential for future low-cost personalized devices based on an array of quantum cascade lasers developed on low-cost C-MOS technology and using photo-acoustic detection. The technology was first developed for gas analyses, but we report on a recent successful wearable device for glucose monitoring, which passed clinical trials. This technology will allow the development of future widespread portable mid-infrared devices with potential application not only in healthcare, addressed here, but also in precise gas and environmental chemical monitoring. The ability to record mid-infrared biomarkers at the point of care will be fundamental for the personalized optical digital twin, which will be the cornerstone of future healthcare systems.