Fibering drop of a chalcogenide glass
In recent years, science, industry, and the society itself has shown a growing interest for optical applications in the mid infrared (IR) region, which can be defined as the 2-20 µm electromagnetic spectral range. Indeed, this spectral region contains the atmospheric transparent windows (3-5 µm) and (8-12 µm) where thermal imaging (civilian and military) can be implemented. Furthermore, in this infrared window, most molecules and biomolecules show specific absorption bands that acts as optical fingerprints for biological or chemical analysis using infrared fiber optical sensors. It can be noted that in the visible spectral range, the silica fiber technology permits the realization of deported systems for imaging and/or spectroscopy. In the mid infrared, these technologies do not exist. For wavelengths longer than 5 µm, among glass materials, only the chalcogenide fibers are still transparent. In addition, no fiber laser emits wavelengths above 4.5 µm. In this context, a promising way to produce broad-band is the generation of supercontinuum. supercontinuum light sources are generated by propagating short, but high-power laser pulses in non-linear media that are most often optical fibers. Popularized in the last decade, these sources have found applications in areas such as coherent optical tomography, materials processing, chemical detection, gas monitoring, imaging and absorption spectroscopy. However, the bandwidth of current SC sources is limited between 400 nm and 2 µm due to the structure of conventional silica glass optical fibers.
Researchers from the FEMTO-ST Institute (CNRS/UFC/UTBM/ENSMM), glass and ceramics group from the "Institut des sciences chimiques de Rennes" (ISCR, CNRS/Université de Rennes 1/ENSC Rennes/INSA Rennes) of Mac Gill University in Montreal and the companies SelenOptics (spin-off company of the glasses and ceramics team), Le Verre Fluoré and Leukos have managed to reach 10 µm, with solutions that can be transposed to current applications.
The scientists have developed a cascaded fiber system that generates a supercontinuum covering the entire mid-infrared range (2-10 µm). Work by other teams is pushing up to 16 µm, but only using installations that are far too expensive and bulky for the method to be practically applicable. Here, a compact pulsed laser is passed through a series of three glass fibers of silica, fluoride and chalcogenide. Its spectrum is then gradually broadened and shifted towards the mid-infrared. The researchers also describe a fully realistic numerical model to simulate laser pulse propagation through the series of fibres, which they use to optimize the process. This technique, ready for commercialization, opens the way to compact and robust mid-infrared sources for detection, spectroscopy and biomedical imaging.
This work is the result of a European H2020 Marie-Curie project: SUPUVIR (Grant agreement n° 722380)
Johann Troles - johann [dot] trolesuniv-rennes1 [dot] fr
Univ Rennes, CNRS, ISCR-6226, F-35000 Rennes, France
2-10 µm Mid-Infrared Supercontinuum Generation in Cascaded Optical Fibers: Experiment and Simulation, S. Venck, F. St-Hilaire, L. Brilland, A. N. Ghosh, R. Chahal, J. Troles, M. Meneghetti, F. Joulain, S. Cozic, S. Poulain, G. Huss, M. Rochette, J. Dudley and T. Sylvestre, Laser and Photonics Reviews, 2020, 2000011
Press release 23/03/2020