Metasurface-engineered thermal emitters enabled chip-scale mid-infrared spectroscopic sensing

Abstract Miniaturized spectroscopy techniques show great potentials in on-site applications, with most progress focused on manipulating the spectral responses of either dispersion elements or detectors. Little attention was paid on light sources, while light source and its optical collimation unit left unsaid in most miniaturized spectrometers actually dominate a majority of the footprint and the cost of the entire platform. Here, we demonstrate light-source engineering as a new paradigm for developing a miniaturized spectroscopic sensing platform in mid-infrared (MIR), where spectral information of the analyte is encoded in the MIR image of a chip-size thermal source. An array of angle-insensitive metasurface sub-emitters that operate at various wavelengths enables a straightforward sensing method by decoding an image of the radiation intensity distribution. Accurate and robust classification of organic solvents and drug sorting, as well as quantitative concentration measurement of mixed organic solutions, were experimentally demonstrated with an imaging angle tolerance up to 40º. Moreover, spectral imaging was explored using this device, achieving distinct images of a plastic covered steel ring. By integrating the functions of light source, dispersion element and collimation unit in conventional spectroscopy platforms into such a chip-size metasurface thermal emitter, the proposed miniaturized MIR spectral sensing technique shows promising potential for portable and on-site material analysis.