Double-Band Metasurface Infrared Optics for Integrated Multichannel Spectral Sensors

Simultaneously identifying the composition of mixtures and determining their concentration levels has aroused much attention in recent years to meet the large demands of compact and low-cost infrared spectral sensors to replace their conventional bulky counterparts with costly separated infrared components. In this work, we propose a design method for multichannel metasurface infrared array optics covering two bands middle-wave infrared (MWIR) and long-wave infrared (LWIR) for construction of integrated infrared gas sensors. The use of metasurface microstructures with the same height realizes the effective filtering and focusing of electromagnetic waves at multiple wavelengths in both infrared bands, which is beneficial to decrease the manufacturing costs. Four-channel metasurface lens arrays and filter arrays with operating wavelengths of 3.5, 9.7, 10.6, and
$3.9 \mu \text{m}$
corresponding to the infrared absorption peaks of three gases of ethanol, ammonia, ethylene, and one reference wavelength, respectively, were designed and produced by photolithographic patterning and dry etching processes on silicon substrates. The multichannel metasurface infrared optics have the advantages of easy fabrication and integration with wideband infrared detector array to form a compact infrared spectral detector, which meets the requirements of small volume and low cost to advanced infrared spectral sensors for applications in portable smart sensing systems and the Internet of Things.