Dielectric metalenses at long-wave infrared wavelengths: Multiplexing and spectroscope

Metalenses, being composed of subwavelength phase-control nanostructures, can achieve peculiar manipulations of incident rays. Dispersion is one of the key optical characteristics to be eliminated or exploited in designing broadband optical systems. In the study, the silicon metalenses made of nanobricks are investigated to achieve multiwavelength multiplexing or spectroscope in the long-wave infrared regime. Firstly, the geometrical dependencies of silicon nanobricks' transmittance, phase difference, and structural dispersion are investigated to obtain the fundament of constructing the metalenses. Then, the metalenses are constructed, of which the chromatic aberration is analyzed. Via spatial multiplexing, two multiwavelength-metalens configurations are proposed to realize achromatism and multifocal features respectively. Furthermore, via exploiting the nanobricks' structural dispersion, a compact spectrometer based on an off-axis metalens is demonstrated. This study gives out an insight into exploiting the structural dispersion of silicon nanobricks in constructing metalenses, which paves an efficient way for the development of integrated imaging and spectroscopy systems in the long-wave infrared range.