We propose truly achromatic metasurfaces at midinfrared and visible spectra using plasmonic and all-dielectric concepts, respectively. The constituting layered elements, with each layer being a capacitive or an inductive structure, behave like low-pass circuit filters with almost linear phase response over the designed spectrum. This allows successful broadband operation. The plasmonic layered elements are limited to work around 50 THz due to the appearance of a plasmonic resonance feature at higher frequencies. On the other hand, the all-dielectric concept can be designed up to the visible range with negligible material dispersion. Design procedures and working principles are fully detailed. Two types of metasurfaces patterned by plasmonic and all-dielectric elements are carefully designed and numerically simulated around 50 and 600 THz, respectively. Chromatic aberration is successfully avoided. The plasmonic metasurface operates well in 5.5-7.5 mu m, and the all-dielectric case has the desired performance over almost the entire visible band. (C) 2015 Optical Society of America
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