Broadband Multifunctional Achromatic Metalens

Metasurfaces offer novel design capability of optical wavefront shaping to realize ultra-compact flat optical components which have remarkable potential to mitigate the constraints of size and design complexities in imaging systems. However, aberration correction and diffraction-limited response over the broad spectrum greatly hindered their applicability because of simultaneous phase engineering at multiple wavelengths on a single metasurface interface. Conventionally reported design methodologies overcome the challenges mentioned earlier by exploiting resonance tuning, layer stacking, and phase mergence strategies. They suppressed the aberration effect with high efficiency but have complex design and meta-atom geometry with limited functionalities. Here in this research script, we have introduced broadband achromatic bifocal metalens based on a single-layer array of nano-rectangular bars in transmission mode. In order to have wavelength-independent focusing, we developed a library of meta-atoms to provide required phase compensations. In addition to this, a novel material zinc selenide (ZnSe) is introduced as a constituent which is a large transparent window in the optical regime. The high efficiency and unprecedented capability of aberration correction along with multi-functionality make the proposed metalens a potential candidate for next-generation advanced imaging technology.