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.
Multi-operational metasurfaces have received a lot of interest because of their significant design improvements for ultra-compact and highly integrated meta-optics. The emergence of near and far-field holography offers an effective solution to enhance the capacity of information encoding in a single metasurface. However, the existing strategies of layer stacking and interleaving, where distinct functionalities are embedded with the help of the combination of multiple meta-atoms, have challenges in terms of design complexity and efficiency. This manuscript proposes a new simplest approach for a tri-channel highly efficient meta-holography based on the photonics spin Hall Effect (PSHE) and Mauls’ Principle of amplitude manipulation. A multi-functional metasurface constituent of a single nano-rectangular pillar over a glass substrate is designed as evidence of conception to highlight the feasibility of parallel manipulation upon near and far-field activities. To achieve control over the entire phase range (0-2π), geometric phase modulation is utilized. Zinc sulphide (ZnS) is used as a constituent material for highly efficient broadband response over the whole visible spectrum due to its characteristics of an extraordinary refractive index and low absorption coefficient. For authentication of the proposed methodology, the designed metasurface is simulated in FDTD, effectively validating the execution of a multi-functional design scheme. For the proof of the broadband operation, optical response over three visible wavelengths (i.e., blue, green, and red) is measured, and it reconstructs all three holograms with high efficiency. Thus, the proposed optical response multiplication approach is a viable contender for various high-end applications in photonics, data storage, and communication.
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