Abstract
Metasurfaces in the ultraviolet spectrum have stirred up prevalent research interest due to the increasing demand for ultra-compact and wearable UV optical systems. The limitations of conventional plasmonic metasurfaces operating in transmission mode can be overcome by using a suitable dielectric material. A metalens holds promising wavefront engineering for various applications. Metalenses have developed a breakthrough technology in the advancement of integrated and miniaturized optical devices. However, metalenses utilizing the Pancharatnam–Berry (PB) phase or resonance tuning methodology are restricted to polarization dependence and for various applications, polarization-insensitive metalenses are highly desirable. We propose the design of a high-efficiency dielectric polarization-insensitive UV metalens utilizing cylindrical nanopillars with strong focusing ability, providing full phase delay in a broadband range of Ultraviolet light (270–380 nm). The designed metalens comprises Silicon nitride cylindrical nanopillars with spatially varying radii and offers outstanding polarization-insensitive operation in the broadband UV spectrum. It will significantly promote and boost the integration and miniaturization of the UV photonic devices by overcoming the use of Plasmonics structures that are vulnerable to the absorption and ohmic losses of the metals. The focusing efficiency of the designed metalens is as high as 40%.
Highlights
Ultraviolet light plays a vital part in human life involving sterilizers, lithography equipment, and laser devices
This work reports on a high efficiency, polarization insensitive, near diffraction-limited UV metalens that operates in the broadband region of ultraviolet light from 270 to 380 nm with a tightly focused spot
The designed metalens is composed of silicon nitride cylindrical nanopillars arranged on a square lattice
Summary
Ultraviolet light plays a vital part in human life involving sterilizers, lithography equipment, and laser devices. Metasurfaces are greatly desired in integrated optics and electronic circuits, portals, and mobile devices They are attaining a great interest in industrial applications due to their high efficiency of manipulating the light [19,20]. Geometrical phase metasurfaces that are proposed and experimentally demonstrated, utilize the employment of a dominant electrical resonance by asymmetric nanopillars to induce local phase retardation by rotating the polarization of incident light This sort of phase retardation, that is called the Pancharatnam–Berry (PB) phase shift, can be employed for beam shaping and spin filter applications. We have recently demonstrated a Pancharatnam–Berry phase-based high-efficiency broadband metalens in the UV spectrum (250–400 nm), which requires circularly polarized (CP) incident light [35]. To the authors’ knowledge, this is the first reported metalens in the UV regime with polarization independence and broadband (over 110 nm bandwidth) ability along with a high Numerical Aperture (NA) of 0.86
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