Featuring shorter wavelengths and high photon energy, ultraviolet (UV) light enables many exciting applications including photolithography, sensing, high-resolution imaging, and optical communication. The conventional methods of UV light manipulation through bulky optical components limit their integration in fast-growing on-chip systems. The advent of metasurfaces promised unprecedented control of electromagnetic waves from microwaves to visible spectrums. However, the availability of suitable and lossless dielectric material for the UV domain hindered the realization of highly efficient UV metasurfaces. Here, a bandgap-engineered silicon nitride (Si3N4) material is used as a best-suited candidate for all-dielectric highly efficient UV metasurfaces. To demonstrate the wavefront manipulation capability of the Si3N4 for the UV spectrum, we design and numerically simulate multiple all-dielectric metasurfaces for the perfect vortex beam generation by combing multiple phase profiles into a single device. For different numerical apertures (NA =0.3 and 0.7), it is concluded that the diffracted light from the metasurfaces with different topological charges results in an annular intensity profile with the same ring radius. It is believed that the presented Si3N4 materials and proposed design methodology for PV beam-generating metasurfaces will be applicable in various integrated optical and nanophotonic applications such as information processing, high-resolution spectroscopy, and on-chip optical communication.
The ultraviolet (UV) and visible regions of the electromagnetic spectrum incorporate many exciting applications, including high-resolution imaging, optical communication, lithography, sensing, and many more. The classic ways of manipulating electromagnetic waves through bulky, large, and expensive components stand between the new technologies like on-chip systems. The advancement of nanofabrication technologies enables the advent of optical metasurfaces that can manipulate approximately the whole electromagnetic spectrum. However, the availability of a suitable and lossless material for the UV and Visible region hinders the creation of metasurfaces and their integration for practical applications. Herein, we exploit the bandgap-engineered silicon nitride (Si3N4) material, which is transparent in most parts of the UV spectrum and can perform efficiently in both regimes. For proof of the concept, we design and numerically simulate different metasurfaces to generate the perfect vortex beam with different topological charges and a numerical aperture of 0.6. Each metasurface is functional for both UV and visible regions and efficiently manipulates the incident light. The independence of phase profile from topological charge helps perfect the vortex beam, to control the shortcomings of the optical vortex beam. The cross-polarization efficiency of the metasurface is also up to the mark. This work may find potential applications in different fields like on-chip communication, lithography, quantum processing, and optical communication.
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