Abstract
Metasurfaces are two-dimensional metamaterials composed of a carefully designed series of subwavelength meta-atom (antenna or aperture) arrays. These surfaces can manipulate the phase, amplitude and polarization of output light by changing the shapes and orientations of the meta-atoms on a subwavelength scale. Using these properties, we experimentally demonstrate variable meta-axicons composed of rectangular nano-apertures arranged in several concentric rings that can focus left circularly polarized (LCP) light into a real Bessel beam and defocus right circular polarized (RCP) light to form a virtual beam. A desired phase discontinuity in cross-polarized transmitted light is introduced along the interface by controlling the orientations of the nano-apertures. In addition, the meta-axicons can generate Bessel beams of arbitrary orders by suitable design of the phase profile along the surface. The meta-axicons demonstrate broadband optical properties that can switch the wavelength of the incident light from 690 nm to 1050 nm. These variable meta-axicons open a path towards the development of new applications using integrated beam shaping devices.
Highlights
Metasurfaces have attracted significant research interest because they offer considerable flexibility in the engineering of their electromagnetic properties
We demonstrate a meta-axicon for use in the generation of a zero-order
The laser light is converted into circularly polarized (CP) light using the quarter-wave plate (QWP1) that is located in front of the sample
Summary
Metasurfaces have attracted significant research interest because they offer considerable flexibility in the engineering of their electromagnetic properties. Metasurfaces have been widely used in applications including nonlinear photonics[18,19,20,21], optical OAM18,22–26, optical rotation[27], invisibility cloaking[28,29,30], metalenses[31,32] and holography[33,34] These surfaces are generally composed of a series of subwavelength meta-atom (antenna or aperture) arrays that have carefully designed shapes and orientations. The Pancharatnam–Berry phase[36,37], which is called the geometric phase, is a widely used method for performing phase modulation via the space-variant optical axis orientations of meta-atoms Based on these properties, one interesting potential application of metasurfaces is the formation of a meta-axicon[38,39,40]. The working wavelength of our meta-axicon extends to the near-infrared band, which could be useful in high-resolution multi-photon imaging applications
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