Aberration-Free Ultrathin Flat Lenses and Axicons at Telecom Wavelengths Based on Plasmonic Metasurfaces

Abstract

The concept of optical phase discontinuities is applied to the design and demonstration of aberration--free planar lenses and axicons, comprising a phased array of ultrathin subwavelength spaced optical antennas. The lenses and axicons consist of radial distributions of V--shaped nanoantennas that generate respectively spherical wavefronts and non--diffracting Bessel beams at telecom wavelengths.Simulations are also presented to show that our aberration--free designs are applicable to high numerical aperture lenses such as flat microscope objectives.The fabrication of lenses with aberration correction is challenging in particular in the mid--and near--infrared wavelength range where the choice of transparent materials is limited.Usually it requires complex optimization techniques such as aspheric shapes or multi--lens designs [1,2], which are expensive and bulky.Focusing diffracting plates offer the possibility of designing low weight and small volume lenses. For example the Fresnel Zone Plate focuses light by diffracting from a binary mask that blocks part of the radiation [1]. A more advanced solution is represented by the Fresnel lens, which introduces a gradual phase retardation in the radial direction to focus light

Analog Computing Using Reflective Plasmonic Metasurfaces

“…7 It should be noted that a single layer of scatterers (due to their Lorentzian-shaped polarizability) only allow for full 2π-phase control of the cross-polarized light component, 8 meaning that such metasurfaces have a theoretical efficiency of maximum 25%, 9 though most realizations show efficiencies of a few percent. 10,11 In order to improve the efficiency of plasmonic metasurfaces, the low-frequency concept of transmit-and reflectarrays has been generalized and adopted to the visible and infrared regimes, where metasurfaces working in transmission consist of several layers in order to reach full phase control and proper impedance matching with surroundings. 9,12 Accordingly, such metasurfaces are quite complex to fabricate at near-infrared and visible frequencies, with a moderate efficiency of ∼ 20 − 50% due to Ohmic losses in the metal.…”

Realization of Zero-Refractive-Index Lens with Ultralow Spherical Aberration

“…Bragg scattering) of photonic crystals, a wellperformed device is in need of large-area size so as to functionalize the zero-index properties. This is why we prefer large-area device.Recent developments of metasurface-based flat lens have revealed many outstanding capabilities to manipulate the phase of light in micro-nano scale by using optical resonators with discrete phase distribution [20][21][22][23][24][25][26] . It is concentrated on out-of-plane operation that the propagating waves are vertical to the chip.…”

Graphene-Based Ultrathin Flat Lenses

“…The ultrathin lens based on a 60 nm thick gold metasurface, fabricated by Federico Capasso et al, 11 is considered to be a milestone to revolutionize consumer technology form factors. Here we report on the development of an ultrathin FZP lens using graphene on glass with a few nanometers thickness.…”

“…The maximum efficiency reported for the ultrathin lens based on a 60 nm thick gold metasurface is approximately 1% for a wavelength of 1550 nm. 11 Also designing such metasurface lenses for the visible range will be a challenge due to the fine nanoscaled structures required. The graphene-based lenses offer more compactness and lower losses, are much easier to fabricate, and also offer tunability in the infrared range.…”