Abstract
The performance of an ultrathin (thickness < 0.04λ 0) metasurface superoscillatory lens (metaSOL) is experimentally demonstrated in the terahertz (THz) range. The metaSOL is designed using two different hexagonal unit cells to improve the efficiency and properties of the conventional transparent–opaque zoning approach. The focusing metastructure produces, at a frequency f exp = 295 GHz, a sharp focal spot 8.9λ exp away from its output surface with a transversal resolution of 0.52λ exp (≈25% below the resolution limit imposed by diffraction), a power enhancement of 18.2 dB, and very low side lobe level (−13 dB). Resolution below the diffraction limit is demonstrated in a broad fractional operation bandwidth of 18%. The focusing capabilities of the proposed metaSOL show its potential use in a range of applications such as THz imaging, microscopy, and communications.
Highlights
Metamaterials and their 2D version, metasurfaces have attracted much attention owing to the possibility they offer to control phase, amplitude, and polarization characteristics of electromagnetic (EM) waves
For far-field super-resolution applications, devices are sought to have long focal length (FL), large field of view (FoV, defined as the area of low intensity around the superoscillatory hotspot that stays below 25% the maximum power value at the focus, see Supporting Information for more information),[34] and good transmission characteristics, aiming to minimize the reflection and absorption in the device, and to improve the focusing efficiency concentrating the electric field in the focal spot
The experimental setup was placed on a planar antivibration table to minimize noise from mechanical vibrations and both the metasurface superoscillatory lens (metaSOL) and receiver probe were surrounded with millimeter wave absorbing material to minimize reflections and mimic anechoic chamber conditions
Summary
Metamaterials and their 2D version, metasurfaces have attracted much attention owing to the possibility they offer to control phase, amplitude, and polarization characteristics of electromagnetic (EM) waves. For far-field super-resolution applications, devices are sought to have long FL, large field of view (FoV, defined as the area of low intensity around the superoscillatory hotspot that stays below 25% the maximum power value at the focus, see Supporting Information for more information),[34] and good transmission characteristics, aiming to minimize the reflection and absorption in the device, and to improve the focusing efficiency concentrating the electric field in the focal spot In this context, SOLs arise as an interesting and powerful alternative, as they can focus light into a subwavelength hotspot located further than 10 times the wavelength in free space.[37,38,39,40,41,42]. Our current work represents one of the few examples of SOLs experimentally demonstrated in the THz spectrum
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