Kobi Cohen


Viterbi Faculty of Electrical Engineering, Technion

Aliasurface: aliasing based metasurface

Metasurfaces (MS) are commonly used today in order to control light in the subwavelength scale. Their deep subwavelength features can control the amplitude and phase of a wave and induce a polarization and wavelength dependent behavior. It was also found that a periodic patterning of such features can significantly modify the refractive index of material and alter the propagation of surface waves  from being normally diffracted to hyperbolic-like behavior, where the waves focus or defocus in anomalous way. This behavior is conventionally described in the effective medium approximation, which requires an ultrasmall size of these features, applying stringent demands on the fabrication techniques and limited to propagation in one axis. Furthermore, it does not take into account all the phenomena and opportunities provided by the periodicity of the system. We present a new degree of control over surface waves enabled by aliasing effects emanating from the periodicity of the surface structure. We show how folding in momentum space in shallow and sparsed periodic MS gives rise to topological transitions, diffraction management and anomalous focusing which were so far found only in dense and high-aspect ratio periodic structures. We demonstrate how the interplay between periodicity and depth affects the equi-frequency contour of surface waves, altering the topology from closed curves to open ones and visualize the near-field surface propagation of diffractionless propagation and backward focusing based on the aliasing effect. We find that the aliasing effect, which occurs in periodic systems, creates new type of  guided surface modes, which we excite and measure. Considering this new type of mode, we design a MS supporting nearly temporally dispersionless propagation and resistant to parameter variations. Such Aliasurface also support excitation of topologically protected surface modes and excitation of a super-broadband waves with plenty of spatial wavenumbers and a single temporal frequency, by engineering the unit cell. The design of Aliasurface does not rely on the inherent isotropy of hyperbolic MS and hence can be extended to 2D gratings, forming both temporal and spatial dispersionless propagation and forming 2-axis anomalous focusing. This technology can be implemented easily in any 2D waveguide, enabling full dispersion control, compatible with the commonly used fabrication techniques.
  •    Graduate seminar by Kobi Cohen, supervised by Prof. Guy Bartal.

Date: Mon 15 Jul 2019

Start Time: 14:30

End Time: 15:30

1061 | Electrical Eng. Building