Broadband diffraction-free on-chip propagation along hybrid metallic grating metasurfaces in the visible frequency

Abstract

Metallic patterned metasurfaces can effectively manipulate the propagation of surface plasmonic waves in the near-field regime. Extraordinary optical phenomena such as diffraction-free propagation also have been enabled by periodic uniform metallic grating metasurfaces (UMGM). However, such metallic patterned metasurfaces usually exhibit a relatively narrow-band non-diffractive property and the realization of visible-frequency broadband diffraction-free on-chip propagation has been quite challenging due to intensive structural dispersive and sensitive wavelength selectivity. Here, we proposed a novel design of a hybrid metallic grating metasurface (HMGM) with two different ridge widths, which could display a broadband diffraction-free on-chip propagation in the visible frequency. By optimization and appropriate hybridization of the ridges of different widths, it enables effective modication of the dispersion of surface plasmons, thus forming the broadband diffraction-free characteristics. Compared to the UMGM, our proposed HMGM can facilitate enhanced propagation of the surface plasmon polaritons and strongly confine the surface plasmonic field to the deep-subwavelength scale. With such hybrid implementation, the surface plasmonic waves propagate parallel to the ridges and their wavefronts remain the original shape without diverging at the broadband wavelength of 600 nm–800 nm. Overall, such broadband diffraction-free propagation along the HMGM could find many potential applications in on-chip plasmonic devices including sub-diffraction resolution imaging, hyperlenses, and photon routing, etc.