Abstract
A compact metallic meta-structure is proposed to realize directional conversion between spoof surface plasmon polaritons (SSPPs) and propagating waves at millimeter wave and THz frequencies. The structure is constructed by embedding two slits or multi-slits array into a subwavelength metallic reflection grating. When the back-side of the structure is illuminated by an oblique beam with a fixed incident angle, the propagating wave will be unidirectionally converted into SSPPs with a considerable efficiency. Both the simulations and experiments demonstrate that the excitation ratio of the SSPPs between the two possible propagating directions (left and right) reaches up to about 340. Furthermore, assisted by the structure, near-field SSPPs can be also converted into far-field narrow beams with particular directions. Through frequency sweeping, wide-angle beam scanning is verified by theory and experiments. The work paves a new way for SSPPs launching and also provides fresh ideas for super-resolution imaging in the longer wavelength range.
Highlights
In the recent years, structures with surface topology engineering[1,2,3,4,5] have been widely employed to manipulate near-field waves in the microwave to terahertz (THz) frequency range[6]
In the optical frequency range, unidirectional launching of surface plasmon polaritons (SPPs) can be realized by Bragg reflection originating from a periodic array of grooves that carved into a metal film[29], or by near-field interference of surface waves emerging from polarization-sensitive apertures[30] and one or two slits[31,32,33,34,35]
By periodically replacing some adjacent grooves in a reflection grating with some slits, back-side incident waves can be coupled into the slits arrays, and transformed into the spoof surface plasmon polaritons (SSPPs)
Summary
Structures with surface topology engineering[1,2,3,4,5] have been widely employed to manipulate near-field waves in the microwave to terahertz (THz) frequency range[6]. In the optical frequency range, unidirectional launching of SPPs can be realized by Bragg reflection originating from a periodic array of grooves that carved into a metal film[29], or by near-field interference of surface waves emerging from polarization-sensitive apertures[30] and one or two slits[31,32,33,34,35]. The unidirectional launching of SSPPs supported on a subwavelength metallic reflection grating is theoretically and experimentally demonstrated in the millimeter wave to THz frequency range. The tunable unidirectional launching of SSPPs emerges from the near-field constructive and destructive interference occurred only when the incident angle of the back-side illuminated beam and the period of the slits arrays are elaborately matched. We find that SSPPs at different frequencies can be directionally converted into far-field narrow beams assisted by the structure, and beam scanning through frequency sweeping is demonstrated by theory and experiments
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