Abstract
We report on the first observation of ‘Spoof’ Surface Plasmon Polariton (SPP) scattering from surface defects on metal-coated 3D printed, corrugated THz waveguiding surfaces. Surface defects, a result of the printing process, are shown to assist the direct coupling of the incident free-space radiation into a spoof SPP wave; removing the need to bridge the photon momentum gap using knife-edge or prism coupling. The free space characteristics, propagation losses and confinement of the spoof SPPs to the surface are measured, and the results are compared to finite-difference time domain simulations. Angular resolved THz spectroscopy measurements reveal the scattering patterns from surfaces and are compared with Mie theory, taking into account the shortened wavelength of the photons in their bound SPP state compared to their free space wavelength. These results confirm yet another similarity between the properties of THz spoof SPPs and their natural, non-spoof, counterparts at optical and infrared frequencies which also, unexpectedly, adds functionality to the structures.
Highlights
The field of plasmonics offers the possibility for sub-wavelength manipulation of electromagnetic radiation which can lead to more compact and efficient optical devices or optical circuits[1,2,3]
We have demonstrated the free space coupling of THz radiation to 3D printed defect-rich spoof Surface Plasmon Polariton (SPP) surfaces
While the SPPs are well confined to the surface, the propagation lengths are only in the order of a few free-space wavelengths
Summary
The field of plasmonics offers the possibility for sub-wavelength manipulation of electromagnetic radiation which can lead to more compact and efficient optical devices or optical circuits[1,2,3]. Given that bound quasi-particles, such as an SPP, have a non-linear dispersion relation that lies to the right of the light line, additional momentum is required for a photon to couple from free space to the surface to form the SPP This momentum gap is usually bridged with either prism coupling or scattering. The structures presented here do not require any additional means to couple radiation from free space, which we suggest is due to the high defect density on the surface offering a multitude of scattering opportunities. This effect is well known for classic, optical SPPs13, but has not been reported for spoof SPP structures. In the following we present a detailed characterization of the 3D printed THz spoof plasmonic waveguide which demonstrates the scattering of the bound spoof plasmons at the defects and an explanation with the classic Mie theory and FDTD simulations
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