Terahertz science and technology promise many cutting-edge applications. Terahertz surface plasmonic waves that propagate at metal-dielectric interfaces deliver a potentially effective way to realize integrated terahertz devices and systems. Previous concerns regarding terahertz surface plasmonic waves have been based on their highly delocalized feature. However, recent advances in plasmonics indicate that the confinement of terahertz surface plasmonic waves, as well as their propagating behaviors, can be engineered by designing the surface environments, shapes, structures, materials, etc., enabling a unique and fascinating regime of plasmonic waves. Together with the essential spectral property of terahertz radiation, as well as the increasingly developed materials, microfabrication, and time-domain spectroscopy technologies, devices and systems based on terahertz surface plasmonic waves may pave the way toward highly integrated platforms for multifunctional operation, implementation, and processing of terahertz waves in both fundamental science and practical applications. We present a review on terahertz surface plasmonic waves on various types of supports in a sequence of properties, excitation and detection, and applications. The current research trend and outlook of possible research directions for terahertz surface plasmonic waves are also outlined.
Surface plasmon polaritons (SPPs) with the features of subwavelength confinement and strong enhancements have sparked enormous interest. However, in the terahertz regime, due to the perfect conductivities of most metals, it is hard to realize the strong confinement of SPPs, even though the propagation loss could be sufficiently low. One main approach to circumvent this problem is to exploit spoof SPPs, which are expected to exhibit useful subwavelength confinement and relative low propagation loss at terahertz frequencies. Here we report the design, fabrication, and characterization of terahertz spoof SPP waveguides based on corrugated metal surfaces. The various waveguide components, including a straight waveguide, an S-bend waveguide, a Y-splitter, and a directional coupler, were experimentally demonstrated using scanning near-field terahertz microscopy. The proposed waveguide indeed enables propagation, bending, splitting, and coupling of terahertz SPPs and thus paves a new way for the development of flexible and compact plasmonic circuits operating at terahertz frequencies.
Anomalous launch of a surface wave with different handedness phase control is achieved in a terahertz metasurface based on phase discontinuities. The polarity of the phase profile of the surface waves is found to be strongly correlated to the polarization handedness, promising polarization-controllable wavefront shaping, polarization sensing, and environmental refractive-index sensing.
Controlling the propagation of surface plasmon polaritons is essential in developing highly integrated photonic devices. By using near-field scanning terahertz microscopy, we experimentally demonstrate that polarization-controlled tunable surface plasmons (SPs) could be directionally excited on a metal surface with carved columns of aperture resonators under special arrangement. The experimental results reveal that terahertz SPs could be unidirectionally launched in opposite directions owning to destructive and constructive interferences on the two sides with circularly polarized incident waves of opposite handedness. Meanwhile, the linearly polarized wave is able to excite the terahertz SPs along either side of the structures. The presented results would be useful to implement functional terahertz plasmonic devices.
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