Research On Terahertz Devices Based Spoof Surface Plasmon Modes

In recent years,Terahertz technology is widely applied in various fields,ranging from semiconductor industry,bio-medicine and health,homeland security,food quality control to environmental testing etc.,due to the unique properties of THz radiation.With the rapid development of terahertz source and detection technology,many new applications in terahertz regime are expected to realize.Surface plasmon photonics has been extensively studied at optical frequencies,and it has great application prospects and values on radiation guiding,optical nanoantennas,ultra-high resolution imaging,and optical metamaterial and so on.However,the relative permittivity of metallic material which can directly support surface plasmons tends to be negative infinity in THz regime,resulting in these applications cannot be directly extended to this region.The theory of “spoof surface plasmon(SSP)”,supported by structured metal surface composed of one-dimensional(1D)arrays of grooves or two-dimensional(2D)arrays of holes perforated in a flat metal surface,has been proposed for several years,but few studies have been taken in terahertz regime,particularly in the design and fabrication of various devices.The main work in this paper is about terahertz sensing,waveguide and antenna,and is divided into three parts:(1)We theoretically design and analyze a novel terahertz refractive index sensor.The sensor is composed of 1D array of grooves milled into the metal surface with prism coupling into an Otto configuration which is based on the principle of spoof surface plasmon resonance.The dependence of the resonant angle on the change of the refractive index is numerically investigated through finite element method and a high angular sensitivity about S=320°/RIU is demonstrated,which leads to a high resolution of 3×10-7RIU assuming 1×10-4 degree for angular resolution.We further show that by using a slanted geometry an even higher sensitivity up to 452°/RIU can be achieved,which is much higher than the previously reported sensitivity in the optical regime,so that high efficient terahertz refractive index sensing is realized.(2)The waveguiding properties of spoof surface plasmon modes propagating along three kinds of one-dimensional groove arrays composed of V-shaped,rectangular,and trapezoid grooves,respectively,are numerically investigated.The results show that the trapezoid groove array demonstrates a tighter confinement compared to the other two groove arrays,and the propagation loss of spoof plasmon waveguides is determined not only by the difference between the operation frequency and asymptotic frequency but also by the loss associated with the TEM mode inside individual grooves.The bending loss through small bending radii of the three structures(?0.5?)is also calculated showing that although the straight trapezoid groove array exhibits highest propagation loss,the transmission loss through a 90° bend of it is lower.This property together with the ease of fabrication makes the trapezoid structure a better candidate for planar terahertz photonic integration on the subwavelength scale.(3)We theoretically propose a kind of novel terahertz antennas for the first time due to the excitation of spoof surface plasmons on a corrugated metal stripe.Due the cut-off of metal groove structure at both ends,SSPs modes will propagate along the corrugated metallic stripe and reflect back and forth,resulting in a sharp Fabry-Perot mode in scattering cross-section spectra which is similar to those supported by the nanostripe antennas working in optical frequencies.And at the frequency of Fabry-Perot mode the local terahertz electric intensity around the antenna has been greatly enhanced,reaching about 7×104 times than the incident terahertz electric field.So that the investigation of terahertz-matter interactions will be enhanced,and many applications of nanostripe antennas in optical frequencies can be directly extended to THz regime.These results provide great potential for sensing,detection,switch,modulation and other fields in the terahertz frequencies.