| In this paper,we mainly investigated the slow-light effects and its applications of the spoof surface plasmon polaritons supported by the subwavelength metallic surface grating structures in the terahertz(THz)frequency range.The majority of my work is listed in the following:First,we investigate the dispersion relation of the spoof spps mode supported by the metal surface grating structure and two-dimensional arrays of holes on metal surface by employing the model expansion method(MEM)and the equivalent medium theory,which is very similar to that of the spps mode supported on the metal surface in the optical frequency range.The two kinds of structures can used to realize the excitation and transmission of the spoof spps mode in microwave and THz frequency range.Moreover,the dispersion relation can be controlled by changing the geometric parameters of the structure.Then,we investigated the slow-light effects of spoof spps supported by metallic surface grating structure in THz frequency range and its sensing applications.Firstly,we analyzed the dispersion relation and transmission characteristics of the spoof spps assisted by metallic surface grating with uniform groove parameters.It's showed that the metal surface grating structure is a excellent THz plasmonic waveguide with very good transmission characteristics,and the refractive index of the medium filled in the grooves is higher,the cutoff frequency of the dispersion curves is lower.Then,we discuss the propagation characteristics of the spoof spps supported by the gradient metal surface grating structure,which can realize the slow-light effects in the broad spectrum band,the structure has the ability to dynamic trap terahertz waves of different frequencies at different positions.Then,we investigated the dispersion relation of spoof spps supported by silicon-filled gradient metal surface grating structure.It's shown that if the changing of the refractive indices of silicon filled in the grooves is optical induced,we can modulate the propagation characteristics of the spoof spps mode.So,we can realize a activelycontrolled slow-light effects of the spoof spps mode.Moreover,we can demonstrate that the trapped position of a certain frequency of the terahertz waves can be moved continuously along the structure in subwavelength scale by ingenious controll of the refractive indices of silicon.Finally,we designed a terahertz refractive index sensor based on spoof spps waveguide,and the performance was analyzed by the finite element method,the sensor can realize the high sensitive sensing.Finally,we design two kinds of terahertz spoof spps coupler and realize ultra-wideband and high-efficiency mode conversion from conventional guided wave mode to spoof spps mode,which can help solve the difficulties in feeding and extracting signals efficiently for terahertz spoof plasmonic devices.We investigate the dispersion relations of the spoof spps supported by the metallic grating with graded period and metallic grating with graded groove width.By using a tapered parallel-plate waveguide,the incident energies are efficiently compressed and coupled into a subwavelength gap.Then,the momenta differences are mitigated with the two kinds of graded grating.Then,we analyze the performance of two couplers with the finite element method(FEM),utilizing commercial software COMSOL Multiphysics.The numerical simulations show that the relative bandwidth reaches up to 88.9%,and the maximum coupling efficiency is 99% for the first kind of coupler;for the second kind of coupler,the relative bandwidth reaches up to 129.8%,and the maximum coupling efficiency is 99%.These two spoof spps couplers have the advantages of high efficiency and ultra broadband,and they are easy to be manufactured.The work provides a technical support for the applications of terahertz spoof plasmonic devices. |
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