Research On Terahertz Functional Devices Based On Surface Plasmon Resonance

With the rapid development of terahertz technology,many excellent characteristics of terahertz wave have been found and show great application value in many fields.However,the terahertz functional devices,compared with the rapid development of terahertz sources and detectors,are developed relatively slowly,which restricts the wide application of terahertz technology.Thus,it is of great significance to research the terahertz functional devices.Surface plasmon resonance(SPR)has unique properties,including the enhanced transmission effect and the near-field enhanced effect.Based on the enhanced transmission effect,terahertz wave with specific frequency can pass through the periodic subwavelength array structure with a high transmittance.Based on the near-field enhanced effect,the interaction between terahertz wave and medium can be enhanced.As a result,performance of the functional devices can be improved.Utilizing the above effects of SPR,research on terahertz functional devices can be promoted.In this article,research on terahertz functional devices based on the SPR of metal and the SPR of graphene are carried out.The main research contents and innovations are as following:(1)A terahertz dual-band band-pass filter based on "metal-dielectric-metal"(MDM)structure with periodic circular-loop-shaped air slots patterned on both metal layers is proposed.The transmission characteristics of the MDM structure are researched,including the propagating surface plasmon resonance(PSPR)and the localized surface plasmon resonance(LSPR)in this structure,the influence of structure parameters and so on.Based on theoretical analysis and simulation results,a prototype is designed and fabricated.The experimental results show that the center frequency and Q-value of the two narrow bands are 0.293 THz and 20.9,0.323THz and 40.4,respectively,which are better than the results in some papers.(2)A terahertz modulation scheme based on the Si-MDM structure is proposed.In the Si-MDM structure,the near-field enhanced effect is used to enhance the interaction between terahertz wave and silicon wafer.As a result,the performance of the terahertz modulation scheme based on the photoconductive effect of silicon wafer can be improved.Simulation results show that the modulation depth of the Si-MDM structure at frequency of 0.302 THz and 0.324 THz is 60%and 97%,respectively,while the modulation depth of silicon wafer is only 17%.The experimental results show that the modulation depth of the Si-MDM structure at frequency of 0.3 THz is 63%,while the modulation depth of silicon wafer is only 49%,which confirms the feasibility of Si-MDM structure in terahertz modulation.(3)Utilizing the different characteristics of LSPR and PSPR,a terahertz polarization filter based on the MDM structure with periodic rectangular-loop-shaped air slots patterned on both metal layers is proposed.The influence of structural parameters on the polarization filtering performance of the structure is analysed based on a lot of simulation results.A prototype is designed and fabricated for measurement considering the current experiment conditions.The measured maximum extinction ratio is 16.4 dB at the frequency of 0.347 THz.Different from the traditional wire grid structure,the proposed structure has both frequency selectivity and polarization selectively,which is significant for terahertz technology.(4)Self-gated graphene monolayers with antidot arrays structure is proposed and terahertz functional devices based on the structure are researched.Transmission characteristics of the structure and the influence of graphene material properties and structural parameters on the transmission characteristics are researched systematically.The proposed structure can be used to realize terahertz functional devices,including:terahertz narrow-band band-stop filter(Q value is 58.6),terahertz modulator(modulation depth is 98.04%),refractive index sensor(sensitivity is larger than 1.5 THz/RIU)and polarization filter(extinction ratio is 16.6 dB).