Design Of Terahertz Metamaterial Resonators Based On Guide Mode Resonance

Metamaterial(MM)is a kind of artificial composite material whose unit cell is cyclically arranged in subwavelength.Because of its electromagnetic effect,such as negative refractive index,perfect lens imaging and stealth clothing,which is not possessed by nature materials,MM have received much interests by researchers over the world.Resonance is a fundamental feature of MMs,which can be evaluated by resonant quality factor(Q).Due to the loss of metallic materials and the loss of resonant radiation in the MMs,the Q value of the MMs is very low,which limits its application in narrowband filters and high sensitivity sensing fields.In this paper,the guided-mode resonances in the waveguide gratings are introduced into MMs,based on which different structures of planar MM are designed and fabricated.The behavior of the guided mode resonance(GMR)including Q values are mainly studied theoretically and experimentally.The main research work includes:(1)Based on the metallic single-closed-ring resonator,a planar MM composed of two-closed-ring resonantor is designed.By changing the size of the two resonant rings,thereafter the strength of the MM's grating,the characteristics of the resonance excited by MM grating diffraction and coupled to the waveguide mode is easily manipulated.Electromagnetic simulation using simulation software show that the closer the size of the two rings,the higher the value of the(GMR),and can reach up to 10~3 or more.When the two resonant ring are in the same size,the GMR disappears.The phenomenon of electromagnetic induction transparency(EIT)was studied,and its application in angle measurement also was discussed.The devices designed were fabricated by laser direct writing and electroless copper plating method,and the transmission spectrum was measured by THz-TDS system and the result is satisfactory.(2)The planar MMs composed of four-closed-ring resonators were designed and fabricated.The GMR can not only be adjusted by the ring size,but also insensitive to the polarization of the incident electromagnetic wave.The simulation and theoretical derivation show that the show that both the TE guide mode and TM guide mode are excited by two oblique MM gratings at the same time,resulting in polarization sensitivity of the guide.In addition,the experimental result is satisfactory.(3)An MM consisting of two-split-ring resonators is designed.The simulation results show that only one broadband(low Q)TE mode resonator is excited when the open positions of the two rings are symmetrically distributed.When the two gaps move,another TM guided mode will be excited except the TE mode.The Q value can be easily adjusted by the gap's position.The influence of the shift of the two gaps on the resonant characteristics of the guide ring is calculated.The result is that the smaller the translational amount of the two split rings,the higher the Q value of the GMR.By combining the guide mode resonance and the planar MMs,not only the GMRs can be easily manipulated,and its Q value greatly improved,but also the structure of MM is very simple,easy fabricated and tested.This kind of devices are of potential in applications,such as in narrowband filter and ultra-sensitive label-free sensing.