Electromagnetic Response Studies Based On Single, Double And Three-body Resonator Metamaterials In The Terahertz Band

Recently,with the development of metamaterials in terahertz technology,metamaterials in terahertz technology play a more and more important role.One of the hottest point is to achieve a cost-effective metamaterial with broadband response and low loss,and the slow light effect origin from plasmonics induced transparency(PIT).Owing to above reasons,we investigate the mechanism of the terahertz response of monomer dimer and trimer metamolecules.With the help of experiment and numerical simulation,the electromagnetic response of metamaterials and the origin of mode interaction are revealed.Our results will be significant to improve the performance of THz metamaterials.The highlights of our works are listed as follows:Terahertz response based on Monomer metamaterials.The interaction between terahertz(THz)resonance modes and element deformation in rectangular split-ring resonator(RSRR)-based meta-atoms(MAs)is investigated experimentally.Two types of RSRR-based MAs are presented: lateral-varied SRR(LV-SRR)and arm-twisted SRR(AT-SRR).When the distances from the gaps to the opposite sides of above meta-atoms increase from 10 to 40 ?m,the inductive-capacitive(LC)resonance modes and dipole oscillation modes exhibit red shift behavior.The quality factor(Q factor)of LC resonance decreases while that of dipole oscillation modes increases.The THz mode interaction is subject to the distance between the gap and opposite side.An extension of lateral side contributes much more to the enhancement of Q factor of dipole oscillation mode than the twisted arms.The relationship between the near-field coupling effect and THz modes is revealed by the analysis of surface currents as well as the electric energy density distribution,as is in agreement with the experimental results.The evolution of terahertz resonance modes in an individual split-ring resonator(SRR)is investigated experimentally by locally structural deformation.The length reduction of opposite-side results in a frequency blueshift of resonance modes.Simultaneously,the Q fact or of inductive–capacitive oscillation mode is enhanced while the dipole oscillation is suppressed.The n?merical simulation indicates that the lateral-side and arms will take the place of opposite-side contributing to the dipole oscillation in deformed SRR.A further apex-angle increasing leads to a huge couplingloss so that the dipole oscillation is suppressed in right triangle SRR and obtuse triangle SRR.We reported a broadband terahertz(THz)plasmon-induced transparency(PIT)phenomenon owing to asymmetric coupling in between the bright-and-dark resonators inmeta-molecules(MMs).Each MM contains a cut-wire resonator and a couple of identical size and gap opposite-directed U-shaped resonators in mirror symmetry.An upside displacement of cut-wire induces an asymmetric deviation of cut-wire away from the X-axis in the MMs.Then,the PIT effect occurs due to the asymmetric coupling of dark resonators.The width of the transparency window extends monotonically with the deviation increasing.A picosecond scale group delay of the THz wave is found at the transparent windows.The distribution of surface currents and electric energy reveals that the asymmetric coupling between cut-wire and U-shaped resonators results in an energy transfer from surface plasmon(SP)oscillations to the inductive-capacitive(LC)oscillation due to the local symmetry breaking in structures of MMs.A couple of counteract SPs cause the transparency window,while the LC resonance gives rise to the side modes in the THz frequency spectr?m.Furthermore,the LC oscillations of side modes take place in between the cut-wire and the local area of the U-shaped resonators,which leads to a magnetic dipole moment?m.The displacement of cut-wire leads to an asymmetric distribution of magnetic moment?m in MMs,which extends the width of the transparency window.Our experimental findings present a new approach to develop broadband slow-light devices in the THz frequency range.We demonstrate a localized slow light phenomenon in a symmetry broken metamolecule(MM)of conductively coupled dark resonators at a terahertz band.Under a dark-mode excitation condition,the single mode resonance becomes dual modes by breaking the uniaxial symmetry of MM.Thus,a transparency window exists in between dual modes.An interaction of V-shaped plasmonic antenna-type(VA)resonances results in a plasmon induced transparency(PIT)when the asymmetric deviation is below 13 ?m.A maxim?m 25.9 ps group-delay of incident THz pulse is observed at the transparency window.When the asymmetric deviation is beyond 13 ?m,one excitation pathway switches from VA resonance to the inductor-capacitor(LC)resonance,which dominates the high-frequency side-mode.Then,the PIT effect transfers to the PIT-like behavior and the slow light phenomenon vanishes.The aforementioned discovery allows for a speed modulationof slow light via symmetry breaking in MM.We experimentally investigate the terahertz(THz)electromagnetically-induced transparency(EIT)-like phenomenon in a metamolecule(MM)of three-body system.This system involves a couple of geometrically identical split-ring resonators(SRRs)in orthogonal layout conductively coupled by a cut-wire resonator.Such a three-body system exhibits two frequency response properties upon to the polarization of incident THz beam:One is the dark bright-bright layout to the horizontally polarized THz beam,where there is no EIT-like effect;the other is bright-dark-dark layout to the vertically polarized THz beam,where an EIT-like effect is observable.The transparency window can be tuned from 0.71 THz to 0.74 THz by the displacement of cut-wire inside the trimer MM.A maxim?m of 7.5 ps group delay of THz wave is found at the transparent window of 0.74 THz.When the cut-wire moved to the midpoint of lateral-side of SRR,the EIT-like phenomenon disappears,this leads to a localized THz slow-light effect.The distribution of surface currents and electric energy reveals that the excited inductive-capacitive(LC)oscillation of bright-SRR dominates the high frequency side-mode,which is isolated to the displacement of cut-wire resonator.However,the low frequency side-mode originates from the constructive hybridization of LC resonance in dark SRR coupled with a localized S-shaped dipole oscillator,which is tunable by the displacement of cut-wire.As a consequence,the group delay as well as the spectral configuration of transparency window can be manipulated by tuning one side-mode while fixing the other.Such an experimental finding reveal the EIT-like effect in a conductively coupled three-body system and manifests a novel approach to achieve tunable THz slow-light device...