| Metamaterials,defined as composite arrays of artificial subwavelength structures,have attracted enormous attention in the scientific community due to their novel physical phenomena which are not available in natural materials.Their appearance breaks the limitation of traditional material design schemes and provides a new paradigm for manipulating electromagnetic wave in the micro/nano scale.Based on the novel microfabrication technologies,a series of planar and three-dimensional metamaterials are designed and fabricated in this thesis.The frequency,phase and spin of light or electromagnetic wave are effectively controlled by using the electromagnetic resonance characteristics of the proposed metamaterials.Meanwhile,the corresponding optical modulation mechanism is investigated in details.The main contents of the thesis are shown in the following six sections:Firstly,a novel metamaterial composed of two mirror-symmetric joint split ring resonators(JSRRs)that support extremely sharp trapped-mode resonance with large modulation depth in the terahertz region is experimentally demonstrated.The electromagnetic response characteristics of mirror-symmetric metamaterial in terahertz regime are simulated by finite difference time domain method,and the mechanism of the electromagnetic resonance responses are explored.The ultrasharp resonance occurs near the Wood-Rayleigh anomaly frequency.At the resonant frequency of 0.71 THz,the quality(Q)factor of the resonance of mirror symmetric metamaterials is as high as 60,which is one order of magnitude higher than that of the traditional metamaterials.The strong coupling between the in-plane propagating collective lattice surface mode originating from the array periodicity and localized surface plasmon resonance in mirror-symmetric JSRRs significantly enhances the coupling efficiency between terahertz wave and metamaterials,which dramatically reduces radiative damping.Moreover,the mirror coupling of the JSRRs greatly restrains the radiation loss of the system,and thus gives rise to the high-Q-factor resonances.This mirror symmetric metamaterial with ultrahigh Q factor resonances shows great potential for multifunctional applications such as high-performance narrow-band filters,ultrasensitive biochemical sensors,optical modulators,plasmonic switching,and low-power nonlinear processors.Secondly,double extremely high-Q-factor resonances is simultaneously obtained in a terahertz metamaterial composed of mirror-symmetric-broken double split ring resonators.In a regular mirror-arranged SRR array,only the low-Q-factor dipole resonance can be excited with the external electric field perpendicular to the SRR gap.Breaking the mirror-symmetry of the metamaterial leads to the occurrence of two distinct otherwise inaccessible ultrahigh-Q-factor modes,which consists of one trapped mode in addition to an octupolar mode.By tuning the asymmetry parameter,the Q factor of the trapped mode can be linearly modulated,whilst the Q factor of the octupolar mode can be tailored exponentially.For specific degree of asymmetry,our simulations revealed a significantly high Q factor(Q>100)for the octupolar mode,which is more than one order of magnitude larger than that of conventional metamaterials.The mirror-symmetry-broken metamaterial offers the advantage of enabling access to two distinct high-Q-factor resonances which could be exploited for ultrasensitive sensors,multiband filters,and photodetectors.Thirdly,an approach to achieve multispectral plasmon-induced transparency is experimentally demonstrated by using hyperfine terahertz metamaterials.The characteristic size of this hyperfine terahertz metamaterial is one order of magnitude smaller than that of the traditional terahertz metamaterial.Numerical simulation and experimental results show that double and triple plasmon-induced transparent windows can be achieved in this hyperfine terahertz metamaterial.Hyperfine terahertz metamaterials provide a large group delay at each transparent window,significantly reducing the corresponding the group velocity of terahertz wave.In the hyperfine terahertz metamaterials,the bright modes can be independently coupled with each quasi-dark mode to excite the plasmon induced transparency window,which makes it possible to accurately control the group velocity and delay bandwidth of transmitted terahertz waves.This hyperfine terahertz metamaterials can be used in optical switching,optical data storage,quantum computing and terahertz communication.Fourthly,a novel three-dimensional toroidal metamaterial was fabricated by focused ion beam induced deformation techniques.Based on this three-dimensional folded metamaterial,surface-plasmon-polariton mediated multiple high-Q-factor toroidal dipole resonances is experimentally demonstrated at infrared frequencies.Field distributions clearly manifest the existence of the toroidal mode with tightly confined magnetic vortex in the subwavelength 3D structures.The metamaterialexhibiting high-Q-factor toroidal resonances may have broad applications in ultrasensitive biochemical sensors,light modulator,narrow-band filters,nonlinear optics,and low-threshold plasmonic laser.Fifthly,an approach to realize spin-selective transmission in the infrared region is experimentally demonstrated based on folded metasurfaces that possesses pronounced intrinsic chirality.The folded metasurface,consisting of folded anti-symmetric SRRs,are capable of transmitting one spin state of light whilst largely prohibiting the other.With the optimization of the folding angle,a remarkable circular dichroism as large as0.7 and the maximum transmittance of the selected spin of circularly polarized light exceeding 92% is experimentally demonstrated in the infrared regime.The intrinsic chiral optical response of the folded metasurface mainly arises from the electric-magnetic dipole coupling as well as contribution from the electric quadrupole and toroidal dipole moments.The proposed folded metasurface may be applied to a range of novel photon-spin selective devices for optical communication technologies and bio-photonics.Finally,a folded ?-shaped metasurface that can implement multispectral spin selective transmission at infrared frequencies is experimentally demonstrated.The intrinsic chiral configuration is achieved by folding the ?-shaped metasurface along the vertical direction to break the mirror symmetries.A remarkable circular dichroism approaching unity(0.8)is experimentally achieved,with the maximum transmittance of the selected spin of circularly polarized light exceeding 93%.The folded ?-shaped metasurface provides a straightforward strategy for achieving and manipulating intrinsic 3D chirality and has great potential for applications in photon-spin selective devices and chiral bio-molecule identification. |
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