Research On Metamaterials Analogy Of Electromagnetically Induced Transparency

Electromagnetically induced transparency(EIT)is a coherent process in three-level atomic systems,which induces EIT transparency window with characteristics of strong slow light and frequency-selection within orginal broad absorption spectrum.Those properties have wide applications such as slow light propagation,optical signal processing,optical data storage,sensors,quantum switch and four wave mixing.However,the generation of EIT needs harsh experimental enviroments,such as extremely low temperature and high intensity lasers,have significantly limited the application of EIT.Zhang et al.theoretically investigated EIT-like with metamaterials at terahertz frequency.Metamaterial EIT-like since then have obtained wide attention.In order to distinguish between EIT in three-level atomic systems and metamaterial analogy of electromagnetically induced transparency,metamaterial analogy of electromagnetically induced transparency is abbreviated as EIT-like.EIT-like can be obtained at room temperature and do not need severe experimental enviroments compared with EIT in three-level atomic systems.The transparency window of EIT-like can be changed by adjusting the size and the coupling distance of the unite resonators.In additon,EIT-like provide a new way to investigate EIT behaviors.In this dissertation,two kinds of new coupling ways are proposed,which can lead to large group index and delay-bandwidth product.Toroidal dipolar resonsator has lagre Q factor,which can be used to deisign low-loss EIT-like.Meanwhile,a non-centrosymmetric EIT-like structure has been proposed,which can cause polarzation insensitive of EIT-like at specific polarization angles.Finally a new way to tailor the Q factor of transparency window of EIT-like has been proposed and the affect of the spatial distribution of four split ring resonator(SRR)to Q factor of transparency window of EIT-like has been investigated.The main innovations of this dissertation are as follows:1.A novel coupling way to realize EIT-like has been proposed,which is simultaneously exciting the electric and magnetic resonance.EIT-like structure consists of the cut wire and SRR.The cut wire and SRR are placed face-to-face along the magnetic field direction.When the electric field direction is along the cut wire and the magnetic field dirction is perpendicular to SRR,which causes that the electric and magnetic resonance can be simultaneously excited.The destructive interference between the cut wire and SRR leads to the transparency window of EIT-like with large group index and strong slow light.The coupling way of the simultaneously exciting the electric and magnetic resonance isdifferent with the existed coupling way of the electric resonance near field coupling to magnetic resonance.EIT-like based on simultaneously exciting the electric and magnetic resonance have large coupling distance and group index compared with EIT-like based on electric resonance near field coupling to magnetic resonance.2.Another novel coupling way to realize EIT-like has been proposed,which is the magnetic resonance near field coupling to electric resonance.The magnetic resonance consisting of six SRR has low Q factor.Six SRR and the cut wire are put on the surface of the FR-4 dielectric substrate.When the incident magnetic field is perpendicular to SRR and the incident electric field is perpendicular to the radial direction of the cut wire,which makes sure that the magnetic resonance can be excited and the electric resonace cannot be excited.The electric resonance can also be excited through the near field coupling of the six SRR.The destructive interference between six SRR and the cut wire leads to the transparency window of EIT-like with large delay-bandwidth product,which has potential application in communication systems.3.A low loss EIT-like has been obtained.Toroidal response can confine the electromagnetic energy inside a dielectric substrate with toroidal geometry,which has large Q factor.The toroidal resonator has been realized with metamaterials and used to design low-loss EIT-like.The toroidal resonator has been chosen as the dark mode.When the destructive interference occurs,the electromagnetic energy is concentrated around the toroidal resonator.The toroidal resonator prevents the radiation of the electromagnetic energy,which can cause low loss EIT-like.4.Tailoring polarization of EIT-like has been realized.Tailoring polarization of EIT-like with non-centrosymmetric metamaterials has been numerically and experimentally demonstrated,which is polarization insensitive of EIT-like transparency window at specific polarization angles.The rectangle ring resonator has the features of the polarization insensitive at specific polarization angles.When two cut wires are perpendicular to each other,which have the features of the polarization insensitive at specific polarization angles.When the rectangle ring resonator and the two cut wires are put together,which make sure that the transparency window of EIT-like is polarization insensitive at special polarization angles.5.A common way to improve the Q factor of the transparency window of the EIT-like has been provide.The effect of the spatial distribution of four SRR to Q factor has been investigated.The results show that four SRR based on centrosymmetric structure has a large Q factor.The Q factor of dark mode has direct impact on the Q factor of transparency window of the EIT-like.Four SRR based on centrosymmetric structure has been chosen as the dark mode.Therefore,large Q factor oftransparency window can be obtained.The proposed design provides a common way to improve the Q factor of the transparency window of the EIT-like.