Terahertz Functional Devices Based On Metamaterials

Terahertz(THz)technology has drawn increasing attentions around the world due to its potential applications in various cutting-edge fields.Developing functional devices at THz frequencies will greatly promote the practical applications of the THz technology.However,such functional devices based on traditional methods are either rare or expensive.Metamaterial is a kind of artificial materials that can manipulate the electromagnetic wave in a controllable manner,which provides an effective method for designing THz functional devices.In this dissertation,we investigated various THz functional devices based on metamaterials.The main content are summarized as follow:1.Analog of the quantum phenomenon of electromagnetically induced transparency(EIT)using metamaterials has gain much interests.However,nearly all the EIT metamaterial structures are strongly relied on the incident polarization.Here,we proposed an EIT metamaterial that consists of structures with 4-fold rotation symmetry in the THz range.The experimental and simulated results show that its function is polarization-independent.The in-depth mechanism of such structure is also well explained using coupled-mode theory.The polarization-independent feature of our design may make it more reliable in the practical applications.2.Metamaterial analogs of EIT have achieved great success.However,its counterpart,electromagnetically induced absorption(EIA),has only been sparely explored.Meanwhile,the existed several works on EIA metamaterials only show small absorption feature,limiting their application range in practice.Here,we propose a new kind of EIA metamaterials that is made up of three resonators in the THz range,which shows obvious absorption feature.The experimental,simulated and theoretical results are agreeing well with each other.Our design may find its application in absorptive photonic switches.3.Recently,controlling the abrupt phase change using metasurfaces has become a hot topic.Using metamaterial resonators to control the local phase at the interface can freely generate nearly arbitrary wavefronts,which is very promising in realizing flat photonic devices.Here,based on such strategy,we proposed a kind of C-shaped resonators to control the output phase and thus wavefront of the THz wave.A broadband THz deflector and a Fresnel meta-zone plate are designed and experimentally demonstrated,illustrating a good agreement with the theoretical predict.Our designs may find their applications in realizing planar spatial THz modulators.4.Currently,the efficiency of most phase control metasurface devices are very low.Meanwhile,they suffer from serious Omega loss due to their metallic components.To overcome them,metamaterials made from dielectric structures are excellent alternatives.Here,we propose a kind of dielectric metamaterials made from silicon to efficiently control the phase of the THz wave.Besides,we also introduce amplitude control strategy to fully control the THz wavefront.Three meta-gratings are designed,where the experimental results are in good consistency with the simulation and theory.Our designs will be very promising in high-efficiency THz spatial modulators.5.Surface wave(SW)is kind of electromagnetic wave that propagates at metal-dielectric interface and is very promising in the next generation of on-chip photonic devices.So far,controlling the wavefront of the SW mostly relies on engineering the propagation phase of the SW or the excitation wave.Here,we propose a new platform of controlling the SW launching wavefront by introducing the phase control concept in the free-space case with metallic apertures in the THz range.Polarization-controlled anomalous SW launching and focused/diverged SW wavefront are achieved.Besides,the proposed designs can also be used in polarimetry and refractive index sensing.Our designs have tremendous potentials in achieving THz circuitries.