Research On Tunable Terahertz Wave Devices Using Metamaterials And Photonic Crystals

In recent years, the terahertz science and technology has become theresearch hotspot in the field of electromagnetics, as a new frontier interdisciplinary.It has a far-reaching scientific value and huge development potential in a wide rangeof disciplines, such as communication, medical science, public security and so on.However, the practical application of terahertz technology is impossible without thesupport of terahertz modulators, filters, switches and other functional devices.Therefore, the lack of terahertz wave devices especially tunable devices limited thefurther development of terahertz technology, enormously. As new types of artificialmaterials, metamaterials and photonic crystals are expected to play an important rolein the development of terahertz wave devices. This dissertation mainly focused ontunable terahertz wave devices which based on metamaterials and photonic crystals,and the main research contents are summarized as follows:1. Two kinds of tunable terahertz wave absorbers are designed.(1) Opticallytunable terahertz wave absorber: As photoconductive silicon material is insertedwithin the two side gaps of the top split-ring resonator, the absorber can realizetunable absorption fuction between two frequencies by controlling the pump laserillumination. When there is no pump laser, the center absorption frequency is0.80THz and the absorptivity is0.9993. However, the center absorption frequencychanges to1.365THz with an absorptivity of0.9924when the pump laser is applied.(2) Thermally tunable terahertz wave absorber: As InSb material is very sensitive totemperature, the permittivity of InSb substrate is altered with the change oftemperature, and thus we could obtain a continuously tuned terahertz wave absorber.When the temperature increases from140K to200K, the absorption peak frequencychanges from0.480THz to0.719THz, the variation range is up to0.239THz and theabsorptivities of all the absorption peak frequencies are more than0.98. It indicatesthat the designed absorber achieves an efficient absorption function to the incidentelectromagnetic wave. 2. An optically-controlled terahertz wave switch is proposed based ontwo-dimensional square lattice photonic crystal, and the switch adopts a sidecoupling combined method of point defect and line defect. The resonance frequencyof the defect mode will be changed by controlling the refractive index of thenonlinear point defect dielectric rod, and thus the terahertz wave switch can berealized. Simulation results show that the extinction ratio, insertion loss and thehighest response rate of the switch at frequency of1.033THz achieve12.86dB,0.61dB and3.33GHz, respectively.3. Based on self-imaging principle of multimode interference, two kinds ofdual-wavelength terahertz wave power splitters are proposed.(1) Directionalcoupling type dual-wavelength terahertz wave power splitter contains two multimodecoupled regions, which are used to implement the energy distribution of two differentfrequency terahertz wave, respectively. The power splitter can keep equal energydistribution at frequency of1.20THz. However, the input beam can even be splittedwith an arbitrary ratio at frequency of1.09THz by tuning the refractive index of therods in the dashed rectangle.(2) Y branch type dual-wavelength terahertz wavepower splitter is mainly composed of a multimode coupled region and a Y-shapewaveguide. The power splitter can also split the input field equally at frequency of1.0THz. Whereas, the input beam can even be splitted with an arbitrary outputenergy ratio at frequency of0.893THz by changing the refractive index of the rod B.