Design, Fabrication, And Characterization Of Terahertz Metamaterials Devices

Metamaterials is a kind of artificial composite materials that composed ofmetal unit cell with sub-wavelength scale. With proper design of metamaterials,numerous intringuing phenomena that not exhibited in naturally can be realized, suchas invisible cloaking, perfect absorption, negative refractive index and so on. Withthe development of terahertz technologies, the reports about terahertz metamateralsdevices are increasing, like terahertz filter, absorber, wire-grid polarizer, etcetera.These terahertz metamaterials devices have great potential applications in terahertzimaging, spectroscopy, and biosensor, Most terahertz metamaterials devices arefabricated by using photolithographic fabrication techniques, which is very complexand time-consuming, and expensive. So, it’s necessary to find a low-cost, simple, andflexible way to process microstructure. In this paper, we firstly proposed andfabricated terahertz devices on polyimide substrate by using laser-induced andchemical non-electrolytic plating with copper at home. Designed terahertz wire-grid，TU-shaped resonator, and multiband filter based on three nested closed-ringsresonators (CRR) by using CST Microwave Studio, and we investigated the spectralresponse of the fabricated devices experimentally with terahertz time-domainspectroscopy (THz-TDS). It will be seen that the experiment results are in goodagreement with the simulated data. Ours original works are listed as follow：(1) We have studied the way to fabricate terahertz device on polyimide (PI)substrate by using laser induced and non-electrolytic plating with copper, includingthe laser exposure system, the technological process of fabrication, and the methodof non-electrolytic plating with copper. Now, the spatial resolution of our fabricationprocess is about7μm which is meeting the preparation condition of most terahertzdevices. And we experimentally results demonstrate that the laser induced andnon-electrolytic plating with copper is a simple, flexible and effective way tofabricate terahertz devices.(2) We numerically analyzed the performance of the wire-grid polarizer by varying the period of the wire-grid，the fill factor, and the thickness of the copper. Inthe current preparation process conditions within the permitted, selection of anoptimal parameter and fabricated a wire-grid polarizer. The experimentally resultsdemonstrate that the transmittance of TM-polarized wave of the fabricated polarizerwas over54%. The extinction ratio was better than20dB between0.2THz and1.5THz, and over37dB at0.3THz, these are accordance to the reports of wire-gridwith silicon or high density polyethylene substrate.(3) We firstly proposed and fabricated a terahertz resonator composed ofindividual T-and U-shaped microstructure, and we investigated the spectral responseof the fabricated devices both numerically and experimentally. The experimentalresults show that different polarized illumination sources have different resonantfrequencies. When the polarizations parallel to the gap between T and U-shape, thesystem supports a triple-band response at0.37THz,0.73THz and0.96THz in the0.2-1.2THz frequency range, while for the polarizations perpendicular to the gapbetween T and U-shape, it provides just one resonant peak at0.84THz. In order tounderstand the physical origin of the response, we monitored the field distributions atthe distinct resonance peaks. We also numerically analyzed the spectral performanceby varying geometrical parameters of the TU-shaped when the polarizations parallelto the gap between T and U-shape.(4) We firstly proposed and fabricated a terahertz multiband filter using threenested closed-rings resonators (CRR) on polyimide substrate. We numericallyanalyzed the physical origin of the multispectral response and discussed thedependence of the resonance frequencies on the geometrical parameters of theclosed-rings. And we found that the three resonant peaks of the proposed filteroriginate not only from the dipole electric response of the three rings, the magneticresponse between the adjacent rings, but also the effect from inner or outer CRR. Theexperimental results show three distinct resonant peaks at0.33THz,0.68THz and1.13THz, which are in good agreement with CST simulations.