Metamaterials and functional oxides for terahertz applications

Recent advances in terahertz (THz) technology have enabled a broad range of applications which includes imaging, sensing, security, spectroscopy and medicine. Although significant progress has been made in those areas, advanced optical components operating at THz frequencies are still not well established. Passive and active devices are needed for filtering, switching, spatial light modulation and sensing applications at THz frequencies. Realization of such components requires detailed investigations of new materials and advanced device design suitable for operation in this frequency range. This dissertation will present details of the fabrication and the characterization of passive and active metamaterialbandpass filters operating at THz frequencies. Different filter designs and substrate choices will be discussed. Passive filters were fabricated using symmetric and asymmetric metamaterial layers with different stacking configuration and unit-cell geometries. This method resulted in filters with superior frequency selectivity when compared to those based on single layers. Active bandpass filters with tuning capabilities were realized using a complementary metamaterial approach which combines patterned gold (Au) and vanadium dioxide (VO2) films in the same substrate. VO2 films experience an insulator to metal phase transition which can be thermally triggered. Remarkable increase in VO2 electrical conductivity by almost five orders of magnitude can be achieved across the phase transition. This attribute was used to dynamically modify the frequency response of the proposed complementary Au-VO2 metamaterial filters. Low insertion losses and center frequency tunability over 0.12 THz was achieved with the complementary filters when the substrate temperature was varied. Experimental results are supported by finite element simulation analysis.