Dynamic metamaterials towards terahertz applications
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Abstract
Metamaterials (MMs) and metasurfaces (MSs) as artificially engineered materials have revolutionized research for efficient manipulation of electromagnetic waves. Recent trends in MMs and MSs research have advanced towards the realization of modulated MMs and MSs that enable real-time control, thereby creating exceptional opportunities in the field of active and dynamic MMs and MSs via external stimulus such as electrical control, thermal gradient, optical excitations among others.
In this work, fundamental physics and engineering applications have been investigated in several dynamic THz metamaterial designs. An optically tunable broadband silicon membrane metasurface absorber is introduced at first with the effective medium theory (EMT) analysis to explain the broadband absorption. The optical tunability is further acheived by optical pump, providing a promising platform to realize compact terahertz devices including detectors, modulators, and switches. Then, a vanadium dioxide (VO2)-integrated metamaterial is investigated with enhanced amplitude modulation upon traversing the insulating-to-metal transition (IMT). Neither Maxwell-Garnett nor Bruggeman EMT adequately describes the observed frequency shift and amplitude decrease during the phase transition. However, a Drude model incorporating a significant increase of the effective permittivity does describe the experimentally observed redshift. Our results highlight that symbiotic integration of metamaterial arrays with quantum materials provides a powerful approach to engineer emergent functionality. Finally, dynamic bound states in the continuum (BIC) is achieved from both a thermally-actuated bi-layer metamaterial and an optically tunable all-silicon metamaterial. Coupled mode theory (CMT) is implemented in both designs to explain the dynamic BIC responses. Both designs provide potential
applications for nonlinear optics and light-matter control at terahertz frequencies.
This thesis work demonstrates several potential methods towards functional terahertz devices through integration of metamaterials with MEMS technology for dynamic light-matter interactions.