DESIGN AND ANALYSIS OF TERAHERTZ METASURFACE DEVICES

Abstract

Terahertz (THz) metasurfaces have emerged as versatile platforms for subwavelength control of electromagnetic waves, enabling compact, high- performance devices for sensing, imaging, and communication. Conventional THz metasurfaces based on noble metals suffer from inherent ohmic losses. All-dielectric designs reduce non-radiative losses but remain limited by radiative leakage, which constrains electromagnetic field confinement and suppresses the Q-factor of resonant modes. Overcoming these challenges is essential for advancing high-Q, high- sensitivity THz devices. This thesis presents the systematic design and analysis of novel THz metasurface structures that exploit resonant phenomena such as surface plasmon polaritons (SPPs), toroidal dipole resonances (TDRs), and bound states in the continuum (BIC), to enhance light–matter interactions and achieve superior device performance. First, InSb-based plasmonic metasurfaces are explored, demonstrating ultrahigh sensing capabilities in both temperature and refractive index sensing. This is followed by the introduction of all-dielectric metasurfaces to minimize non-radiative losses. Radiative suppression is then achieved through TDR and BIC enabled metasurface structures, which deliver sharp resonances and strong field localization. The TDR-based metasurfaces exhibit selective biomolecular detection capabilities, including the ability to distinguish between healthy and malaria-infected red blood cells. BIC-based metasurfaces, transformed into quasi-BIC modes via symmetry breaking, yield ultra-narrow linewidths and enhanced figures of merit through structural optimization. Multipolar analysis has been used to reveal the underlying physics of the excited modes, while structural tunability provides additional design flexibility. The metasurfaces designed and reported in this thesis enable applications such as refractive index sensing, temperature monitoring, and label-free biomolecular diagnostics. Collectively, these results establish a pathway for compact, high- performance THz devices with significant potential in precision sensing, nonlinear optics, and on-chip optoelectronic integration.