Intensity based multispectral terahertz polarimetric imaging using frequency-selective surfaces

Abstract

Terahertz (THz) technologies offer unique capabilities for non-destructive sensing, material characterization, and imaging; however, their widespread adoption remains limited by the size, cost, and complexity of conventional spectroscopic and polarimetric systems. This thesis addresses these challenges by investigating reconfigurable terahertz frequency-selective surfaces (FSSs) and their integration into compact, intensity-based THz polarimetric systems, with an emphasis on scalable fabrication and practical system architectures. Following a comprehensive literature review covering THz generation and detection techniques, reconfigurable FSS concepts, and THz polarimetric spectroscopy and imaging, the core contributions focus on the development of distinct reconfigurable techniques on printed THz FSSs. Tunable spectral responses are demonstrated using inductive metallic checkerboard structures and Moiré-based FSS configurations, where reconfigurability is achieved through lateral translation and relative rotation of stacked layers, respectively. These approaches enable compact and mechanically simple spectral tuning without the need for active materials or complex biasing schemes. Free standing polarization-sensitive FSS designs are subsequently investigated to enable frequency selective polarization dependent modulation in the THz regime. Symmetric and asymmetric FSS geometries fabricated using laser-cutting techniques exhibit distinct polarization-dependent transmission characteristics, allowing their use as frequency-selective polarizers and tunable band pass filters. Building on these components, a compact multispectral THz polarimetric imaging system based solely on intensity measurements is developed using Schottky diode detector and experimental results closely followed the expected simulation results. By acquiring intensity images at multiple analyzer orientations and discrete frequencies, the system enables direct extraction of polarization metrics such as Stokes parameter (S0, S1, S2), the degree and angle of linear polarization without phase-sensitive detection and mechanical delay stages. The system is validated through polarimetric imaging of anisotropic samples, demonstrating high polarization contrast and practical robustness. Additional studies presented in the annexes extend the scope of the thesis to a compact CMOS-based THz polarimetric spectrometer with intrinsic polarization sensitivity, and a simplified pyroelectric-detector-based approach for birefringent material characterization. Collectively, this work advances reconfigurable THz FSS technologies and compact polarimetric systems, contributing toward scalable, robust, and industrially relevant THz sensing and imaging platforms.

Date	21 May 2026
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	François Blanchard (Supervisor)