Thèse des Guides d'Ondes Thz en Plastique aux Systèmes Guidés Complexes Boîte à Outils de Conception et Démonstrateurs de Détection Basés sur la Technologie Fmcw H/F

Doctorat.Gouv.Fr

Établissement : Université de Bordeaux École doctorale : Sciences Physiques et de l'Ingénieur Laboratoire de recherche : Laboratoire de l'Intégration du Matériau au Système Direction de la thèse : Jean-Paul GUILLET ORCID 0000000344348052 Début de la thèse : 2026-10-01 Ce projet de thèse vise à développer un écosystème cohérent de composants guidés térahertz à base de guides d'onde plastiques, afin de permettre la conception rapide de systèmes THz intégrés, compacts et robustes. Le travail portera sur l'optimisation, la fabrication additive et la caractérisation de guides d'onde, coupleurs, transitions, diviseurs de puissance, multiplexeurs et diplexeurs/duplexeurs. Les composants seront étudiés par simulations électromagnétiques, notamment FDTD, puis validés expérimentalement à l'aide des plateformes disponibles à l'IMS : spectroscopie THz temporelle, analyseur de réseau vectoriel jusqu'à 750 GHz et radars FMCW.

L'objectif final est d'assembler ces briques technologiques en systèmes guidés complexes pour des applications de détection, d'imagerie et de contrôle non destructif. Une attention particulière sera portée aux architectures associant guides d'onde plastiques et radar FMCW, afin de proposer des solutions THz plus compactes, stables et accessibles. Le projet contribuera ainsi au développement d'une boîte à outils réutilisable pour l'instrumentation THz, avec des perspectives en inspection industrielle, analyse de matériaux et futurs systèmes de télécommunications haute fréquence. Terahertz (THz) technology is attracting growing interest for sensing, imaging, and spectroscopy because THz waves are non-ionizing and can reveal material properties that are difficult to access with optical or microwave methods [1]. In parallel, guided THz propagation is developing rapidly: although waveguides were initially driven by telecommunication needs, they are increasingly relevant for sensing-oriented systems where compactness, stability, and robust alignment are critical [2].
Among the different THz guiding solutions (metallic, planar, hollow-core), plastic waveguides are particularly promising thanks to their low loss potential, low cost, and strong compatibility with additive manufacturing [3]. However, the current research landscape remains fragmented: many plastic THz waveguides have been demonstrated [4], but far fewer studies address the essential system-level elements such as efficient connections, couplers, transitions, and guided functionalities (power dividers, diplexers/duplexers, multiplexers). This lack of a coherent waveguide ecosystem limits the development of complex THz guided systems.
Developing a complete set of compatible plastic waveguides and guided components therefore represents a timely opportunity to enable advanced THz systems-not only for future telecom/6G perspectives, but also for practical sensing and imaging [5,6]. In particular, combining such guided optics with FMCW radar approaches can open a route toward compact, robust, and lower-cost THz inspection platforms for nondestructive testing and scientific measurements [7]. The scientific objective of this PhD is to develop a coherent ecosystem of low-loss, low-cost plastic terahertz guided components enabling the rapid design and integration of complex THz guided systems. A first objective is to optimize and experimentally validate the core building blocks required for system-level integration: plastic waveguides, efficient couplers, low-reflection transitions (including interfaces to other guiding solutions or free-space), and key guided functionalities such as power dividers, multiplexers, and diplexers/duplexers. This will be supported by a practical design toolkit (simulation models, component libraries, and performance metrics) to ensure compatibility and scalability across the different elements. A second objective is to assemble these validated components into integrated guided THz systems, with a focus on sensing architectures coupled to FMCW radar techniques. The goal is to demonstrate compact and robust guided systems that can support advanced sensing and imaging use-cases, ultimately providing a reusable technological framework for future THz instrumentation. Rather than optimizing isolated components, this project follows a system-driven approach: it will first build a consistent set of compatible plastic THz guided elements, then use this toolbox to design and demonstrate complex guided sensing/imaging systems.
3.1 Plastic Waveguide ecosystem
The first part focuses on building the plastic waveguide ecosystem. Although several THz guiding solutions exist (metallic, planar, or hollow-core), plastic waveguides are particularly attractive because they can offer low loss while remaining low cost and compatible with additive manufacturing. Today, the main limitation is not only the waveguide itself, but the lack of system-level elements that make a technology usable in practice: efficient couplers, low-reflection transitions and interconnects, and optimized guided functionalities such as power dividers and diplexers/duplexers. These elements will be designed and optimized through electromagnetic simulations, mainly using FDTD approaches, in order to obtain compact, low-loss, and fabrication-tolerant geometries. The components will then be fabricated by additive manufacturing and iteratively improved based on experimental feedback. Characterization will rely on complementary platforms available at IMS, including THz time-domain spectroscopy (Teraview system), a vector network analyzer up to 750 GHz, and FMCW radar setups, allowing detailed extraction of propagation losses, coupling efficiencies, reflections and S-parameters across the targeted frequency bands.
3.2 Guided THz optical systems
The second part aims at going beyond component characterization by assembling the validated building blocks into integrated guided THz systems. While much of the literature concentrates on waveguide performance alone, the objective here is to leverage the IMS component framework to conceive multi-element architectures that integrate couplers, transitions, power dividers and diplexers/duplexers within the same guided platform. Building on previous demonstrations of guided reflectometric imaging using both pulsed and FMCW approaches, the project will extend toward more advanced sensing and imaging demonstrators, including multi-band systems operating between 100 and 300 GHz, architectures combining FMCW and TDS capabilities, and guided/endoscopic-like concepts for complex or confined environments. Full-system experiments will include calibration strategies and data processing for sensing and imaging, with performance evaluated through application-relevant metrics such as stability, repeatability, contrast and resolution. The overall workflow-from simulation and fabrication to measurement and system demonstration-will provide a practical pathway to rapidly design and implement complex THz guided systems based on a coherent ecosystem of plastic waveguide components.