<p dir="ltr">This thesis presents novel methodologies to integrate AI-driven and physics-inspired methodologies into photonic inverse design, setting new benchmarks for high-performance photonic devices in different branches of photonics. By blending advanced computational techniques with the foundational principles of electromagnetism, this research tackles key challenges in optimizing device efficiency, robustness, and functionality. The aim is to propel photonic technology beyond its current capabilities, offering transformative solutions for a range of novel applications.</p><p dir="ltr">The first major contribution focuses on adjoint-based topology optimization for on-chip single-photon coupling. We developed an adjoint topology optimization scheme to design high-efficiency couplers between photonic waveguides and single-photon sources (SPSs) in hexagonal boron nitride (hBN). This algorithm addresses fabrication constraints and SPS location uncertainties, achieving a remarkable average coupling efficiency of 78%. A library of designs is generated for different positions of the hBN flake containing an SPS relative to a silicon nitride (SiN) waveguide. These designs are then analyzed using dimensionality reduction techniques to investigate the relationship between device geometry and performance, infusing the design process with deep physical intuition and insight.</p><p dir="ltr">The second key advancement is presented through a neural network-based inverse design framework specifically developed for optimizing single-material, variable-index multilayer films. This neural network-driven technique, supported by a differentiable analytical solver, enables the realistic design and fabrication of these multilayer films, achieving high performance under ideal conditions. The approach also addresses the challenge of bridging the gap between these ideal designs and practical devices, which are subject to growth-related imperfections. By incorporating simulated systematic and random errors—reflecting actual deposition challenges—into the optimization process, we demonstrate that the neural network, initially trained to produce the ideal device, can be reconfigured to create designs that compensate for systematic deposition errors. This method remains effective even when random fabrication inconsistencies are present. The results provide a practical and experimentally viable strategy for developing single-material multilayer film stacks, ensuring reliable performance across a wide range of real-world applications.</p><p dir="ltr">The final cornerstone of this research investigates the two-stage inverse design of superchiral dielectric metasurfaces. We propose a two-stage inverse design scheme for dielectric lossless metasurfaces with central superchiral hot spots. By leveraging the excitation of high-quality factor modes with low mode volumes, we achieve up to 19,000-fold enhancements of optical chirality. This method extends the local density of field enhancements for non-chiral fields into the chiral regime and significantly surpasses previous enhancements in superchiral field generation. Our results open new avenues in chiral spectroscopy and chiral quantum photonics, exemplifying the powerful synergy of AI techniques and physics-based design principles in creating highly innovative and functional photonic structures.</p><p dir="ltr">Collectively, the methodologies developed in this thesis signify a major advancement in the field of photonic inverse design. By merging AI-driven techniques with rigorous physics-based optimization frameworks, this research paves the way for the next generation of photonic devices.</p>

L’intégration photonique permet de réduire la taille et la consommation d’énergie des systèmes de communication par fibre optique par rapport aux systèmes assemblés à partir de composants unitaires. Cette technologie a récemment suscité un grand intérêt avec les progrès de l’intégration sur InP et le développement de la photonique sur silicium. Cette dernière challenge la plate-forme d’intégration sur InP car des composants à hautes performances et faibles coûts peuvent être fabriqués dans des fonderies originellement développées pour la microélectronique. Les lasers sont l'une des pièces maitresses des émetteurs-récepteurs pour les communications optiques. Leur intégration sur la plateforme silicium permet de développer des émetteurs-récepteurs comprenant les fonctions critiques d’émission de lumière, de modulation et de détection sur une même puce. L’intégration de matériaux III-V par collage moléculaire sur plaque silicium permet de produire de grands volumes : plusieurs dizaines voire centaines de composants sont réalisés par wafer. Dans cette thèse, j’ai étudié théoriquement et expérimentalement les propriétés des lasers accordables basés sur des résonateurs en anneau en silicium, des lasers à rétroaction distribuée modulés directement et des lasers à haut facteur de qualité qui présentent un faible bruit de phase et d’intensité. / Photonic integration reduces the size and energy consumption of fiber optic communication systems compared to systems assembled from discrete components. This technology has recently attracted a great interest with the progress of integration on InP and the development of silicon photonics. The latter challenges the integration platform on InP as high-performance and low-cost components can be manufactured in foundries originally developed for microelectronics. Lasers are one of the main parts of transceivers for optical communications. With their integration on the silicon platform, transceivers that include the critical functions of light emission, modulation and detection on the same chip can be made. In the heterogeneous integration platform, components are manufactured in high volumes: several tens or even hundreds of components are produced per wafer. In this thesis, I studied theoretically and experimentally the properties of tunable lasers based on silicon ring resonators, directly modulated distributed feedback lasers and low noise high-quality factor lasers

The widespread adoption of photonic circuits requires the economics of volume manufacturing offered by integration technology. A Complementary Metal-Oxide Semiconductor compatible silicon material platform is particularly attractive because it leverages the huge investment that has been made in silicon electronics and its high index contrast enables tight confinement of light which decreases component footprint and energy consumption. Nevertheless, there remain challenges to the development of photonic integrated circuits. Although the density of integration is advancing steady and the integration of the principal components – waveguides, optical sources and amplifiers, modulators, and photodetectors – have all been demonstrated, the integration density is low and the device library far from complete. The integration density is low primarily because of the difficulty of confining light in structures small compared to the wavelength which measured in micrometers. The device library is incomplete because of the immaturity of hybridisation on silicon of other materials required by active devices such as III-V semiconductor alloys and ferroelectric oxides and the difficulty of controlling the coupling of light between disparate material platforms. Metamaterials are nanocomposite materials which have optical properties not readily found in Nature that are defined as much by their geometry as their constituent materials. This offers the prospect of the engineering of materials to achieve integrated components with enhanced functionality. Metamaterials are a class of photonic crystals includes subwavelength grating waveguides, which have already provided breakthroughs in component performance yet require a simpler fabrication process compatible with current minimum feature size limitations. The research reported in this PhD thesis advances our understanding of the structure-property relations of key planar light circuit components and the metamaterial engineering of these properties. The analysis and simulation of components featuring structures that are only just subwavelength is complicated and consumes large computer resources especially when a three dimensional analysis of components structured over a scale larger than the wavelength is desired. This obstructs the iterative design-simulate cycle. An abstraction is required that summarises the properties of the metamaterial pertinent to the larger scale while neglecting the microscopic detail. That abstraction is known as homogenisation. It is possible to extend homogenisation from the long-wavelength limit up to the Bragg resonance (band edge). It is found that a metamaterial waveguide is accurately modeled as a continuous medium waveguide provided proper account is taken of the emergent properties of the homogenised metamaterial. A homogenised subwavelength grating waveguide structure behaves as a strongly anisotropic and spatially dispersive material with a c-axis normal to the layers of a one dimensional multi-layer structure (Kronig-Penney) or along the axis of uniformity for a two dimensional photonic crystal in three dimensional structure. Issues with boundary effects in the near Bragg resonance subwavelength are avoided either by ensuring the averaging is over an extensive path parallel to boundary or the sharp boundary is removed by graded structures. A procedure is described that enables the local homogenised index of a graded structure to be determined. These finding are confirmed by simulations and experiments on test circuits composed of Mach-Zehnder interferometers and individual components composed of regular nanostructured waveguide segments with different lengths and widths; and graded adiabatic waveguide tapers. The test chip included Lüneburg micro-lenses, which have application to Fourier optics on a chip. The measured loss of each lens is 0.72 dB. Photonic integrated circuits featuring a network of waveguides, modulators and couplers are important to applications in RF photonics, optical communications and quantum optics. Modal phase error is one of the significant limitations to the scaling of multimode interference coupler port dimension. Multimode interference couplers rely on the Talbot effect and offer the best in-class performance. Anisotropy helps reduce the Talbot length but temporal and spatial dispersion is necessary to control the modal phase error and wavelength dependence of the Talbot length. The Talbot effect in a Kronig-Penny metamaterial is analysed. It is shown that the metamaterial may be engineered to provide a close approximation to the parabolic dispersion relation required by the Talbot effect for perfect imaging. These findings are then applied to the multimode region and access waveguide tapers of a multi-slotted waveguide multimode interference coupler with slots either in the transverse direction or longitudinal direction. A novel polarisation beam splitter exploiting the anisotropy provided by a longitudinally slotted structure is demonstrated by simulation. The thesis describes the design, verification by simulation and layout of a photonic integrated circuit containing metamaterial waveguide test structures. The test and measurement of the fabricated chip and the analysis of the data is described in detail. The experimental results show good agreement with the theory, with the expected errors due to fabrication process limitations. From the Scanning Electron Microscope images and the measurements, it is clear that at the boundary of the minimum feature size limit, the error increases but still the devices can function.