http://depot.umc.edu.dz/handle/123456789/5505 Thu, 12 Nov 2026 22:58:21 GMT 2026-11-12T22:58:21Z http://depot.umc.edu.dz/handle/123456789/14867 Etude de commutateurs optiques à base de guide d’ondes en matériaux III-V. Brik, Fatima; Bouchemat -Boumaza, Touraya Plusieurs études ont été menées sur des commutateurs tout optiques à base de semiconducteurs III-V, ayant pour structure de base un Fabry- Pérot ou un guide d’onde. Lors de la caractérisation de ces dispositifs, des effets non linéaires ont été observés. Toutefois, le développement rapide des effets thermiques limite souvent les performances du composant et notamment sa vitesse de commutation Cependant, il est possible de limiter ces effets et de les stabiliser. A cet effet, nous avons entrepris la modélisation du fonctionnement d’un dispositif en guide d’onde avec coupleur à réseau, constitué d’un film actif en matériau III-V épitaxié sur un miroir de Bragg. En régimes statique et dynamique, la simulation des effets thermiques, a permis la détermination d’une structure équivalente quant à l’amplitude et à la dynamique des effets thermiques, et qui de plus réduit considérablement le temps de calcul. Les résultats de simulation confirment que l’amplitude des effets thermiques dépend fortement des propriétés optiques du miroir de Bragg via la conductivité thermique des différentes couches le constituant, et que la présence du substrat empêche l’évacuation de la chaleur produite lors de l’éclairement du dispositif. Comme le fonctionnement d’un commutateur rapide est basé sur le renforcement des non linéarités optiques d’origine électronique par rapport à celles d’origine thermique, nous avons exploré deux voies pour minimiser les effets thermiques : la diminution des dimensions de la source d’éclairement, facile à réaliser et qui permet d’augmenter notablement la durée de stabilité du commutateur, et le remplacement du réflecteur de Bragg par un miroir métallique : cette deuxième solution, est beaucoup plus efficace à mettre en œuvre technologiquement et permet d’envisager des solutions intermédiaires. Thu, 14 Oct 2010 00:00:00 GMT http://depot.umc.edu.dz/handle/123456789/14867 2010-10-14T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14859 La modélisation de nouvelles structures dans le domaine du guidage et du filtrage des ondes acoustiques. Amrani, Hamza; Grine, Farouk Acoustic metamaterials represent an exciting frontier in the control of waves and vibrations. The precise control of acoustic waves is fundamental for key technological applications, ranging from sound insulation to ultrasonic detection. In this work, the design, modeling, and analysis of novel two-dimensional phononic crystal (PnC) structures that integrate the architecture of auxetic materials are addressed. The objective is double: to create new structures capable of generating and controlling wide and tunable phononic bandgaps (PBGs), and to control the direction of energy flow and the propagation of acoustic waves. The study relies on the Finite Element Method (FEM) and the rigorous application of the Floquet-Bloch theory for the calculation of dispersion relations. We introduce and analyze two specific auxetic architectures derived from star-shaped honeycomb structure: the concave circular-headed structure and the Arabesque structure. A parametric study is performed on the geometric variables to optimize structural and vibrational performances. The results obtained not only confirm the auxetic behavior of these designs but demonstrate their excellent ability to open robust complete PBGs. By exploiting Iso Frequency Contours (EFCs), we have modeled the phenomenon of self-collimation. This mechanism proves that these PCs can naturally focus and guide vibrational energy along precise trajectories, offering a promising trajectory for the unconventional manipulation of waves. This project opens concrete prospects for the development of high-precision acoustic insulation and filtering devices. Thu, 18 Dec 2025 00:00:00 GMT http://depot.umc.edu.dz/handle/123456789/14859 2025-12-18T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14858 Contributions to fractional-order fault-tolerant control of nonlinear systems. Daoudi, Islam; Chemachema, Mohamed The primary aim of this thesis is to develop adaptive control strategies tailored for specific categories of uncertain single-input single-output (SISO) and interconnected multi-input multi-output (MIMO) fractional-order nonlinear systems. The investigation includes the analysis of the effect of saturation on the control inputs along with the external disturbances on the dynamics of systems. In all the proposed methodologies, neural networks or fuzzy logic systems serve as universal approximators to estimate the unknown nonlinear dynamics of the systems. The architectures of the proposed controllers address the well-known challenges associated with complexity explosion while circumventing the conventional back-stepping technique thanks to the introduction of a new fractional systems transformation into the controllable Bronovsky form. By using the implicit function theorem and the strictly positive real (SPR) property, output feedback approaches become feasible. Compared to similar approaches, the proposed adaptive neural/fuzzy controllers exhibit minimal online learning parameters. Furthermore, the integration of the Eventtriggered mechanism optimizes resource utilization by updating control actions only when necessary, thereby reducing computational burden and communication overhead. Additionally, stability analysis of all control loops is conducted using the Lyapunov method, and simulation results are provided for each scheme to demonstrate its efficacy. Mon, 22 Dec 2025 00:00:00 GMT http://depot.umc.edu.dz/handle/123456789/14858 2025-12-22T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14857 Conception d’un coupleur optique Chergui, Imane; Labbani, Amel The primary objective of this thesis is to develop models and optimize the performance of optical switches and power splitters based on directional couplers. These devices are essential components in optical telecommunication systems, as they enable the switching and splitting of optical signals into multiple paths. A key advantage of directional couplers over conventional switches and power splitters is their significantly lower radiation losses, which enhance system efficiency. To analyze the optical properties and evaluate the performance of these devices, simulations were conducted using RsoftCAD software, employing the FiniteDifference Time-Domain (FDTD) method and the Plane Wave Expansion (PWE) method. The coupler consists of two linear waveguides separated by a row of silicon columns. Various technologies have been proposed to enhance the performance of photonic crystal-based directional couplers (DCs) and minimize the coupling length between the two waveguides. The proposed directional coupler replaces the central row of silicon rods with core/shell (C/S) particles, which are created by perforating the silicon rods to introduce air holes. The internal and external radii of the silicon rods in the central row of the C/S structure are denoted as rin and rout, respectively. The modified directional coupler reduces the coupling length (Lc) to 5a, where a is the lattice constant. Simulation results show that increasing the inner radius rin enhances the coupling coefficient while reducing the coupling length (Lc). The first devices designed using the new directional coupler architecture are 2×2, 3×3, and 4×4 optical switches based on photonic crystals. The basic structure consists of rows of silicon (Si) rods arranged in an air medium on a hexagonal lattice. The influence of varying the inner and outer rods, as well as modifications to the permittivity or refractive index of the core and shell, on the coupling length and output power was also studied. Simulation results demonstrate that the three proposed switches exhibit high normalized transmission, negligible reflection, fast delay times, and low crosstalk (measured in dB). The areas of the 2×2, 3×3, and 4×4 optical switches are 185.35 μm², 273.53 μm², and 356.53 μm², respectively.The modified directional coupler reduces the coupling length (Lc) to 5a, where a is the lattice constant. Simulation results show that increasing the inner radius rinenhances the coupling coefficient while reducing the coupling length (Lc). The first devices designed using the new directional coupler architecture are 2×2, 3×3, and 4×4 optical switches based on photonic crystals. The basic structure consists of rows of silicon (Si) rods arranged in an air medium on a hexagonal lattice. The influence of varying the inner and outer rods, as well as modifications to the permittivity or refractive index of the core and shell, on the coupling length and output power was also studied. Simulation results demonstrate that the three proposed switches exhibit high normalized transmission, negligible reflection, fast delay times, and low crosstalk (measured in dB). The areas of the 2×2, 3×3, and 4×4 optical switches are 185.35 μm², 273.53 μm², and 356.53 μm², respectively. Moreover, the proposed switches are compact and can be integrated into optical telecommunication systems. The second set of devices in this thesis focuses on the design and modeling of 1×2 and 1×4 Y-junction power splitters, based on the new directional coupler architecture. These devices split the signal into two or four paths with minimal radiation losses, particularly in curved regions. An ideal power splitter uniformly divides the optical signal injected at its input into multiple outputs without any radiation loss. To minimize radiation losses while maximizing total transmission, an optimization technique was proposed that involved modifying the inner radii of the (C/S) structure. The optical properties of the optimized splitters are significantly improved, achieving total transmission of up to 99% of the incident light. The sizes of the proposed 1×2 and 1×4 Y-junction dividers are 177.63 μm² and 449.45 μm², respectively. These devices are highly compact and deliver excellent splitting performance, making them particularly suitable for applications in optical telecommunications and photonic integrated circuits. Thu, 27 Nov 2025 00:00:00 GMT http://depot.umc.edu.dz/handle/123456789/14857 2025-11-27T00:00:00Z