Conception d’un coupleur optique

Abstract

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.