Eficiência de acoplamento entre fibras de cristal fotônico e circuitos integrados fotônicos

Abstract

Research interest: In this dissertation, the coupling problem between silicon nanoguides and the "outside world,"namely an optical fiber, was numerically investigated using the FDTD method. The process of guiding light from the fiber into a nanoguide is referred to as optical coupling, and the coupling problem arises from the dimensional incompatibility between the conventional optical fiber core and the cross-sectional area of the integrated nanoguides. Currently, this is one of the most significant challenges faced by researchers in the field of silicon nanophotonics. Although the manufacturing of silicon photonic devices has achieved high quality due to compatibility with CMOS fabrication processes, the transition at the interface between the fiber and the nanoguide is characterized by considerable insertion losses due to the coupling problem. Thus, solving this problem holds great importance for the application of silicon photonic integrated circuits in optical communications.. Objectives: The objective of this work is to address the coupling interface problem between optical fibers and silicon nanoguides, using photonic crystal fibers instead of conventional optical fibers. For this purpose, uniform Bragg gratings are employed as a coupling technique, and the coupling efficiency to the photonic crystal fiber is investigated through numerical simulations, considering the coupling angle, lattice parameters, as well as the physical parameters of the fiber, specifically the air hole diameter. Therefore, this study focuses on the examination, modeling, and optimization of the coupling technique using Bragg gratings to achieve efficient coupling between photonic crystal fibers and silicon nanoguides. Results obtained: The simulations results show that efficient coupling can be achieved between photonic crystal fibers and SOI waveguides. The coupling efficiency was investigated based on two types of uniform Bragg couplers. The first one is a simple grating coupler etched on the surface of a nanoguide integrated in the SOI platform. The second one is a Bragg grating coupler with a bottom metallic reflector. In the latter, a gold reflector was added to maximize the reflection at the oxide/substrate interface of the SOI platform and reuse the radiated energy to the substrate. Efficiency simulations with the standard coupler demonstrate a maximum coupling efficiency of 32.6% at a coupling angle of 10◦. Meanwhile, a maximum coupling efficiency of 70.3% is demonstrated when the reflector is added. Furthermore, an interesting dependence of the coupling efficiency on the air hole diameter of the photonic crystal fibers has also been determined, indicating that this parameter should be appropriately chosen to optimize the coupling efficiency.