A fiber-to-waveguide, 1D grating coupler design using genetic algorithm for 1550 nm applications

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Silicon photonics on silicon-on-insulator (SOI) technology has great potential in the integrated photonics field. Propagation modes are mostly confined within Silicon waveguides because of the high refraction index difference between silicon waveguide and silicon dioxide cladding. Nowadays, couplers designed using this special feature of SOI are in demand. Edge coupler and grating coupler are the two most preferred coupler types for coupling light between integrated photonic circuits and single-mode optical fibers. In this work, we focused on grating couplers to couple light from fiber to horizontal waveguide since their advantages are easy fiber alignment, lower cost, compact design, and more possible optic inputs/outputs. However, in the literature, the fabrication process of grating couplers with high coupling efficiency is complicated. Therefore, in this paper, we are proposing a grating coupler design with standard SOI lithography technology with a minimum feature size of 250 nm. In our research, the finite difference time domain (FDTD) method is utilized to analyze and design the grating coupler structure with a center of 1.55 μm. We used a genetic algorithm (GA) and particle swarm optimization (PSO) to optimize grating coupler features. SiO₂ cladding thickness, SiO₂ buried oxide layer thickness, grating widths, and fiber distance from grating couplers are optimized with these optimization processes. Our design is an apodized grating coupler with a -3.29 dB (46.8%) coupling efficiency and a 3 dB bandwidth of 78 nm. The design layer of the grating coupler is 12 μm × 16 μm.