Design of a Full Etch Grating Coupler

The design of a full etch, constant pitch grating coupler with upper oxide cladding is documented and analyzed for coupling to the dominant TE mode of a waveguide on a commercially available SOI platform at 1550nm. A high level design approach using Fresnel reflection theory, waveguide mode theory, and wave interference principles is used to develop a parametric model of the grating coupler, and this model is tested and analyzed using a rigorous coupled mode analysis engine contained within the FIMMWAVE software package. To automate testing and analysis of the high level grating model, a GUI plugin to FIMMWAVE was also developed using Python’s PyQT package. It will be shown that this high level, “Device Modes” modelling process is very capable of describing specific optical behaviors of the grating structure, and is also very capable of producing efficient couplers. Simulated coupling efficiencies between the grating waveguide’s dominant mode and single mode fiber reach as high as -3.55 dB at 1550nm for this full etch, constant pitch design. This methodology is easily adapted to different index profiles, and when coupled with its minimum of fabrication complexity will allow quick access to a coupling technology for novel photonic integrated circuit platforms