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Silicon photonic mid-infrared grating coupler based on silicon-on-insulator technology

A novel vertical grating coupler design and optimization is presented to enable coupling of mid-infrared light into silicon-on-insulator integrated optical gas sensor circuit. The target wavelength is around 3100 nm, where the acetylene gas and a group of hydrocarbons possess a strong absorption. The grating coupler dimensions are optimized according to the limits of a standard and low-cost fabrication technology for silicon on silica by Interuniversity Micro Electronics Center (IMEC). The design simulations were carried out using 2D and 3D finite difference time domain simulation in the mid-infrared. The optimized coupling efficiency is found to be approximately 10% and the 3-dB bandwidth of the coupler is approximately 160 nm depending on the grating fill factor. The reported bandwidth is compatible with the gas sensing application