Bottom to in-plane grating coupler with high coupling efficiency and directionality

Here, we have presented the first design of a bottom to in-plane grating coupler with a high coupling efficiency and directionality. The grating coupler consists of a high contrast grating (HCG) and an etched silicon-on-insulator (SOI) grating device. The final coupling efficiency is 82.2% at 1.55µm, with a 57nm 3dB bandwidth, and the directionality is 14:1 (left to right ratio). This grating coupler can be further optimized with different low index materials. This grating coupler could work as the vertical to in-plane coupler for the label free silicon photonic bio-sensor.