High Efficiency Grating Coupler for Coupling between Single-Mode Fiber and SOI Waveguides

A high efficiency grating coupler between single?mode fiber and silicon-on-insulator waveguide is designed by a formula method. Over 78.5% coupling efficiency (>-1.05 dB) with 3 dB bandwidth about 50 nm for one grating coupler is obtained experimentally and this result is the highest one as far as we know. This grating coupler is CMOS compatible which needs only one etch-step and is designed for a standard SOI chip without any Bragg reflector or bottom reflector.