A record-high efficiency and bandwidth for a fiber-to-chip grating coupler have been achieved with a robust design and cost-effective fabrication on a silicon-on-insulator platform. The design optimization involves the usual geometrical parameters, period, and fill factor, and a mode matching for the fiber output and grating. The measured coupling efficiency for TE polarization and 1 dB bandwidth are -2.64 dB (54 %) per grating and 67 nm, respectively. The 3 dB bandwidth exceeds 100 nm, fully covering the C + L band. The results fill the gap between theory and experimental realization in the existing literature.