High Directivity, Vertical Fiber-to-Chip Coupler with Anisotropically Radiating Grating Teeth

Efficient vertical grating-coupler designs are proposed that allow near 50:1 up/down directivity using only two lithographic layers, without top/bottom mirrors, in high-index-contrast silicon waveguides. FDTD simulations predict single-mode-fiber-coupling efficiencies of 75% even for non-apodized gratings.