  We develop a single-layer waveguide surface grating structure to vertically
couple near infrared (NIR) light at ~1.55 um wavelength from a large area (~100
um length scale) Si waveguide on a Silicon-On-Insulator (SOI) substrates to
free-space for high-power laser applications. Our design approach is based on
the optimization of local emission angles and the out-coupling intensities.
Simulation results show that a focal spot with a 1/e2 width of 3.82 um can be
achieved at the desired focal position, with 33% (-4.81 dB) simulated source to
free-space focusing efficiency, while initial measurements show an efficiency
of 22% (-6.58 dB).
