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).
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