Fabrication Development of a Large Area Grating for Out of Plane Beam Coupling

TL;DR

This paper presents a novel large-area surface grating on silicon for efficient vertical coupling of near-infrared light, achieving high focusing efficiency suitable for high-power laser applications.

Contribution

It introduces a single-layer waveguide surface grating design optimized for large-area vertical coupling on SOI substrates, with both simulation and initial experimental validation.

Findings

Achieved a focal spot with 3.82 um width at the target position.

Simulated coupling efficiency of 33%, measured at 22%.

Demonstrated potential for high-power laser integration.

Abstract

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).