Grating Couplers for Coupling between Optical Fibers and Nanophotonic Waveguides

TLDR

Nanophotonic waveguides and components promise large‑scale photonic integration, yet efficient coupling to single‑mode fibers remains challenging, prompting many proposed solutions and the use of grating couplers that can be placed anywhere on a circuit and integrated easily. The paper proposes a grating coupler approach and theoretically predicts that optimized designs and layer stacks could raise coupling efficiency above 90 %. The authors discuss fabricating these couplers on silicon‑on‑insulator and indium phosphide membranes. Experimentally, they achieved over 30 % coupling efficiency with a 1 dB bandwidth of 40 nm on standard wafers.

Abstract

Nanophotonic waveguides and components are promising for use in the large-scale integration of photonic circuits. Coupling light between nanophotonic waveguides and a single-mode fiber is an important problem and many different solutions have been proposed and demonstrated in recent years. In this paper, we discuss a grating coupler approach. Grating couplers can be placed anywhere on a circuit and can easily be integrated. We have experimentally demonstrated >30% coupling efficiency with a 1 dB bandwidth of 40 nm on standard wafers. Theoretically, the coupling efficiency can be improved to >90% using an optimized grating design and layer stack. The fabrication of the couplers in silicon-on-insulator and in indium phosphide membranes is also discussed.