An apodized SOI waveguide-to-fiber surface grating coupler for single lithography silicon photonics

• Published in: Optics express 2011-02, Vol.19 (4), p.3592-3598
• Main Authors: Antelius, Mikael, Gylfason, Kristinn B, Sohlström, Hans
• Format: Article
• Language: English
• Subjects: 1550 nm; Apodizing; Buried oxide thickness; Coupled circuits; Coupling efficiency; Diffracted waves; Etched gratings; Etched surface; Fiber surface; Grating couplers; Lithography; Mode profiles; Nanophotonic circuits; Nanophotonics; Photonic devices; Silica; Silica fibers; Silicon devices; Silicon photonics; Silicon-on-insulator substrates; Single mode; SOI substrates; SOI waveguides; TE mode; TECHNOLOGY; TEKNIKVETENSKAP
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/oe.19.003592

We present the design, fabrication, and characterization of a grating for coupling between a single mode silica fiber and the TE mode in a silicon photonic waveguide on a silicon on insulator (SOI) substrate. The grating is etched completely through the silicon device layer, thus permitting the fabrication of through-etched surface coupled silicon nanophotonic circuits in a single lithography step. Furthermore, the grating is apodized to match the diffracted wave to the mode profile of the fiber. We experimentally demonstrate a coupling efficiency of 35% with a 1 dB bandwidth of 47 nm at 1536 nm on a standard SOI substrate. Furthermore, we show by simulation that with an optimized buried oxide thickness, a coupling efficiency of 72% and a 1 dB bandwidth of 38 nm at 1550 nm is achievable. This is, to our knowledge, the highest simulated coupling efficiency for single-etch TE-mode grating couplers. In particular, simulations show that apodizing a conventional periodic through-etched grating decreases the back-reflection into the waveguide from 21% to 0.1%.