Three-Wave Interaction Grating Coupler with Sub-Decibel Insertion Loss at Normal Incidence

TL;DR

This paper presents a high-efficiency, normal incidence grating coupler for silicon photonics with sub-decibel insertion loss, verified through fabrication and experiments, enabling improved vertical coupling solutions.

Contribution

The paper demonstrates a commercially fabricated, high-efficiency grating coupler with sub-dB insertion loss at normal incidence, validated by experimental results matching theoretical predictions.

Findings

Maximum coupling efficiency of 85.4% (-0.69 dB)

20 nm bandwidth at 1546 nm wavelength

Verification of theoretical and simulation results

Abstract

We report the design, fabrication in a commercial foundry, and experimental results of high-efficiency, normal incidence grating couplers for silicon photonics. We observe a maximum coupling efficiency of 85.4% (-0.69 dB) with a 1 dB bandwidth of 20 nm at a central wavelength of 1546 nm. These experimental results verify earlier theoretical and simulation results and pave the way for the use of perfectly vertical grating couplers, as an alternative to edge coupling, in silicon photonics applications that are sensitive to input coupling loss. Further, these results enable the use of grating couplers for vertically oriented elements, such as multicore fibers and VCSELs, and address challenges associated with coupling to free space beams.