Highly-efficient fiber to Si-waveguide free-form coupler for foundry-scale silicon photonics

TL;DR

This paper presents a highly-efficient, broadband, and scalable 3-D fiber-to-silicon waveguide coupler using free-form micro-optics and two-photon polymerization, significantly improving coupling efficiency and tolerance for silicon photonics integration.

Contribution

It introduces a novel free-form 3-D coupler design that achieves low loss, broad bandwidth, and high tolerance, advancing scalable packaging solutions for silicon photonics.

Findings

Coupling loss of 0.8 dB for TE mode

Bandwidth exceeding 180 nm

High tolerance to misalignments

Abstract

As silicon photonics transitions from research to commercial deployment, packaging solutions that efficiently couple light into highly-compact and functional sub-micron silicon waveguides are imperative but remain challenging. The 220 nm silicon-on-insulator (SOI) platform, poised to enable large-scale integration, is the most widely adopted by foundries, resulting in established fabrication processes and extensive photonic component libraries. The development of a highly-efficient, scalable and broadband coupling scheme for this platform is therefore of paramount importance. Leveraging two-photon polymerization (TPP) and a deterministic free-form micro-optics design methodology based on the Fermat's principle, this work demonstrates an ultra-efficient and broadband 3-D coupler interface between standard SMF-28 single-mode fibers and silicon waveguides on the 220 nm SOI platform. The coupler achieves a low coupling loss of 0.8 dB for fundamental TE mode, along with 1-dB bandwidth exceeding 180 nm. The broadband operation enables diverse bandwidth-driven applications ranging from communications to spectroscopy. Furthermore, the 3-D free-form coupler also enables large tolerance to fiber misalignments and manufacturing variability, thereby relaxing packaging requirements towards cost reduction capitalizing on standard electronic packaging process flows.