Multimode grating couplers via foundry-compliant inverse design

TL;DR

This paper presents a systematic inverse design method for creating foundry-compliant multilayer grating couplers that efficiently couple multiple waves from free space to on-chip modes, considering fabrication constraints.

Contribution

It introduces a practical inverse design framework that accounts for foundry constraints and robustness to fabrication errors for multimode grating couplers.

Findings

Designs maintain high efficiency despite feature size constraints.

Robust optimization yields stable efficiencies under fabrication imperfections.

Efficiency penalties increase with larger feature sizes, following predictable scaling laws.

Abstract

We apply a systematic inverse design approach to discover foundry-compliant, multilayer grating couplers that can efficiently couple a number of independent waves from free space to on-chip propagating modes. For visible- and near-infrared couplers, we find that minimum feature sizes are by far the most important constraint to tailor the design algorithms around. If, additionally, one forces the optimization to be robust to over- and under-etch errors, the resulting designs exhibit stable optimal efficiencies in the presence of other imperfections (critical dimension variations, overlay mismatch, and sidewall angle variation). The foundry-compliant designs exhibit moderate efficiency penalties as feature sizes increase, but no change to simple underlying scaling laws with respect to requisite numbers of layers and layer thicknesses. These results establish a practical, generalizable framework for high-efficiency multimode coupling within the constraints of modern semiconductor foundries.