Scalable and Robust Beam Shaping Using Apodized Fish-bone Grating Couplers

TL;DR

This paper introduces a fish-bone grating coupler design that enables scalable, robust, and precise beam shaping at short wavelengths, overcoming fabrication limitations of traditional apodized gratings.

Contribution

The authors develop a fish-bone grating coupler that decouples feature size from scattering strength, compatible with standard photolithography, for improved beam shaping at 461 nm.

Findings

Successfully generated millimeter-scale beams at 461 nm

Decoupled feature size from scattering strength for fabrication ease

Reduced sensitivity to fabrication variability

Abstract

Efficient power coupling between on-chip guided and free-space optical modes requires precision spatial mode matching with apodized grating couplers. Yet, grating apodizations are often limited by the minimum feature size of the fabrication approach. This is especially challenging when small feature sizes are required to fabricate gratings at short wavelengths or to achieve weakly scattered light for large-area gratings. Here, we demonstrate a fish-bone grating coupler for precision beam shaping and the generation of millimeter-scale beams at 461 nm wavelength. Our design decouples the minimum feature size from the minimum achievable optical scattering strength, allowing smooth turn-on and continuous control of the emission. Our approach is compatible with commercial foundry photolithography and has reduced sensitivity to both the resolution and the variability of the fabrication approach compared to subwavelength meta-gratings, which often require electron beam lithography.