Towards compact high-efficiency grating couplers for visible wavelength photonics

TL;DR

This paper introduces two innovative grating coupler designs for visible wavelength photonics, significantly improving efficiency and compactness in silicon nitride platforms, with potential applications in quantum photonics.

Contribution

It proposes dielectric and embedded metal grating approaches to enhance diffraction efficiency and reduce footprint in visible wavelength grating couplers.

Findings

Dielectric grating increases output intensity by mode summation.

Embedded metal grating enhances refractive index contrast.

Experimental results demonstrate potential for compact, efficient photonic interconnects.

Abstract

While grating couplers have become the de-facto standard for optical access to integrated silicon photonics platforms, their performance at visible wavelengths, in moderate index contrast platforms like silicon nitride, leaves significant room for improvement. In particular, the index contrast governs the diffraction efficiency per grating tooth and the resulting overall coupler length. In this work, we develop two approaches to address this problem: a dielectric grating that sums multiple optical modes to increase the overall output intensity, and an embedded metal grating that enhances the attainable refractive index contrast, and therefore reduces the on-chip footprint. We present experimental results that can be developed to realise compact efficient visible wavelength photonic interconnects, with a view towards cryogenic deployment for quantum photonics, where space is constrained and efficiency is critical.