Scalable 3D silicon nitride photonic interposer for high-density optical interconnects

TL;DR

This paper presents a scalable 3D silicon nitride photonic interposer with optimized routing that significantly reduces crossings and losses, enabling denser and more efficient optical interconnects for high-performance computing.

Contribution

The work introduces a novel 3D routing scheme for silicon nitride photonic interposers, achieving substantial reductions in crossings and losses compared to traditional planar designs.

Findings

Reduced intralayer crossings by 69.7% using 3D routing.

Achieved 45.8% reduction in average waveguide loss.

Demonstrated a fully connected 12-node optical network with improved scalability.

Abstract

Modern computing workloads demand energy-efficient, high-bandwidth interconnects, motivating photonic interposers as an alternative to electrical links. Here we demonstrate a compact 3D silicon nitride (SiN) photonic interposer prototype comprising two routing layers, with the 3D routing scheme optimized by a global optimization algorithm. The 3D interposer realizes a fully connected 12-node optical network that reduces the total number of intralayer crossings from 495 for all-planar routing to merely 150 (69.7% reduction), below the theoretical lower bound of 153 for all-planar interconnects. Comparing the two schemes, our 3D design achieves a 45.8% reduction experimentally in the average loss per waveguide. The proposed 3D routing architecture also features inherent symmetry and is scalable to higher node counts, flexible node placements, additional routing layers, and other operating wavelengths, enabling denser, lower-loss photonic interposers for next-generation scale-up and high-performance computing (HPC) systems.