Reviving holographic photonic integration

TL;DR

This paper discusses the challenges and importance of integrating thick holograms into waveguiding structures for advanced optical computing, highlighting fabrication and design difficulties in high-dimensional photonic systems.

Contribution

It introduces methods to revive holographic photonic integration, addressing fabrication accuracy and design complexity for high-dimensional optical neural networks.

Findings

Holographic integration is crucial for compact optical transformations.

Current fabrication techniques face accuracy challenges.

Design complexity increases with large architectures.

Abstract

Photonic integration of thick holograms in waveguiding structures could be considered the chimera of photonics; multi-faceted and hard to tame. It is the fundamental, and hence indispensable, concept behind compact and monolithically integrated linear optical transformation1. The true relevance of this becomes apparent in the high-dimensional context of unconventional optical computing, that is, in optical neural networks. Yet, integrating such holographic connections is very challenging. It demands high fabrication accuracy, and numerical design of the circuit is often non-tractable for large architectures. Both challenges are intrinsically linked to the usually large refractive index differences between sections of such holographic optical waveguides when using standard techniques of silicon photonics.