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  • Perspective
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The physics of optical computing

Nature Reviews Physics volume 5, pages 717–734 (2023)Cite this article

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Abstract

There has been a resurgence of interest in optical computing since the early 2010s, both in academia and in industry, with much of the excitement centred around special-purpose optical computers for neural-network processing. Optical computing has been a topic of periodic study since the 1960s, including for neural networks in the 1980s and early 1990s, and a wide variety of optical-computing schemes and architectures have been proposed. In this Perspective article, we provide a systematic explanation of why and how optics might be able to give speed or energy-efficiency benefits over electronics for computing, enumerating 11 features of optics that can be harnessed when designing an optical computer. One often-mentioned motivation for optical computing — that the speed of light is fast — is emphatically not a key differentiating physical property of optics for computing; understanding where an advantage could come from is more subtle. We discuss how gaining an advantage over state-of-the-art electronic processors will likely only be achievable by careful design that harnesses more than 1 of the 11 features, while avoiding a number of pitfalls that we describe.

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Fig. 1: The three features most likely to have a key role in any future optical processor that does deliver an overall advantage in latency, throughput or energy efficiency.
Fig. 2: Signal transmission in optical systems.
Fig. 3: Additional ways that optical systems are different from electrical systems.
Fig. 4: The quantum nature of light.

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Acknowledgements

The author gratefully acknowledges many helpful conversations with co-workers including D. Brunner, R. Hamerly, H. Mabuchi, A. Majumdar, A. Marandi, E. Ng, T. Onodera, T. Wang, L. Wright and Y. Yamamoto; these conversations over several years have shaped his understanding of optical computing. The author also gratefully acknowledges S. Agarwal for explanations about analog-electronic crossbars and B. Govind for discussions about electrical interconnects. The author thanks M. Anderson, T. Wang and F. Wu for providing detailed feedback on a draft of this manuscript. This work has been financially supported in part by the National Science Foundation (Award CCF-1918549), NTT Research and a David and Lucile Packard Foundation Fellowship.

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    Peter L. McMahon

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The author is listed as an inventor on several U.S. provisional patent applications relating to optical computing (63/149,974; 63/178,318; 63/392,042).

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McMahon, P.L. The physics of optical computing. Nat Rev Phys 5, 717–734 (2023). https://doi.org/10.1038/s42254-023-00645-5

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