DARPA: Photonic Circuits Challenge Physics Limits

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DARPA Bets $35 Million on photonic Computing Breakthroughs

DARPA is investing $35 million in a new initiative aimed at overcoming essential physics limitations and accelerating the progress of large-scale photonic circuits – technology that uses light instead of electrons to process data.

The Defense Advanced Research Projects Agency (DARPA) recently launched the Photonic Integrated Circuit architectures for Scalable System Objectives (PICASSO) program, seeking proposals from researchers who can demonstrate how innovative circuit-level design can unlock the full potential of photonics, particularly for demanding applications like artificial intelligence.

For the uninitiated,photonic computing offers meaningful advantages over conventional electronic computing,including greater bandwidth,reduced latency,and improved energy efficiency. Though, despite these benefits, systems incorporating photonic circuits have yet to consistently outperform their electronic counterparts. As one senior official stated, “systems incorporating photonic circuits struggle to show significant system-level performance advantages over electronic systems.”

Did you know? – Photonic circuits use light to transmit data, potentially offering faster speeds and lower energy consumption than traditional electronic circuits.

The Limits of Current Photonic Technology

Current photonic circuits are limited in their complexity, typically capable of only simple mathematical operations. A major bottleneck is the need to convert optical signals to electronic ones when interfacing with other components. This conversion negates the speed advantage of photonics, resulting in a 10⁶ performance degradation due to the slower processing speeds of electronic circuits.

The core challenge, according to DARPA, isn’t a lack of promising components, but rather a focus on component-level research instead of holistic system design. But beyond that, the very nature of light presents obstacles. “The primary limitation to further scaling of circuit size and functionality is rooted in the fundamental properties of signaling with light,” DARPA noted.

Pro tip – Holistic system design,rather than focusing solely on individual components,is key to unlocking the potential of photonic computing.

Tackling the Physics Problem

DARPA has identified two primary technical hurdles.The first is signal degradation. Unlike traditional metal-oxide-semiconductor circuits,which can regenerate signals and filter out noise,photonic circuits suffer from optical attenuation and noise that cannot be simply amplified without also amplifying the unwanted noise.

The second challenge is spurious wave interference, leading to scattering, coupling, mode leakage, back reflections, and unwanted resonance. “Over many components, control of these errors becomes unpredictable, especially when combined with manufacturing variability and thermal and environmental instabilities,” DARPA explained.

These limitations have historically led to a reliance on electronic components to compensate, but DARPA is steadfast to avoid this approach. “Heavy usage of electronics prevents system-level gains in latency, efficiency, and bandwidth offered natively by photonics,” the agency said.

Reader question – signal degradation and wave interference are major obstacles in photonic circuits, as light-based signals are harder to amplify and control than electronic ones.

PICASSO: A New Paradigm for Photonic Circuit Design

The PICASSO program aims to foster a new paradigm: designing advanced photonic circuits using existing components. The program seeks to emulate the successes of modern electronics, where clever circuit design overcomes the inherent limitations of individual transistors. As DARPA stated,”PICASSO confronts these challenges by embracing a new paradigm: creating tomorrow’s photonic circuits using today’s components.”

DARPA has set enterprising milestones for the program. By July 2025, approximately 18 months after the program’s launch, the agency expects a “demonstration of predictable performance of photonic circuits.” An additional 18-month phase will focus on demonstrating “generalized circuit functionality.”