USC engineers have demonstrated a new kind of optical device that lets light organize its own route using the principles of thermodynamics.
Instead of relying on switches or digital control, the light finds its own path through the system. This approach could transform data transmission, computing, and communications by making optical technologies more natural and efficient.
Breakthrough in Optical Thermodynamics
Researchers at the Ming Hsieh Department of Electrical and Computer Engineering have achieved a major advance in photonics with the creation of the first optical device based on the emerging concept of optical thermodynamics.
Their study, published in Nature Photonics, presents a completely new method for directing light within nonlinear systems (systems that operate without switches, external control, or digital input). In this setup, light doesn't need to be steered or adjusted—it naturally travels through the device, following the basic laws of thermodynamics.
From Valves to Routers to Light
Routing is a common principle across many fields of engineering. In mechanical systems, a manifold valve controls which outlet a fluid flows through. In electronics, routers and network switches manage the flow of digital data, ensuring information from multiple inputs reaches the right destination. But directing light works differently and is far more difficult. Traditional optical routers depend on intricate arrays of switches and electronic circuits to control pathways, which makes the process complex and slows performance.
The photonics researchers at the USC Viterbi School of Engineering have discovered an entirely new approach. They describe it as being like a marble maze that organizes itself. Normally, you would have to lift barriers and guide the marble step by step to reach the right hole. In the USC team's design, the maze is structured so that wherever you drop the marble, it automatically rolls to its correct endpoint—no manual guidance required. In the same way, light in this device finds the right path on its own, driven purely by thermodynamic behavior.
Potential Industry Impact
This innovation could have significant effects beyond basic research. As computing and data systems approach the physical limits of electronic speed and efficiency, many companies (including chip developers like NVIDIA and others) are turning to optical interconnects as a faster, more energy-efficient alternative. By introducing a natural, self-organizing way to control light, the principles of optical thermodynamics could help advance this next generation of optical technology. The framework may also influence broader areas such as telecommunications, high-performance computing, and secure data transfer, opening the door to devices that are both more powerful and less complex.
How it Works: Chaos Tamed by Thermodynamics
Nonlinear multimode optical systems are often dismissed as chaotic and unpredictable. Their intricate interplay of modes has made them among the hardest systems to simulate—let alone design for practical use. Yet, precisely because they are not constrained by the rules of linear optics, they harbor rich and unexplored physical phenomena.
Recognizing that light in these systems undergoes a process akin to reaching thermal equilibrium—similar to how gases reach equilibrium through molecular collisions—the USC researchers developed a comprehensive theory of "optical thermodynamics." This framework captures how light behaves in nonlinear lattices using analogues of familiar thermodynamic processes such as expansion, compression, and even phase transitions.
A Device that Routes Light by Itself
The team's demonstration in Nature Photonics marks the first device designed with this new theory. Rather than actively steering the signal, the system is engineered so that the light routes itself.
The principle is directly inspired by thermodynamics. Just as a gas undergoing what's known as a Joule-Thomson expansion redistributes its pressure and temperature before naturally reaching thermal equilibrium, light in the USC device experiences a two-step process: first an optical analogue of expansion, then thermal equilibrium. The result is a self-organized flow of photons into the designated output channel—without any need for external switches.
Opening a New Frontier
By effectively turning chaos into predictability, optical thermodynamics opens the door to the creation of a new class of photonic devices that harness, rather than fight against, the complexity of nonlinear systems. "Beyond routing, this framework could also enable entirely new approaches to light management, with implications for information processing, communications, and the exploration of fundamental physics," said the study's lead author, Hediyeh M. Dinani, a PhD student in the Optics and Photonics Group lab at USC Viterbi.
The Steven and Kathryn Sample Chair in Engineering, and Professor of Electrical and Computer Engineering at USC Viterbi Demetrios Christodoulides added, "What was once viewed as an intractable challenge in optics has been reframed as a natural physical process—one that may redefine how engineers approach the control of light and other electromagnetic signals."
Reference: "Universal routing of light via optical thermodynamics" by Hediyeh M. Dinani, Georgios G. Pyrialakos, Abraham M. Berman Bradley, Monika Monika, Huizhong Ren, Mahmoud A. Selim, Ulf Peschel, Demetrios N. Christodoulides and Mercedeh Khajavikhan, 25 September 2025, Nature Photonics.
DOI: 10.1038/s41566-025-01756-4
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