USC engineers just made light smarter with “optical thermodynamics”

From Valves to Routers to Light

The idea of routing is common across engineering disciplines. In mechanics, a manifold valve controls where fluids flow. In electronics, a Wi-Fi router or Ethernet switch sends digital information from multiple input sources to the correct output port, ensuring every signal reaches its destination. Achieving a similar kind of routing with light, however, has long been much more complex. Traditional optical routers rely on intricate switch networks and electrical control systems to change light’s path, which adds layers of complexity and limits both speed and performance.

Researchers at the USC Viterbi School of Engineering have now demonstrated a completely different approach. The concept can be imagined as a marble maze that organizes itself. Normally, a person would need to lift barriers and adjust the path to guide a marble to the right hole. In the USC team’s device, the maze is structured so that no matter where you drop the marble, it will roll toward its correct destination automatically. Light behaves in the same way within this system—it finds the appropriate path on its own by following the rules of thermodynamics.

Potential Industry Impact

The potential applications of this discovery reach well beyond academic research. As modern computing and data transfer continue to stretch the limits of conventional electronics, leading companies (including chip designers such as NVIDIA and others) are investigating optical technologies as faster and more energy-efficient alternatives. By offering a natural, self-organizing method for directing light signals, optical thermodynamics could speed up progress in these efforts. In addition to chip-level communication, this principle may also influence fields such as telecommunications, high-performance computing, and secure information transfer, paving the way for simpler yet more powerful optical systems.

How it Works: Chaos Tamed by Thermodynamics

Nonlinear multimode optical systems have often been viewed as chaotic and difficult to control. Their many overlapping light patterns make them extremely challenging to model or design for practical purposes. Yet this very complexity hides rich physical behavior that has remained largely untapped.

The USC researchers realized that light in these nonlinear environments behaves much like a gas moving toward thermal equilibrium, where random collisions eventually create a stable distribution of energy. Based on this insight, they developed the theoretical framework of "optical thermodynamics," describing how light in nonlinear lattices can undergo processes analogous to expansion, compression, and even phase transitions. This model provides a unified way to understand and harness the natural self-organization of light.

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."