First device based on 'optical thermodynamics' can route light without switches

A team of researchers  has created a new breakthrough in photonics: the design of the first optical device that follows the emerging framework of optical thermodynamics.

The work, reported in Nature Photonics, introduces a fundamentally new way of routing light in nonlinear systems—meaning systems that do not require switches, external control, or digital addressing. Instead, light naturally finds its way through the device, guided by simple thermodynamic principles.

Universal routing is a familiar engineering concept. In mechanics, a manifold valve directs inputs to a chosen outlet. In digital electronics, a Wi-Fi router at home or an Ethernet switch in a data center directs information from many input channels to the correct output port, ensuring that each stream of data reaches its intended destination.

When it comes to light, the same problem is far more challenging, however. Conventional optical routers rely on complex arrays of switches and electronic control to toggle pathways. These approaches add technical difficulty, while limiting speed and performance.

The photonics team has now shown that there is another way. The idea can be likened to a marble maze that arranges itself.

Normally, you'd have to lift barriers and guide a marble step-by-step to make sure it reaches its destination—the right hole. In the team's device, however, the maze is built so that no matter where you drop the marble, it will roll on its own toward the right place—no guiding hands needed. And this is exactly how light behaves: it finds the correct path naturally, by following the principles of thermodynamics.

Party 1

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 researchers developed a comprehensive theory of "optical thermodynamics." This framework captures how light behaves in nonlinear lattices using analogs of familiar thermodynamic processes such as expansion, compression, and even phase transitions.
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 new device experiences a two-step process: first an optical analog 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.

Hediyeh M. Dinani et al, Universal routing of light via optical thermodynamics, Nature Photonics (2025). DOI: 10.1038/s41566-025-01756-4

Part 2

Women Have Twice as Many Depression Genes as Men, Says  Study

Women are genetically at higher risk of clinical depression than men, Australian researchers found in a study published last week that could change how the disorder is treated.
Billed as one of the largest-ever studies of its kind, scientists pored through the DNA of almost 200,000 people with depression to pinpoint shared genetic "flags".

Women had almost twice as many of these genetic markers linked to depression as men, according to the study.
The genetic component to depression is larger in females compared to males. Around 13,000 genetic markers were linked with depression in women, the researchers found, compared with 7,000 markers in men.

Some of these genetic changes could alter biological pathways linked to metabolism or hormone production.

https://www.nature.com/articles/s41467-025-63236-1