The use and control of light is vital to the development of technologies including energy harvesting, computing, communications and biomedical sensing. However, in real-world scenarios, the complexity of light behavior creates challenges for effective control. Physicist Andrea Alou likens the behavior of light in chaotic systems to a breakthrough move in a billiards game.

“Small changes in the way the cue is thrown in billiards will result in different bounce patterns of the balls on the table,” said Alou, Einstein Professor of Physics at the CUNY Graduate Center and founding director of the CUNY Photonics Initiative. Center for Advanced Study and CUNY Distinguished Professor.

“Light rays behave similarly in a chaotic vacuum. It becomes difficult to simulate to predict what will happen because you can run the experiment multiple times with the same settings and get a different response each time.”

In a new study published Natural PhysicsA team led by researchers at the CUNY Graduate Center describes a new platform for controlling the chaotic behavior of light by tailoring scattering patterns using the light itself. The project was led by co-authors Xuefen Jiang, a former postdoctoral researcher in Alu’s lab and now an assistant professor in the Department of Physics at Seton Hall University, and Shixiong Yin, a graduate student in Alu’s lab.

Conventional platforms used to study the behavior of light typically use resonance cavities of circular or regular shapes, where light is reflected and scattered in more predictable patterns. For example, in a circular space, only predictable and distinct frequencies (colors of light) survive, and each continuous frequency is associated with a specific spatial pattern or mode.

A single mode at a single frequency is sufficient to understand the physics operating in a circular cavity, but this approach does not reveal the full complexity of light behavior seen on complex platforms, Jaing said.

“In a cavity that supports chaotic light patterns, any single frequency injected into the cavity can excite thousands of light patterns, which is believed to destroy any chance of controlling the optical response,” Jaing said. “We showed that this chaotic behavior can be controlled.”

To solve this problem, the team designed a large stadium-shaped void with an open top and two channels on opposite sides that direct light into the void. As incoming light reflects off the walls and bounces around, a camera above records the amount of light exiting the stadium and its spatial patterns.

On the sides of the device are buttons to control the light intensity at the two inputs and the delay between them. Opposing channels cause light beams to interact with each other in the stadium space, allowing the distribution of one beam to be controlled by the other through a process known as coherent steering, which is essentially the use of light to direct light, according to Alu. By adjusting the relative intensity and delay of the light rays entering the two channels, the researchers repeatedly changed the pattern of light radiation outside the cavity.

This control was made possible by the rare behavior of light in resonant cavities called “reflective scattering modes” (RSMs), which had previously been predicted theoretically but not observed in optical cavity systems. According to Yin, the ability to manipulate RSMs demonstrated in this study enables efficient excitation and control of complex optical systems, which has implications for energy storage, computing, and signal processing.

“We found that at certain frequencies our system can support two independent, overlapping RSMs, allowing all light to enter the stadium cavity without being reflected back into our channel ports, thereby ensuring its control,” Yin said. said. “Our demonstration concerns optical signals within the bandwidth of the optical fibers we use in our daily lives, so this discovery opens up a new way to better store, direct and control light signals in complex optical platforms.”

The researchers aim to include additional switches in future studies that offer greater degrees of freedom to reveal greater complexity in the behavior of light.