Harnessing and controlling light is essential for advancing technology, encompassing energy harvesting, computation, communications, and biomedical sensing.
However, in practical situations, the intricate nature of light’s behavior presents challenges for its effective manipulation. Physicist Andrea Alù draws a parallel between light’s behavior in chaotic systems and the opening break shot in a game of billiards.
In billiards, tiny variations in the way you launch the cue ball will lead to different patterns of the balls bouncing around the table. Light rays operate in a similar way in a chaotic cavity. It becomes difficult to model to predict what will happen because you could run an experiment many times with similar settings, and you’ll get a different response every time.
Andrea Alù, Professor, Physics, Advance Science Research Center
Alù is also the Founding Director of the Photonics Initiative at the CUNY Advanced Science Research Center and a distinguished professor at CUNY.
In a recent publication in the journal Nature Physics, a group of researchers from the City University of New York (CUNY) introduced a novel approach to manipulate the unpredictable nature of light by customizing its scattering patterns through the utilization of light itself.
Leading the project were co-first authors Xuefeng Jiang, previously a Postdoctoral Researcher in Professor Alù’s laboratory and now an Assistant Professor of Physics at Seton Hall University, and Shixiong Yin, a Graduate Student in Professor Alù’s research group.
Unlike traditional methods that involve circular or regularly shaped resonant cavities to study light’s behavior, this innovative platform offers a more dynamic and controlled means to investigate and shape light’s scattering behaviors.
In a circular cavity, only well-defined and specific frequencies corresponding to different colors of light remain viable, and each of these supported frequencies corresponds to a particular spatial pattern or mode.
While a single mode at a specific frequency suffices to comprehend the physics within a circular cavity, this approach does not unlock the complete intricacy of light’s behaviors, as observed in more intricate platforms, as explained by Jaing.
In a cavity that supports chaotic patterns of light, any single frequency injected into the cavity can excite thousands of light patterns, which is conventionally thought to doom the chances of controlling the optical response. We have demonstrated that it is possible to control this chaotic behavior.
Xuefeng Jiang, Assistant Professor, Physics, Seton Hall University
To tackle this challenge, the team devised a stadium-shaped cavity, notable for its open top and two channels positioned on opposite sides that guide incoming light into the cavity.
As the incident light scatters off the inner walls and undergoes multiple reflections, an overhead camera captures the escaping light’s quantity and its spatial distribution.
The device incorporates adjustable controls on its sides to regulate the intensity of light entering the two input channels and manipulate the timing between them.
The opposing channels induce interference between the light beams inside the stadium cavity, allowing for the manipulation of one beam’s scattering behavior through a process called coherent control. Essentially, this involves using light itself to govern the behavior of light, as explained by Alù.
Remarkably, by fine-tuning the relative intensity and time delay of the light beams entering the two channels, researchers consistently managed to modify the external radiation pattern of the light emitted from the cavity.
This level of control was made possible by a unique phenomenon of light within resonant cavities known as “reflectionless scattering modes” (RSMs).
Although these modes had been theoretically postulated in the past, they had not been observed in optical cavity systems until now.
Yin emphasized that the demonstrated capability to manipulate RSMs in this study opens up possibilities for efficiently exciting and managing intricate optical systems. This development has significant implications for fields such as energy storage, computing, and signal processing.
We found at certain frequencies our system can support two independent, overlapping RSMs, which cause all of the light to enter the stadium cavity without reflections back to our channel ports, thus enabling its control.
Shixiong Yin, Graduate Student, Advance Science Research Center
Yin added, “Our demonstration deals with optical signals within the bandwidth of optical fibers that we use in our daily life, so this finding paves a new way for better storage, routing, and control of light signals in complex optical platforms.”
In future research, the scientists intend to introduce additional controls, providing an increased number of adjustable parameters, to delve deeper into the intricate behaviors of light.
Jiang, X., et al. (2023) Coherent control of chaotic optical microcavity with reflectionless scattering modes. Nature Physics. doi.org/10.1038/s41567-023-02242-w.