Utilizing and controlling light is important for developing technology, such as communications, computation, biomedical sensing, and energy harvesting. In real-world scenarios, however, light has complex behavior, which poses challenges for its efficient control.
Disordered Nature of Light
Chaos is an intrinsic feature of many nonlinear systems which demonstrate the transition from a steady to a disorderly state independently of the physical properties of the system. Such behavior can be observed in optics, both in lasers and in nonlinear optical devices.
According to physicist Andrea Alù from the City University of New York (CUNY), the behavior of light in chaotic systems resembles the initial break shot in a game of billiards. In this game, there are tiny variations in which the player can launch the cue ball, and each can lead to various patterns of the balls bouncing around the table.
Light rays work similarly in a chaotic cavity. Experts can run an experiment many times with similar settings but still get a different response every time, making it difficult to predict what might happen next.
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Bartering Light for Light
Scientists at the CUNY Graduate Center developed a new platform for controlling the chaotic behavior of light. Led by Xuefeng Jiang and Shixiong Yin, the researchers tailored the scattering patterns of light using light itself.
Conventional methods of studying the behavior of light use platforms with circular or regularly shaped resonant cavities where light bounces and scatters in a more predictable manner. For instance, in a circular cavity, only predictable and distinct frequencies survive, and each supported frequency is linked to a specific spatial pattern or mode.
A mode at a single frequency is enough to understand the mechanisms of a circular cavity, but this method does not unleash the entire complexity of the behavior of light observed in complex platforms. In a cavity that supports chaotic optical patterns, any single frequency injected into the cavity can excite thousands of light patterns. This is conventionally believed to break the chances of controlling the optical response, yet the researchers claim to have demonstrated the possibility of controlling this disorderly behavior.
To make this possible, the scientists designed a large stadium-shaped cavity with an open top and a pair of channels on both sides, which direct the light into the cavity. The incoming light scatters off the walls and bounces around, and the amount of light that escapes the stadium is recorded by a camera, along with its spatial patterns.
The device has knobs on its sides for managing light intensity at the two inputs. As the researchers adjusted the relative intensity and delay of the light beams that entered the channels, they consistently altered the radiation pattern of light outside the cavity.
This control was enabled using a rare behavior of light in resonant cavities known as "reflectionless scattering modes" (RSM). This ability had been theoretically predicted before but was not observed in optical cavity systems. According to Yin, the successful manipulation of RSMs enabled the efficient excitation and control of complex optical systems, which can impact computing, energy storage, and signal processing.
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