For storing light in optical resonators, chaos proves superior to order

Thuwal, Saudi Arabia--In a collaboration led by the King Abdullah University of Science and Technology (KAUST), researchers have found that chaos (in other words, a hypersensitivity to initial conditions) can beat order when it comes to light storage in optical resonators. The team includes researchers from the Universities of York and St. Andrews (York, England and Fife, Scotland respectively) and from the University of Bologna (Bologna, Italy).

The experiments were carried our in photonic-crystal resonators and in polystyrene microspheres. The researchers deformed mirrors in order to disrupt the regular light path in these optical resonators; the resulting chaotic light paths allowed more light to be stored than with ordered paths. The work has applications for many branches of physics and technology, such as quantum optics and processing optical signals over the internet, where light needs to be stored for short periods to facilitate logical operations and to enhance light-matter interactions.

"Even very simple cavities, such as glass spheres, show the effect: when the spheres were squashed, they stored more light than the regular spheres," says Thomas Krauss, a professor in the department of physics at the University of York. The researchers demonstrated a sixfold increase of the energy stored inside a chaotic cavity in comparison to a classical counterpart of the same volume. The results were reported in Nature Photonics.

"The concept behind broadband chaotic resonators for light-harvesting applications is very profound and complex," notes Andrea Di Falco, who is from the school of physics and astronomy at the University of St. Andrews. "I find it fascinating that while we used state-of-the-art fabrication techniques to prove it, this idea can in fact be easily applied to the simplest of systems."

"Chaos, disorder, and unpredictability are ubiquitous phenomena that pervade our existence and are the result of the never-ending evolution of Nature," says Andrea Fratalocchi, who is from KAUST. "The majority of our systems try to avoid these effects, as we commonly assume that chaos diminishes the performance of existing devices. The focus of my research, conversely, is to show that disorder can be used as a building block for a novel, low-cost, and scalable technology that outperforms current systems by orders of magnitude."

"The cost of many semiconductor devices, such as LEDs and solar cells, is determined to a significant extent by the cost of the material," says Krauss. "We show that the functionality of a given geometry, here exemplified by the energy that can be trapped in the system, can be enhanced up to six-fold by changing the shape alone, i.e. without increasing the amount of material and without increasing the material costs."