13 December 2007

Engineers Generate "Rogue Waves"

by Kate Melville

"Rogue waves" or "freak waves" can appear and disappear without warning in the open ocean and have been the stuff of maritime folklore for centuries. Once dismissed by scientists as fanciful sailors' stories, recent observations have shown that they are a real phenomenon, capable of destroying even large modern ships. But studying how they form has been problematic as researchers have not been able to recreate them in water or any other medium.

Now, however, researchers at the UCLA Henry Samueli School of Engineering and Applied Science have succeeded in creating and capturing rogue waves. In their experiments, they have discovered optical rogue waves - freak, brief pulses of intense light analogous to the infamous oceanic monsters - propagating through optical fiber.

"Optical rogue waves bear a close connection to their oceanic cousins," said lead investigator Daniel Solli. "Optical experiments may help to resolve the mystery of oceanic rogue waves, which are very difficult to study directly."

It is believed that rogue waves are a nonlinear, perhaps chaotic, phenomenon, able to develop suddenly from seemingly innocuous normal waves. While the study of rogue waves has focused on oceanic systems and water-based models, light waves traveling in optical fibers obey very similar mathematics to water waves traveling in the open ocean.

But detecting a rogue wave is like finding a needle in a haystack, according to Solli. The wave is a solitary event that occurs rarely, and, to make matters worse, the timing of its occurrence is entirely random. But using a novel detection method they developed, the UCLA research group was able to not only capture optical rogue waves but to measure their statistical properties as well.

Reporting their findings in Nature, the team noted that, similar to freak waves in the ocean, optical rogue waves obey "L-shaped" statistics - a type of distribution in which the heights of most waves are tightly clustered around a small value but where large outliers also occur. While these occurrences are rare, their probability is much larger than predicted by conventional statistics.

"This discovery is the first observation of man-made rogue waves reported in scientific literature, but its implications go beyond just physics," said UCLA's Bahram Jalali. "For example, rare but extreme events, popularly known as 'black swans,' also occur in financial markets with spectacular consequences. Our observations may help develop mathematical models that can identify the conditions that lead to such events."

Solitons Observed In A Solid

Source: University of California - Los Angeles