Maritime folklore tells tales of freak waves that appear without warning in the open ocean, devouring ships, but leaving no trace. These fabled sea monsters have featured in literary works from the Odyssey to Robinson Crusoe. But as far as science was concerned, so-called "rogue waves" have always been dismissed as sailors' tall tales.

Nevertheless, rumours have persisted, thanks to a series of real life mysteries which some say can only be explained by freak waves.

In December 1900, three lighthouse keepers were found to have vanished from the Flannan Isles, west of Lewis, leaving chairs overturned and beds unmade. They are thought to be the victims of a freak swell which tore them from rocks 33 metres (110ft) above sea level.

So too are the crew of the cargo ship MS Munchen, which disappeared in the North Atlantic in 1978, after a garbled mayday message.

More than 200 super-carriers - ships over 200m long - have been lost in the last two decades, many, say eye-witnesses, sunk by waves whose scale defied belief.

Until, that was, New Year's Day of 1995, when the world's first freak wave was officially recorded - as it crashed into the Draupner oil platform, in the North Sea off the coast of Norway. While the waves either side of it were a steady 4m high, the "Draupner wave" was 18.5m at its peak. It seemed to appear from nowhere.

Since then, satellite observations by the European Space Agency have shown that rogue waves are not mythical phantoms, but a real phenomenon. Their MaxWave project detected 10 giant waves, all of which were over 25m (81ft) high.

Scientists have been racing to simulate freak waves and discover what causes them. But true to their nature, answers continue to elude researchers.

Detecting a rogue wave in nature is practically impossible, as is recreating one in the laboratory. Consequently, man-made rogue waves have not been reported in scientific literature, in water or in any other medium.

But now a team of researchers at the University of California, Los Angeles, have succeeded in creating and capturing rogue waves, using an ingenious model. Instead of using water, they looked at light.

Light waves travelling in optical fibres obey similar mathematics as water waves travelling in the open ocean. Using this model, the UCLA team discovered optical rogue waves - freak brief pulses of intense light analogous to the infamous oceanic monsters. Their findings are reported this month in the journal Nature.

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

So what are the conditions which trigger a freak wave? The team were able to show they can arise when packets of normal waves combine to form one "super wave".

The phenomenon will be familiar to concert-goers who have experienced the howl of feedback that occurs when repeated sound waves collide to form one giant squeal.

In a similar way, Solli's team showed that extremely steep light waves may arise in optical fibres by injecting a series of smaller, almost identical optical pulses. Random variation, known as noise, in the system can upset the initially smooth pulses, and will generate a mighty wave if it causes a certain frequency shift.

"This is the first observation of man-made rogue waves. But its implications go beyond physics," said Bahram Jalali, professor of electrical engineering at UCLA.

"Rare but extreme events, 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."

Can it be that the Flannan Isles lighthouse keepers were victims of the same phenomenon which governs Wall Street's fortunes?

The mathematics of nature are stranger than any seafarer's fiction.