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Experiments in optics could eventually help understand and predict rogue waves

Associate Professor, Academy Research Fellow Göery Genty from Tampere University of Technology (TUT) was part of an international team investigating how lasers and optical fibres can be used to understand freakishly large waves on the ocean.

Rogue waves, also known as freak waves, monster waves or killer waves, are rare, abnormally large waves that can unexpectedly emerge from the sea, potentially causing maritime disasters. These giant walls of water that suddenly appear from nowhere were considered part of maritime folklore for a long time, but now experimental evidence is available. Interestingly, under certain conditions, the propagation of ocean waves and that of short and intense pulses of light in an optical fibre are analogous and can both be described using the same mathematical equations.

In two recent papers published in Nature Photonics and Nature Communications, Associate Professor, Academy Research Fellow Goëry Genty from the Optics Laboratory at Tampere University of Technology, together with his international network of collaborators, highlights how optics can be an ideal test-bed to study a wide range of fascinating natural phenomena that cannot be easily studied in their original environments.

The collaborators are Professor John M. Dudley from the University of Franche-Comté, France, Professor Frédéric Dias from the University College Dublin, Ireland, and PhD Miro Erkintalo, who completed his doctorate at TUT under the supervision of Goëry Genty and presently works in New Zealand at the University of Auckland's Department of Physics. The researchers present a synthetic overview of the field of optical rogue waves in the October issue of Nature Photonics (Instabilities, breathers and rogue waves in optics).

The review paper summarises the major advances in the field, clarifying the underlying physics and highlighting the regimes of propagation where the knowledge between optics and hydrodynamics can be shared. The review is the result of a long-term collaboration established within the framework of the optical rogue waves project funded by the Academy of Finland in 2009 between researchers recognised as experts in fibre optics on one hand and water waves on the other hand. The project has explored extensively the optics-ocean analogy and resulted in the publication of more than 30 papers in international peer-reviewed journals with several seminal results that have highlighted how optics can play a role in clarifying ideas from other research fields in physics.

Another example of a natural phenomenon that can be mimicked in an optical fibre is the event horizon that occurs when the gravitational pull becomes so intense that light cannot escape black holes or enter white holes. For this reason, the event horizon is often referred to as the "point of no return" in the case of black holes or as the "point of no entry" in the case of white holes. Similar physics underlie the nonlinear interaction of intense light in an optical fibre with a weaker pulse of light wave travelling at different velocities.

“This picture not only suggests interesting links with general relativity but the underlying dynamics have also been postulated to influence the formation of optical rogue waves,” says Göery Genty.

In the September issue of Nature Communications (Nonlinear optics of fibre event horizons), again together with his colleagues from the University of Franche-Comté and from the University of Auckland, Genty provided a novel physical description of fibre-optic event horizons using only continuous wave lasers.

Such a simple and neat description of the physics may have immediate impact in the analysis of quantum characteristics of optical gravitational analogs. The results were obtained within the framework of Genty's Academy Research Fellow post, which led to the publication of more than 50 peer-reviewed articles in major international journals over the last five years.

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