Magnifying time reveals fundamental rogue wave instabilities of nature
Researchers from the Photonics Laboratory of the Tampere University of Technology, working in collaboration with colleagues from France, Ireland and Canada, have used a novel measurement technique that magnifies time to reveal how ultrafast intense pulses of light can be generated from noise on a laser as it propagates in optical fibre. These experiments confirm theoretical predictions made decades ago, and may have implications in understanding the science of giant rogue waves on the ocean and the formation of other extreme events in nature. The work is published in the journal Nature Communications last December.
Instability and chaos are common in natural systems that are highly sensitive to initial conditions - where a small change in the input can lead to dramatic consequences. To understand chaos under controlled conditions, scientists have often used experiments with light and optics that allow the study of even the most complex dynamics on a benchtop. A serious limitation of these existing experiments in optics, however, is that the chaotic behaviour is often seen on ultrafast picosecond timescales - a millionth of a millionth of a second that is simply too fast to measure in real time using ordinary experimental equipment.
The recent experiments reported in the Nature Communications article by the team of Prof. Goëry Genty in collaboration with teams in France, Ireland and Canada have now overcome this limitation, using a novel experimental technique known as a time lens to magnify picosecond chaotic pulses by over 100 times so that they can be conveniently measured using a much slower ordinary electronic detector. The particular phenomenon that was studied is known as modulation instability, an optical Butterfly Effect that amplifies microscopic noise on a laser beam to create giant pulses of light with intensity over 1000 times that of the initial fluctuations. The experimental results have confirmed theoretical studies dating back to the 1980s. The results are also important in providing new insights into modulation instability, an ubiquitous noise amplification process considered as one of the possible mechanisms for describing giant rogue waves on the ocean, but also relevant to many other areas of physics including plasma dynamics in the early universe. Prof. Goëry Genty says that “these experiments are remarkable not only because they have allowed for a better understanding of modulation instability and extreme events in general, but also because they have now opened a new avenue to study, in real-time, chaotic dynamics on ultra-short time scales."