An unstable modulation instability optical field consisting of picosecond pulses that are normally too fast to be detected. The use of the technique of time magnification allows these chaotic pulses to be measured for the first time. © Benjamin Wetzel
Researchers from INRS and the FEMTO-ST Institute in France 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. In optics, these waves occur as short and intense light pulses. The work is published in the journal Nature Communications on December 19 2016.
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, which 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 even using the fastest available experimental equipment.
An international collaboration with teams in Canada, France, Finland and Ireland have now overcome this limitation, using a novel experimental technique known as a time lens. “In a similar way as a stroboscope can resolve the evolution of a bouncing ball in the dark or the movements of dancers in a night club, this time lens technique can take one million snapshots of the optical field every second, while additionally increasing the temporal resolution by a factor of 100. This approach allowed us to efficiently measure the chaotic dynamics of the light pulses and their temporal characteristics via available electronic detectors.” explains Benjamin Wetzel, researcher in the group of Pr. Morandotti at INRS, Canada.
The experimental results have confirmed theoretical studies dating back to the 1980s. 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 noise on the injected laser beam.
These results are important because there is currently intense interest in studying noise amplifying instabilities in many different areas of physics, from trying to unravel the physics describing giant rogue waves on the ocean, to understanding plasma dynamics in the early universe. John Dudley, the lead Investigator of the work at FEMTO-ST highlights that “there are many systems in nature where it is very difficult to study rapid fluctuations associated with instabilities, but the ability to magnify ultrafast dynamics in optics now opens a new window into performing more experiments in this field.” ♦
Real-time measurements of spontaneous breathers and rogue wave events in optical fibre modulation instability. M. Narhi, B. Wetzel, C. Billet, S.Toenger, T. Sylvestre, J.-M. Merolla, R. Morandotti, F. Dias, G. Genty, J. M. Dudley. Nature Communications 7, DOI: 10.1038/ncomms13675 (2016).
Single-shot observation of optical rogue waves in integrable turbulence using time microscopy. P. Suret, R. El Koussaifi, A. Tikan, C. Evain, S. Randoux, C. Szwaj & S. Bielawski. Nature Communications 7, Article number: 13136 (2016).
The international research team is constituted by researchers from the Tampere University of Technology (Finland), Institut national de la recherche scientifique (INRS) (Canada), University College Dublin (Ireland) and Institut FEMTO-ST, CNRS (France).