Researchers at the Photonics Laboratory of 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. The experiments confirm theoretical predictions made decades ago and may have implications for understanding the science of giant rogue waves on the oceans and the formation of other extreme events in nature. The study was published in Nature Communications last December. The Finnish part of the research was funded by the Academy of Finland.
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.
Time magnified magnification reveals the chaotic structure of an unstable modulation instability optical field that is otherwise too fast to be detected.
The recent experiments reported in the Nature Communications article by the team of Professor 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 more than 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 an intensity more than 1,000 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 oceans, but also relevant to many other areas of physics including plasma dynamics in the early universe.
Professor Genty said: "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've now opened a new avenue to study, in real-time, chaotic dynamics on ultra-short time scales."
Source: Press release by Tampere University of Technology