A new optical device will strip solitons—particle-like light pulses that resist distortion—out of a laser beam, one by one, without disturbing the rest of the signal. Today’s optical communications and laser systems rely on Fourier analysis to process signals, but this standard method fails in nonlinear systems such as optical fibres, where different frequencies mix and the signal’s spectrum shifts unpredictably. The nonlinear Fourier spectrum, by contrast, stays stable as the signal travels. Its building blocks are solitons, but until now no optical method could add or remove individual solitons from that spectrum. The Optical Darboux Transformer, developed in this project, will allow researchers to control the nonlinear Fourier spectrum directly—adding or removing any number of solitons while leaving the rest of the signal intact. The team will test the device in optical fibres, fibre lasers, and resonators. If successful, the work could improve the performance of pulsed lasers, enable more robust optical communications, and allow researchers to engineer exotic states of light called soliton gases. The project is primarily fundamental science, but past work on nonlinear optics has led directly to technologies such as ultrafast lasers and long-haul fibre-optic networks.
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In this project we aim at demonstrating novel methods to perform signal processing in the optical domain for nonlinear systems such as lasers, optical fibres. Traditionally Fourier analysis is used to investigate the output of several devices including in the field of photonics where experimentalists look at the frequency spectrum of light emitted by lasers or propagating through optical fibres. In nonlinear systems several frequencies can interact and mix together and the standard Fourier spectrum dramatically changes upon evolution, which poses some challenges in preserving the content of information carried by the signal. It is however possible to mathematically define a nonlinear Fourier spectrum of a signal, which analyses the latter in such a way that the nonlinearity of the system is properly taken into account. While the the signal temporal profile is changing, its nonlinear Fourier spectrum remains substantially invariant, preserving the information content carried by the signal. In particular, the nonlinear Fourier spectrum contains, as building blocks, special waves called solitary waves or solitons. Optical solitons correspond to robust and localised structures (typically bright light pulses) behaving in a particle-like fashion, whose shape is unchanged upon propagation and collision. While a vast range of techniques, methods and optical devices have been developed and are available for the manipulation of the traditional Fourier spectrum (e.g. removing, adding or amplifying certain frequency components), so far the control of the nonlinear Fourier spectrum has not been achieved using optical methods. In this project we will develop, both theoretically and experimentally, special devices called Optical Darboux Transformers which enable to optically control the nonlinear Fourier spectrum of light wave signals. An Optical Darboux Transformer is a device which enables adding or removing an arbitrary number of solitons from the nonlinear spectrum of a signal without affecting its remaining properties. The proposed approach will be tested in several optical systems including optical fibres, fibre lasers and resonators in order to achieve shape and design the nonlinear Fourier spectrum of light in these setups. Possible applications of this research include, optical communications, improving the performance of pulsed lasers and controlling special states of light called soliton gases.
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