Multimode Photonics

The recent use of multimode fibers within ultrafast lasers unveils a rising paradigm, where nonlinear processes such as beam self-cleaning can promote a wealth of spatiotemporal pulses and patterns, overcoming the adverse effects of the intermodal dispersion. The development of the next generation of telecommunication systems and ultrashort fiber laser sources will lead to a huge versatility in terms of system capacity, spectral coverage, and energy scalability, thus meeting an extended range of applications.

However, the fundamental understanding of nonlinear multimode propagation is still in its infancy. In this meeting, we will combine the complementary expertise from national and international leading scientists in optical fiber transmission, optical frequency combs and lasers, covering experimental, numerical, and theoretical aspects.

Multimode fiber systems will open the way to new spatial division multiplexing and laser architectures, whose performance can be developed in an unequalled manner, in particular in terms of information capacity, optical power and spectral coverage. New mode-locking techniques, as well as the generation of frequency combs that can be transposed in the infrared as well as in the visible range, will be exposed. Novel intracavity control schemes and numerical simulation techniques based on artificial intelligence will be discussed, which will permit to unbridle the full potential of nonlinear spatiotemporal coupling among different degrees of freedom.

Multimode (MM) optical fibers were used in optical telecommunications in the early 1980s, but considering the poor output radiation quality that resulted from the large number of propagation modes involved, they were mostly replaced by single-mode (SM) fibers. In particular, it has long been thought that ultrashort optical pulses required single transverse mode propagation in optical fibers and waveguides, owing to the expected impact of the large intermodal dispersion. Surprisingly, MM fibers are now experiencing a huge revival of research interest.

Indeed, recent advances are building up a new paradigm, in which well-designed nonlinear coupling processes in multimode (MM) waveguides, such as beam self-cleaning can promote the self-formation of spatiotemporal pulses and patterns, thus overcoming the adverse effects of the intermodal dispersion.

The increased interest for MM fibers is due in great part to their power upscaling possibilities, for which standard single-mode fibers cannot compete. Furthermore, novel efficient wavelength conversion processes specific to MM fibers pave the way for extending the wavelength range of coherent sources, which could become an alternative to supercontinuum generation in single mode (SM) fibers.

MM fibers have become again the object of active research, from fundamental prospects to the practical means to overcome the reached limits of single-mode fiber systems. Likewise in the telecom domain, MM fibers are considered as an efficient way to circumvent the current transmission limit of SM fibers and potential capacity crunch of our internet, by using spatial-domain multiplexing (SDM) as a potent signal multiplexing layer. SDM is a challenging technology that requires fine modal control and currently drives significant research efforts from high-tech companies.

To summarize, two major keys appear to enable this novel MM fiber paradigm: nonlinearity and control. Nonlinearity drives self-organization possibilities, such as beam self-cleaning, spatiotemporal optical solitons, and enhanced wavelength coverage. Nonlinearity implies high peak power, which is scalable through the design of optical waveguides. Control refers to the way a beam can be launched with a specific modal composition, selected, reshaped, and analyzed.

In the workshop, talks will describe how nonlinearity and control can be combined, in what we believe to be the most relevant physical system: the multimode fiber laser. In particular, the use of artificial intelligence could be the key for tackling the inherent complexity of using these two enabling keys, and unveil a wide range of new spatiotemporal dynamics with a high potential of applications. Talks shall address these issues and prospects from experimental, numerical and theoretical standpoints, benefitting from the complementarity expertise of top national and international researchers.

Presentations will review spatiotemporal nonlinear optics within multimode comb sources, fiber lasers and transmissions, considering the crossroad between fundamental and applied problems belonging to different research areas. The workshop will combine experiments with their analytical/numerical analysis: such a symbiotic description will provide appropriate interpretations of the experimental results, and inspire new ideas with the scope of identifying, explaining and controlling the key mechanisms of beam shaping and control in dissipative fiber lasers and comb sources, and transmission structures.

Self-organization effects in multimode systems involve fundamental aspects of nonlinear science, complexity, dissipative systems, optical pattern formation and their associated concepts and tools. From the application point of view, breakthrough advances are expected in high-power beam delivery from a fiber laser oscillator, and subsequent applications such as lidar or supercontinuum generation.

Main topics addressed

• Multimode optical frequency comb sources
• Spatial division multiplexing transmissions
• Machine learning photonics
• Multimode fiber lasers
• Biomedical multi-photon nonlinear imaging
• Fiber lasers for cultural heritage preservation
• Green photonics
• Nonlinear science and complex systems

Learning outcomes

Students will gain a strongly interactive learning experience of the state-of-the-art and applications for an emerging research field, jointly with the top experts at the world level.