Light by light manipulation in multimode fibers
Résumé
We demonstrate that a low-intensity beam can be severely cleaned or distorted by a high-energy pump beam copropagating in a multimode optical fibre at different wavelengths. Thus, the M² coefficient of the weak beam is either enhanced or degraded relative to the pump intensity, allowing an ultra-fast light-by-light control. This unconventional development extends the concept of the self-cleaning process where a single beam undergoes a significant brightness improvement under its own peak power. Providing additional degrees of freedom, a multimode beam propagation has been attracting a great interest, as it allows unveiling various new processes based on its highly complex dynamics [1-4]. Among others, Kerr-induced beam self-cleaning is one of the most debating phenomenon recently discovered. It permits changing a speckled structure into a quasi-single mode beam by using the light intensity itself. Such a self-transformation can be explained in terms of four-wave-mixing interactions, so far, demonstrated only at a single wavelength due to a nonlinear non-reciprocity of the mode coupling process [4]. This behaviour arises from a presence of self-phase-modulation differently impacting high-order and low-order modes. However, up to now this process seems resulting only in particular, Rayleigh-Jeans, energy distribution without allowing an on-demand control of the energy distribution over the guided modes [5].
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