Spatial Division Multiplexing for Multiplex Coherent Anti-Stokes Raman Scattering

We demonstrate how a narrowband pump and a broadband spectrum can be spatially multiplexed by selective coupling them in two distinct modes of a few-mode microstructure fiber. The first mode carries most of the input pump energy, and experiences spectral broadening. Whereas the second mode preserves the narrow bandwidth of the remaining part of the pump. Bimodal propagation, with a power unbalance strongly in favor of the fundamental mode, is naturally obtained by maximizing coupling into the fundamental mode of the fiber. At the fiber output, the nearly monochromatic beam and the supercontinuum carried by the two different modes are combined by a microscope objective, and used as a pump and a Stokes wave for self-referenced multiplex coherent anti-Stokes Raman scattering micro-spectroscopy. The spectral resolution, the signal-to-noise-ratio, and the possible amplification of the remaining pump beam are discussed.Comment: 10 pages, 9 figure

Light-by-Light Control Enabled by Incoherent Beam Superpositions in Multimode Fibres

International audienc

Light by light manipulation in multimode fibers

International audienceWe 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]

Spatial Division Multiplexing for Multiplex Coherent Anti-Stokes Raman Scattering

International audienceWe demonstrate how a narrowband pump and a broadband spectrum can be spatially multiplexed by selective coupling them in two distinct modes of a few-mode microstructure fiber. The first mode carries most of the input pump energy, and experiences spectral broadening. Whereas the second mode preserves the narrow bandwidth of the remaining part of the pump. Bimodal propagation, with a power unbalance strongly in favor of the fundamental mode, is naturally obtained by maximizing coupling into the fundamental mode of the fiber. At the fiber output, the nearly monochromatic beam and the supercontinuum carried by the two different modes are combined by a microscope objective, and used as a pump and a Stokes wave for self-referenced multiplex coherent anti-Stokes Raman scattering micro-spectroscopy. The spectral resolution, the signal-to-noise-ratio, and the possible amplification of the remaining pump beam are discussed