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.

Automated summary

This paper demonstrates the spatial multiplexing of a narrowband pump and a broadband spectrum in a few-mode microstructure fiber by selectively coupling them in two different modes. One mode preserves the narrow bandwidth of the pump while the other mode experiences spectral broadening. Bimodal propagation is achieved by maximizing the coupling into the fundamental mode of the fiber. The combined output beam is used for self-referenced multiplex coherent anti-Stokes Raman scattering micro-spectroscopy.