Suppression of modal noise in a multimode fiber optic delivery output from an ultra-broadband supercontinuum light source

We have tested various methods to suppress the modal noise in multi-mode fiber (MMF) output from an ultrabroadband supercontinuum light which is generated in a nonlinear photonic-crystal fiber (PCF) pumped with a 1.06-μmwavelength, sub-nanosecond-pulse-width, 8-kHz-rep-rate Nd:YAG laser source. Significant amount of modal noise including spectral fluctuations was observed when the output from the photonic crystal single-mode fiber (SMF) was directly coupled into MMF. Standard mode-exciting and -mixing techniques such as mode scrambling and fiber stretching showed minimal effect on noise suppression. We observed significant suppression of modal noise by expanding the output beam from the PCF and tightly focus back into MMF using multiple lenses. The resulting spectra of the different MMFs are compared with the output from different SMFs coupled to the supercontinuum source, which are necessary to cover the broadband range of the supercontinuum source over more than two octaves, from 450 nm up to 2100 nm wavelength.

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