Extended blue supercontinuum generation in cascaded holey fibers

By combining multiple photonic crystal fibers with sequentially decreasing zero-dispersion wavelengths we have produced a $1.2\mathrm{W}$ average-power white-light continuum, covering the visible–near-infrared spectrum from $0.44\text{to}1.89\mu \mathrm{m}$ ($10\mathrm{dB}$ width), with an all-fiber picosecond ytterbium pump laser. Wavelengths as short as the ultraviolet $\left(0.35\mu \mathrm{m}\right)$, and spectral power densities of more than $2\mathrm{mW}∕\mathrm{nm}$ in the blue spectral region, have been generated. The process is understood in terms of optimizing four-wave mixing phase matching to enhance short-wavelength generation.