Ultraviolet-Extended Supercontinuum Generation in Zero-Dispersion Wavelength Decreasing Photonic Crystal Fibers

Supercontinuum covering the ultraviolet-blue region is highly useful for fluorescence microscopy. Four zero-dispersion wavelength decreasing photonic crystal fibers with different fiber cross structures and taper profiles are fabricated to extend the short wavelength edge of supercontinuum. Both nanosecond and picosecond pump pulses at 1 μm are used to generate supercontinuum. With a 3 ns pump pulse, the short wavelength edge of supercontinuum is extended to below 400 nm in a fiber with high air-hole ratio (named T3). The underlying mechanism of supercontinuum generation is explored. The short and long wavelength edges of supercontinuum are highly related with the phase-matching condition which decided by the group velocity curve of fiber small core end. With a 10 ps pump pulse, the spectral intensity around ∼800 nm increases in all four fibers. However, the intensity in shorter wavelength band decreased in fibers with a high air-hole ratio (named T3, T4). The experimental results imply that a zero-dispersion wavelength decreasing photonic crystal fiber suitable for nanosecond pulse pumping is not necessarily suitable for picosecond pulse pumping, especially for fibers with high air-hole ratio.