Simultaneous generation of spectrally distinct third harmonics in a photonic crystal fiber

By coupling femtosecond pulses at $\lambda =1.55 \mu \mathrm{m}$ in a short length $\left(Z=95 \mathrm{cm}\right)$ of photonic crystal fiber, we observe the simultaneous generation of two visible radiation components. Frequency-resolved optical gating experiments combined with analysis and modal simulations suggest that the mechanism for their generation is third-harmonic conversion of the fundamental pulse and its split Raman self-shifted component.