Coherent supercontinuum generation up to 2.2 µm in an all-normal dispersion microstructured silica fiber

For the first time to our knowledge, we demonstrate a coherent supercontinuum in silica fibers reaching 2.2 µm in a long wavelength range. The process of supercontinuum generation was studied experimentally and numerically in two microstructured fibers with a germanium doped core, having flat all-normal chromatic dispersion optimized for pumping at 1.55 µm. The fibers were pumped with two pulse lasers operating at 1.56 µm with different pulse duration times equal respectively to 23 fs and 460 fs. The experimental results are in a good agreement with the simulations conducted by solving the generalized nonlinear Schrödinger equation with the split-step Fourier method. The simulations also confirmed high coherence of the generated spectra and revealed that their long wavelength edge (2.2 µm) is related to OH contamination. Therefore, improving the fibers purity will result in further up-shift of the long wavelength spectra limit.