Grating phase matching beyond a continuum edge.

We show that fiber Bragg gratings can extend an optical continuum to spectral regions where continuum generation is very weak. Highly nonlinear fibers with Bragg grating resonances at 700, 750, and $800\mathrm{nm}$ were pumped with $70\mathrm{fs}$ pulses at $1580\mathrm{nm}$ and exhibited enhancement peaks up to $25\mathrm{dB}$ above the extremely weak continuum at these wavelengths, normally more than $40\mathrm{dB}$ below the average power in the continuum. We show that the grating peaks may be computed by treating the continuum pulse as an undepleted pump and including the grating dispersion as a phase-matching term.