Electric-arc-induced long period fiber gratings for gain equalization of erbium-doped optical amplifiers.

Long-Period Fiber Gratings (LPFGs) were fabricated in single mode fibers (SMF28) by using electric arc discharges produced from a commercial fiber splicer. In our experimental set-up, we noticed that, during each arc, the fiber becomes slightly tapered due to the presence of the longitudinal tension: the quantitative effect depends on the time length and arc power. We have experimentally studied how the LPFG performance may be affected by the arc discharge process, and we found that, with periods typically of few hundreds microns, the spectral response of the grating depends on the period &Lgr;, the intensity of the perturbation, the grating length and the type of mode-coupling induced. The reproducibility of the grating is very important, in particular for applications like a gain equalizer for an erbium-doped optical amplifier. In the modelling of the process, the mode coupling induced by the LPFG cannot be estimated directly from the transmission spectra; therefore, we propose a method to determine the mode-coupling occurring in the fiber and to assess the index modulation induced by the electric arcs. This method combines experimental and simulated data, and its use is not limited to the case of electric-arc-induced LPFGs.