Characterization of Dark Soliton Sidebands in All-Normal-Dispersion Fiber Lasers

We experimentally investigated the spectral side-bands formation in all-normal-dispersion fiber lasers. It was found that the sidebands always appear in a pair, in a spectral configuration symmetric to the laser emission wavelength. Although the positions of the sidebands are independent of the laser intensity, they varied with the total cavity dispersion. With the help of numerical simulations, we demonstrated that the laser delivers dark solitons and the sidebands are of the Kelly type, which is an experimental evidence of the generation of Kerr-type dark solitons in fiber lasers.