Identification of Coherent and Incoherent Spectral Sidebands in an Ultrafast Fiber Laser

Ultrafast fiber lasers, as the soliton pulse sources, offer great platforms for the investigations of soliton dynamics. Since both the coherent and incoherent spectral sidebands could be shown on the soliton spectrum, herein we proposed a method to identify them by using the dispersion Fourier transformation (DFT) technique. According to the principle of DFT technology, for the coherent spectral sidebands, that is, Kelly sidebands in the mode-locked fiber laser, they could be mapped to the temporal waveforms after the DFT process. However, the incoherent spectral sidebands, namely continuous waves, would disappear on the shot-to-shot spectra after DFT due to their uncertain phase relation. The obtained results would deepen our understanding of spectral sidebands.