Spectral sidebands of dissipative soliton in a positive fourth-order-dispersion fiber laser

Recently, the dissipative soliton (DS) generation in the positive fourth-order-dispersion (FOD) fiber laser has been theoretically predicted, namely dissipative pure-quartic soliton (DPQS), featuring a higher energy-scaling ability compared to conventional DS dominated by positive group velocity dispersion. Here, we discover that the formation of spectral sidebands is always accompanying by the stabilized DPQS in the fiber laser, which is different from the conventional DS. Due to the combination of positive FOD and self-phase modulation, low- and high-frequency components are distributed at the leading and trailing edges of the pulse, forming the pedestals that propagate with it. In the frequency domain, these high- and low-frequency components of the spectrum provide the conditions necessary for the interference between dispersive waves and DPQS. Furthermore, the unique U-shaped phase curve of FOD results in densely distributed phase-matching frequencies, i.e., densely distributed sidebands. The characteristics of spectral sidebands are also numerically studied, which are well consistent with the experimental results. These findings enable a deeper understanding of DPQS and further optimize the performance of fiber lasers.