Width- and amplitude-tunable double-scale pulse in a low-repetition-rate mode-locked fiber laser

• Achievement of a width- and amplitude-tunable double-scale pulse output from a single fiber laser system. • Verification of noise-like square pulse output in the near-zero dispersion regime. • Pump-controlled evolution of the pedestal width of the NLSPs and its effect on femtosecond peaks. • Numerical simulations confirming the physical mechanism of width- and amplitude-tunable double-scale pulse formation. The generation and evolution of double-scale pulse from a single low-repetition-rate fiber laser cavity are theoretically and experimentally investigated. A 4.5-MHz-repetition-rate mode-locked laser cavity is constructed by introducing sufficient long fiber and nonlinear polarization evolution. By finely adjusting the intracavity state of polarization and pump parameters, noise-like square pulses are demonstrated in the near-zero dispersion regime. Besides, the individual control of amplitude and pulsewidth of noise-like square pulses is obtained by configuring bidirectional pumps. These results provide valuable theoretical and experimental insights for the design, construction, and control of low-repetition-rate, noise-like square pulses fiber lasers.