Improving the formation probability and stability of noise-like pulse by weakening the spectrum filtering effect

Noise-like pulses (NLP) are extremely sought after in low-coherence tomography and supercontinuum, etc. Here, we propose an effective method to form the NLP in the all-normal-dispersion (ANDi) fiber laser by weakening the spectrum filtering for the first time. Numerical explorations are performed in detail and demonstrate that the NLP can be originated from the clustering behavior of amplified random sub-pulses led by the saturable absorber. By simulating the pulse-pattern distribution in the two-dimensional parameter space, it is further found that this kind of NLP pattern is widely distributed where are with a weak spectrum filtering. Since, the weaker the filtering, the harder the dissipative system to achieve balance, which helps to avoid the evolution from the pulse cluster to other coherent states and supports the NLP stability. To prove the feasibility experimentally, we built an ANDi fiber laser based on the nonlinear polarization rotating (NPR). The built laser can operate at the stable dissipative soliton (DS) state with a spectrum filter, which also with a 45 nm wavelength tuning performance. Replacing the filter, only NLP with a 40.2 ps pedestal and 237 fs spike can be attained. The experiments agree well with the numerical predictions. This exploration significantly broadens the design possibilities for ultrafast lasers, making them much more accessible to produce desired pulse patterns.