Noise characterization of the ∼915 nm figure-9 mode-locked fiber lasers operating in dissipative and dispersion-managed soliton regimes

Polarization-maintaining Nd-doped mode-locked fiber lasers at ∼915 nm find extensive applications in precision machining and other fields. These applications are sensitive to the noise characteristics of lasers, which differ significantly with the chosen mode-locking mechanism. However, systematic research in the noise characterization of the Nd-doped fiber lasers with different mode-locking mechanisms is currently lacking. This study investigates noise in ∼915 nm dissipative soliton (DS) and dispersion-managed soliton (DMS) figure-9 fiber lasers. The DMS laser achieves an integrated root-mean-square (RMS) phase noise of 0.04 rad, which is significantly lower than the 1.51 rad measured for the DS laser, owing to weak time-frequency noise coupling (and other factors). In terms of the relative intensity noise (RIN), the DS has an integrated RMS RIN of 0.035%, which is comparable to the one of the DMS (0.019%). Despite the weak self-amplitude modulation saturation, narrowband filtering provided by a fiber Bragg grating in the DS laser suppress amplified-spontaneous-emission-induced noise and consequently results in comparable integrated RMS RIN. These findings clarify mechanism-dependent noise profiles and key parametric trade-offs, providing a scientific basis for laser design and selection across diverse application scenarios.