Performance optimization of a GHz-repetition-rate fundamentally mode-locked Tm-fiber laser using tapered fiber...

In this work, we report on the optimization of GHz-repetition-rate passively mode-locked Tm³⁺-doped fiber lasers by tapering the gain fiber. By leveraging a versatile mode field diameter of a single-sided conical tapered fiber that attaches to the saturable absorber, evident spectral broadening and femtosecond pulse generation are fulfilled in the soliton mode-locking operation. In this scenario, a mode-locked pulse operating at a fundamental repetition rate of 1.03 GHz has a 3-dB spectral bandwidth of 10.26 nm and a pulse width of ∼524 fs. The phase noise in the high-frequency range of >200 kHz, in contrast to the untapered case, is well suppressed. The present work offers an approach to manipulate effective intracavity nonlinearity and realize a significant optimization of the mode-locking performance.