We successfully demonstrate a widely all -parameter-tunable ultra-narrow-linewidth nearly transform-limited mode -locked erbium-doped fiber laser. Pulse -width -adjustable (100150 ps) low -repetition -rate (-2 MHz) dissipative solitons are generated over the pulse breakup -free wavelength tuning range of 34.3 nm (1529.3-1563.6 nm). 2020 The Author(s)