75 fs-Pulse Duration, ∼200 Nm-Span, Distributed Dispersion Managed 2 μm Ultrafast Fiber Laser

In this letter, we presented a stable and self-starting Thulium-doped fiber oscillator based on nonlinear polarization rotation (NPR) mode-locking method. The dispersion inside the fiber oscillator is managed with different dispersive fibers distributed to different position inside the fiber oscillator. The output pulse has a broad spectrum extending from 1.824 μm to 2.005 μm with a pulse repetition frequency of 45.5 MHz. A maximum output power of 123 mW is achieved with a single pulse energy of 2.70 nJ. The obtained laser pulse can be linearly compressed to the Fourier transform limitation of 75 fs. Additionally, we theoretically investigated the influence of the amount of dispersion and distribution of the dispersion on the characteristics of the output laser pulse. Such a distributed dispersion-managed laser offers a straightforward approach for direct generation of ultrafast laser pulses in sub-100 fs regime.