Passively Mode-Locked Tm3+-Doped Fiber Laser With Gigahertz Fundamental Repetition Rate

We propose and demonstrate a compact passively mode-locked Tm
³⁺
-doped fiber laser with a fundamental repetition rate up to 1.6 GHz. A 5.9 cm home-made, heavily Tm
³⁺
-doped barium gallo-germanate glass fiber with a gain coefficient of 2.3 dB/cm at 1950 nm is employed as gain medium. The compact Fabry-Perot (FP) laser cavity contains a fiber mirror by directly coating the SiO
₂
/Ta
₂
O
₅
dielectric films on a fiber ferrule. The miniature FP laser pumped by a 793-nm laser diode is passively mode-locked by a semiconductor saturable absorber mirror. Stable self-started mode-locking is successfully achieved at a low pump threshold of 107 mW. The mode-locked operation at the central wavelength of 1959.7 nm has a spectral bandwidth of 12.2 nm, and the pulse duration of 7.2 ps. In particular, the pulse repetition frequency of the fundamental mode-locking can be as high as 1.6 GHz. Moreover, numerical simulation for the 2-μm mode-locked Tm-doped fiber lasers is performed using the lumped model, and the numerical results are in good agreement with the experimental ones. This is, to the best of our knowledge, the highest fundamental repetition frequency for the 2-μm mode-locked fiber lasers.