1 W single-frequency Tm-doped ZBLAN fiber MOPA around 810 nm.

We demonstrate a tunable narrow-linewidth fiber MOPA system around 810 nm for the light source of the Sr optical lattice clock. The coherent cw light source with a wavelength of 813.42 nm was generated by a combination of a narrow linewidth external-cavity laser diode and a Tm-doped ZBLAN fiber amplifier, which was upconversion-pumped by an Yb-doped fiber laser at 1064 nm. The maximum output power of 1.1 W was obtained with the launched power of 17 W, which is the highest power obtained from a Tm-doped fiber amplifier ever reported.