Single-frequency fiber laser operating at 2.9 μm.

We report the demonstration of a single-longitudinal-mode fiber laser operating at 2914 nm, which exhibits a spectrometer-limited linewidth of <0.4 nm, in a 49 mm long holmium/praseodymium co-doped ZBLAN fiber. Narrow-linewidth feedback is provided by a fiber Bragg grating inscribed directly in the ZBLAN fiber using the femtosecond laser point-by-point technique. Measurements of the temporal stability and coherence confirm that the laser is operating on a single longitudinal mode.