Fluoro-sulfo-phosphate fiber with long-wavelength gain for an L-band laser

In this work, a self-developed Er 3+ /Yb 3+ co-doped fluoro-sulfo-phosphate (FSP) fiber with long-wavelength gain characteristics has been reported. The mixed-ion strategy manipulates the ligands of rare-earth ions, leading to a broad gain bandwidth (almost twice that of phosphate fiber) and excellent amplification ability at the extended wavelength (>2dB/cm at the L-band). As showcases of its features, a 1617-nm fiber laser based on a 1-cm-long FSP fiber is constructed. Furthermore, an all-fiber-integrated L-band passively mode-locked laser based on a 2.2-cm-long fiber with a fundamental repetition rate of 4.3 GHz is demonstrated. The generated pulse exhibits a high signal-to-noise ratio larger than 80 dB in the radio-frequency domain and a low relative intensity noise of 0.04%.