Nd3+-doped double-clad fluoro-sulfo-phosphate fiber for a compact kilohertz-linewidth single-frequency laser

The utilization of single-frequency fiber lasers spans critical domains including gravitational wave detection, coherent optical communication, and atomic physics. Glass fibers doped with rare earth ions serve as pivotal gain media for them, and the quest for advanced fiber matrices is paramount. Herein, a newly developed Nd 3+ -doped AlF 3 -Na 2 SO 4 -KPO 3 -Zn(PO 3 ) 2 glass is reported. The glass showcases exceptional attributes including high anti-crystallization stability (>150 ∘ C), elastic modulus (75 GPa), chemical durability (8.1×10 −7 g⋅cm −2 ⋅min −1 ), Nd 3+ concentration (>10 20 ions/cm 3 ), broad effective linewidth (45 nm), and extended lifetime (465 µs), surpassing those of conventional silica and phosphate glasses. Moreover, a custom-designed double-clad Nd 3+ -doped fiber with a net gain coefficient of 3.2 dB/cm at 1064 nm is fabricated, and single-frequency laser output with a narrow linewidth of 11 kHz has been obtained utilizing a 1.4-cm-long fiber, indicating the potential of this fiber as a promising gain medium for ultra-narrow-linewidth single-frequency fiber lasers.