Watt-level two-micron single-frequency DBR fiber lasers

We report the development and characterization of watt-level fiber lasers operating at 2050 nm using a low-OH- 4 wt.% Ho^3+-doped germanante fiber with a 10 μm core. Fiber lasers incorporating 5-cm, 7.5-cm, and 10-cm gain fibers were tested, yielding a maximum output power of 15.6 W with the 10 cm fiber laser at 21 W pump power, corresponding to a record-high optical-to-optical efficiency of 80%. An all-fiber distributed Bragg reflector (DBR) laser employing 3 cm gain fiber in-band pumped at 1940 nm by a Tm^3+-doped fiber laser was then developed and characterized. Owing to the low quantum defect of in-band pumping, this laser achieved a maximum output of 8.6 W at 20 W of pump power. These results demonstrate the strong potential for realizing a 10-W single-frequency DBR fiber laser at 2-μm through further optimization of thermal management and cavity design.