Compact single-frequency fiber laser oscillator emits watts-level output power at 1.5 mm

The design of an all-fiber single-frequency Er-Yb laser oscillator, that produces 1.9 W of direct output power at 1.5 μm, is described. The 11-cm-long, side-pumped active fiber section is composed of soft phosphate glass, which allows a massive doping concentration, 1 weight percent of Er and 8 weight percent of Yb. An active fiber, used as a gain medium of a multimode fiber laser, can produce as much as 1.33 W of output power per centimeter of fiber. To improve the longitudinal mode selection in the laser, a Bragg grating is spliced behind the primary single-mode reflector.