A high-power all-fiberized Yb-doped laser directly pumped by a laser diode emitting at long wavelength

We demonstrate a high power, laser diode pumped, all-fiberized Yb-doped fiber laser operating at 1173 nm wavelength at room temperature by using standard commercial double cladding fiber. A record output power of 15.7 W is obtained with respect to the pump power of 28 W; the slope efficiency is as high as 60%. We have experimentally studied the relationship of the threshold of parasitic lasing to the reflectivity of the output coupler. The results show that high reflectivity of the output coupler has more potential to suppress the parasitic lasing. From our experiments we can learn that long gain fiber has more potential to suppress amplified spontaneous emission (ASE) and increase the efficiency, but the effect decreases after the pump light is totally absorbed. We have also experimentally evaluated that there is no obvious difference between a 915 nm laser diode (LD) and a 976 nm LD as the pump source in suppressing the self-oscillation. All our experiments are demonstrated at room temperature which implies that the high-power long wavelength Yb-doped fiber laser can be achieved without heating the gain fiber.