Experimental study of a 100-W all-fibre amplifier operating near 980 nm

A 100-W all-fibre amplifier operating near 980 nm is demonstrated with a double-clad Yb-doped fibre (DCYF) having a 60/125-μm core/cladding diameter. By preliminarily optimising the length of DCYF (about 1.4 m), a total output power of about 113.4 W is obtained with 9-W seed light, the peak-to-peak suppression of 1030-nm ASE being about 21.5 dB. The effect of active fibre length is studied using the experimental setup. With the help of spectrum integration, it is found that while the total output power decreases, the output power around 980 nm is enlarged with the active fibre (i.e., DCYF) further shortened to 1.2 m, which is due to better suppression of 1030-nm ASE. It means that the effect of 1030-nm ASE cannot be simply neglected when its peak-to-peak suppression is lower than 30 dB. The effect of seed power on the output properties of the amplifier is also studied experimentally. It is found that a stronger seed power is beneficial to the 1030-nm ASE suppression and slope efficiency improvement. Then, with the 1.2-m DCYF and 14-W seed power, the largest output signal power around 980 nm (estimated about 108.2 W) is eventually obtained and the peak-to-peak suppression of 1030-nm ASE is more than 33 dB at the maximum output power. The pertinent results can provide significant guidance for the design and study of a 980-nm laser and other sorts of three-level fibre laser.