Experimental study of spectral broadening in kW-level narrow linewidth FBG-based fiber amplifiers under different pumping configurations

Abstract

In this work, experimental investigations were presented on the variation of spectral broadening and optical efficiency in a kW-level narrow linewidth MOPA fiber laser under different pumping configurations. The results revealed that the backward-pumping scheme could reduce the spectral broadening and enhance the optical efficiency compared with the forward-pumping scheme. For a detailed study, the bidirectional pumping setup was employed. It could be seen that by removing the pump diodes from the forward direction and adding them to the backward direction one by one, the spectral bandwidth and the optical efficiency gradually decreased and increased, respectively. By coiling the gain fiber on a plate with a bending diameter of 9-13 cm, a multi-peak and unstable spectrum was observed. When this fiber was coiled on a cylinder with a fixed diameter of 10.5 cm, the spectral instability was removed and a single-peak spectrum was observed. For forward pumping only, the spectral bandwidth, the optical efficiency, and the maximum output power were measured to be 0.121 nm, 78.92%, and 822 W, respectively, while for backward pumping only, these values were measured to be 0.084 nm, 82.65%, and 860 W.