Laser Performance of Active Segment Cladding Fiber Under Heat Load

An amplifier model based on the Yb-doped segment cladding fiber (SCF) is proposed in this paper. Three contributions to heat source are taken into account in the proposed model, including the quantum defect (QD), photodarkening (PD), and propagation loss (PL). Thermal-induced mode characteristics, amplification performance, modal gain competition, and high order modes (HOMs) filtering effect are theoretically investigated. Results show that the heat load generated from the Yb-doped SCF core makes the pre-design refractive index distribution into parabolic profile, and results in mode loss and effective mode area decline. Therefore, HOMs with low mode loss are amplified easily. Modal gain competition increases power content of HOMs that leads to laser performance degradation. Leaky cladding and bending operation introduce HOMs discrimination that can suppress HOMs amplification effectively. In high power pump, the counter-pumping amplifier presents higher temperature increase than the co-pumping one, while the high temperature location in Yb-doped SCF depends on pumping schemes. The results in this paper will provide guidance to optimize the structure of Yb-doped large mode area SCF and improve the thermal management of the high-power fiber lasers.