Theoretical Investigation of Thermal Effects in High Power Er3+/Yb3+‐ Codoped Double‐Clad Fiber Amplifiers for Space Applications

In this paper, a multiphysics numerical model based on the spatial-dependent rate equations and 3-D non-homogeneous heat conduction model is used to investigate the performance of Er3þ/Yb3þ-codoped double-clad fiber amplifiers with respect to the constraints associated with space applications. The effects of fiber length, coating thickness, and core radius changes are analyzed. Furthermore, the impact of thermal heating due to the high power optical signals propagating along the fiber on the amplifier gain is examined. The temperature dependence of the refractive index, emission and absorption cross sections, as well as the radiation induced attenuation is derived and modeled. It is observed that the coating thickness affects the temperature distribution along the whole fiber length. Thicker coating mitigates the temperature variation along the fiber as well as it improves the temperature difference between the core center and the outer fiber surface. Moreover, larger core results in higher optical gain and shorter fibers. By numerical results, it is inferred that the thermal effects could strongly degrade the whole amplifier performance.