Effect of thermal expansion to the coupling efficiency of (1 + 1) long distance side pumping fiber

Abstract

With the same fiber preform, two long distance side pumping fibers were fabricated and measured based on a master oscillator power structure. The residual pump power tendency of the two fibers were obtained in experiment. It was found the residual pump power would arise rapidly when the power reached turning point, which was defined by derivative value of residual pump power to pump power equal to 2.5%. Numerical analysis reveals that the thermal expansion of low refractive polymer between signal and pump fibers, will increase the distance between fibers, deteriorate the coupling efficiency, and lead to an exponential increasing of the residual pump power.