Numerical simulation based optimization of the absorption efficiency in double-clad fibres

摘要

A computationally inexpensive method for the numerical calculation of the absorption efficiency in double-clad fibres (DCFs) for high power fibre lasers is presented. A three-dimensional (3D) ray tracing technique is used to record the network of ray spatial paths occurring inside the core finite volume elements. Each ray represents a beam of parallel photons that conveys a fraction of the launched pump power. The corresponding energy is space-time propagated along the established spatial path network inside the absorbing regions. Absorption spectra as well as illustrative 3D images of the beam's transverse overlapping strength are generated to help with the assessment and design of a practical optical fibre. As proven by a comparison with reported results, the method correctly describes the absorption trends inside DCFs of general geometry. Furthermore, it serves as a numerical simulation based tool for the optimization of the cross-sectional geometry and the corresponding refractive index profile. To demonstrate this, an all-solid-state holey DCF with superior absorption characteristics is designed and numerically evaluated.