Numerical optimisation of pump absorption in doped double-clad fiber with transverse and longitudinal perturbation

Abstract

We report on the impact of the cross-sectional shape of the inner cladding of double-clad fiber on pump absorption using a Beam Propagation Method based on azimuthal harmonics expansions and the so-called "superformula" to describe complex shapes. The impact of shaped cladding and of the fiber layout on pump absorption of double-clad fiber is studied. We observe that for nearly circular cross-section fibers the pump absorption can be enhanced to match that of fiber with strong azimuthal asymmetry, through optimised fiber layout that maximizes pump mixing.