Influence of double clad fibre shapes on their real active cross-sections

The double-clad-fiber absorption active cross-section of pump radiation depends upon the first-cladding area shape. The following work determines the result of experimental comparison of the optimisation of first-cladding cross-section shapes in collection of sufficiently simple structures, so that the production was not too difficult. The best fibre structure presents 60% higher active cross-section than the fiber with axial symmetry.