Launching condition dependence of graded-index multimode fiber loss and bandwidth

Theoretical and experimental studies of the launching-condition dependence of graded-index 50-μm core, 0.2-numerical aperture multimode fiber transmission loss and baseband bandwidth are discussed. A combination of a SGS mode scrambler and a mandrel wrap mode filter was used as the launching system. It was found that steady-state fiber loss measurements should be carried out at an approximate mandrel curvature of ρ=0.07 mm^-1. This curvature is much smaller than the curvature ρ=0.15 mm^-1 which produces an equilibrium-mode distribution as defined by the International Telegraph and Telephone Consultative Committee (CCITT). Measurement at ρ=0.15 mm^-1 is shown to underestimate steady-state loss. It was also found that reproducible and reasonable bandwidth measurement can be obtained by choosing ρ=0 to 0.07 mm^-1