New method for calculating the coupling coefficient in graded index optical fibers

•A simple method is proposed for determining the mode coupling coefficient D in GI multimode optical fibers.•It only requires observation of the output modal power distribution P(m, z) for one fiber length z.•The input light launched centrally along the graded index optical fiber axis (θ0=0) has to be known. A simple method is proposed for determining the mode coupling coefficient D in graded index multimode optical fibers. It only requires observation of the output modal power distribution P(m, z) for one fiber length z as the Gaussian launching modal power distribution changes, with the Gaussian input light distribution centered along the graded index optical fiber axis (θ0=0) without radial offset (r0 = 0). A similar method we previously proposed for calculating the coupling coefficient D in a step-index multimode optical fibers where the output angular power distributions P(θ, z) for one fiber length z with the Gaussian input light distribution launched centrally along the step-index optical fiber axis (θ0=0) is needed to be known.