Method for calculating coupling coefficient in W-type multimode optical fibers

Abstract A simple method is proposed for determining the mode coupling coefficient D in W-type (double clad) multimode optical fibers. It only requires the observation of the far-field output pattern for one fiber length with the input light launched centrally along the fiber axis ( θ 0 = 0). For illustration, the coupling coefficient determined by this simple method for a W-type multimode glass optical fiber was used to calculate the coupling length L c at which the equilibrium mode distribution is achieved.