Intensity Distribute Properties After Planar Wave Coupled Into Step-index Optical Fiber

This paper enclose the mode and the density distribution property of the step-index optical fiber after plane wave coupled into it.The first part is theory. First the equation of the plane wave should be obtained in equably medium. Second, for the sake of the optical fiber is cylinder, the wave equation should be showed under column coordinate system. Third, the mode solution is obtained using the separation of variables. The last, the mode transition property is discussed when the plane wave transmit in the step-index optical fiber.The second part is the mode transition property and the energy occupation of each mode in step-index optical fiber according to the mode solution. It is concluded that TE11 mode is the main mode, and it always possesses the most energy. The energy occupation of TE11 changes from 100% to 70%. The other two modes TE01 and TE21 possesses the second occupancy. TE01 possesses 15%, and TE21 possesses 4.7%.The last part is to analyze the density distribution at the end face of the optical fiber. According to the interference of light source, two conditions should be considered. The first is incoherent incidence light. The density distribution shows coronet as to the single mode. And the density distribution shows equality as to the multi-modes, except the little hollow in the optical fiber core. The second is coherent incidence light. It concluded that the density distribution is different from the incidence face very much because of interference.