The New Method Of Fiber Longitudinal Coupling Theory

The optical coupling technology is the key technology in optical communication, optical sensor and optical integration, and it will hold the primary status in optical networks in the future. So it is necessary to study the optical coupling theory deeply. The thesis comprises the following:Firstly, we present a new method that is similar to that of one dimension scattering theory in quantum mechanics. And this method can be used to calculate the return loss and coupling efficiency with a longitudinal separation between two single mode fibers. A more accurate expression of the return loss can be obtained by solving the longitudinal wave equation in our method, which takes into account the coherence effect mentioned above. As the same time, the coupling efficiency of two fibers with an angular misalignment and with a longitudinal separation between two single mode fibers was calculated.Secondly, in order to increase the coupling efficiency of single mode fiber to multimode fiber, The G—lens is used to expand the mode field radius of single-mode fiber. The girdling radius of single mode fiber has been expanded to match the girdling radius of fundamental-mode of multimode fiber, and to excite the fundamental-mode of multimode fiber, improves the coupling efficiency from single-mode fiber to multimode fiber.Because of the disadvantage of multimode fiber, such as mode dispersion, and the bandwidth of multimode fiber system is limited. In order to improve the bandwidth of multimode fiber system, a mode filter device that made by a single mode fiber is adopted.Thirdly, according to the statistical optics theory, the output of multimodefiber was taken as a quasi-homogeneous source; geometry optics and wave-guide optics were taken to analyze the output of multimode fiber collimator. We obtain that the output field of multimode fiber satisfy Gauss distributing.