Research On Multi-mode Selective Coupled Converter Based On Two-core Photonic Crystal Fiber

Mode conversion is the key technology in mode division multiplexing.According to the unique optical properties and flexible design of photonic crystal fiber,a mode selective coupling converter based on asymmetric two-core photonic crystal fiber is proposed in this paper.The conversion between fundamental mode and higher order modes is discussed and the bandwidth characteristics of the mode-selective coupling converter is analyzed further by using mode coupling theory and beam propagation method.The content in detail is listed as follows:1.A mode selective coupler based on asymmetric hybrid two-core photonic crystal is proposed according to the mode coupling theory.The results show that the fundamental mode can be transformed to more high-order modes at 1550nm by choosing appropriate structure parameter of photonic crystal fiber,it fits the rapid increase of network perfectly and the transmission capacity of the optical fiber transmission system can be improved greatly.2.The rationality of doping rate in the cladding of the mode selective coupler is explained.The refractive index of the right core cladding of the asymmetric photonic crystal fiber can be reduced significantly by adjusting the structure of the asymmetric two-core photonic crystal fiber that provides an effective reference for engineering application.3.The size,the filling refractive index,the position of the dielectric hole which is between the two cores have an important influence on the wavelength bandwidth.By changing one or several factors,the unique wavelength bandwidth characteristics can be obtained.The research shows that the minimum bandwidth of the coupling converter can be up to 2 nm,which can achieve the effect of narrow band filtering.4.The effect of process errors on the coupling performance is analyzed.The result will provide reference for the fabrication of optical fibers and the limitation of error.At the same time,it can accelerate the process of the practical application of photonic crystal fibers and mode division multiplexing system,promoting the further improvement of optical fiber communication.