The Research Of Fiber-based Broadband Counter-tapered Mode Converter For Mode-Division Multiplexing System

With the High-speed development of society,people demand a much faster information transmission system to meet their increasing needs.However,the traditional optical fiber communication system based on single-mode-fiber is approaching its theoretic Shannon Limit,unable to satisfy the social needs.Fortunately,mode division multiplexing is put up forward to tackle the problem,and draws a lot attention from the researchers rapidly.As a key component in mode division multiplexing system,mode converter becomes a rising research direction and focus.In this paper,we firstly introduce the background and current research status of mode division multiplexing briefly.Then we spend some lines to analysis the theoretical basis of mode division multiplexing.On this principle,a fiber-based broadband counter-tapered mode converter is designed to convert LP01 mode to LP11 mode,Simulation results show that such a kind of all-fibered based converter is suitable for mode division multiplexing.We further analysis the effect of its parameters,finding that it can achieve more than 80% coupling efficiency over a broad band over 300 nm,while 220 nm bandwidth with a coupling efficiency of 90%.and it has a characteristic of insensitive to certain parameters,such as component width,core diameters,gap width etc.most importantly,the fiber-based design makes it compatible with pre-exist fiber communication system.What makes the converter imperfect is that the length is too long to be integrated into the optical system.To shorten the length,we put up with two new structure,an optimization of the first one.And the later one can achieve a band of nearly 210 nm of 80% coupling efficiency with a length of only 0.28 cm,reserving the characteristic of parameter insensitivity.We also study the effect of some parameters to observe its performance changes,and some important conclusion is reached.