Research On Key Few-mode Waveguide Devices For Optic Fiber Mode Multiplexing System

In recent years,due to the limited transmission capacity of single mode fiber,the communication technology based on few-mode optical fiber has aroused wide interest.The technology of using different modes of few-mode optical fiber to transmit different information,which is called mode multiplexing technology,can greatly increase the transmission capacity of optical fiber.More importantly,the few-mode optical fiber can have larger core area,which can reduce the nonlinear effects owing to the applications of multiplexing technologies.Besides the application in mode division multiplexing technology,few-mode fiber can also selectively excite high-order modes,therefore can be applied to large mode-area single-mode operation,dispersion compensation,and nonlinear propagation of ultrashort pulse,etc.In a mode division multiplexing system,mode converters and mode multiplexing/demultiplexing devices are the key factors determining the performance of the system.In this dissertations,a new type of mode converter is designed based on the adiabatic mode evolution.This device can achieve mode conversion between different modes,combine different optical signal optical signal into different modes in few mode fiber by launching the signal from a core of this device,so as to realize the mode multiplexing.It can couple the modes in the few mode fibers to different auxiliary cores,so as to achieve the separation of different mode signals,namely demultiplexing.It can also operate as an add-drop multiplexer,or selectively remove high-order modes so that operating single mode transmission in few mode fibers,and achieve mode conversion between degenerated modes.In additional to the presentation of mode converter based on few-mode optical fibers,mode converters based on rectangular waveguide configuration is also proposed.The configuration is able to convert each mode to a higher-order or lower-order mode by launching light from different ports.