Research On Selective Mode Converter Based On Waveguide

Mode Division Multiplexing(MDM)is a very promising research direction in the optical fiber communication system.The capacity of optical fiber communication system can be greatly increased if MDM is used in the mode multiplexer and mode demultiplexer of few mode fiber(FMF).The technologies of mode mode excitation and mode conversion are two key problems that must be faced in the primary stage of the study of the MDM.They are the basis and precondition for the system of MDM to be operated.In this paper,the theory analysis and simulation realization of mode conversion condition and mode conversion method based on waveguide are studied for the purpose of solving the problem of mode conversion in the FMF communication system.In this paper,with coupled-mode theory as the main guiding principle,based on photonics crystalfibers fiber(PCF),we propose three model conversion schemes on the basis of traditional PCF,the all-solid photonics band gap fiber(AS-PBGF),and based on hybrid PCF,respectively.Then we implement the design and simulation of those schemes,etc.The innovations in detail are listed as follows:Firstly,we propose a mode conversion scheme based on the common PCF,then an optimization scheme is also proposed.PCF post-processing technology is used for the scheme of core diameter and core refactive index modulation mode effective refractive index based on PCF,making the designed mode converter based on PCF more close to the requirement of actual production process.Secondly,we put forward a mode conversion scheme on the basis of the AS-PBGF,inheriting both advantages of the flexible and devisable PCF,resistance to mechanical squash and stretch,and easy to welding of fiber.At the same time,put forward an extension scheme from the double core mode converter to multicore converter,providing reliable train of thoughts to achieve multiple mode conversion and reuse in future.Thirdly,we design the mode conversion schemes based on hybrid PCF.By designing PCF structure,a dual-core PCF in which light can be guided by both total internal reflection(TIR)and photonic band gap(PBG)principle has been realized.Then we realize the mode conversion on this basis.The 3 dB wavelength bandwidth of LP01 mode to LP11 mode converter is more than 200 nm.This is because the dynamic matching law of the mode's effective index which make the converter maintain a high efficient mode conversion in a wide range of bandwidth.This law has far-reaching significance for designing wide bandwidth mode converter based on the optical waveguide in the future.