Research On The Mode Conversion Technology In Mode Multiplexing System

Entering the 21st century,the human society has an ever-increasing demand for data.With the continuous development of many new technologies and new services,the demand for data continues to grow at an explosive rate,and the existing optical fiber transmission capacity has become increasingly tense.Therefore,it is urgent to expand the transmission bandwidth to increase the information transmission capacity.It is urgent to find a new method for greatly increasing the capacity of optical fiber communications.Space-division multiplexing based on the new physical dimension of space is a popular technology that is expected to increase the capacity of optical fiber communications.Mode division multiplexing is one of the space division multiplexing techniques.It uses the orthogonality of different modes of multimode fiber to transmit information independently.A new kind of mode selective switch needs to be designed to realize higher mode switch efficiency for the mode division multiplexing networks.In this thesis,the key technologies of the conversion,reuse,and exchange based on free space in the mode division multiplexing network are studied.The main contents are as follows:Firstly,the principle of mode conversion and multiplexing base on a single plane in free space is studied and experimentally verified.A free space mode conversion system based on phase plate and spatial light modulator are established and got a variety of high-order mode.Secondly,the basic principle of mode control based on multi-plane light conversion is studied and a theoretical model is established.The phase plane optimization distribution of multi-plane light conversion system is calculated by SPGD optimization algorithms.The numerical simulation results show that this three-plane system can effectively improve the mode conversion efficiency to 90%from fundamental mode to high-order mode.Thirdly,a three-mode multiplexing/demultiplexing and conversion system based on LP01,LP21a,LP21b and based on multi-plane light conversion is designed and simulated by SA algorithm.The conversion efficiency of each mode is about 0.8.Fourthly,the mode switching method based on multi-plane light conversion is proposed and the 6-mode 3-way mode switching simulation is carried out.The simulation results show that the conversion efficiency of each switch states can reach above 0.89 and the maximum mode crosstalk is below-24dB.