Research On The Design And Transmission Characteristics Of Few Mode Multi-core Fiber

At present,due to the huge needs of users for Internet data,optical communication network is facing unprecedented pressure.Although the ultra-high transmission capacity of 100 Tb/s per fiber has been achieved with the use of various multiplexing technologies,the existing standard single-mode fiber may no longer meet the growing capacity requirements.Therefore,the multi-core optical fiber multiplexing technology is proposed.Although a variety of multi-core optical fiber schemes have been proposed,the multi-core optical fiber still has shortcomings in bending resistance,which is difficult to meet the needs of fiber to home and other occasions.In order to achieve the design goal of low crosstalk and low bending loss,this paper focuses on the influence of multi-core fiber structure parameters on inter core crosstalk and bending loss,and proposes two design schemes: low crosstalk bend insensitive multi-core fiber based on gradient structure and low crosstalk few-mode multi-core fiber based on ring core structure.The main research work is as follows:1.The development history of multi-core optical fiber communication and the research progress and design ideas of multi-core optical fiber are described and explored.In addition,other applications of multi-core optical fiber are also introduced.On this basis,the main performance parameters of multi-core fiber,including the definition and calculation method of bending loss,inter core crosstalk and mode field diameter,are introduced.2.The theoretical model of multi-core fiber is established by COMSOL Multiphysics,and a seven-core few-mode fiber with few-mode gradient index distribution structure is proposed.The bending loss characteristics of the center core and the outer core are analyzed in detail by using the finite element method,and the mode crosstalk characteristics between the core and the influence of the core parameters on the crosstalk performance are emphatically analyzed.The simulation results show that the fundamental modes in the seven-core fiber can work at a small bending radius of 5 mm with low loss,and the mode crosstalk between adjacent cores is less than – 27 d B/km,so the independent information transmission between cores can be realized at a small bending radius.3.Ring-core few-mode multi-core fiber structure is investigated.A low refractive index region and a high refractive index ring are inserted into the step-index core to form a core structure with five linear polarization modes,and a seven-core few-mode fiber is constructed.The crosstalk characteristics and bending resistance of multi-core fiber are studied from the influence of bending radius,core spacing,effective refractive index difference between core and cladding,combined with bending mode field diameter.The results show that the core mode has a large mode field diameter,and the crosstalk between modes mainly comes from the coupling between higher-order modes.Adjusting the appropriate core spacing can ensure that all modes in the fiber have low crosstalk even when the bending radius is 50 mm.Therefore,the designed multi-core fiber has certain advantages in medium and long-distance transmission.