| With the rapid development of emerging technologies such as big data,cloud computing,Internet of Things and industrial intelligence,network traffic is exploding,and the capacity of transmission systems based on ordinary single-mode fiber is approaching the Shannon limit,so it is urgent to alleviate the capacity crisis.In recent years,in order to further enhance the transmission capacity of optical transmission systems,space division multiplexing(SDM)technology has been rapidly developed,Multi Core Fiber(MCF),Few Mode Fiber(FMF)and Multi Core Few Mode Fiber(MC-FMF)have become the core transmission media in the new generation of high capacity fiber optic communication systems.The spacedivision multiplexing technology is capable of expanding the transmission capacity of a single fiber by tens of times and has great potential for future applications in fiber optic communication systems.Therefore,it is significant to study the design of new optical fiber based on air division multiplexing technology,which is expected to bring a new breakthrough for high-capacity optical network transmission system.This thesis mainly focuses on the structural design and performance simulation of multi-core fiber and few-mode fiber in space-division multiplexing system based on fiber waveguide theory,theoretically analyzes the performance parameters of multi-core fiber and few-mode fiber,proposes a heterogeneous 19-core 3-mode fiber structure design method based on refractive index hierarchy,simulates and studies the performance of 6-LP few-mode fiber with gradient refractive index distribution,a strongly coupled 8-core supermode fiber structure is designed and its performance is simulated and analyzed.The main research work of this thesis is as follows:1.To address the problem of inter-core crosstalk in multi-core fiber,a heterogeneous 19-core 3-mode fiber structure based on refractive index layering is designed,using heterogeneous fiber core arrangement instead of auxiliary structures with high manufacturing accuracy requirements,and the heterogeneous fiber cores are layered according to the core refractive index to effectively increase the core spacing between the cores and reduce the impact of inter-core crosstalk.The optical properties of the fiber,such as inter-core crosstalk,bending radius threshold and bending loss,are simulated and analyzed.The results show that the fiber can reach the bend insensitive region more quickly and the XT is less than-60dB/100km when the bend radius is greater than 10cm.2.To address the problem of inter-mode coupling in few-mode fiber,a 6-LP few-mode fiber structure with a gradient refractive index distribution structure is designed.The core refractive index distribution is designed to reduce the inter-mode coupling by changing the effective refractive index difference between modes.The fiber structure is first modeled using finite element simulation software to analyze the main factors affecting the inter-mode coupling,and the parameters of the gradient refractive index distribution structure are simulated and analyzed.The results show that the minimum mode refractive index difference of the fiber is improved by 0.61 × 10-3 compared with the original ordinary step mode fiber,which is expanded by about 1.79 times.3.A strongly coupled 8-core supermode fiber structure is designed and performance simulations are performed.Eight identical single-mode fibers are used for asymmetric distribution in the x-and y-axes to maintain the polarization mode discrepancy.The effects of geometric and optical parameters on the mode effective refractive index difference and mode field area of the strongly coupled 8-core fiber were analyzed in detail using COMSOL software.The simulation results show that the fiber supports the transmission of 12 vector modes separated from each other with a minimum mode refractive index difference of 1.34 × 10-4,and the dispersion between each mode is kept at-70 ps/nm/km to 10 ps/nm/km. |
