Research On Photonic Lantern Mode Multiplexer/Demultiplexer

With the advent of the 5G era and the rapid development of the Internet,the demand for high-bandwidth and large-capacity communication networks has become more and more urgent.As the backbone network of modern communication,optical fiber communication network has always played an important role in modern communication.However,the traditional single-mode optical fiber communication system is limited by nonlinear effects,and its capacity gradually tends to the Shannon limit.In order to avoid a"bandwidth crisis",Therefore,a new expansion plan needs to be developed.The mode division multiplexing technology based on few-mode fiber is currently the most recognized expansion technology.It uses few-mode fiber as the transmission medium to increase the system capacity by multiplexing multiple independent orthogonal spatial modes in the few-mode fiber.The core component of the mode division multiplexing system is the mode multiplexer/demultiplexer,which realizes the mutual conversion between the fundamental mode and other modes,and multiplexes it into the few-mode fiber for transmission.Therefore,the research on mode multiplexer/demultiplexer is of great significance.In this paper,the photonic lantern type mode multiplexer/demultiplexer has been studied in detail from three aspects:theory,simulation and experiment.The specific work and innovation are as follows:Firstly,the basic theory of few-mode fiber is studied,and the orthogonal relationship between fiber modes and modes is deduced.Then,the related theories of photonic lantern-type mode multiplexer/demultiplexer are studied in detail,starting from supermode theory,and then The transmission principle,pattern number matching principle,adiabatic tapering principle and structure of the photonic lantern are analyzed.Secondly,the three-mode and six-mode model selection photonic lantern structure and parameters are designed,and the designed photonic lantern model is simulated and analyzed based on the finite element method.The results show that the designed photonic lantern can realize the mode selection function and prove the structure Correctness.Then,an optimization method is proposed for the two structural parameters of the photonic lantern's tail end sleeve inner diameter and sleeve refractive index designed in this paper,and simulation analysis and performance optimization are carried out based on the finite element method and the beam propagation method.The results show that After optimizing the inner diameter of the tube at the end of the three-mode mode selection photonic lantern designed in this paper to 25um and the tube refractive index to about 1.42,the coupling efficiency of each mode is higher than 93%,and the mode selectivity is higher than 20d B.Crosstalk is lower than-21d B;the inner diameter of the tube at the tail end of the photonic lantern designed in this paper is optimized to 23um and the tube refractive index is optimized to 1.40.With the exception of the mode LP₀₂coupling efficiency of 86.4%,the coupling efficiency of each mode is equal Higher than 91%,the selectivity of each mode is higher than 21d B,and the crosstalk between each mode is lower than-23d B.Finally,according to the optimized structure parameters,three-mode and six-mode photonic lanterns were made,and performance tests were carried out.The test results show that the photonic lanterns made can realize the mode selection function,but the overall loss is too large.At the same time,the influence of the inner diameter of the photonic lantern tail tube on its performance was compared and verified,and the result showed that the change law was basically the same as the simulation analysis.