Mode-selective Photonic Lantern Simulation And Design Based On Finite Element Method

Finite element method is one of the important methods in the field of numerical calculation.It has also been widely used in the field of electromagnetic problems.For example,the eigenmode problem,scattering problems,radiation problems.In this paper,we proceed from the solving steps of finite element method,such as meshing and selected selecting interpolation function,and give a detailed introduction to the solving process of finite element method.According to this process,we write a finite element simulation software based on MATLAB language,and realize the functions of solving the eigenmode of optical waveguide and the effective refractive index.Taking the solution of optical fiber as an example,we introduce the function realization and usage of our software.Comparing the result of the solution with that calculated by the commercial software,we found that the two results match well,indicating that our algorithm can be used to provide simulation support for some optical devices.Then,we use the finite element method to optimize a novel mode multiplexing/demultiplexing device that we propose.The device is mode-selective photonic lanterns?PLs?that based on the idea of designing a number of unit cores using direct laser writing?DLW?approach.The proposed PLs can?de?multiplex different spatial modes including modes within the same mode group with good scalability.What more,the design our proposed also simplifies the manufacturing process.Based on the above scheme,we present the design of a3×1 mode-selective PL,and use the finite element method to simulate the eigenmode and dispersion curve of the structure to improve the design.Then,the beam propagation method is used to verify that the device can be used to?de?multiplex theLP₀₁,LP_11a andLP_11b1b modes.By calculating the overlap between the modes of the photonic lantern and the modes of single?multi?mode fiber,we find that the crosstalk of the of begin facet and end facet of the PL is below-30 dB,and-50 dB respectively.To illustrate the scalability of the design we proposed,we have also designed a 6×1 PL that can be used to?de?multiplex theLP₀₁,LP_11a,LP_11b,LP_21a,LP_21b andLP₀₂ modes.