Computational Simulation Study On The Characteristics Of Intermode Interferometric Refractive Index Sensing In Microstructured Fiber

Computer simulation technology has received extensive attention from researchers in various fields since its birth.Based on computer technology,it can effectively simulate the evolution results of practical problems by establishing simulation mathematical model,analyzing localized mathematical model and simulating experimental calculation according to the requirements of practical problems.Optical fiber sensing technology for its advantages of small volume,light quality and high sensitivity is widely used in different fields,but due to the microstructure optical fiber processing technology has certain difficulty,and small changes in the optical fiber structure parameters can have a huge impact,and fiber optic sensor before put into application in success often requires a large number of repeated experiments to grope for sensing parameters,eliminate the disturbance factors,the process will take huge time and manpower cost.Therefore,the application of computer simulation technology to optical fiber sensing can not only realize the complex structure of optical fiber technology that cannot be achieved in the experimental environment,but also can quickly find the optimal solution after processing a large amount of simulation experimental data,improve the sensing accuracy,and the actual experimental operation provides practical and feasible theoretical guidance,reduces unnecessary repetitive operations in the experimental process and saves experimental resources.This paper uses computer simulation technology to simulate and design two kinds of microstructure fiber structures,calculate and analyze their mode characteristics and refractive index sensing performance.The main content is composed of the following three aspects:1.Designed and proposed an elliptical core microstructure optical fiber,the cladding is arranged by six layers of air holes to form a hexagonal array,the finite element simulation method is used to calculate the optical fiber core mode characteristics,and establish the fiber core with the M-Z between polarization mode interference theory model,the calculation and analysis its refractive index sensing properties and the optimized scheme.The simulation results show that the number of layers filled with air holes has little influence on the regular characteristics of the interference spectrum between the fiber core and the polarization modes,and the longer the fiber length is,the lower the response of M-Z interference spectrum to the refractive index sensing.When the fiber length is 5mm and the monolayer air hole is filled with 1.39 refractive index solution,the maximum refractive index sensing sensitivity can reach 5200 nm/RIU.2.Based on the above-mentioned elliptical core photonic crystal fiber,due to the introduction of the elliptical core,the fiber has certain polarization-related characteristics.The birefringence mode characteristics are calculated using the finite element multiphysics simulation platform.The core LP₁₁mode is higher than the LP₀₁mode.So the theoretical model of Sagnac interference between the orthogonal polarization modes of the core LP₁₁is established.The simulation results show that when the length is 12cm and the refractive index of the filled single-layer air hole is1.39,the refractive index sensing sensitivity of the interference spectrum is 12000nm/RIU,is 14 times that of the M-Z interferometer with the same parameters.3.A tiwn-core photonic crystal fiber is proposed and designed.The fiber introduces two defects in the hexagonal air hole array to form a symmetrical dual-core structure.In order to improve the birefringence characteristics of the fiber,it is calculated to fill half of the air holes on the right side of the fiber.The characteristics of the tiwn-core mode at the time,and the theoretical model of interference in the tiwn-core and inter-core modes is established.The results show that the response sensitivity of the interference effect between the LP₀₁and LP₁₁modes with the same polarization between the two cores to the filling refractive index is far greater than that of the interference sensing performance between the two modes with the same polarization within the core.When the length is 6mm,the sensor sensitivity can reach13800 nm/RIU.In addition,the interference effect of Sagnac between the orthogonal polarization modes within the core shows that the polarization interference spectral response of the filled region is 5 times higher than that of the non-filled region.