Study On Spreading And Correction Of Orbital Angular Momentum Spectra Of Vortex Beam In Atmospheric Turbulence

With the rapid development of society economy,the major power plants and mining sector release toxic gases without regulation,which cause a serious threat to the safety of human being.Therefore,importance to monitor the gas emission timely is obvious for the reasons of environment,economy and security of our country.The traditional electrochemical gas sensor has the disadvantages of low sensitivity,high loss rate and low safety.In contrast,the gas sensor based on photonic crystal fiber has the advantages of high sensitivity,low loss rate,variety structures,easy to construct a network.These factors promote the study in the application of photonic crystal fiber,which has become an important research topic in optical fiber.At present,there are many types of photonic crystal fiber structured gas sensors,however their sensing performances are not that satisfied.In order to improve the sensing performance of PCF gas sensor,this paper introduces the design of a gas sensor based on hexagon-hole PCF,and studies in detail the sensing performance of this hexagon-hole PCF structure.Further,this paper compares PCF gas sensor based on the structure of circular hole with hexagon-hole.The main research contents include the following aspects:1.Briefly introduce the significances and values of the research,and the development of PCF in the application of gas sensors.2.Introduce the theoretical foundations of Crystal(Photonic,PC)and PCF,including the basic concepts and classification,light guiding principle,optical properties,numerical methods and so forth.This paper also introduces the finite element analysis method,which is used in this paper.This paper expounds the advantages of the photonic crystal fiber gas sensor by comparing with traditional gas sensor,and highlights the importance of this research.3.Based on the PCF gas sensor with circular hole structure,a hexagonal hole PCF structure is designed in this article.By using the CAD software,this paper draws the theoretical model of hexagonal hole structure,and explains the advantages of the hexagonal hole PCF compared with circular structure in geometry.This paper also introduces briefly the main steps of numerical calculation of photonic crystal fiber.Based on the finite element method(COMSOL)software,the optical and gas sensing properties of hexagonal hole structure are calculated numerically,and the influence of the parameters on the performance is analyzed.The structural parameters of hexagonal hole are optimized by compared with circular hole structure.The result shows that the hexagonal hole fiber structure has higher sensitivity and lower confinement loss than conventional circular hole structure.