Research On Transmission Performance Of Negative Curvature Anti-Resonance Hollow Core Fibers

With the development of fiber technology,photonic crystal fiber（PCF）has been widely used in fiber communication,fiber sensing,nonlinear optics,high power laser transmission,fiber lasers and other fields,due to its superior optical properties and flexible design than traditional fiber since it was proposed.Negative curvature anti-resonance hollow core fibers（NC-AR-HCFs）belong to one kind of hollow core fibers.Because most optical power propagates in the air core,high power transmission can be realized by using low non-linearity,high damage threshold and low material absorption.In this paper,the transmission performance of negative curvature anti-resonance hollow fiber are studied by using finite element analysis.A kind of fiber structure which can suppress the high order mode is designed.The fabrication error of the fiber and the thermal effect in the transmission of high power laser are studied.The main contents are as follows:（1）The background and significance of negative curvature antiresonance hollow core fiber are introduced,and the classification of hollow core fiber is briefly described.The research status of negative curvature antiresonance hollow fiber is introduced.（2）The basic theory of negative curvature anti-resonance hollow fiber is described,the optical performance index and calculation formula of the hollow fiber are introduced,and the existing problems of suppressing higher order mode in negative curvature anti-resonance hollow fiber are analyzed.In addition,the finite element analysis is introduced and the convergence test of the simulation data is studied to prove the accuracy of the simulation data.（3）In this paper,a method of multi-resonance coupling is proposed to suppress the high order mode in the negative curvature anti-resonance hollow core fiber,and the fiber structure which can realize the multi-resonance coupling is presented.The simulation results show that,based on multiple resonant coupling,the confinement loss of LP₁₁ mode is greater than 10⁵d B/km in a wide band range,and the loss ratio between LP₁₁ mode and LP₀₁ mode is 10⁵ orders of magnitude in the range of 1200～1550nm,which indicates the superior character of multi-resonant coupling in suppressing higher order mode.The effective suppression of higher order modes(LP₂₁ mode and LP₀₂mode)by incomplete multiple resonance coupling is analyzed in detail.In addition,we show that reducing the fractional optical power of the outer tube wall by changing the thickness of the outer tube can reduce the additional loss caused by the node.The limitation between the suppression of the higher order mode and the reduction of bending loss is discussed.（4）The errors caused by the rotation of the outer tube,the collapse of the outer tube,the thermal effect and the dispersion effect on the loss of the fundamental mode and LP₁₁ mode of the fiber as well as their loss ratio in the optical fiber drawing process are analyzed,and the manufacturing tolerance is given.