利用光纤环腔衰荡技术测量单模光纤的弯曲损耗

Measurement of the Bending Loss of Single-Mode Fibers by Use of Fiber Loop Cavity Ring-Down Technique

提出用光纤环腔衰荡技术研究单模光纤的弯曲损耗及其随弯曲半径和温度变化的振荡特性。光纤弯曲时,从基模辐射出去的一部分能量在包层-涂敷层或涂敷层-空气界面处发生反射形成回音壁(WG)模,当满足同向耦合条件时,WG模又重新耦合回纤芯与基模发生干涉,使光纤的弯曲损耗产生振荡。实验结果表明,在弯曲半径为9.33～27.63 mm的范围内,单模光纤的弯曲损耗除了随弯曲半径的减小呈指数增大外,还伴随有振荡现象,且WG模与纤芯基模之间还会发生二阶耦合,导致次级振荡的存在;弯曲损耗随温度的变化也存在振荡现象,振荡周期随温度的升高和弯曲半径的减小而减小。实验得到的振荡峰的位置和幅值及振荡周期与理论分析结果一致。

The oscillations of the bending loss for single-mode fibers with the bending radius and the temperature are investigated experimentally by use of fiber loop cavity ring-down technique.When the fiber is bent,the light ejects from the fundamental mode to form whispering gallery（WG） modes produced by reflection at the cladding-coating interface,or at the coating-air interface.On the synchronous coupling condition,the light from the WG modes will couple back and interfere with the fundamental mode,which leads to bending loss oscillations.The experimental results demonstrate that the bending loss follows an oscillatory and exponential growth trend when the bending radius decreases from 27.63 mm to 9.33 mm.In addition,the secondary oscillations are observed because of the secondary coupling between the fundamental mode and the WG modes.Change of the bending loss with temperature is oscillated,and the oscillatory period decreases with the decrease of the bending radius and the increase of the temperature.The locations and the amplitudes of the loss peaks and the oscillatory period are consistent with the theoretical results.