熔锥光纤的模场传输特性分析

Analyses of mode field propagation properties in fuse-tapered fibers

在近场光学显微镜、高功率光纤耦合器等应用场合,需要对熔锥光纤中的光场分布有更精确的了解。基于锥形函数,应用时域有限差分法模拟了熔锥光纤中的光场分布,分析了熔锥参数对单锥形光纤和双锥形光纤传输效率的影响,并与使用基模高斯近似得到的结果进行了比较。结果表明:使用基模高斯近似分析熔锥光纤的光场会产生较大误差;在形态分布对称的熔锥光纤中光场分布是非对称性的,基模场入射熔锥光纤后会在熔锥光纤中激发出泄漏模,对于单锥形和双锥形结构的熔锥光纤,初始熔融长度和拉伸长度对传输效率均有影响。应根据具体的应用情况,确定熔锥参数,以获得更高的传输效率。

Applications such as near-field optical-microscope and high power fiber coupler require more precise understanding of light field in fuse-tapered fiber.To study propagation properties of the fuse-tapered fiber,field distributions were simulated by finite-difference time-domain method（FDTD）,assuming that the incident beam was fundamental mode.Theoretical model of fuse-tapered fiber used in the simulation was based on a tapering function which was close to the real shape of fuse-tapered fiber.Mode field radius and transverse field distribution of the fuse-tapered fiber in the fundamental mode Gaussian approximation were compared with the simulation results.Finally,the influences of the initial melting length and extension length on the transmission efficiency were analyzed.The results show that field distribution in the fuse-tapered fiber is asymmetric though the shape of fuse-tapered fiber is symmetric.When a fundamental mode field propagates through a fuse-tapered fiber,the light field propagates not only as fundamental mode which is corresponding to the core diameter of the fuse-tapered fiber.The fundamental mode Gaussian approximation may introduce considerable errors to the calculation of field distribution in fuse-tapered fiber.When fuse-tapered fiber is of single cone type or double cone type,the influences of their shapes are different.To get higher transmission efficiency,initial melting length and extension length should be optimized according to the specific applications.