为了减小在长距离光纤通信中存在的弯曲损耗和利用光纤激光器中的弯曲损耗获得单模输出，利用速度法解释了光纤弯曲损耗机制，采用Marcuse理论研究了弯曲损耗随弯曲半径、波长和纤芯半径变化的关系。通过计算机仿真和实验得出弯曲损耗随弯曲半径的减小而增大，随波长的增大而增大，随纤芯半径的增大而增大，高阶模式的损耗大于低阶模式。利用这一结论就可以通过控制弯曲半径在临界半径以内来减小通信中的弯曲损耗，通过增大模场半径来实现光纤激光器中的单模输出。

In order to reduce the bending loss in long distance fiber communication and use the bending loss in fiber laser to obtain the single mode output, velocity method is introduced to explain the mechanism of bending loss in fiber. Marcuse theory is adopted to research the variation between the bending loss and bending radial, wavelength and the radial of fiber core.By the computer simulation, we can draw the conclusion that with the reducing of bending radial, the increasing of wavelength and the increasing of the radial of fiber core, the bending loss is increasing, the bending loss of higher mode is higher than that of low mode. We can reduce the bending loss in long distance fiber by controlling the bending radial lower than the critical radial. We can obtain the single mode output in fiber laser by increasing the radial of mode field.