Er_fiber

代码说明：

  掺铒光纤，四能级的matlab功率仿真，凝聚了我的时间和经验。很好的反映了功率随光纤长度变化的关系.(Erbium-doped fiber, the matlab power four-level simulation, the combination of my time and experience. Well reflected the changing power relations with the fiber length.)