单项选择题
A. fiber loss
B. OSNR level
C. post amplification
D. index of reflection
E. index of refraction
F. power post amplification budget
多项选择题 What three in combination are factors that can cause four-wave mixing in fiber-optic cables? （）(Choose three.)
单项选择题 Why are the 1300 nm and 1550 nm regions of the fiber spectrum primarily used for optical communications?（）
单项选择题 What is an advantage of an externally modulated laser over a directly modulated laser?（）