请教前辈们几个光纤光学方面的问题

1 对于光通信中的光脉冲，已知其时域的电场矢量表达式，要得出其频谱，只取电场表达式的慢变包络做傅立叶变换，请问如何理解
2 一般书上给出光脉冲经光纤传输后，由于spm作用，会使脉冲产生正啁啾（沿光脉冲前沿到后沿，频移由负变正），也就是说，脉冲前沿产生红移光，后沿是蓝移光，请问如何理解脉冲不同点处（时域）产生不同瞬时频率的光
小弟为这几个问题思索良久，终不得解，望赐教以解苦闷心情！！！

why you don’’t go to find answer from some textbooks.
It is cleary answered in nonlinear fiber optics

thank you for your reply!
I have athe texbook named nonlinear fiber optics, but I still feel confused after reading the chapters on the topic.
can you give me any more about your understanding ? thanks a lot!