Recently I encounter the problem during my experiment of B-OTDR fiber sensor. Once the length of sensing fiber is too long, the backscattered signal is very weak (about -80dBm by theoretical prediction). It's not reasonable to directly detect weak signal. Then I want to amplify the weak signal with EDFA. Then the problem comes out: if the signal is directly inputted into homemaded or commercial EDFA, the output signal is buried into EDFA ASE and could not be coherently detected even with fiber grating filter.
Now I want to know whether EDFA can amplify the very weak signal? Who can give me some help to solve this problem, or give me new method to amplify the weak signal?
Thank in advance for your help.