So when the length of SMF 2 is 6.5 km, the maximum difference decreases to 6.001 dB as
shown in Fig.3 (c). It means that the power loss of the odd-order Stokes lines is the minimum after the odd-order Stokes lines pass twice the SMF 2. The length of SMF 2 is longer than the length of SMF 1, so pump absorption in SMF 2 is larger than in SMF 1. The power of the odd-order Stokes lines generated from SMF 1 is weakened significantly after passing twice SMF 2.