Thank yoi alisthu.But i got lot of questions about this paper that word length only depend in case of where hybrid amplifiers are used? Is this due to raman fiber only? Or is it play some role in every system where fiber is used? I got your point about the discussion here of sequence length and varied results..And in paper author explained some interesting point of non linear effects depends upon WL..But every time i read similer discussion on forum ,increased seq. Length suggesred in order to get mote accurate results.Now i am bit confused? I will start new topic if required,if it confused here?