hi umar syed,
as mentioned by alll, gennerally we use EDFA as the main amplifier along the fiber link..but the gain of EDFA depends on both length of fiber and wavelength in particular..
use of raman amlifier (which has nearly equall gain for all wavelength)is usually restricted to the rx end, but it amplifiers the signal by large amont can cause fiber non-linearities ,if used before fiber.
wirh regaerds