There are three main types of today’s amplifier technology:Doped fiber amplifier (The typical representative: EDFA), Semiconductor optical amplifier (SOA), Fiber Raman amplifier (FRA). Each of them has their own working principle, features and applications. Here is the comparison of them according to their specific properties and hope it helps. http://www.fiber-optic-tutorial.com/comparison-of-different-optical-amplifiers.html