Anoverviewofopticalamplifiers,whichareusedfordirectamplificationofopticalsignals,ispresented.Thearticleincludesthephysicsanddeviceperformanceofpracticalopticalamplifiers,suchassemiconductoropticalamplifiers,rare-earthiondopedfiberamplifiers,fiberRamanamplifiersandfiberBrillouinamplifiers.S