Abstract
Rare earths doped fiber amplifiers have been investigated actively and are now used in many optical fiber transmission systems. It offers high gain, high efficiency, low noise, low insertion loss and polarization insensitive characteristics. This paper reviews the latest results on fiber amplifiers doped with erbium (Er), neodymium (Nd), praseodymium (Pr) and thurium (Tm) ions from the viewpoint of spectroscopic characteristics. Also reviewed are the improvement in minimum recieved power by using optical fiber amplifier as a pre-amplifier.
