We present a rate equation approach (REA) based on the propagation equations in single-mode Erbium-Doped Fiber Amplifiers (EDFAs). Special attention is paid to the gain and the amplified spontaneous emission (ASE) noise as functions of position including the effects of some main parameters such as pump power, signal power. | Gain and noise in erbium-doped fiber amplifier EDFA - A rate equation approach REA