Erbium-doped fiber amplifiers (EDFAs) have shown to be a very attractive alternative to improve the capacity of optical-fiber communications systems operating in the third transmission window of conventional fibers (lambda = 1.55 mi m). Considered efforts have been made towards the performance enhancement of these devices. The possible application potential in telecommunications is indeed large, and has simulated the study of system performance using EDFAs. Most of the previous theoretic contribuitions on the influence of optical amplifiers in the receiver performance consist of methods that are either easy to use but over-approximated - what can lead to quite inaccurate evaluations - or very precise but extremely difficult to use - due to some inherent complexity. Models for the simulation of digital optical communication systems are presented, which account for signal loss and distortion - due to laser chirping, fiber dispersion and detector finite bandwidth. A new semi-analytical method for the evaluation of bit-error rate (BER) and receiver sensitivity is introduced, which possesses the desired accuracy and simplicity. It takes into account the presence of inter-symbol interference (due to signal distortion) and the optical amplifier noises. These modesl and the developed method jhave been the used for introducing simulation of optical systems with EDFAs into a previously existing system evaluation software package. A numbe of simulations was carried out in order to estimate the contribution of EDFA parameters and implications of some system properties in the final performance of the optical system. The comparison with results from rigorous analysis, found in the literature, has validated the proposed approach.