"This thesis presents experimental results on stochastic and deterministic dynamics studies carried out in an Erbium doped fiber lasers (EDFL) which are presented to be compared with the results of numerical simulation using an advanced two-level laser model. The dynamics of this laser under external modulation is very rich; it can exhibit different bifurcations, chaos, and crises; furthermore, for different modulation parameters, one can encounter the coexistence of multiple periodic regimes (attractors). In the experiments with EDFL we demonstrate a strong noise amplification in the vicinity of the critical points. Many are the situations in nature where this phenomenon can be experienced: heart strokes, eruptions, earthquakes, etc. Another phenomenon studied in this thesis is the attractor hopping. As the noise added to a system is increased, the laser brings out different periodic states defining multistability zones. Then, as noise is augmented, more and more of these states come to form part of the hopping attractor. For certain input noise, when more and more states are involved in the hopping process, there is a little change in the output noise. Such a noise-independent regime can be promising for some important applications, in particular, detectors transparent to noise."