We present a consistent method to calculate the probability distribution of
soliton parameters in systems with additive noise. Even though the noise i
s weak, we are interested in probabilities of large fluctuations (generally
non-Gaussian) which are beyond perturbation theory. Our method is a develo
pment of the instanton formalism (method of optimal fluctuation) based on a
saddle-point approximation in the path integral. We first solve a fundamen
tal problem of soliton statistics governed by a noisy nonlinear Schrodinger
equation. We then apply our method to optical soliton transmission systems
using signal control elements (filters and amplitude and phase modulators)
.