  We present a consistent method to calculate the probability distribution of
soliton parameters in systems with additive noise. Even though a weak noise is
considered, we are interested in probabilities of large fluctuations (generally
non-Gaussian) which are beyond perturbation theory. Our method is a further
development of the instanton formalism (method of optimal fluctuation) based on
a saddle-point approximation in the path integral. We first solve a fundamental
problem of soliton statistics governing by noisy Nonlinear Schr\"odinger
Equation (NSE). We then apply our method to optical soliton transmission
systems using signal control elements (filters, amplitude and phase
modulators).
