Nonlinear laser theory and natural linewidth in semiconductor lasers

Our approach to the problem is based on the following basic concepts: using a spatially-distributed laser model; using an approximate Kovalevski-Noppe (KN) expression for effective natural linewidth for semiconductor lasers with application of generalized parameters. Physical representations of secondary spontaneous fluctuations have been formulated. These allow deriving formulas for generalized parameters in the KN expression for linewidth, on the basis of which the gain, foundation of the nonlinear system of equations, is derived. The effective natural linewidth is calculated after solving the nonlinear system of equations. Thus, the theory of natural linewidth is an integral part of the nonlinear theory on the basis of which the output power, linewidth, and threshold current for Fabry-Perot semiconductor lasers are calculated. The calculations made allow explaining some experimental measurements of natural linewidth for the Fabry-Perot semiconductor lasers.