Semiconductor Laser Linewidth Theory Revisited

More and more applications require semiconductor lasers distinguished not only by large modulation bandwidths or high output powers, but also small spectral linewidths. The theoretical understanding of the root causes limiting linewidth is therefore great practical relevance. In this paper, we derive a general expression for calculation step in self-contained manner. We build on theory developed 1980s 1990s look from modern perspective, sense that choose as our starting points time-dependent coupled-wave equations forward backward propagating fields an expansion terms stationary longitudinal modes open cavity. As result, obtain rather expressions excess factor spontaneous emission ($K$-factor) effective $\alpha$-factor including effects nonlinear gain (gain compression) refractive index (Kerr effect), dispersion spatial hole burning multi-section cavity structures. effect narrowing due to feedback external often described so-called chirp reduction automatically included. propose new analytical formula dependence carrier density avoiding use population inversion factor. presented framework applied numerical study two-section distributed Bragg reflector laser.