Stability and Dynamic Properties of Multielectrode Laser Diodes Using a Green's Function Approach

In DFB lasers the shape of the longitudinal intensity and carrier density distributions changes above threshold as a result of spatial holeburning. The longitudinally distributed coupling of spontaneous emission into the lasing mode also plays an important role for the noise properties. In this paper we demonstrate how both effects can be included in a dynamic analysis and extend our previously developed theory for multielectrode lasers to enable calculation of stability properties as well as small-signal modulation responses and noise spectra. The theory is used to study global and local stability of the stationary solutions (modes), and numerical results for several laser structures are presented. We show that symmetric DFB lasers are likely to exhibit pitchfork bifurcations in their static tuning characteristics as the current is increased, and we discuss how the presence or proximity of such instabilities can affect the modulation and noise properties, in particular the spectral line width. As a result of the semianalytic treatment we also obtain the local modulation responses for a given device, which show how the intensity and frequency modulation is composed along the cavity. These local responses are very useful for optimizing the FM response of multielectrode DFB lasers.