TRANSFER-MATRIX ANALYSIS OF THE INTENSITY AND PHASE NOISE OF MULTISECTION DFB SEMICONDUCTOR-LASERS

A general small-signal model for the intensity and phase noise spectra of multisection distributed feedback (DFB) semiconductor lasers is developed by using the transfer-matrix approach based on the Green's function method. The spontaneous emission enhancement due to nonuniform longitudinal field distribution and the effective amplitude-phase coupling effect (the effective linewidth enhancement factor) are taken into account in the formulation. This model can be applied to any laser structures composed of grating and non-grating sections such as Fabry-Perot lasers, conventional DFB lasers, phase-shifted DFB lasers, multiple phase-shift DFB lasers, and tapered or chirped DFB lasers. Analytical expressions for the spectra of the relative intensity noise and the FM noise of the main mode in the multimode operation are presented by using the transfer functions in a flow-graph representation. Facet reflectivities and external optical feedback are included in the model. As an example of the applications, a lambda/4-shifted DFB laser is taken, and the effects of the grating coupling coefficient, the random grating-phase at the facets, the phase-shift position, the external optical feedback, and the side mode on the noise spectra are analyzed systematically.