Spatial hole burning effects in the emission characteristics of DFB laser diodes

Abstract

Distributed-feedback (DFB) laser diodes offer good single-mode emission characteristics when operated in CW conditions. However, spectral degradation during transients or under modulation conditions has been observed due to either the switching of a side-mode [1] or to wavelength chirping of the main-mode [2], The spectral spread of directly modulated DFB laser diodes reduces the performance of optical-fiber communication systems through fiber dispersion [3, 4]. Different attempts to modelling the static and dynamical behaviour of DFB lasers have been carried on using a variety of models [5], but only recently models including spatial effects, multimode dynamics and spontaneous emission noise have been developped [6, 7, 9, 8], but only [9] allows for large signal analysis. The model presented in [9] is based on an equivalent electrical circuit describing the laser diode, but in order to understand the physical processes governing the dynamical response of the laser diode, a description based on Maxwell’s equations for the electrical field and fundamental equations for the material variables seems preferrable. This description is frequently used in connection with a modal expansion for the electric field [8, 10], but these models have been only applied to the analysis of the CW operation of the diode.