Influence of a nonuniform coupling coefficient on the static and large signal dynamic behavior of Bragg-detuned DFB lasers

A time domain model is used to study the large signal dynamics of general Bragg-detuned cavities. Such structures, in which the grating pitch is spatially nonuniform so that a distributed phase shift is produced along the cavity, are often called corrugation-pitch-modulated distributed feedback lasers (CPM-DFB). Furthermore, by introducing a longitudinally dependent coupling coefficient κ, a corrugation-pitch-modulated distributed-coupling-coefficient DFB laser (CPM-DCC-DFB) with quite different spectral properties can be realized. We present in this paper a comparison between these two kinds of components. It is shown that an adequate profile of the coupling coefficient (stronger coupling at the center of the cavity) in a CPM-DCC-DFB structure can help to achieve better steady-state singlemode operation with respect to conventional CPM-DFB lasers (uniform coupling coefficient). However, in CPM-DCC-DFB lasers, side modes are liable to be excited during the turn-on transient interval, thus imposing a limitation to the modulation depth requirement