Eye closure due to spatial hole-burning dynamics in lambda /4-shifted DFB lasers

The dynamics of longitudinal spatial hole-burning (SHB) in a DFB laser are shown to cause significant pattern-dependent eye closure during transmitted ´ones´ at 2.5 Gbit/s. This closure is caused by recovery dynamics of the SHB during several ´zeros´ and the subsequent time to reburn the hole This eye closure can be reduced by biasing above threshold during ´zeros´ to prevent recovery of the SHB, however higher biases cause significant turn-on peaks during ´zeros´.