The oscillation characteristics of separated-electrode distributed feedback (DFB) lasers are analyzed by a numerical approach. In the calculation, coupled-mode equations are used including the carrier-density nonuniformity along the laser axis, which is introduced by the spatial hole burning and/or the nonuniform current injection. When the center section of a DFB laser, with three equally separated electrodes, is more strongly pumped than the side sections, high performance is achieved: the mode stability is maintained in the high-power state, resulting in a narrow linewidth. This is because the spatial hole burning is compensated by the larger current injection into the center region. The wide tunable range is also obtained under this bias condition.
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