Elimination of light scattering from grating irregularities by using a quantum well grating in index or gain-coupled distributed feedback lasers

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Abstract
Grating irregularities in distributed feedback (DFB) laser structures form strong light scattering centers during lasing operation. The existence of such scattering centers may possibly affect the laser reliability. We report an elimination of the light scattering centers in index or gain-coupled DFB lasers using a quantum well (QW) grating under the active laser stripe. The improved grating quality is a result of an inherent uniformity of the QW grating amplitude determined by a precharacterized QW structure as well as an improved crystalline perfection of the overgrown InP instead of a quaternary waveguide layer in a regular substrate grating structure.