ELIMINATION OF LIGHT-SCATTERING FROM GRATING IRREGULARITIES BY USING A QUANTUM-WELL GRATING IN INDEX OR GAIN-COUPLED DISTRIBUTED-FEEDBACK LASERS

Grating irregularities in distributed feedback (DFB) laser structures form strong light scattering centers during lasing operation. The exis tence of such scattering centers may possibly affect the laser reliabi lity. We report an elimination of the light scattering centers in inde x or gain-coupled DFB lasers using a quantum well (QW) grating under t he active laser stripe. The improved grating quality is a result of an inherent uniformity of the QW grating amplitude determined by a prech aracterized QW structure as well as an improved crystalline perfection of the overgrown InP instead of a quaternary waveguide layer in a reg ular substrate grating structure.